nano-stratospheric aerosol measurement (nanosam

University of ColoradoDepartment of Aerospace Engineering Sciences

Senior Projects - ASEN 4018

Nano-Stratospheric Aerosol Measurement(NanoSAM)

Conceptual Design DocumentMonday 30th September, 2019

1. Information

1.1. Project CustomersName: Jim BaerAddress: 1600 Commerce St, Boulder, CO 80301Email: [email protected]: 303-939-6297

1.2. Group MembersProject Manager: Hui Min TangEmail: [email protected]: 720-401-9621

Chief Systems Engineer: Jacob RomeroEmail: [email protected]: 720-384-8158

Electronics Lead: Jared CantilinaEmail: [email protected]: 850-502-0347

Structures Lead: Jessica HarrisEmail: [email protected]: 719-373-9936

Financial Lead: Josh HorstEmail: [email protected]: 503-616-1707

Materials Lead: Quinn LabargeEmail: [email protected]: 720-746-8779

Optics Lead: Conner McLeodEmail: [email protected]: 907-350-3378

Manufacturing Lead: Aanshi PanchalEmail: [email protected]: 630-965-5002

Optics Lead: Sara ReitzEmail: [email protected]: 720-378-1573

Integration Lead: Conner ShaverEmail: [email protected]: 970-768-7522

Software Lead: Matt WeberEmail: [email protected]: 303-241-5804

Safety & Testing Lead: Jaykob VelasquezEmail: [email protected]: 719-281-9849

Contents1 Information 1

1.1 Project Customers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Group Members . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2 Project Description 42.1 Project Purpose & Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42.2 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.3 Concept of Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.4 Functional Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.5 Functional Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3 Design Requirements 10

4 Key Design Options Considered 164.1 Electronics System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

4.1.1 Photodiode Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164.1.2 ADC Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184.1.3 On-Board Controller Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214.1.4 External Memory Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

4.2 Optics System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234.2.1 Reflector Telescope Type Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234.2.2 Mirror Shape Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254.2.3 Mirror Substrate Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264.2.4 Mirror Surface Coating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274.2.5 Optical System Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284.2.6 Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

5 Trade Study Process and Results 305.1 Electronics System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30


5.2 Optics System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345.2.1 Reflector Telescope Type Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345.2.2 Mirror Substrate Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355.2.3 Mirror Surface Coating Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365.2.4 Filter Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

6 Selection of Baseline Design 386.1 Electronics System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38


6.2 Optics System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396.2.1 Reflector Telescope Type Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396.2.2 Mirror Substrate Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396.2.3 Mirror Surface Coating Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396.2.4 Filter Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

09/30/19 2 of 51

University of Colorado Boulder

CDD

7 Appendix 427.1 Metric Score Justification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

7.1.1 Photodiode Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 427.1.2 ADC Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437.1.3 On-Board Controller Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447.1.4 External Memory Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 457.1.5 Optics System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467.1.6 Reflector Telescope Type Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467.1.7 Mirror Substrate Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 487.1.8 Mirror Surface Coating Type Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 497.1.9 Filter Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

7.2 Contact Times for Mock Orbital Trajectory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

NomenclatureADC = Analog-to-Digital ConverterADCS = Attitude Determination Control SystemASTP = Apollo Soyuz Test ProjectCONOPS = Concept of OperationsCOTS = Commercial Off-The-ShelfCTE = Coefficient of Thermal ExpansionCWL = Center of WavelengthEFL = Effective Focal LengthFOV = Field of ViewFPGA = Field-Programmable Gate ArrayFWHM = Full Width at Half MaximumGe = GermaniumGMAT = General Mission Analysis ToolInGaAs = Iridium, Gallium, ArsenicLEO = Low Earth OrbitNanoSAM = Nano-Stratospheric Aerosol MeasurementPDD = Preliminary Design DocumentRVM = Requirement Verification MatrixSAGE = Stratospheric Aerosol and Gas ExperimentSAM = Stratospheric Aerosol MeasurementSAR = Successive Approximation RegisterSBC = Single Board ComputerSi = SiliconSNR = Signal-to-Noise RatioSSD = Solid State DriveSTK = Systems Tool Kit

09/30/19 3 of 51


CDD

2. Project Description

2.1. Project Purpose & OverviewNanoSAM seeks to measure stratospheric aerosol concentrations by measuring solar attenuation using a CubeSat mis-sion. This continues the work started by the Stratospheric Aerosol Measurement (SAM) experiment for the ApolloSoyuz Test Project (ASTP). Stratospheric aerosol measurements and modelling are critical in understanding the radia-tive balance of the Earth’s atmosphere and its role in environmental processes. Aerosols are minute particles suspendedin the air. Their presence affects radiation and energy budgets, the climate, and visibility in the atmosphere when theyscatter or absorb radiation. Aerosol particles can also directly impact human quality of life, an example being theinhalation of smoke that irritates the respiratory system. Therefore, monitoring the concentrations of aerosols in theatmosphere is important in understanding environmental processes and is further refining models that anticipate theeffects of these processes. Several operational instruments have been engineered for this purpose, including SAGE-IIIon the ISS, the third generation solar occultation instrument used to measure the irradiance of the sun through a narrowspectral band. SAGE-III self-calibrates near the top of the stratosphere and deconvolves aerosol loading in discreteatmospheric layers. Although these instruments have been successful, orbital constraints on the instrument’s locationas well as the relative infrequency of dawn and dusk measurement windows have limited the spatial and temporaldensity of the data acquired. The NanoSAM project seeks to address these limitations by implementing a CubeSatconstellation to improve the quantity and density of data while maintaining optical precision. The increased data den-sity of the stratospheric aerosol measurements will heighten the reliability of the models and aid in related analyses ofthe Earth’s atmosphere.

The purpose of this project is to design, build, and test an optical instrument that will be capable of measuringaerosol concentrations in the stratosphere. Engineers at Ball Aerospace Corporation and a senior design projects teamfrom the Ann H.J. Smead Aerospace Engineering Department of the University of Colorado Boulder will collaborateto construct a functioning optics system that is able to detect irradiance in a narrow spectral band at 1.02 µm. Anaccompanying electronics system capable of collecting and packetizing the irradiance data for download will also beproduced. These systems will be compatible with an off-the-shelf CubeSat bus or bus architecture. Due to financialand time constraints, the deliverables will only include the optics system, electronics system, and an accompanyingsoftware. Recommendations about CubeSat size and architecture, ADCS selection, orbit parameters, power require-ments, and ground systems will be made for future applications. Figure 1 below shows a visual representation of thescope of the full mission and the aspects of the NanoSAM project that will be focused on this year. The objects ingreen will be directly produced. Even though the objects in gray will not be directly produced or selected, they will betaken into consideration when designing the objects in green.

Figure 1. Scope Tree

09/30/19 4 of 51


CDD

2.2. ObjectivesThe table below outlines the criteria for various levels of success for different project elements. Level 1 successdescribes the objectives that must be met to achieve a successful project. Meanwhile, the Level 3 goals describes thefinal project deliverables which will have the highest level of success. The table is an updated version of the sametable from the PDD with increased detail.

09/30/19 5 of 51


CDD

Project Elements Level 1 Level 2 Level 3

Payload Instrumentation SizeThe payload (radiometer and supporting electronics) is compatible with a CubeSat

platform.

The payload consisting of a radiometer and its supporting electronics are

compatible with a 3U CubeSat bus (high end of customer's desired size range).

The payload consisting of a radiometer and supporting electronics is compatible with a 2U CubeSat bus (the low end of

customers desired size range).

Data CaptureThe photodiode will capture light and

convert it into electrical current that is able to be read by supporting electronics.

Supporting electronics and software acquires, digitizies, packetizes, and

downloads raw data from the photodiode to a laptop computer.

Supporting electronics and software acquires, digitizes, packetizes, and

downloads raw data from the photodiode to a laptop computer. The software also

incorporates synthetic data that simulates the spacecraft health, slew rate, and other

housekeeping (if applicable) digital outputs to represent actual operating

conditions.

Instrument LinearityThe instrument produces a current in

response to the incident radiation from a light radiation source such as a light bulb

with known power output or the sun.

The instrument produces a repeatable functional relationship between current and the optical attenuation of a known

radiation source.

The instrument produces a repeatable linear relationship between current and

the optical attenuation of a known radiation source.

Vertical ResolutionThe optical instrument's FOV facilitates a vertical resolution that will produce useful

scientific data. Same as level 1

The optical instrument's FOV facilitates a vertical resolution of 1 km of atmosphere

when placed in a 500x500 km circular orbit.

Instrument SNRThe optical instrument has a large enough

SNR that will produce useful scientific data.

Same as level 1

The optical instrument has a SNR above 1.2E4. The level three goal shall be

determined from the instrumental errors used in the Chu and McCormick sensitivity simulation as well input from atmospheric

scientists

Mechanical Structure The payload will be arranged on a lab-bench for demonstration purposes.

The payload will be able to fit inside the chosen CubeSat bus. Elements will not be

secured or fastened but rather placed inside the bus to verify the selected

CubeSat size can house all components.

The payload will be secured into a mock CubeSat bus architecture. The instrument and supporting electronics will be secured

into place along with "black boxes" that represent items that will be present in the final mission but that are not present in this year's project such as the ADCS.

2.3. Concept of OperationsThe general concept of operations (CONOPS) for the NanoSAM CubeSat project proposed by Ball Aerospace includesthe design, construction, launch and operation of a solar occultation data acquisition CubeSat. Its solar occultationdata will be used to calculate aerosol concentrations in the Earth’s atmosphere. This project will span several yearsfrom launch until the satellite falls out of orbit and burns up in the atmosphere. The complete mission CONOPS forthe NanoSAM project, from launch (Step 1) to burning up in Earth’s atmosphere (Step 9), is illustrated in Fig. 2.After launch, the CubeSat will be deployed into a low-Earth-orbit (LEO) of 500 km using a CubeSat deployer suchas Nanoracks or similar. Once in orbit, the NanoSAM CubeSat will boot-up and perform a bus checkout to ensurethat all subsystems are operational. Once the spacecraft verifies its functionality, it will begin its solar occultationdata acquisition process. This includes the prediction of the location of a sunrise/sunset event. Then, the satellite willvertically scan to measure the irradiance of the Earth’s atmosphere at 1.02 µm through a narrow spectral band. Oncemeasurements are collected, the irradiance data will be converted from an analog signal to a digital signal, packetized,and stored for later transmission. When the NanoSAM CubeSat passes over designated ground pass locations, it willdownlink the collected irradiance measurements for post-processing at ground stations. The NanoSAM CubeSat willcontinue to take measurements over its mission lifetime until the spacecraft de-orbits and burns up in the Earth’satmosphere.

Figure 2. General NanoSAM CONOPS

The student team’s objective for the initial year of the Ball Aerospace project is to design, build, and test an opticalinstrument intended for integration into the NanoSAM CubeSat. The optical instrument will consist of optics and anelectronics system with ancillary software. The student team’s testing CONOPS is illustrated in Fig. 3.

09/30/19 7 of 51


CDD

Figure 3. NanoSAM Team Testing CONOPS for This Year’s Project

The team will begin testing the optical instrument in a dark room with a 0.25 W LED representing the Sun as aradiation source. A laptop computer will be used to communicate with the optical instrument and direct when theinstrument should collect data. With the instrument powered on, a 0.25 W LED, simulating a sunrise or sunset event,will be pointed towards the instrument and focused through the optics system. A 1.02 µm filter will filter the radiatedlight before reaching a photodiode detector located within the instrument. To verify that the photodiode is detectingthe incoming light, the change in the photodiode’s electrical properties will be observed. A trans-impedance amplifierwill then convert the signal produced by the photodiode to a voltage signal. An analog-to-digital converter will convertthe analog voltage signal to a digital voltage signal for data packetization and storage in the instrument. Finally, theirradiance data will be transferred to a laptop computer for further data analysis.

2.4. Functional Block DiagramFig. 4 shows the complete functional block diagram for NanoSAM. The team will only focus on producing thecomponents within the red dashed box on the right side of Fig. 4. The components will form the payload consistingseveral elements. An optics system will utilize an optical bandpass filter and a reflector to filter and focus on thesunlight through the atmosphere.

09/30/19 8 of 51


CDD

Figure 4. NanoSAM Functional Block Diagram

2.5. Functional RequirementsThe NanoSAM project contains 7 functional requirements that will flow down to top-level design requirements. Thefunctional requirements are listed below while the other levels of requirements can be found in section 3 of the docu-ment.

1. The payload shall detect and measure solar attenuation via the solar occultation method.

• Verification: The payload will be tested in a simulation of the solar occultation method by measuring solarattenuation at various points in the day when the sun is obscured by varying amounts of atmosphere.

2. The payload shall predict the location of the sun to initiate a data capture sequence.

• Verification: The predictions of the sun’s location will be verified by analysis in a physics-based softwaresuch as STK or GMAT.

3. The payload shall self-calibrate before or after each data capture instance.

• Verification: The instrument will be tested with a known radiation source such as lasers or LEDs in a darkroom to ensure the measured data matches theoretical & manufacture data for the known source.

4. The payload shall collect and store solar attenuation data.

• Verification: The instrument will be tested with a radiation source to verify that data was collected andstored.

5. The payload shall be able to be commanded from an external source.

• Verification: The payload will be tested by uploading commands to it via a laptop.

6. The payload shall draw no more than 4.5 W at any instant.

• Verification: The power consumed by the payload can be measured during testing and through calculations.

7. The payload shall be compatible with an off-the-shelf CubeSat bus or bus architecture.

09/30/19 9 of 51


CDD

• Verification: The compatibility will be verified by testing the payload in a mock CubeSat bus or busarchitecture.

3. Design RequirementsThe complete set of requirements for the team’s NanoSAM project can be found in Tables 2, 3, and 4 below. TheLevel 0 requirements are the functional requirements that were also mentioned in Section 2.5 above. These functionalrequirements were used to derive the Level 1 and Level 2 requirements shown in subsequent tables. The orbital andground station parameters used to determine some of the values for various design requirements are shown in Table 1.In order to ensure that all of the requirements that were developed are verifiable, a Requirements Verification Matrix(RVM) was created. This RVM can be found in is Tables 5, 6, and 7 below.

Parameter ValueOrbit Altitude 500 km

Orbit Eccentricity 0 (circular orbit)Orbit Inclination 45◦

Orbit Right Ascension of the Ascending Node 0◦

Orbit Argument of Perigee 0◦

Ground Station Location 40.11◦N, 105.27◦WMinimum Contact Elevation Angle 15◦

Table 1. Orbital and Ground Station Parameters

The orbital and ground station parameters for a mission starting on January 1st, 2021 at 12:00 am resulted in severalcontact times and duration that lasts 7 days. A table of these contact times and duration can be found in Appendix 7.2.From these results, there were on average 5 contacts per day with an average duration of 332.24 secondsa.

aThese values were obtained using NASA Goddard’s General Mission Analysis Tool (GMAT) with a default Earth Gravitational Field Propagatorand Model.

09/30/19 10 of 51


CDD

RequirementID

RequirementTitle

Requirement Text Rationale

Level 01.0 Solar

OccultationThe payload shall detect andmeasure solar attenuation viathe solar occultation method.

This method for measuring solarattenuation was specified by the customer.

2.0 Solar Position The payload shall predict thelocation of the sun to initiate a

data capture instance.

In order to start a data capture instance theoptics must be pointed at the sun.

3.0 Calibration The payload shall self-calibratebefore or after each data

capture instance.

Solar radiation can vary in magnitude dueto the elliptical orbit of Earth. A baselinemeasurement of an unattenuated radiationsource for each data capture instance will

ensure the instrument is calibrated.4.0 Data Storage The payload shall collect &

store the solar attenuation data.Solar attenuation data is the critical databeing taken by the instrument and will

need to be collected and stored for futurepurposes.

5.0 Commanding The payload shall be able to becommanded from an external

source.

The payload is not a standalone device andtherefore needs to receive commands

externally from a ground system6.0 Average Power

DrawThe payload shall draw an

average of 4.5 W over an entireorbit.

The power required for the CubeSat tooperate should be within reason and aslow as possible to make sure that the

power budget will be valid. [12]

7.0 BusCompatibility

The payload shall becompatible with an off-the-shelfCubeSat Bus/Bus Architecture

The customer specified that the systemmust be compatible with a CubeSat

Bus/Bus Architecture. The exact size wasnot specified as the size of the instrument

was unknown at the proposal of theproject.

Table 2: Level 0 Requirements Flow Down Matrix

09/30/19 11 of 51


CDD

RequirementID

RequirementTitle


Level 11.1 FOV The payload shall have a

field-of-view of 1.3 arcminutes.When placed in a 500x500 km circular

orbit the field-of-view must be 1.3arcminutes to achieve 1 km vertical

resolution.1.2 Wavelength The optical system shall

measure solar attenuation at acenter wavelength of 1.02

micron with a bandwidth of 40nm

This is a wavelength at which aerosolparticles can be detected. Other

wavelengths at which aerosol particles canbe detected have interference from other

constituent absorption or Rayleighscattering.

1.3 SNR The payload shall have asignal-to-noise ratio (SNR)

between incoming photons andthe instrument of 1.2 · 104 or

greater. [16]

This SNR will ensure the data has anacceptable level of noise to obtain

scientifically accurate measurements.

2.1 GroundComputation

The external command sourceshall predict solar location andassociated payload pointing.

By doing the calculations required topredict solar location and associated

payload pointing via an external commandsource the onboard computer will require

less capability.3.1 Baseline The instrument shall measure

an unattenuated radiationsource to obtain a baseline

measurement

Solar attenuation can be calculated using adecibel system by comparing an

unattenuated baseline measurement to anattenuated data point.

4.1 Storage Size The instrument shall collect andstore attenuation data for 2 days

minimum.

This storage size will ensure that no datawill be lost in case of two missed downlinkopportunities. This ensures future work onthe project will have adequate storage incase of missed downlink opportunities.

5.1 CommandStorage

The payload shall be able tostore 15 commands at one time.

Uplink opportunities might be missed sothe payload will need to store commandsuntil the next window of opportunity. 15commands is the minimum number of

commands needed to operate.5.2 Command

TimeThe uplink of commands to the

payload shall take no longerthan 150 seconds.

The time it takes to transfer data betweenground systems and payload will affect

how much data it can send over oneground pass. 150 seconds is slightly less

than 1/2 of the average ground pass.6.1 Maximum

VoltageThe payload shall draw no more

than 7.1 VDC.The maximum voltage used by the

instrument needs to be specified to makesure that the electronics components are

not short-circuited.7.1 Payload

VolumeThe payload shall have volumedimensions no greater than thatallotted in the chosen CubeSat

form factor.

This ensures the payload will fit within thechosen CubeSat form factor to allow for

future work to continue within thecustomer’s specification of compatibility

with a CubeSat Bus/Bus Architecture.7.2 Payload Mass The payload shall have a mass

no greater than that alloted inthe chosen CubeSat form factor.

This ensures the mass of the payload andbus will be less than the maximum

allowable mass for the chosen CubeSatsize.


09/30/19 12 of 51


CDD

RequirementID

RequirementTitle


Level 21.1.1 Aperture The optical system shall have

an aperture of at least 3.29 mm.The specified aperture will allow thepayload to achieve the desired FOV.

1.2.1 Filter The optical system shall utilizea filter with a center wavelength

of 1.02 micron with abandwidth of less than 40 nm.

A filter will ensure that only the desiredwavelength of light will be measured.

2.1.1 TimeComputation(Initiation)

The external command sourceshall predict the time at which a

data capture instance isinitiated.

The payload will not have to calculatewhen to initiate a data capture instanceand will instead be commanded to start

capturing data.2.1.2 Time

Computation(Baseline)

The external command sourceshall predict the time at which abaseline measurement will be

taken.

The payload will not have to calculate thetime at which the baseline measurement istaken and will instead be commanded to

take the baseline measurement at apre-determined time.

2.1.3 TimeComputation(Termination)

The external command sourceshall predict the time at which a

data capture instance isterminated.

The payload will not have to calculatewhen to terminate a data capture instance

and will instead be commanded toterminate data capture.

3.1.1 Baseline Time The instrument shall captureand store the baseline data at

the commanded time.

The instrument will capture the baselinedata at the commanded time to compareall other data points during that specific

data capture instance to.5.2.1 Command Size The payload shall be able to

receive 15 commands at time ofdownlink/uplink.

The payload will need to receive enoughcommands at time of downlink/uplink sothat if two downlink/uplink opportunities

are missed the payload will be able tocontinue its function. This will allow for

an entire new set of commands to beuplinkied.


The verification methods for all levels of the requirements can be found in Tables 5, 6, and 7. These tables areorganized according to the levels of requirements. The X’s in the tables within the verification method represents theapproach used to ensure that the project meets the requirements. A brief description is also provided in the tablesunder verification method breakdown. Additionally, the description provided in the Level 0 Requirements Flow DownMatrix (Table 2) are equivalent to the information in Section 2.5 of the functional requirements.

09/30/19 13 of 51


CDD

RequirementID

RequirementTitle

Verification Method Verification Method BreakdownTest Analysis InspectionLevel 0

1.0 Solar Occultation X The payload will be tested in asimulation of the solar occultationmethod by measuring solar attenuation atvarious points in the day when the sun isobscured by varying amounts ofatmosphere.

2.0 Solar Position X The predictions of the sun’s location willbe verified by analysis in a physics-basedsoftware such as STK or GMAT.

3.0 Calibration X The instrument will be tested with aradiation source to verify that data wascollected and stored.

4.0 Data Storage X The instrument will be tested with aradiation source to verify that data wascollected and stored.

5.0 Commanding X The payload will be tested by uploadingcommands to it via a laptop.

6.0 Peak Power Draw X X The power consumed by the payload canbe measured during testing and throughcalculations.

7.0 Bus Compatibility X The compatibility will be verified bytesting the payload in a mock CubeSatbus or bus architecture.

Table 5: Level 0 Requirements Verification Matrix

09/30/19 14 of 51


CDD

RequirementID

RequirementTitle


1.1 FOV X The field-of-view will be calculatedusing equations.

1.2 Wavelength X X The center wavelength can be verifiedthrough inspection while thebandwidth can be calculated.

1.3 SNR X The SNR can be calculated bymeasuring the signal power and thenoise power.

2.1 Ground Computation X Calculations will be performed inGMAT/STK.

3.1 Baseline X The instrument will be tested with aknown radiation source at maximumintensity to simulate an unattenuatedmeasurement. The intensity will bedecreased and additional readings willbe taken, simulating attenuatedmeasurements.

4.1 Storage Size X The instrument will be tested with aradiation source and data will becollected and stored. This test willcapture an amount of data that willcorrespond to 7 days of on orbitoperation.

5.1 Command Storage X The payload will be connected to alaptop and run with commandsuploaded to ensure the commands areproperly stored and followed.

5.2 Command Time X The payload will be connected to alaptop which will supply commands.The upload time per command will berecorded.

6.1 Maximum Voltage X X The voltage can be measured using avoltmeter.

7.1 Payload Volume X The payload’s volume will becalculated in a modeling software.

7.2 Payload Mass X The payload will be be measured to atleast 1 decimal place.


09/30/19 15 of 51


CDD

RequirementID

RequirementTitle


1.1.1 Aperture X The aperture can be verified by calculations.1.2.1 Filter X X The center wavelength can be verified

through inspection while the bandwidth canbe calculated.

2.1.1 TimeComputation(Initiation)

X A Simulation will be performed inGMAT/STK in conjunction with groundbased testing.

2.1.2 TimeComputation

(Baseline)


2.1.3 TimeComputation(Termination)


3.1.1 Baseline Time X A Simulation will be performed inGMAT/STK in conjunction withground-based testing.

5.2.1 Command Size X The payload will be connected to a laptopand the upload rate for command packets ofvarying sizes will be recorded.


4. Key Design Options Considered

4.1. Electronics SystemAs described in the requirements above, the primary goal of the electronics system is to collect, packetize, and storeoptical data. The electronics system shall detect irradiance from a focused beam of light, linearly convert the incidentsolar flux to a digital package of data, and store it for data processing. This part is essential to the NanoSAM projectsince any important irradiance data must be processed, converted, and stored with care for the project to be successful.This can be achieved most effectively via 4 primary components. The first major design decision would be to selecta photodiode to detect irradiance from the focused beam. The second major design decision is to select an ADC toconvert the data into a digital package. The third major design decision is to select an on-board computer to storethe irradiance data for data processing. The final major design decision is to select an external memory to have theon-board computer store the data onto after data processing for future analysis.

4.1.1. Photodiode Selection

A photodiode is a diode which converts light into an electrical current. This product would become essential toNanoSAM’s mission since this would allow the ADC to process the current changes to an irradiance data point. Thetrade study for the NanoSAM’s radiometer is based on finding a reliable photodiode. This is because this project is thesuccessor of SAGE II modified to fit into a CubeSat. The trade study will bounce off of SAGE II’s trade study in thata photodiode will be used, but the team decided to look at common photodiode materials to see what the best optionfor this mission could be.

Photodiodes are primarily differentiated by the structure and the materials used to make them. Fig. 5 below depictsa standard p-i-n (PIN) photodiode.

09/30/19 16 of 51


CDD

Figure 5. A cross section of a typical PIN photodiode, showing the P layer, the Intrinsic layer, and the N layer.

The intrinsic layer is the most important layer since it allows for the active area to increase - allowing more light tobe measured. Different types of material can be inserted into the photodiode layers (primarily P+ and intrinsic layers),affecting the wavelength sensitivity and the level of noise produced. This, along with active area, are some of the mostimportant factors to consider for this project. The team decided to look at the three most common materials used forthe PIN photodiode for our project. This way, our trade study can make sure that the best possible material can get themost accurate data [1].

1. SiliconSilicon (Si) photodiodes are excellent at measuring smaller wavelengths from 190-1100 nm. They also producerelatively low dark current, ranging from 35 pA-600 nA (@ 5V). A large advantage is that on average, the activearea is bigger than both the Ge and InGaAs photodiodes. Additionally, the average price for a Si photodiode issignificantly less expensive than the other types, which addresses a critical element for the project [2]. However,this particular photodiode would require typically more voltage to run than some of the other types. Furthermore,this was the type of diode used on SAGE II - which has proven to be reliable for that mission. A summary ofthe pros and cons for Si photodiodes can be seen below in Table 8.

Pros ConsLess noise than Ge photodiodes Higher max bias voltage

Larger active areaProduces low dark current

Table 8. Pros and Cons of Silicon Photodiodes

2. InGaAsIndium (In), Gallium (Ga), Arsenic (As) Photodiodes (InGaAs) are photodiodes that are excellent at measuringthe shorter wavelength end of the infrared spectrum, from about 800 nm to 1700 nm. They also produce rela-tively low dark current when compared to Ge photodiodes but similar to more dark current than Si photodiodes.The dark current measured by the InGaAs diodes is on the scale of about 0.05 nA to 1µA. Secondly, thesephotodiodes are very high speed; the rise time of the current is on the scale of 300 ps to 25 ns. However, adownside of these photodiodes is their price. They are moderately expensive, being more expensive than theirsilicon counterparts but often cheaper than the gallium photodiodes [2]. Due to the cost of the materials neededfor these photodiodes, their size is limited by the cost of manufacturing a larger diode, making the active areasof these photodiodes particularly small.

An important consideration to note for InGaAs photodiodes is that the structure is slightly different than thetypical PIN photodiode structure (Figure 5). Looking at Figure 6, most InGaAs photodiodes are more exposed.Some added benefits include having additional flexibility as to how it receives light since it can also receive lightfrom its substrate, not just the contact zones. However, this structure has a larger energy gap [1].

09/30/19 17 of 51


CDD

Figure 6. A typical cross section view of the heterojunction PIN photodiode

A summary of the pros and cons for the InGaAs photodiodes can be seen below (Table 9)

Pros ConsCan measure 1020 nm wavelength Moderately Expensive

Low dark current Smaller active areasHigh speed (low rise time)

Table 9. Pros and Cons of InGaAs Photodiodes

3. GermaniumGermanium (Ge) photodiodes are the photodiodes which have the largest active area comparatively to the Si andInGaAs counterparts, ranging at an average of 36 mm2. However, that comes with several drawbacks. First, Gephotodiodes are quite expensive, ranging to hundreds of dollars a piece [2]. Secondly, the sensitivity at 1020 nmis quite low, as most Ge photodiodes are better at measuring more than 1020 nm. A summary of the pros andcons of Germanium photodiodes can be seen below in Table 10.

Pros ConsLarge active area Low responsivity at 1020 nm

Very expensiveSlow rise time

Large dark current

Table 10. Pros and Cons of Germanium Photodiodes

4.1.2. ADC Selection

The function of the analog-to-digital converter (ADC) is to translate the analog electric signal to a digitized signal fordata processing. The ADC will take input from the transimpedance amplifier and output to the on-board computersystem. The ADC must be capable of providing the necessary resolution and range to deconvolve simulated aerosolconcentrations via light source intensity. A variety of specifications will be compared for three different ADC types toselect the most effective ADC for our mission requirements.

1. FlashFlash ADCs are the fastest and least accurate type of ADC available. They use a network of resistors andcomparators to determine the voltage level of an input signal. This results in an extremely fast conversion,however inaccuracies in resistor network resistance means this ADC is less accurate than other types.

09/30/19 18 of 51


CDD

The primary advantage of a flash ADC is it’s speed. Flash ADCs have incredibly high sample rates compared toother ADCs however for this mission the signal we will be measuring will not require a high sample rate. FlashADC types are also common, easy to use, and cost less than other ADC types.

The primary disadvantage of a flash ADC is the low resolution and inaccuracies. Flash ADCs require 2n com-parators on the chip, where n is the resolution of the ADC. This limits the resolution of flash ADCs to around 8bits. This mission will require a highly accurate conversion of relatively small signals, therefore this is a largedisadvantage.

Figure 7. Flash ADC

A summary of the advantages and disadvantages of Flash ADCs can be seen below:

Pros ConsHigh Sampling Rate Low SNR

Low resolutionHigh Power Consumption

Table 11. Pros and Cons of Flash ADCs

2. Successive Approximation (SAR)Successive Approximation (SAR) analog-to-digital converters have high accuracy, lower power consumption,low latency time, and are easy to use. The SAR ADC samples an analog electric signal and converges to adigital representation via a binary search of all quantization levels. The internal circuitry completes the fol-lowing functions: (1) the analog signal is sampled and held, (2) the sample is compared for each bit to theinternal digital-to-analog converter’s most significant bit scaled by a reference voltage, and (3) outputs a digitalapproximation at the end of the conversion. A block diagram of the SAR ADC is presented below.

09/30/19 19 of 51


CDD

Figure 8. Successive Approximation ADC Block Diagram

Primary advantages of the SAR ADC are low power consumption and volume. They are also common andintuitively easy to use. The resolution of the SAR ADC is ideal for our application requiring 8-16 bits, and itslow power consumption and volume is advantageous to our CubeSat design.

The primary disadvantage of the SAR ADC is low sample rates for higher resolutions. The ADC frequency isimportant for data processing and must meet the functional requirements of the system design. The SAR ADCalso increases in size as resolution increases. A summary of the pros and cons can be seen below

Pros ConsLow power consumption Low sampling rate (for greater resolution)

Medium SNRMedium Resolution

Table 12. Pros and Cons of SAR ADCs

3. Sigma-DeltaSigmas-delta ADCs offer high resolution, high integration, low power consumption, and low cost. They includea 1-bit modulator, a digital filter or integrator, and a decimator. Sigma-delta ADCs utilize oversampling andnoise shaping to provide a high resolution and low noise digital representation of the analog signal. A circuitdiagram of the sigma-delta ADC is presented below.

Figure 9. Sigma-Delta ADC Block Diagram

Primary advantages of the sigma-delta ADC are high resolution, high signal-to-noise ratio (SNR) and low cost.The utilization of digital filtering increases the SNR directly and simplifies our design. This will aid in acquiringa more accurate digital representation of the analog signal at a low cost and low power consumption.

09/30/19 20 of 51


CDD

The primary disadvantages of the sigma-delta ADC are low speed, and high latency time. The hardware of thisADC must operate at the oversampled rate which is larger than the maximum signal bandwidth demanding greatcomplexity of the digital circuitry. The sigma-delta ADC has a reduced throughput time because it takes manyclock cycles for the digital filter to settle after switching channels.

A summary of the advantages and disadvantages of Sigma-Delta ADCs can be seen below:

Pros ConsHigh resolution Low sampling rate

High SNR High latency timeLow power consumption

Table 13. Pros and Cons of Sigma-Delta ADCs

4.1.3. On-Board Controller Selection

1. Field-Programmable Gate Array (FPGA)A field-programmable gate array, or FPGA, is a microchip consisting of configurable logic gates. This allows forcustom integrated circuit design. FPGA synthesis tools allow for high level programming to be implemented inthe FPGA fabric. FPGAs are extremely versatile, but are difficult to program, as they have a very steep learningcurve. A microprocessor can be instantiated on the FPGA fabric to run high level C code. Almost any hardwareinterface can be implemented in firmware, allowing the flight software to communicate with other parts of thespacecraft, such as the instrument, radio, and ADCS system.

The primary advantage of an FPGA for the on-board computer comes from it’s versatility. Any software orfirmware required could be implemented on an FPGA, and it would be possible to create interfaces for allperipheral electronics.

The primary disadvantage is the complexity of programming an FPGA. The primary languages used to programan FPGA, Verilog and VHDL, are very different from more traditional programming languages, and are difficultto master. However multiple team members have experience with programming FPGAs.

A summary of the advantages and disadvantages of FPGA controller can be seen below:

Pros ConsExtremely versatile Very complex

Allows for fast measurements Difficult to program

Table 14. Pros and Cons of FPGA Controller

2. Micro-controllerA microcontroller consists of a microprocessor, supporting electronics, and hardware interfaces. The micro-controller runs pre-compiled code stored in on-board flash memory. This allows for reading data from theinstrument. Micro-controllers are well suited for well defined repetitive tasks, are very lightweight and haveminimal power requirements. However, due to their small size, they are limited in processing power. Due to thepre-built hardware interfaces, compatibility with other components must be considered.

A summary of the advantages and disadvantages of micro-controllers can be seen below:

Pros ConsLow cost Limited processing powerSmall size Limited interfaces

Simple programming

Table 15. Pros and Cons of Micro-Controller

3. Single Board ComputerA single board computer (SBC) is a processor and supporting electronics on a single printed circuit board.

09/30/19 21 of 51


CDD

These generally have much more processing power than a microcontroller, but are also limited in their hardwareinterfaces.

A summary of the advantages and disadvantages of micro-controllers can be seen below:

Pros ConsLow cost Complex to code, not the best for prototyping

High speed Large size

Table 16. Pros and Cons of Micro-Controller

4.1.4. External Memory Selection

An external memory source is essential to make sure all the data collected could be stored in some memory bank onthe instrument. Considering most of our data will be saved as a raw data and there will be relatively few measurementsper ground station pass, not much data storage is needed to store a substantial amount of irradiance data.

1. Solid State Drive (SSD) CardBenefits of using an SSD would be having a very high storage capacity and be able to write fast - which cankeep up with the 50 Hz sampling rate frequency, while drawing relatively little power. However, they have thelargest mass of options considered. Solid state drives consist of flash memory arrays controlled by an on cardprocessor. These processors can be extremely susceptible to radiation damage, taking down the entire storagesystem when they fail.

A summary of the advantages and disadvantages of SSDs can be seen below:

Pros ConsHigh storage capacity Larger volume/mass for CubeSat

Fast writing speedsDraws little power

Table 17. Pros and Cons of SSDs

2. Micro-SD CardMicro-USB cards are external memory cards that are similar to traditional SD cards with the benefit that they aresmaller in mass and volume. SD cards are an extremely popular storage solution for cubesats due to their priceand ease of use. Many microcontroller boards have built in SD card slots. However, there are many drawbacksto SD cards in space. Like SSDs, they consist of arrays of flash memory controlled by a microcontroller. Thismicrocontroller commonly fails due to radiation damage. Additionally, thermal expansion and contraction ofthe contacts between the SD card and SC card slot can cause failure of the SD card.

A summary of the advantages and disadvantages of Micro-SDs can be seen below:

Pros ConsSmall in volume and mass Can be damaged by radiation

Cheap and easy to use

Table 18. Pros and Cons of Micro-SDs

3. USB (Flash Drive)Flash drives are very similar to SD cards, an array of flash memory accessed through a microcontroller over aUSB interface. They also have similar pitfalls from radiation and interface. The advantage of USB drives is thatthey can plug into almost any system isn’t useful for a a CubeSat application.

A summary of the advantages and disadvantages of USBs can be seen below:

09/30/19 22 of 51


CDD

Pros ConsSusceptible to radiation damage

Large volume

Table 19. Pros and Cons of USBs

4. NAND FlashAll the devices listed above use flash storage, and differ primarily in interface type. It would be possible tobypass the interface and radiation sensitive controller by building a custom PCB with on board computer andflash memory chip. This would limit our on board computer to FPGAs and controllers that can interface withexternal flash memory.

A summary of the advantages and disadvantages of NAND Flash can be seen below:

Pros ConsMore immune to radiation damages More complex to use

Fastest read/write Limits main processor selection

Table 20. Pros and Cons of NAND Flash

4.2. Optics SystemThe NanoSAM irradiance measurements rely on a focused light source centered around the 1.02 µm wavelength il-luminating the contact surface of the photodiode. A telescope is utilized to focus collimated sunlight at the sensorlocation, while a separate filtering component is used to isolate the wavelength of interest. Various telescope designsare capable of focusing the light within the NanoSAM payload size constraint. These designs fall into two main cat-egories: refractor telescopes and reflector telescopes. Refractor telescopes employ lenses and the law of refraction toalter the path of light rays. In contrast, reflector telescopes apply the law of reflection to manipulate the incident rays.Both telescope types have been implemented for space-based missions; however, most recent telescope designs takeadvantage of lightweight, highly reflective mirrors. In most cases, mirrors are smaller in size, less massive, and lessexpensive to produce than lenses. Refractor telescopes, due to the use of lenses, often produce chromatic aberrations.Chromatic aberration is a failure to focus all of the incident light to one focal point. The significance of this dispersionis wavelength dependent. Chromatic aberration is avoided with reflector telescopes as the wavelengths of light do notreflect off the mirrors differently. Consequently, the telescope design options in this section are limited to reflectortelescope configurations. Furthermore, the mirror compositions are considered. Both the mirror substrate and surfacecoating are design aspects that will be studied for this specific application.

4.2.1. Reflector Telescope Type Selection

1. Schmidt-Cassegrain TelescopeSchmidt-Cassegrain reflector telescopes utilize concave primary mirrors in conjunction with a convex secondarymirror in order to focus an image [? ]. The image is reflected through a gap between the primary mirrors ontothe detector. The curvature of the primary and secondary mirrors determines the effective focal length and mag-nification of the image [15]. Since the light is redirected back and forth along the optical axis, relatively largeeffective focal lengths can be achieved with limited space. Longer focal lengths reduce errors due to uncolli-mated light. In addition, for precisely aligned mirrors, other geometrical aberrations are minimal. Althoughthere is an obstruction caused by the secondary mirror, the Cassegrain configuration is typically able to collectsufficient light for a specific aperture area. Optical windows and spider vanes are common secondary mirrormounts, which introduce another design challenge (i.e. more light loss, refraction, etc.).

09/30/19 23 of 51


CDD

Figure 10. Schmidt-Cassegrain Reflector Ray Trace Diagram [21]

A summary of the advantages and disadvantages of the Schmidt-Cassegrain telescope can be seen below:

Pros ConsShort overall length Requires precise mirror alignment

Relatively long effective focal lengths Relatively large secondary mirrorNo chromatic aberration Requires secondary mirror mount

Table 21. Pros and Cons of Schmidt-Cassegrain Telescope

2. Newtonian TelescopeIn contrast to the Schmidt-Cassegrain reflector, the Newtonian telescope [15] uses a planar secondary mirror tofocus the light at the desired location. As a result, the secondary mirror does not affect the effective focal length.Tilting the secondary mirror allows the telescope to focus the image at a point off of the optical axis. Placingthe detector away from the optical axis allows for more flexibility in the placement of the electronics subsystem.Additionally, there is no gap in the primary mirrors, which decreases the overall manufacturing complexity.

Figure 11. Newtonian Reflector Ray Trace Diagram [22]

A summary of the advantages and disadvantages of the Newtonian telescope can be seen below:

Pros ConsFewer curved mirrors Requires precise mirror alignment

Low obstruction (relatively small secondary mirror) Shorter effective focal lengths possibleNo chromatic aberration Requires secondary mirror mount

Table 22. Pros and Cons of Newtonian Telescope

3. Herschelian TelescopeThe Herschelian reflector telescope design is relatively simplistic. Incident light is reflected off of a single,curved mirror to a focal point off of the optical axis. No obstructions are present due to the absence of asecondary mirror. As a result, the Herschelian design accepts the most light for a given aperture size. Also,the mirror alignment is greatly simplified. Tilting the mirror introduces aberrations not present in the idealCassegrain telescope configuration.

09/30/19 24 of 51


CDD

Figure 12. Herschelian Reflector Ray Trace Diagram [23]

A summary of the advantages and disadvantages of the Herschelian telescope can be seen below:

Pros ConsRequires a single mirror Tilt aberrations are possible

No obstruction Shortest effective focal lengths possibleNo chromatic aberration

Table 23. Pros and Cons of Newtonian Telescope

4. Prime Focus TelescopeThe prime focus telescope [15] utilizes a single concave mirror to focus the light at some point along the opti-cal axis. For the purpose of the NanoSAM project, a detector must be placed within the optical tube to gatherirradiance data. Placing the sensor in the optical tube inherently causes blockage. Moreover, connecting the pho-todiode to the various components of the electronics subsystem may further obstruct the aperture (i.e. blockagefrom mount, wiring, etc.).

Figure 13. Prime Focus Reflector Ray Trace Diagram [24]

A summary of the advantages and disadvantages of the Prime focus telescope can be seen below:

Pros ConsNo secondary optics Obstruction

No chromatic aberration

Table 24. Pros and Cons of Prime Focus Telescope

4.2.2. Mirror Shape Overview

Mirror shape is a factor to consider when designing the optical system. Possible mirror shapes considered are spher-ical and parabolic mirrors (including off-axis parabolic mirrors). Spherical mirrors are not commonly used as theyintroduce spherical aberrations that are not present in parabolic mirrors. Spherical aberration is where collimated lightrays focus to different points depending on where they reflect off the mirror, thus resulting in multiple focal points.This disrupts the focusing of the light and needs to be corrected with compensation lenses. The use of parabolicmirrors is more common in reflecting telescopes as they do not lend to spherical aberrations. Parabolic mirrors canbe symmetrical (centered) or off-axis. Off-axis parabolic mirrors are commonly used in optical systems and are made

09/30/19 25 of 51


CDD

from a side section of a parent parabolic mirror. The main advantage of an off-axis parabolic mirror versus a centeredparabolic mirror is that an off-axis parabolic mirror allows for more interactive space around the focal point withoutaffecting the reflected beam. [19] [25]

4.2.3. Mirror Substrate Selection

Substrate refers to the base material used to construct the mirror. Because no light is required to pass through thesubstrate, the optical properties of the substrate do not need to be considered. This allows a selection of a substratebased solely on its thermal and mechanical properties. The substrate trade study for NanoSAM was narrowed down tofour considerations: the coefficient of linear thermal expansion, the possibility for a consistent CTE, the density of thematerial, and the cost. It should be noted that the cost study for the various substrates was conducted by comparingun-coated mirrors with a 50mm diameter and a 100 mm focal length. These conditions are not meant to represent therequirements of NanoSAM, but instead provide a consistent metric for cost comparison.

1. Aluminum 6061-T6Aluminum 6061-T6 is a commonly used metallic substrate for off-axis parabolic mirrors. The main attractionfor the use of Aluminum 6060-T6 substrate is material consistency thorough out the optic. Given that the surfacecoating selected is also an aluminum, the CTE of the entire optic will be consistent eliminating thermal stresses.The thermal and mechanical properties for this type of aluminum were pulled from a MatWeb data sheet [4], andthe cost comparison utilized the Edmund’s COTS mirror pricing. The resulting pros and cons summary can beseen below.

Pros ConsAllows for consistent CTE High CTE

High densityHigh cost

Table 25. Pros and Cons of Aluminum 6061-T6

2. Floated BorosilicateFloated Borosilicate is a type of silicate glass that is distinguished by the ”floated” manufacturing process usedin production. This material is a popular substrate for both spherical and off-axis parabolic mirrors. The thermaland mechanical properties for this type of silicate glass were pulled from a Schott data sheet [3], and the costcomparison utilized the Edmund’s COTS mirror pricing. The resulting pros and cons summary can be seenbelow.

Pros ConsVery Low CTE Consistent CTE not possible

Very Low DensityMed-Low Cost

Table 26. Pros and Cons of Floated Borosilicate

3. BorosilicateBorosilicate, also know as N-BK7, also falls in the silicate glass family. This material is the most popular silicateglass used in lenses optics, but is also used with spherical mirrors. The thermal and mechanical properties forthis type of silicate glass were pulled from a Schott data sheet [5], and the cost comparison utilized the Edmund’sCOTS mirror pricing. The resulting pros and cons summary can be seen below.

Pros ConsLow Density Consistent CTE not possible

Very Low Cost Med-High CTE

Table 27. Pros and Cons of Borosilicate

4. Fused SilicaThe final substrate considered was fused silica. Fused silica is a common material used for spherical laser

09/30/19 26 of 51


CDD

mirror applications. The thermal and mechanical properties for this type of silica were pulled from a TOSOHdata sheet [6], and the cost comparison utilized the Edmund’s COTS mirror pricing. The resulting pros and conssummary can be seen bellow.

Pros ConsVery Low Density Consistent CTE not possible

Med-High CostMed-High CTE

Table 28. Pros and Cons of Fused Silica

4.2.4. Mirror Surface Coating

Mirror surface coatings are metallic and/or dielectric coatings applied to the surface of a variety of mirror shapesincluding parabolic, spherical, and flat mirrors. Metallic surface coatings are designed to be optimized for differentregions of the light spectrum depending on the type of metallic coating. Some common metallic coatings are alu-minum, silver, and gold. Dielectric surface coatings are often applied as an overcoat on a metallic surface coating toimprove the durability of the mirror and in some cases enhance the reflectance of the metallic coating. The mirrorsurface coatings considered for the NanoSAM optical instrument trade study were compared by cost, reflection % @1020 nm, surface quality, and durability. In order to evaluate cost for the various mirror surface coatings a 50 mmdiameter and a 100 mm focal length spherical floated borosilicate mirror was chosen to provide a consistent metric forcost comparison.

1. Protected AluminumProtected aluminum is one of the most common metallic mirror coatings for use in the visible and near infraredlight spectrum. A coating of silicon monoxide is used to provide durability against abrasion. The pros and conssummary for protected aluminum can be seen below.

Pros ConsLess expensive Low reflection % @ 1020 nm

DurablePrecision surface quality

Table 29. Pros and Cons of Protected Aluminum

2. Enhanced AluminumEnhanced aluminum is a metallic aluminum surface coating with an additional multi-layer dielectric coatingapplied to the mirror. The dielectric overcoat aims to protect the delicate aluminum surface coating whileimproving the reflectance of the mirror in the visible and ultraviolet light spectrum. The pros and cons summaryfor enhanced aluminum can be seen below.

Pros ConsDurable Moderately expensive

Good reflection % @ 1020 nmPrecision surface quality

Table 30. Pros and Cons of Enhanced Aluminum

3. Protected SilverThe protected silver surface coating is often used for applications where multiple spectral regions must bemeasured due to silvers high reflectance in the visible and infrared light spectrum. However due to silver’stendency to tarnish in high humidity environments a protective coating must be applied. The pros and conssummary for protected silver can be seen below.

09/30/19 27 of 51


CDD

Pros ConsVery good reflection % @ 1020 nm Tarnishes easily

Precision surface quality Very expensive

Table 31. Pros and Cons of Protected Silver

4. Protected GoldThe protective gold mirror surface coating is optimized for use in the near infrared and infrared light spectrumsdue to its high reflectance in those regions. Due to the gold coatings very delicate nature a protective coating isusually required. The pros and cons summary for protected gold can be seen below.

Pros ConsVery good reflection % @ 1020 nm Very expensive

Precision surface quality Poor durability

Table 32. Pros and Cons of Protected Gold

4.2.5. Optical System Layout

Before light enters the detector, it must be filtered for the 1.02 µm center wavelength. Rays of light entering the filtermust be collimated, or parallel to preserve the transmittance properties of the filter. This collimation can be achievedby either filtering the light before the light passes through focusing optics or by adding a collimating instrument (e.g.a lens) after the light has been focused.

Because the instrument will operate sufficiently far away from the sun that the incident light rays may be consid-ered parallel, then a design choice could be to place the filter before the telescope aperture. Stray or scattered lightmay enter the filter at non-orthogonal angles of incidence. However, the relative irradiance of non-solar light sourcesis likely much less than the direct solar irradiance at the filter location. As is evident in the reflector telescope designs,the focused light is not collimated before reaching the detector. By placing the filter before the aperture, collimatingthe light after the telescope would not be required. However, the aperture area will be larger than the region before thediode, so this design choice require a larger filter area and thus an expected increase in cost. Additionally, this designchoice might be preferable, since designing with off the shelf components is simplified when the waveband is aroundor less than 50 nm or monochromatic. This filter location reduces the complexity of the optical design and allows thetelescope to be exposed to less radiation, but has the cost of a larger filter. [13]

Another design choice would be to place the filter after the telescope. This may be required if the parallel rayassumption is not valid or if the cost of the larger filter is out of budget. Placing the filter after the telescope wouldallow for a smaller filter area to be selected and thus the filter cost would be less than the previous option. However,the light would need to be collimated before reaching the filter, as the light leaving the telescope does not have parallelrays. This could be done by adding a lens after the telescope or collimating system. This placement would requireanother system to collimate the light, but would allow for the use of a smaller filter for the 1.02 µm wavelength. Itis important to note that, when collimating light, there will always be some divergence of light that would have to beminimized or justified to be negligible. [14]

4.2.6. Filter

1. Linear Variable FilterLinear variable filters allow selecting for a specific center wavelength by varying the wavelength transmitted bythe filter linearly along the length of the filter. Using this filter requires that the photodiode is precisely placedat the correct location along the filter length to intercept the desired wavelength. [26]

Pros ConsCan be centered at 1020 nm Expensive

Wide passbandRequires alignment

Table 33. Pros and Cons of Linear Variable Bandpass Filtering

09/30/19 28 of 51


CDD

2. Traditional CoatingTraditional coating produces cheap filters with relatively broad passbands. Filters made this way tend to be lessresistant to environmental stress due to the process by which dielectric material is applied to the filter substrate,and they tend to transmit between 50 and 60 percent of incident light in the desired passband. Because thesefilters are acquired as off-the-shelf components, only certain wavelengths are available - this trade study assesses990 nm and 1064 nm CWL filters as the closest equivalent to the desired 1020 nm CWL.

Pros ConsInexpensive Wide passband

Low transmissionOnly available with certain CWL

Table 34. Pros and Cons of Traditional Coating

3. Hard CoatingHard coating produces cheap filters with very narrow passbands. Filters made with hard coating transmit morethan 85 percent of incident light in the desired passband. Because these filters are acquired as off-the-shelfcomponents, only certain wavelengths are available - this trade study assesses 980 nm and 1030 nm CWL filtersas the closest equivalent to the desired 1020 nm CWL.

Pros ConsInexpensive Only available with certain CWL

High transmission

Table 35. Pros and Cons of Hard Coating

4. Custom CoatingIt is possible to commission a custom coated filter which combines the advantages of the hard or traditionalcoated filters but is centered at 1020 nm as required. A preliminary quote indicates that pursuing this option islikely not financially feasible. [27]

Pros ConsControl over CWL Very expensive

Table 36. Pros and Cons of Custom Coating

09/30/19 29 of 51


CDD

5. Trade Study Process and Results

5.1. Electronics System5.1.1. Photodiode Selection

Metric Weight DrivingRequirements

Description and Rationale

Bandwidth 0.2 1.2 Having the photodiode be sensitive to the wavelengthswe are looking at while not measuring any other

wavelengths is ideal so if the optics filtering fails, thephotodiode can measure the necessary data without

incurring more noise from other wavelengths.Dark Current 0.3 1.3, 3.2 Dark current is one of the primary noise sources that the

photodiode can have. Having a calibrated photodiode thathas minimal dark current is crucial to the success of

NanoSAM since accurate data can only be made if noiseis reduced as much as possible.

Active Area 0.1 1.2 The active area is the amount of area the light is allowedto hit the photodiode in order to measure irradiance.

Having a large active area is ideal since it would allow forthe optical system to have a room of error for precision -

which is good to have in a CubeSat mission.Responsivity@ 1020 nm

0.3 1.2 The responsivity of the photodiode is particularlyimportant so the photodiode is able to collect as much

data in its bandwidth as possible.Cost 0.1 Project Budget The cost is important in every project with a limited

budget, however, it’s average cost would be much lessthan some of the more costly optical components.

Table 38. Photodiode Trade Study Metrics and Weighting

Metric 1 3 5Bandwidth 1020 nm ± 1500 nm 1020 nm ± 1000 nm 1020 nm ± 500 nm

Dark Current High Average LowActive Area Small Average Large

Responsivity @ 1020 nm Low Average HighCost High Average Low

Table 39. Photodiode Metric Score Categorization. Note that the numbers in the responsivity section is the range where the photodiode isable to measure.

Metric Weight Si InGaAs GeBandwidth 0.2 3 3 5

Dark Current 0.3 4 3 3Active Area 0.1 4 2 5

Responsivity @ 1020 nm 0.3 5 4 3Cost 0.1 5 3 1Total 1 4.2 3.2 3.1

Table 40. Photodiode Trade Study Scoring

09/30/19 30 of 51


CDD




Resolution 0.3 1.0, 3.1 The ADC is responsible for converting the continuousanalog signal to an accurate digitized signal. It is

imperative that the resolution of the ADC is great enoughto deconvolve simulated aerosol concentrations from a

radiation source.Signal to Noise

Ratio0.3 1.3, 3.1, 3.2 A high signal-to-noise ratio is required to accurately

represent the analog signal in a digital form. The SNRwill be the largest source of error in digitally representing

the analog signal.Dynamic

Range0.1 1.0, 6.1 A large dynamic range is optimal for our ADC design

because the strength of the signal output will varyconsiderably. The ADC must be able to resolve weak andstrong signals to measure the changes in intensity of ourlight source. However, the output of the analog front end

electronics can be scaled to the range of the ADC.Sampling Rate 0.1 1.0, 3.2, 4.1 Sampling rate is important to precisely and accurately

represent the continuous signal however our requirementof 50 Hz is very achievable for most modern electronics.

PowerConsumption

0.1 6.0, 6.1 Power Consumption is important in our applicationbecause power will be limited by batteries however the

spacecraft bus will supply this power which is outside ofthis project scope.

Latency 0.1 2.1.1, 2.1.2,2.1.3

A low latency time is required to accurately clock thesignal to a specific time stamp. The data acquisition mustbe synchronous with the analog signal to receive viable

data.

Table 42. Analog-to-Digital Converter Trade Study Metrics and Weighting

Metric 1 3 5Resolution < 8 bits < 16 bits < 24 bits

Signal to Noise Ratio Low Middle HighDynamic Range Small Average Large

Sampling Rate (Typical) > 1 kHz > 1 MHz > 100 MHzCost High Average Low

Latency Time (Typical) < 1 ms < 1 µs < 1 ns

Table 43. Analog to Digital Converter Metric Score Categorization

Metric Weight Flash Successive Approximation Delta-SigmaResolution 0.3 1 3 5

Signal to Noise Ratio 0.3 2 3 5Dynamic Range 0.1 3 3 3Sampling Rate 0.1 5 3 1

Power Consumption 0.1 1 4 4Latency 0.1 5 3 1

Total 1 2.3 3.1 3.9

Table 44. Analog to Digital Converter Trade Study Scoring

09/30/19 31 of 51


CDD




Size & Weight 0.1 7 In order for this system to fit in a CubeSat, the mass mustbe limited to under the required mass and volume limits.Some options considered for the on-board controller haveconsiderable mass, and that must be considered in their

selection.HardwareInterfacing

0.2 6.1 In order for this mission to be successful, the on-boardcontroller must be able to interface with a number of

different systems, such as the ADC, on-board storage,and spacecraft systems.

Ease ofprogramming

0.15 Resources While some of the systems selected can be very easilyprogrammed, some are extremely difficult. In order for

this mission to be successful, the on-board controller willneed to be programmed to acquire and store the data.This challenge is somewhat mitigated by the fact that

multiple team members have experience with thedifferent design options considered.

ProcessingPower

0.1 6.1 There is a large range in processing power available fromthese different design options. In order to successfully

acquire and store data at the specified rate, the controllerwill need sufficient processing power. However, therequired rates for collecting data are not difficult to

achieve.Power Draw 0.1 6.1 Different controller options have different power

requirements. In a space environment, power is generallyat a premium. Selecting a system with a low power draw

is important for mission success.AvailableSoftwaresolutions

0.15 Resources Some design options require extensive custom softwareto achieve the necessary tasks, while others have

open-source solutions already available. By leveragingexisting software for the on board controller, the design

time can be significantly reduced.

Table 46. On-Board Controller Trade Study Metrics and Weighting

Metric 1 3 5Mass less than .025kg less than .01kg less than .005kg

Volume Large - SmallHardware interfacing No interfaces Some interfaces Many interfacesEase of programming Difficult to program - Simple to program

Processing Power Low Middle HighPower Draw High Middle Low

Available Software Solutions None Some Many

Table 47. On-Board Controller Metric Score Categorization

09/30/19 32 of 51


CDD

Metric Weight FPGA Micro-Controller Single Board ComputerSize & Weight .3 4 5 1

Hardware Interfaces .2 3 2 4Ease of Programming .15 1 3 4

Processing Power .1 5 3 4Power Draw .1 1 5 3

Available Software Solutions .15 2 3 4Total 1 2.85 3.6 3

Table 48. On-Board Controller Trade Study Scoring




Complexity of Use 0.3 Resources The ability to a) use our external memory with ouron-board computer and b) be able to use it with relative

ease with the team’s given expertise is quite crucial giventhe nine-month time limit for the project.

Storage Capacity 0.1 4.1 The storage capacity of the external memory is importantgiven the relatively high rate of data collection and how

often data will be captured. In the event of a missedground station pass, the payload will have to store data

on-board until the next downlink can be achieved.Read/Write Speed 0.1 3.1.1 The read/write speed metric is simply how quickly the

external storage can read the incoming data and store it.The read/write speed is an important metric as it will

ensure no backups in the electronics system occur andthat data will be collected efficiently.

Reliability 0.2 4.1 The ability for the external memory to be durable inspace is crucial to the NanoSAM mission since the data

should not be compromised due to any thermal andradiation damages.

Size/Weight 0.2 7.1, 7.2 Since the completed instrument should be able to fitcomfortably in a CubeSat, the mass and volume are

important considerations to be a viable payload in thefuture. The size/weight is given its 0.1 weight because

the given design choices are typically small so this metricis not as important as some others.

Cost 0.1 Project Budget The cost of the external memory is important given thelimited budget of this project. However, it is not weightedas strongly as other metrics due to the relatively low cost

of the design choices for this selection.

Table 50. External Memory Trade Study Metrics and Weighting

09/30/19 33 of 51


CDD

Metric 1 2 3 4 5Complexity of Use Impossible Difficult Medium Easy Trivial

Storage Capacity [GB] <1 2 3 4 >5Read/Write Speed [MB/s] <100 100-200 200-300 300-400 >400

Reliability Unreliable Many Concerns Some Concerns Few Concerns No concernsSize/Weight Too large Large Medium Small Negligible

Cost [$] >30 20-30 10-20 5-10 <5

Table 51. External Memory Metric Score Categorization

Metric Weight SSD Micro-SD USB NAND FlashComplexity of Use 0.3 2 5 5 4Storage Capacity 0.1 5 5 5 4Read/Write Speed 0.1 5 1 1 2

Reliability 0.2 4 3 4 5Size/Weight 0.2 1 4 3 5

Cost 0.1 1 3 3 5Total 1 2.7 3.8 3.8 4.3

Table 52. External Memory Trade Study Scoring

5.2. Optics System5.2.1. Reflector Telescope Type Selection



Cost 0.3 Project Budget The reflective telescope components are relativelyexpensive. Stock mirrors, lenses and filters may require a

significant portion of the project budget. Thus, anunderstanding of the estimated cost for each telescope

configuration is of paramount importance.Manufacturing

Complexity0.2 1.1, Resources The overall scale of the telescope is small compared to its

predecessors, and miniaturization of optical instrumentsposes a challenge. Precision alignment and installation ofmultiple mirrors necessitates additional equipment, time,

and material resources.Optical

Aberrations0.1 1.1, 3.1 Optical aberrations introduce uncertainty into the

telescope design. Different types of opticalaberrations [17] alter the image at the sensor location. The

accuracy of the focal point(s) influence(s) theperformance of the detector.

Effective FocalLength

0.25 1.1.2, 3.1 First, controlling the effective focal length of thetelescope can mitigate certain optical aberrations.

Second, the effective focal length affects the sensor sizeand placement.

Obstruction 0.15 1.1.1 Obstruction of the optical tube affects the amount of lightgathered (i.e. the effective aperture). Capturing less light

reduces the illumination of the photodiode.

Table 54. Telescope Type Trade Study Metrics and Weighting

09/30/19 34 of 51


CDD

Metric 1 2 3 4 5Cost High High/Medium Medium Medium/Low Low

Manufacturing Complexity High High/Medium Medium Medium/Low LowOptical Aberrations High Risk - Moderate Risk - Low Risk

Effective Focal Length Small - Medium - LargeObstruction High - Medium - Low

Table 55. Telescope Type Metric Score Categorization

Metric Weight Schmidt-Cassegrain Newtonian Herschelian Prime FocusCost 0.3 1 2 4 3

Manufacturing Complexity 0.2 1 2 4 3Optical Aberrations 0.1 3 3 1 5

Effective Focal Length 0.25 5 3 1 1Obstruction 0.15 3 3 5 1

Total 1 2.5 2.5 3.1 2.4

Table 56. Telescope Type Trade Study Scoring




Coefficient ofLinear Thermal

Expansion

0.25 1.1 Because reflecting telescopes use mirrors rather thanlenses, the mirror substrate optical properties will notaffect its performance. The thermal properties of the

substrate, however, remain a key selection parameter. TheCTE was compared directly using material data sheets.

ConsistentCTE Benefit

.05 1.1 The benefit of a consistent substrate and surface coatingCTE is a reduction in the thermal stress within the optic.

Density 0.3 7.2 Given the instrument must be compatible with a CubeSatplatform, the mass of each component remains a key

selection parameter. The values were compared directlyusing material data sheets.

Cost 0.4 Project Budget The budget of $5000 will be a constraining factorthroughout the design of the instrument. The telescope

mirrors will likely require a sizable portion of the budget,thus finding the best value in mirror substrate is essential

for success. The price’s used in the comparisoncorrespond to a 50mm diameter mirror with an effective

focal length of 100mm

Table 58. Mirror Substrate Trade Study Metrics and Weighting

Metric 1 2 3 4 5CTE [ 1

K ∗ 10−6] α > 10 10 > α > 8 8 > α > 6 6 > α > 4 4 > α > 2Consistent CTE Not Possible - - - PossibleDensity [ g

cm3 ] ρ > 2.6 2.6 > ρ > 2.5 2.5 > ρ > 2.4 2.4 > ρ > 2.3 2.3 > ρ > 2.2Cost C > $300 $300 > C > $240 $240 > C > $180 $180 > C > $120 $120 > C > $60

Table 59. Mirror Substrate Metric Score Categorization

09/30/19 35 of 51


CDD

Metric Weight Aluminum 6061-T6 Floated Borosilicate Borosilicate Fused SilicaCTE 0.3 1 5 2 4

Consistent CTE 0.05 5 1 1 1Density 0.3 1 5 2 5

Cost 0.4 1 5 5 3Total 1 1.2 4.8 3.15 3.75

Table 60. Mirror Substrate Trade Study Scoring

5.2.3. Mirror Surface Coating Selection



Cost 0.4 Project Budget The budget of $5000 will be a constraining factorthroughout the design of the instrument. The telescope

mirrors will likely require a sizable portion of the budget,thus finding the best value in mirror surface coating is

essential for success. To distinguish the cost of differentmirror surface coatings a spherical 50mm diameter

mirror with a 100mm focal length was chosen. Then thetype of surface coating was varied.

Reflection %@ 1020 nm

0.3 1.0, 3.0 Reflection % was evaluated using Figure 4 from EdmundOptics Metallic Mirror Coatings resource document. [8]

Surface Quality 0.15 1.0, 3.0 Surface quality was evaluated using the the scratch-digspecification described by MIL-PRF-13830B. [9]

Durability 0.15 1.0 Durability was evaluated using qualitative descriptions ofthe durability of each surface coating from the EdmundOptics Metallic Mirror Coatings resource document. [8]

Table 62. Mirror Surface Coating Trade Study Metrics and Weighting

Metric 1 2 3 4 5Cost C > $400 $400 > C > $350 $350 > C > $300 $300 > C > $250 C < $250

Reflection %@ 1020 nm R < 80 80 > R > 85 85 < R < 90 90 < R < 95 95 < R < 100

Surface Quality 80-50 standard 60-40 precision 20-10 high precisionDurability Poor Average Good

Table 63. Mirror Surface Coating Metric Score Categorization

Metric Weight Protected Aluminum Enhanced Aluminum Protected Silver Protected GoldCost 0.4 5 4 3 3

Reflection %@ 1020 nm 0.3 3 4 5 5

Surface Quality 0.15 3 3 3 3Durability 0.15 5 5 1 3

Total 1 4.1 4 3.3 3.6

Table 64. Mirror Surface Coating Trade Study Scoring

09/30/19 36 of 51


CDD

5.2.4. Filter Selection

Metric Weight Requirements Description and RationaleDeviation from1020 nm CWL

0.4 1.2.1 While the ideal instrument would transmit at 1020 nm, itis difficult to source affordable off-the-shelf filterscentered at this wavelength. Incorporating a filter’sdeviation from the ideal CWL allows assessing how

much deviation from the ideal CWL should be toleratedin favor of other criterion [8].

Cost 0.3 Project Budget The budget of $5000 will be a constraining factorthroughout the design of the instrument. Acquiring a

high-quality filter with well-characterized thermalperformance could become very expensive. To mitigatethis, a the prices for a variety of off-the-shelf filters werecompared to custom filtering options for a 50 mm filter

aperture. [20] Coating process and filter design mostsignificantly impacted this parameter.

Transmission 0.2 3.1 The transmission of the filter is necessary in assessing theresponsiveness of the instrument to small changes in

occultation. Transmission is reported as the percentage ofincident light at the CWL which is allowed through the

filter. [20]

Optical Density 0.1 3.1 Optical density improves the accuracy of the instrumentby removing . [20]

Table 66. Filter Trade Study Metrics and Weighting

Metric 1 2 3 4 5Deviation from <60 nm <45 nm <30 nm <15 nm 0 nm1020 nm CLW

Cost C > $1500 C > $1200 C > $600 C > $300 C < $300Transmission >50% >60% >70% >80% >90%

Optical Density 3 3.5 4

Table 67. Filter Metric Score Categorization

09/30/19 37 of 51


CDD

Metric Weight Linear Variable Traditional Coating Traditional Coating1020 nm CWL 990 nm CWL 1064 nm CWL

Deviation from 0.4 5 3 21.02 µm CLW

Cost 0.3 2 5 5Transmission 0.2 5 1 1

Optical Density 0.1 3 5 1Total 1 3.8 3.4 2.6

Metric Weight Hard Coating Hard Coating Custom Coating980 nm CWL 1030 nm CWL 1020 nm CWL

Deviation from 0.4 2 4 51.02 µm CLW

Cost 0.3 4 4 1Transmission 0.2 4 4 3

Optical Density 0.1 5 5 3Total 1 3.3 4.1 3.2

Table 68. Filter Trade Study Scoring

6. Selection of Baseline Design

6.1. Electronics System6.1.1. Photodiode Selection

Based on the results from Table 40, the best design choice for the photodiode is the silicon photodiode. In nearly everymetric, the Si photodiode always comes up on top. It is imperative that the photodiode is able to be high in responsivityand be able to measure 1020 nm, and the Si diode would be the best selection for the project. Furthermore, it is acomparable active area and is very cost effective to allow for better optical hardware.


Based on the results from Table 44, the best design choice for the analog-to-digital converter is the sigma-delta ADC.While the flash and SAR ADC may be faster, the sigma-delta ADC has unparalleled resolution, and lesser signal-to-noise ratio. It is more important that we obtain accurate rather than frequent results. It is also more cost efficient, andconsumes less power making the sigma-delta ADC the best ADC selection for our project.


Based on the results from Table 48, the best choice for an on-board controller is a microcontroller. A microcontrolleris the smallest and lowest power option. Its ease of programming avoids the risks present with an FPGA, where thedifficulty of writing firmware could sink the mission, and its lack of complexity and software layers makes managingthe risk of an unexpected bug much easier than with a single board computer. Selecting a microcontroller with thenecessary interfaces for ADC, GN&C, external memory, and a radio is feasible.


Based on the results from Table 52, the NAND Flash will be the best choice for the project. The combination ofreliability, size/weight, and cost form the major benefits of using flash memory chips for on board storage. The majordrawback is the increased interfacing complexity. This issue can be minimized by selecting a flash chip with a simpleSPI interface. Read/Write speed is not a major concern for this mission, as our required data sampling rate is fairlylow. Similarly, storage size is not a major concern, as we will only be taking data for a brief time twice per orbit.

09/30/19 38 of 51


CDD

6.2. Optics System6.2.1. Reflector Telescope Type Selection

Based on the results of the reflector telescope trade study, seen in Table 56, the NanoSAM team has selected theHerschelian Telescope. The compound telescope designs, namely the Schmidt-Cassegrian and Newtonian, were foundto require relatively large financial budgets and manufacturing resources. Given the nature of the NanoSAM project,these negative aspects were seen to outweigh the positive optical properties. When comparing the single mirrortelescopes, namely the Herschelian and Prime Focus, the Herschelian was found to be superior in cost, manufacturingcomplexity, and obstructions. The Herschelian’s high risk for optical aberrations must taken into consideration, butthese aberrations will not affect the performance of the instrument provided the light can be properly focused on thedetector. The EFL of the Herschelian telescope was a concern for the NanoSAM project, however the the team isconfident that an adequate focal length is possible given the degrees of freedom within the Herschelian telescopedesign.


Based on the results of the mirror substrate trade study, outlined in Table 60, floated borosilicate will be the substrateused for NanoSAM’s optics. The advantages of floated borosilicate include an exceptionally low density, CTE, andrelative cost. Although selecting this substrate eliminates the opportunity for a unified CTE thought the optic, a fullyaluminum optic would strain NanoSAM’s mass and financial budgets. This in addition to the relatively high CTE ofAluminum 6061-T6 greatly reduced the appeal of a unified optic. Floated borosilicate had the best mechanical andthermal properties within the silicate glass family, and was the clear choice based on the results of the trade study.

6.2.3. Mirror Surface Coating Selection

Based on the results of the mirror surface coating trade study, outlined in Table 68, protected aluminum will be themirror surface coating of choice for NanoSAM’s optical instrument. The advantages of using protected aluminum asa mirror surface coating are as follows: Protected aluminum is a popular mirror coating for use in the visible and nearinfrared light spectrum. NanoSAM’s optical instrument will be measuring light in the 1020 nm wavelength which isin the near infrared light spectrum. Protected aluminum is one of the least expensive mirror surface coatings availablewhich is ideal for NanoSAM’s constrained budget. Protected aluminum is also one of the more durable mirror surfacecoatings due to its coating of silicon monoxide. The improved handling characteristics will be advantageous to theNanoSAM team during assembly of the fragile optical instrument. One disadvantage of using protected aluminumas a mirror coating is that it does not produce the highest reflection percentage when compared to other mirror coat-ing materials. However, the protective aluminum mirror coating is optimized for the infrared light spectrum whichNanoSAM will be operating in. Ultimately, protective aluminum appears to be the best mirror surface coating forNanoSAM’s optical insrument when considering cost, reflectivity at 1020 nm, surface quality, and durability whencompared to enhanced aluminum, protective silver, and protective gold mirror surface coatings.


The filter selection results suggest that a hard-coated 1030 nm filter offers the best compromise in center wavelength.Given that a filter with a true 1020 nm CWL wasn’t available from any of the off-the-shelf suppliers consulted, eithera custom filter or a linear variable filter would be necessary to acquire this center wavelength. However, a 1030 nmfilter with a 10 nm FWHM pass band captures comparable data at a fraction of the price. Hard-coated filters alsooffer the best transmission, generally in excess of 85% transmission, and this translates to more light entering theinstrument and thus greater sensitivity to occultation due to small aerosol concentrations. Finally, this filter choiceoffers good optical density which serves to further improve the instrument’s sensitivity by reducing its measurementof light outside of the passband’s wavelengths.

09/30/19 39 of 51


CDD

References[1] “Photodiode Structures.” Electronic Notes, 2019, www.electronics-notes.com/articles/electronic components/diode

/photodiode-detector-structures-fabrication-materials.php.

[2] “Photodiodes.” Photodiodes, ThorLabs, 2019, www.thorlabs.com/newgrouppage9.cfm?objectgroup id=285.

[3] ”Schott Borofloat 33” Data Sheet, Schott, 2019, https://psec.uchicago.edu/glass/borofloat 33 e.pdf.

[4] ”Aluminum 6061-T6” Data Sheet, MatWeb, 2019, http://amet-me.mnsu.eduUserFilesShared/DATAACQUISITION/mts/met277/9 13-12/MaterialData 9391 Al-6061.pdf

[5] ”Schott N-BK7” Data Sheet, Schott, 2019, https://www.us.schott.com/d/advanced optics/31255521-bf27-46f1-ab3b-f35290482499/schott-datasheet-nbk7-english.pdf

[6] ”Fused Silica Glass” Data Sheet, TOSOH, 2019, http://www.gmassoc.com/pdf/Tosoh%20SGM%20-%20Fused%20Silica%20Glass.pdf

[7] ”Optical Glass Specifications” Optical Glass, Edmunds, 2019, https://www.edmundoptics.com/resources/application-notes/optics/optical-glass/

[8] ”Metallic Mirror Coatings” Optical Glass, Edmunds, 2019, https://www.edmundoptics.com/resources/application-notes/optics/metallic-mirror-coatings/

[9] ”SURFACE SPECIFICATIONS” Optical Glass, Edmunds, 2019, https://www.edmundoptics.com/resources/application-notes/optics/understanding-optical-specifications/

[10] “SAR Analog to Digital Converters - ADC.” Mouser Electronics - Electronic Components Distrib-utor, www.mouser.com/Semiconductors/Data-Converter-ICs/Analog-to-Digital-Converters-ADC/-/N-4c43g?P=1z0t3by.

[11] “Sigma-Delta ADCs.” Maxim Integrated, www.maximintegrated.com/en/design/technical-documents/tutorials/1/1870.html.

[12] Crail, Clayton B. ”Ranking CubeSat Communication Systems Using a Value-centric Framework.” MassachusettsInstitute of Technology, 2013,

[13] “5 Tips for Designing with Off-the-Shelf Optics.” Edmund Optics,https://www.edmundoptics.com/resources/application- notes/optics/5-tips-for-designing-with-off-the-shelf-optics/.

[14] “Considerations in Collimation.”Edmund Optics, https://www.edmundoptics.com/resources/application-notes/optics/considerations-in-collimation/.

[15] “ASEN ASTR GEOL 6050 Space Instrumentation: Lecture 16 Remote Sensing Instruments” University of Col-orado Boulder, Lecture 16 Remote Sensing Instruments.pdf.

[16] Randall, C. E., et al. ”POAM III retrieval algorithm and error analysis.” Journal of Geological Research. Vol.102, No. D21. doi:10.1029/2002JD002137, 2002.

[17] ”Comparison of Optical Aberrations.”Edmund Optics, https://www.edmundoptics.com/resources/application-notes/optics/comparison-of-optical-aberrations/

[18] Horne, S. “10 - Concentrating Photovoltaic (CPV) Systems and Applications.” Concentrating Solar Power Tech-nology: Principles, Developments and Applications, by Keith Lovegrove and Wes Stein, Lightning Source UK,2015.

[19] “Parabolic shape eliminates spherical aberration in telescope mirrors.” Telescopes from the Ground Up,https://amazing-space.stsci.edu/resources/explorations/groundup/lesson/basics/g12/.

[20] “Bandpass Interference Filter — Edmund Optics.” Edmund Optics Inc.,https://www.edmundoptics.com/f/bandpass-interference-filters/14371/.

09/30/19 40 of 51


CDD

[21] Krishnavedala [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)].https://upload.wikimedia.org/wikipedia/commons/b/b1/Cassegrain Telescope.svg

[22] Krishnavedala [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)].https://upload.wikimedia.org/wikipedia/commons/8/86/Newtonian telescope2.svg

[23] User:Eudjinnius [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/)].https://upload.wikimedia.org/wikipedia/commons/e/e8/Herschel-Lomonosov reflecting telescope.svg

[24] Oleg Alexandrov [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/)].https://upload.wikimedia.org/wikipedia/commons/b/b4/Prime focus telescope.svg

[25] “Off-Axis Parabolic Mirror Selection Guide.” Edmund Optics, https://www.edmundoptics.com/resources/application-notes/optics/off-axis-parabolic-mirror-selection-guide/.

[26] ”Linear Variable Bandpass Filter.” Edmund Optics, https://www.edmundoptics.com/f/linear-variable-bandpass-filters-5fd8f505/14865/

[27] ”Optical Filters.” Edmund Optics, https://www.edmundoptics.com/c/optical-filters/610/

09/30/19 41 of 51


CDD

7. Appendix

7.1. Metric Score Justification7.1.1. Photodiode Selection

1. Si

(a) Bandwidth (3/5) The score was a 3 here because it does not meet the best bandwidth requirements that a5 required. However, it has a small range of sensitivity on the upper bound of the nanometer spectrum, sothe bandwidth is limiting in that respect. However, on the lower bound, it can detect wavelengths as smallas 190 nm.

(b) Dark Current (4/5) Since the dark current is in the pico- to nano- Amperes range, it is scored the highestamong the three photodiodes. Ideally, no dark current would be preferable since the data’s sensitivity topA levels of current – so it is not ranked a 5.

(c) Active Area (4/5) Since the average active area is significantly larger than InGaAs but slightly smaller thanGe, the score is placed at a 4 – close but not above Ge, and significantly higher than InGaAs

(d) Responsivity @ 1020 nm (5/5) The responsivity is the the highest in Si compared to the other two types ofphotodiodes when it doesn’t have a filter – at around 0.6 A/W.

(e) Cost (5/5) The cost of Si photodiodes are insanely inexpensive compared to the InGaAs and Ge photodi-odes – averaging at around $50/piece, and the range of price ranging from $15- $114. This is a price thatis completely affordable in the $5000 budget.

2. InGaAs

(a) Bandwidth (3/5) The score was a 3 here because it does not meet the best bandwidth requirements that a5 required. However, it has a small range of sensitivity on the lower of the nanometer spectrum, so thebandwidth is limiting in that respect. However, on the upper bound, it can detect wavelengths as large as2600 nm which far exceeds the maximum range of wavelengths the photo

(b) Dark Current (3/5) Since the max dark current is in the nano- to micro- Amperes range, while it is stillrelatively small, it is significantly larger than the Si photodiodes. However, since the current on average issmaller than Ge’s dark current, it is scored higher than it.

(c) Active Area (2/5) The average active area for InGaAs is two orders of magnitude smaller than both Si andGe. Since the active area is also measured in mm2, this area is significantly smaller than ideal.

(d) Responsivity @ 1020 nm (4/5) The responsivity is the highest in InGaAs compared to the other two typesof photodiodes. However, it is not placed at a 5 since it is unsure how much sensitivity a photodiode canhave that it is considered large.

(e) Cost (3/5) The cost of InGaAs photodiodes are reasonable for the given budget – around $150/piece witha range of prices from $58-$240. Since the average price is more than Si and less than Ge, the score isaround that middle – a 3.

3. Ge

(a) Bandwidth (5/5) The score was given a 5 since according to our source [1], it states that the wavelengthsensitivity is around 800-1700 – which is really close to our ideal wavelength.

(b) Dark Current (2/5) Since the max dark current is in the micro Amperes range, while it is still relativelysmall, it is significantly larger current flow than the other photodiodes

(c) Active Area (5/5) Ge photodiodes have the largest average active area than any of the other photodiodeswe are trade studying – around 36 mm2! This is big for a tiny photodiode, and therefore, placed at a 5.

(d) Responsivity @ 1020 nm (3/5) The responsivity in Ge is between the InGaAs and the Si photodiodes.

(e) Cost (1/5) The cost of Ge photodiodes are quite expensive – as they average to around $300/piece with arange of prices from $150-$500! This is by far more expensive than the Si and InGaAs photodiodes, andfar more unreasonable in the given budget.

09/30/19 42 of 51


CDD


1. Flash

(a) Resolution (1/5) - The resolution of the flash ADC is the lowest compared to the other ADC types, typicallyless than 8 bits.

(b) SNR (2/5) - The SNR of the flash ADC is typically lower than other ADC types however it is not cripplingto the accuracy of the signal output, therefore it deserves a 2/5 score.

(c) Dynamic Range (3/5) - The dynamic range for most flash ADC’s varies depending on the certain model,therefore it deserves a mid-tier 3/5 score.

(d) Sampling Rate (5/5) - Flash ADC types have the greatest sampling rates when compared to other ADCtypes. They typically have sampling rates upwards of hundreds of MSPS (mega-samples per second).

(e) Power Consumption (1/5) - Flash ADC types typically consume the most power compared to other ADCtypes. This is due to the high power demand of the comparator and internal circuitry.

(f) Latency (5/5) - The latency time of flash ADC types is the shortest amongst our ADC selection. Theirinternal circuitry is designed to rapidly convert analog to digital signals, and offers the most time efficientchoice, with conversion times typically less than 1 nano-second.

2. Successive Approximation

(a) Resolution (3/5) - The resolution of the successive approximation ADC is mid-tier compared to the otherADC types, typically 8 - 16 bits.

(b) SNR (3/5) - The SNR of the successive approximation ADC is mid-tier compared to other ADC types,therefore it deserves a 3/5 score.

(c) Dynamic Range (3/5) - The dynamic range of successive approximation ADC types varies greatly anddepends on the model of the specific ADC, therefore a mid-tier 3/5 shall suffice.

(d) Sampling Rate (3/5) - Successive Approximation ADC types generally have mid-tier sampling rates whencompared to other ADC types. They typically have sampling rates greater than 1 MSPS (mega-samplesper second).

(e) Power Consumption (4/5) - Successive Approximation ADC types typically require low power, and are thedefault ADC types for low power mission design.

(f) Latency (3/5) - The latency time of successive approximaton ADC types is mid-tier compared to otherADC’s. They typically convert the analog signal to digital in less than 1 micro-second.

3. Sigma-Delta

(a) Resolution (5/5) - The output resolution of the sigma-delta ADC is the greatest compared to the otherADC types, typically greater than 16 bits. Although the delta-sigma ADC uses a single bit comparator, theoutput resolution is much greater due to digital filtering.

(b) SNR (5/5) - The SNR of the delta-sigma ADC is unparalleled when compared to the other ADC types dueto oversampling and noise shaping of its internal digital filter.

(c) Dynamic Range (3/5) - The dynamic range of sigma-delta ADC types also varies with the specific modelof the ADC, therefore it deserves a mid-tier 3/5 score. This metric will need to be taken into account whenpurchasing the final ADC selected for our project.

(d) Sampling Rate (1/5) - Sigma-delta ADC types have the lowest sampling rates when compared to otherADC types. They typically have sampling rates of 0.001 to 1 MSPS (mega-samples per second).

(e) Power Consumption (4/5) - Sigma-delta ADC types also require low power due to it’s internal digitalcircuitry.

(f) Latency (1/5) - The latency time of sigma-delta ADC types is the greatest compared to ther ADC types.The settling time of the sigma-delta ADC is the greatest malefactor to its conversion rate and typicallytakes time near the magnitude of a milliseconds to convert the analog to digital signal.

09/30/19 43 of 51


CDD


1. FPGA

(a) Size & Weight (4/5) FPGAs are available as either single chips or as small breakout modules. Either of theseoptions have relatively low mass. Using a single chip requires supporting circuitry already present on abreakout module. FPGA modules can be directly integrated with custom PCBs containing other neccessaryelectronic components. This minimizes the volume used by the FPGA in the CubeSat electronics.

(b) Hardware Interface (3/5) An FPGA can implement almost any hardware interface in firmware, makingthis the most versatile option when it comes to interfacing with hardware. However, writing that firmwareis not trivial, and requires significant development time. This is what decreases the hardware interfacescore to 3/5.

(c) Ease of Programming (1/5) An FPGA is by far the most difficult to controller to program of the optionsconsidered. Verilog or VHDL has an extremely steep learning curve. This is somewhat mitigated by theexistence of available software solutions, especially for systems such as Xilinx FPGAs.

(d) Processing Power (5/5) The access to low level logic fabric in FPGAs allows for extremely quick digitalprocessing. Instead of waiting for instructions to be completed on subsequent clock cycles, as on a tradi-tional processor, an FPGA allows for many tasks to be completed in parallel with dedicated circuits foreach one.

(e) Power Draw (1/5) FPGAs can draw a large ammount of power, especially during start up and duringcomplex operations.

(f) Available Software Solutions (2/5) FPGAs have a decent library of available software solutions, especiallyfor the Xilinx family of devices, where large IP catalogs are available, including implementations of mi-croprocessors, block memory, and hardware interfaces. However, using these software solutions is morecomplex than with other design options

2. Micro-controller

(a) Size & Weight (5/5) Micro-controllers are available as single chips and as breakout modules. The singlechips require fewer supporting electronics than FPGAs, meaning a single chip implementation is morefeasible. This makes them the smallest option available

(b) Hardware interfacing (3/5) While interfacing with hardware is more limited on a micro-controller thanan FPGA, and generally these limits cannot be overcome in firmware, implementation of the interface ismuch simpler, making it more feasible for this team than on an FPGA.

(c) Ease of programming (3/5) Micro-controllers are much easier to program than FPGAs, often running oncompiled C or C++ code. Writing code to achieve the mission objectives would be relatively simple.

(d) Processing Power (3/5) Many micro-controllers have very limited processing power, with extremely lim-ited clock speeds and memory, while others can have extremely capable ARM processors with speeds upto 600MHz and large amounts of RAM (Teensy 4.0).

(e) Power Draw (5/5) Micro-controllers draw the least ammount of power of the options considered.

(f) Available Software Solutions (3/5) Many open-source libraries exist for micro-controllers, implementingsolutions for interfacing with a wide variety of hardware.

(g)3. Single Board Computer

(a) Size & Weight (1/5) Single board computers generally occupy a large volume and have a considerablemass. They are only available as discrete circuit boards, and interfacing with other circuit boards generallyrequires cables. This is a large concern for this CubeSat.

(b) Hardware Interfaces (4/5) Like micro-controllers, single board computers have limited hardware inter-faces, and these limits cannot be overcome in firmware or software. However, there are generally morehardware interfaces on an SBC than on a micro-controller. When it comes to storage with a single boardcomputer, some have sufficient on-board flash that external storage is unnecessary, while others do not,and require the use of potentially undesirable storage, such as SC cards, to function at all (Raspberry Pi).

09/30/19 44 of 51


CDD

(c) Ease of Programming (4/5) Single board computers are much easier to program than FPGAs or micro-controllers once the single board computer system is up and running. However, to get to that state, flashingan operating system to either on-board memory, or an SD card is necessary to start using the system. Anyuser code would run on top of this operating system. This means high level languages such as MATLABcan be used. However, running mission critical code on top of an operating system could be considered anoverly complex solution that’s more difficult to debug and find all potentially mission ending issues.

(d) Processing Power (4/5) Single board computers generally have more processing power than micro-controllers,but less than FPGAs.

(e) Power Draw (3/5) Single board computers generally draw more power than microcontrollers but less thanFPGAs.

(f) Available Software Solutions (4/5) Single board computers have a wide array of software solutions avail-able, but again, the large amount of underlying systems for these solutions present a mission risk.


1. SSD

(a) Complexity of Use (2/5) A lot of SSD cards require SATA connections, which would be very difficult tointerface with our micro-controller. Other external SSDs can be connected using a microUSB connectionwhich would be easy to interface with, however, this would cost read/write speed.

(b) Storage Capacity (5/5) Out of all of the external memory options, SSDs have the highest storage capacity,typically on the range of hundreds of GB to a few TB.

(c) Read/Write Speed (5/5) The read/write speed is on the order of hundreds of MB/s, making SSDs one ofthe fastest external storage options offered.

(d) Reliability (4/5) The SSDs are very reliable as they are heavily used in many tablets, laptops, etc. However,on a mission like NanoSAM, where it will eventually be exposed to the harsh conditions of space, SSDsmay lose reliability. Thus, SSDs were not scored the highest on reliability.

(e) Size/Weight (1/5) SSDs are far too large to fit in a CubeSat of NanoSAM’s scale. Some smaller SSDoptions would even take up much of the area/volume of a 1U CubeSat. The weight of an SSD is also muchheavier than the other external storage option considered.

(f) Cost (1/5) The cost of SSDs is large and could take up a decent chunk of our limited budget. SSDs for lessthan $30 are not common and other external memory options are far cheaper. Therefore, the cost metricreceived the lowest possible score.

2. Micro-SD Card

(a) Complexity of Use (5/5) A microSD card is very trivial to use as it only takes a microSD card slot on amicro-controller, thus is received the highest score in this metric.

(b) Storage Capacity (5/5) MicroSD cards have high capacities and could easily cover the storage necessaryfor this mission so it received a very high score in this area.

(c) Read/Write Speed (1/5) The read speed was found to be about a maximum of 100 MB/s upon researchin the subject. The maximum write speeds were found to be less than about 60 MB/s, so the microSDreceived a low score in this metric.

(d) Reliability (3/5) MicroSD cards are fairly reliable because they are so simple and small and can stay lockedinto a microSD slot pretty well. However, many CubeSat missions (including a few at LASP) have faileddue purely to SD card failures. They are prone to charged particle strikes that could cause them to fail. Forthese reasons, the microSD cards received an average score in this area.

(e) Size/Weight (4/5) MicroSDs are very tiny and would normally be considered negligible in size/weight,however, relative to our other option considered (specifically the NAND Flash chip), the microSD is notthe smallest in size/weight. Therefore, the microSD did not score the highest in this metric.

(f) Cost (3/5) The microSD card is fairly cheap but finding one for less than $10 is not common as they areusually in the $10-$20 range so it scored an average score in this metric.

3. USB

09/30/19 45 of 51


CDD

(a) Complexity of Use (5/5) The USB stick is probably one of most trivial external storage devices as it justinvolved a USB drive on the micro-controller so it received the highest score in this category.

(b) Storage Capacity (5/5) The storage capacity of USB sticks is more than enough for this mission, so itreceived the highest score in this metric.

(c) Read/Write Speed (1/5) The read/write speed of a USB stick is among the lowest of the options considered.The read/write speeds are typically much less than 100 MB/s, so it received the lowest score in this area.

(d) Reliability (4/5) The reliability of a USB stick has few concerns other than the connection between thedrive and the USB stick can be prone to thermal contraction/expansion and can be faulty in this manner.Therefore, it did not receive the highest score in this area.

(e) Size/Weight (3/5) The size and weight of a USB stick is about average as it would not take up muchmass/volume in a CubeSat compared to an SSD, but it would take up more space than a NAND Flash chipand a microSD card, so it received an average score in this area.

(f) Cost (3/5) The cost of many typical USB sticks are on the scale of $10-$20 for the storage necessary forthis mission, therefore it received an average score in this metric.

4. NAND Flash

(a) Complexity of Use (4/5) NAND Flash is available in packages designed to interface over an SPI bus. Thisallows them to easily connect to all of the on-board controller options.

(b) Storage Capacity (4/5) NAND Flash has the least storage per chip of the available options, however, it istrivial to include multiple chips on a circuit board, allowing for large amounts of data storage.

(c) Read/Write Speed (2/5) NAND Flash uses SPI, same as microSD. The difference is that SD cards generallyuse a file access table to allocate memory, which adds some overhead to transfer speeds compared toNAND Flash.

(d) Reliability (5/5) NAND Flash forms the basis of all the other storage options considered. The microcon-troller that handles the transfer of data for the other options considered is susceptible to radiation damagein the space environment. By bypassing this and interfacing directly with the NAND flash, this risk isremoved. Additionally, thermal expansion and contraction can cause failure of the contacts on an SD card,SSD, or USB drive. Directly soldering a flash chip eliminates this risk

(e) Size/Weight (5/5) NAND Flash is the smallest of the considered options.

(f) Cost (5/5) NAND Flash is the cheapest of the considered options.

7.1.5. Optics System

7.1.6. Reflector Telescope Type Selection

The telescope type cost trade-off score was computed using a weighted scheme. The cost of each reflector design isprimarily a function of the number of optics and the shape of optics. Curved mirrors are assigned a weight of 2.5, flatmirrors are assigned a weight of 1, and spider vane mounts are assigned of weight of 0.5. The following is based onresearch conducted through the Edmund Optics website. Mirror cost is influenced by the substrate composition, sur-face coating, surface accuracy, and size. 51 mm and 25.4 mm diameter spherical and flat mirrors composed of FloatedBorosilicate (highest trade score), coated with Protected Aluminum (highest trade score), and having surface accuracyratings of λ/4 were compared. These parameters are not meant to represent the final requirements of NanoSAM.Rather, they provide a consistent metric for cost comparison similar to the substrate and surface coating studies. Thesmaller spherical mirror costs $103.00, while the larger spherical mirror costs $139.00. The corresponding flat mirrorscost $32.00 and $52.50. The ratio of mirror costs are 3.22 and 2.65, or 2.93 on average. Curved mirrors are assumed tobe roughly 2.5 times more expensive than their flat mirror counterparts, resulting in the weights described above. Thefunctional form of the weighted scheme is as follows: Cost Rating = (2.5) x Number of Curved Mirrors + Number ofFlat Mirrors + (0.5) x Number of Mounts. Trade scores, in descending order correspond to cost ratings on the intervals:[0,2), [2,3), [3,4), [4,5), [5,∞). Cost is a critical project element to consider. The price of COTS optics componentscan extend into the hundreds to thousands of dollars. Working within a $5000 project budget, the cost of the reflectortelescope requires proper attention. The weight of the cost factor is chosen to be 0.3 (highest individual weight).

In a similar manner, the reflector manufacturing complexity trade study was scored using a weighted scheme. Themanufacturing complexity was evaluated based on the required number of optic alignments, optic mounts (excluding

09/30/19 46 of 51


CDD

the primary mirror mount), and custom manufacturing specifications (e.g. a hole in the primary mirror). The hierarchyof these factors, in order of most complex to least complex, was chosen as: optic alignment, optic mounting, thencustom manufacturing specification. Assigning the weights 3, 2, and 1 to these factors, respectively provides a quan-titative measure of the relative complexities associated with each reflector. An individual reflector type is assigned atrade score of 5, 4, 3, 2, or 1 for a sum of complexities on the interval [1,2], [3,4], [5,6], [7,8], or [9,10], respectively.The manufacturing complexity will directly expend time, equipment, and labor resources. There is little flexibility inthe project schedule and appropriate equipment may be difficult to access. Therefore, a weight of 0.2 is assigned tothe manufacturing complexity.

The EFL is an important metric used to define the relative sizes of the mirrors as well as their curvatures. The EFLalso affects the location and size of the sensor making irradiance measurements. Moreover, manipulating the EFL canalter the effects of certain aberrations, namely comatic aberrations associated with curved mirrors. Due to its extensiveimpact on the overall design and indirect influence over the performance of the sensor, the EFL metric is given aweight of 0.25. Optical aberrations are the least significant metric. Aberrations are usually mitigated through the useof different mirror shapes and corrective lenses. Furthermore, the precision manufacturing of mirrors decreases theprobability of aberrations caused by surface defects. In the end, a weight of 0.1 is assigned to the optical aberrationsmetric. Lastly, the obstruction metric is considered. The efficiency of the photodiode is dependent upon the numberof photons impacting the contact surface. Restricting the number of incident photons limits the photodiode output. Asufficient photon stream is necessary for the photodiode to operate effectively. With that said, the obstruction metricis not as important as the cost or manufacturing complexity metrics and is assigned a weight equal to 0.15.

1. Schmidt-Cassegrain

(a) Cost (1/5) The Cassegrain reflector is composed of two curved mirrors and one secondary mirror mount.The cost rating is 5.5, which falls into the High cost trade score category.

(b) Manufacturing Complexity (1/5) For a Cassegrain reflector, the two mirrors require two alignments, asingle interior mirror mount, and a precisely dimensioned hole through the primary mirror. According tothe simple weighted scheme, the Cassegrain reflector has a complexity rating of 9, corresponding to theHigh trade score.

(c) Optical Aberrations (3/5) Cassegrain telescopes will have comatic, spherical, and astigmatism aberrations.Assuming the spherical aberration can be diminished by using parabolic mirrors, the comatic and astig-matism aberrations are more likely. Both result from a slight misalignment of the mirrors relative to theoptical axis. There is moderate risk of producing these two aberrations.

(d) Effective Focal Length (5/5) The telescope length is constrained by the size constraint of the payload. Fora given telescope length, Cassegrain reflectors are capable of achieving large effective focal lengths. As aresult, the Cassegrain reflector was assigned the highest trade score of 5.

(e) Obstruction (3/5) The secondary mirror will cause an obstruction of the optical tube. The decrease inthe effective aperture is typical for a reflector telescope with a secondary mirror located between the lightsource and the primary mirror. Thus, the trade score assigned for the obstruction is the average.

2. Newtonian

(a) Cost (2/5) The Newtonian reflector utilizes one curved mirror, one flat mirror, and one secondary mirrormount. The cost rating of 4 is considered Medium/High.

(b) Manufacturing Complexity (2/5) Newtonian reflectors require two optic alignments and a single secondarymirror mount. Newtonian reflectors receive a complexity rating of 8, corresponding to a trade score ofMedium/High.

(c) Optical Aberrations (3/5) Newtonian telescopes are at risk of generating comatic, sperical, and tilt aberra-tions. Again, assuming the spherical aberration can be addressed, the comatic and tilt aberrations domi-nate. Although the effects are minimal, the intermediate risk of inducing these aberrations is similar to theCassegrain telescope.

(d) Effective Focal Length (3/5) The EFL of a Newtonian telescope is less than the EFL of the Cassegrainconfiguration. The EFL can be larger than the length of the optical tube. Placing the focal point of thesecondary mirror away from the optical axis allows for an EFL larger than both the Herschelian and PrimeFocus telescopes. Thus, the Newtonian telescope is assigned a trade score corresponding to Medium EFL.

09/30/19 47 of 51


CDD

(e) Obstruction (3/5) For a given primary mirror with a specific focal length, the Newtonian secondary mirroris slightly smaller than the Cassegrain secondary mirror due to the tilt angle. However, for the scale of theNanoSAM telescope, this disparity is very small. The Newtonian configuration produces an obstructionsimilar in size to the Cassegrain telescope. The obstruction size is typical for a reflector telescope with asecondary mirror located between the light source and the primary mirror.

3. Herschelian

(a) Cost (4/5) The Herschelian telescope design employs a single curved mirror. The cost rating of 2.5 is thelowest of the four design options. Herschelian reflectors are assigned a Low/Med trade score.

(b) Manufacturing Complexity (4/5) Herschelian telescopes require a single mirror alignment, correspondingto a complexity rating of 3 according to the simple weighted scheme. Ultimately, the manufacturingcomplexity of the Herschelian reflector is given a trade score of Low/Medium.

(c) Optical Aberrations (1/5) The tilted primary mirror for the Herschelian reflector is at a high risk for devel-oping comatic aberration. Moreover, the tilt generates tilt aberration. The tilt aberration may be mitigatedby employing an off-axis parabolic primary mirror. Nevertheless, the risk for developing aberrations isgreater than Newtonian and Cassegrain reflectors.

(d) Effective Focal Length (1/5) For small diameter apertures, the EFL of a single reflector telescope is limited.In general, the Herschelian telescope type will have smaller EFLs than Newtonian telescopes. Due to theirrelatively short EFLs, the Herschelian configuration is awarded a trade score of 1.

(e) Obstruction (5/5) The Herschelian telesope eliminates the secondary mirror and is capable of focusinglight to a point outside of the optical tube. Consequently, an ideal Herschelian configuration will have noobstruction, and therefore, no decrease in effective aperture. The obstruction trade score is the highestpossible.

4. Prime Focus

(a) Cost (3/5) Prime Focus telescopes require an optical mount in addition to a single curved mirror. Applyingthe weighted scheme produces a cost rating of 3, corresponding to a trade score of 3 (Medium).

(b) Manufacturing Complexity (3/5) The Prime Focus reflector manufacturing complexity is a function of theprimary mirror alignment and the optical mount needed to install the sensor and supporting electroniccomponents. The complexity rating of 5 coincides with a trade score of Medium.

(c) Optical Aberrations (5/5) The Prime Focus reflector is at risk of producing comatic aberrations and spher-ical aberrations. Ignoring the spherical aberrations, the Prime Focus telescope is at a relatively low risk fordeveloping aberrations compared to the other telescope types.

(d) Effective Focal Length (1/5) The EFLs of Prime Focus telescopes are severely limited. The focal pointlies along the optical axis. For a constant sensor size and image size at the sensor location, the EFL ofthe Prime Focus telescope is typically less than the multi-mirror reflectors. Compared to the Herschelianconfiguration, the EFLs are similar.

(e) Obstruction (1/5) The prime focus telescope design requires that the sensor is placed between the lightsource and the primary mirror. In addition to the photodiode, any wires or other components required tomeasure and record the solar irradiance will obstruct the telescope. At smaller scales, this obstruction ismore significant. The worst-case trade score is assigned due to the increased risk of high obstruction.


1. Aluminum 6061-T6

(a) CTE (1/5) Aluminum 6061-T6 has a CTE of α20−300K = 2.36 ∗ 10−5K−1. This is the highest CTE seenwith the substrates considered.

(b) Consistent CTE (5/5) Aluminum 6061-T6 is a viable surface coating thus a consistent CTE optic is possi-ble.

(c) Density (1/5) Aluminum 6061-T6 has a density of ρ = 2.7 gcm3 . This is the highest density of all substrates

considered.

(d) Cost (1/5) An un-coated 50 mm dia. off-axis parabolic mirror with a 100mm EFL costs ≈ $330

09/30/19 48 of 51


CDD

2. Floated Borosilicate

(a) CTE (5/5) Floated Borosilicate has a CTE of α20−300K = 3.25 ∗ 10−6K−1. This is the lowest CTE seen withthe substrates considered.

(b) Consistent CTE (1/5) Floated Borosilicate is not a viable surface coating thus a consistent CTE optic is notpossible.

(c) Density (5/5) Floated Borosilicate has a density of ρ = 2.2 gcm3 . This is tied for the lowest density of all

substrates considered.

(d) Cost (5/5) An un-coated 50 mm dia. parabolic mirror with a 100mm EFL costs ≈ $112

3. Borosilicate

(a) CTE (2/5) Borofloat Borosilicate has a CTE of α20−300K = 8.3 ∗ 10−6K−1.

(b) Consistent CTE (1/5) Borosilicate is not a viable surface coating thus a consistent CTE optic is not possible.

(c) Density (2/5) Floated Borosilicate has a density of ρ = 2.5 gcm3 .

(d) Cost (5/5) An un-coated 50 mm dia. spherical mirror with a 100mm EFL costs ≈ $58

4. Fused Silica

(a) CTE (4/5) has a CTE of α20−300K = 5.84 ∗ 10−6K1.

(b) Consistent CTE (1/5) Fused silica is not a viable surface coating thus a consistent CTE optic is not possible.

(c) Density (5/5) Fused silica has a density of ρ = 2.2 gcm3 . This is tied for the lowest density of all substrates

considered.

(d) Cost (3/5) An un-coated 50 mm dia. spherical mirror with a 100mm EFL costs ≈ $197

7.1.8. Mirror Surface Coating Type Selection

1. Protected Aluminum

(a) Cost (5/5) A protected aluminum coated 50 mm dia. spherical mirror with a 100 mm EFL costs approxi-mately $220.

(b) Reflection % @ 1020 nm (3/5) Protected aluminum has a reflection of approximately 88% @ 1020 nm.

(c) Surface Quality (3/5) Protected aluminum has a MIL surface quality rating of 60-40.

(d) Durability (5/5) Protected aluminum is coated with a silicon monoxide layer which provides durabilityagainst abrasion, general handling, and cleaning.

2. Enhanced Aluminum

(a) Cost (3/5) A enhanced aluminum coated 50 mm dia. spherical mirror with a 100 mm EFL costs approxi-mately $260.

(b) Reflection % @ 1020 nm (4/5) Enhanced aluminum has a reflection of approximately 93% @ 1020 nm.

(c) Surface Quality (3/5) Enhanced aluminum has a MIL surface quality rating of 60-40.

(d) Durability (5/5) Enhanced aluminum has a multi-layer dielectric coating that shares the same durabilityand handling characteristics of protected aluminum.

3. Protected Silver

(a) Cost (3/5) A protected silver coated 50 mm dia. spherical mirror with a 100 mm EFL costs approximately$305.

(b) Reflection % @ 1020 nm (5/5) Protected silver has a reflection of approximately 95% @ 1020 nm.

(c) Surface Quality (3/5) Protected silver has a MIL surface quality rating of 60-40.

(d) Durability (1/5) Protected silver has a tendency to tarnish when exposed to a high humidity environment.A protective coating is added as an overcoat to reduce the effects of tarnishing. However it is still recom-mended that silver mirror coatings be operated in a low humidity environment.

09/30/19 49 of 51


CDD

4. Protected Gold

(a) Cost (3/5) A protected gold coated 50 mm dia. spherical mirror with a 100 mm EFL costs approximately$305.

(b) Reflection % @ 1020 nm (5/5) Protected gold has a reflection of approximately 96% @ 1020 nm.

(c) Surface Quality (3/5) Protected gold has a MIL surface quality rating of 60-40.

(d) Durability (3/5) Gold as a surface mirror coating is very delicate and requires a protective overcoat formany applications to maintain its high reflectance.


1. Linear Variable (1.020 µm CWL) [26]

(a) Deviation from 1.02µm CLW (5/5) The CWL is exactly 1.02 micron as required. 0 nm deviation.

(b) Cost (2/5) Cost of the filter is $2000.

(c) Transmission (5/5) These filters can transmit 90-95% of incident light in the passband.

(d) Optical Density (3/5) The average optical density of this filter type is 3.5.

2. Traditional Coating (0.990 µm CWL)

(a) Deviation from 1.02µm CLW (3/5) Deviation from required CWL is 30 nm.


(c) Transmission (1/5) Transmission is greater than or equal to 50%.

(d) Optical Density (5/5) Minimum Optical Density is 4.

3. Traditional Coating (1.064 µm CWL)





4. Hard Coating (0.980 µm CWL)





5. Hard Coating (1.030 µm CWL)


(b) Cost (4/5) The cost of the filter is $595.



6. Custom Coating (1.020 µm CWL)

(a) Deviation from 1.02µm CLW (5/5) CWL is exactly as required. 0 nm deviation.

(b) Cost (1/5) Cost of the filter is on a quote basis. Uncertain given that it varies based on aperture but generallyvery expensive.


(d) Optical Density (3/5) Minimum Optical Density 3.5.

09/30/19 50 of 51


CDD

7.2. Contact Times for Mock Orbital Trajectory

Table 69. Contact Times

Start Time (UTC) Stop Time (UTC) Duration (s)02 Jan 2021 02:18:42.216 02 Jan 2021 02:22:59.093 256.8773304702 Jan 2021 03:56:19.344 02 Jan 2021 04:02:33.456 374.1120785602 Jan 2021 05:35:47.623 02 Jan 2021 05:41:27.028 339.4048971902 Jan 2021 07:14:54.700 02 Jan 2021 07:20:54.959 360.2593955102 Jan 2021 08:53:54.951 02 Jan 2021 08:59:35.376 340.4244617303 Jan 2021 01:52:17.607 03 Jan 2021 01:56:29.899 252.2920650303 Jan 2021 03:29:51.788 03 Jan 2021 03:36:06.254 374.4659729903 Jan 2021 05:09:19.696 03 Jan 2021 05:14:59.687 339.9912542803 Jan 2021 06:48:27.242 03 Jan 2021 06:54:27.509 360.2660559803 Jan 2021 08:27:26.920 03 Jan 2021 08:33:09.486 342.5654394204 Jan 2021 01:25:53.133 04 Jan 2021 01:30:00.582 247.4489573704 Jan 2021 03:03:24.269 04 Jan 2021 03:09:39.016 374.7471227704 Jan 2021 04:42:51.778 04 Jan 2021 04:48:32.316 340.5374294604 Jan 2021 06:21:59.785 04 Jan 2021 06:28:00.020 360.2353370404 Jan 2021 08:00:58.905 04 Jan 2021 08:06:43.534 344.6297663805 Jan 2021 00:59:28.802 05 Jan 2021 01:03:31.135 242.3328103705 Jan 2021 02:36:56.788 05 Jan 2021 02:43:11.742 374.9537095405 Jan 2021 04:16:23.875 05 Jan 2021 04:22:04.915 341.0399161705 Jan 2021 05:55:32.330 05 Jan 2021 06:01:32.493 360.1627250305 Jan 2021 07:34:30.907 05 Jan 2021 07:40:17.520 346.6133146406 Jan 2021 00:33:04.626 06 Jan 2021 00:37:01.553 236.9272038806 Jan 2021 02:10:29.349 06 Jan 2021 02:16:44.434 375.0844989806 Jan 2021 03:49:55.988 06 Jan 2021 03:55:37.484 341.4957591706 Jan 2021 05:29:04.882 06 Jan 2021 05:35:04.926 360.0440938606 Jan 2021 07:08:02.929 06 Jan 2021 07:13:51.441 348.5122189907 Jan 2021 00:06:40.614 07 Jan 2021 00:10:31.828 231.2141279107 Jan 2021 01:44:01.954 07 Jan 2021 01:50:17.092 375.1388504907 Jan 2021 03:23:28.122 07 Jan 2021 03:29:10.024 341.9025790307 Jan 2021 05:02:37.444 07 Jan 2021 05:08:37.320 359.8757408207 Jan 2021 06:41:34.975 07 Jan 2021 06:47:25.298 350.3229448707 Jan 2021 23:40:16.779 07 Jan 2021 23:44:01.952 225.1734948108 Jan 2021 01:17:34.603 08 Jan 2021 01:23:49.720 375.1167200608 Jan 2021 02:57:00.278 08 Jan 2021 03:02:42.537 342.2586061308 Jan 2021 04:36:10.020 08 Jan 2021 04:42:09.674 359.6544321708 Jan 2021 06:15:07.047 08 Jan 2021 06:20:59.089 352.04233022

09/30/19 51 of 51


CDD

nano-stratospheric aerosol measurement (nanosam

Documents