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HASP Student Payload Application for 2010
Payload Title:
Hatchling I BalloonSat
Payload Class:
Small
Institution:
Embry-Riddle Aeronautical University
Submit Date:
December 18, 2009
Project Abstract
The Embry-Riddle HASP payload will provide a test bed for the multi-mission satellite
subsystems under development at ERAU for future proposed NanoSat- and CubeSat-class
spacecraft. This core satellite bus will consist of power, computer, and communications
subsystems. The bus is being developed to accommodate a variety of scientific payloads. For the
2010 HASP mission, a cooperative demonstration payload experiment under development by
Pima Community College Northwest Campus Science Department will be included. This
experiment will provide calibration of sun photometers, which is critically dependent on the
extraterrestrial (ET) constant, i.e. the intensity of sunlight at the top of the atmosphere using an
array of detectors.
Team Name:
ERAU HASP
Team or Project Website:
http://spacegrant.pr.erau.edu/programs.shtml
Student Team Leader Contact Information: Faculty Advisor Contact Information:
Name: Seth Guberman John “Jack” Crabtree
Department: Aerospace Engineering College of Engineering
Mailing
Address:
Embry-Riddle Aeronautical Univ
3700 Willow Creek Rd
#7382
Embry-Riddle Aeronautical University
3700 Willow Creek Rd
Bldg. 75 AXFAB
City, State,
Zip code:
Prescott, AZ 86301 Prescott, AZ 86301
e-mail: [email protected] [email protected]
Office
telephone:
(928) 458-5148 (928) 777-6916
Cell: (832) 657-5688 (928) 713-2756
FAX: (928) 777-6945
(928) 777-6945
http://mail.google.com/mail/?ui=2&ik=c6b3c35381&view=a
tt&th=122e1390dbbe97d3&attid=0.1.2&disp=inline&zw2010 HASP Proposal ERAU Hatchling I BalloonSat and PCC BrightStar Payload
Prepared by Seth Guberman
ABSTRACT
Embry-Riddle Aeronautical University’s submission for HASP 2010 is a test
bed for the multi-mission satellite subsystems currently in development
for future NanoSat- and CubeSat-class spacecraft. This satellite bus
consists of electrical power, onboard computer, and communications
subsystems and will support a variety of scientific payloads. For the
2010 HASP mission, a cooperative payload experiment under
development by Pima Community College Northwest Campus Science
Department will be included.
ERAU Hatchling I and PCC BrightStar 2
Introduction As part of Embry-Riddle Aeronautical University’s goal to have a satellite in orbit
in the next five years, and with experience stemming from past successful
balloon launches, development of the Hatchling I BalloonSat began in early
2009. Its three core satellite subsystems (electrical power, onboard computer,
and communications) comprise a bus that will provide support for a variety of
scientific experiments while meeting the dimensional constraints of a CubeSat-
class spacecraft. For the 2010 launch, a scientific payload developed by Pima
Community College Northwest Campus Science Department has been selected
for integration with Hatchling I’s core subsystems. In addition, a composite
structure is being fabricated to accommodate the payload and comply with
HASP requirements.
Payload Description The 2010 HASP submission consists of two main parts: the Hatchling I satellite bus
(developed by ERAU), and the BrightStar scientific payload (developed by
PCC). Because BrightStar is the science driving the mission, and likely of greater
interest to the members of the HASP administration, it will be discussed first.
PCC BrightStar The Earth’s atmosphere is a complex system that requires the application of
physics, chemistry, astronomy, and biology concepts to explain climate change
and global weather systems. Of particular importance to students in the
physical sciences is solar and terrestrial radiation. The question of what happens
when sunlight interacts with the atmosphere leads to the investigation of
terrestrial radiation reflected from Earth’s surface. Ground based measurements
of solar radiation are dependent on the knowledge of the extraterrestrial
constant, or ET. While many studies of the air mass above the surface of Earth
utilize an average value for ET (1350 W/m2 ), this may not be sufficient to explain
or understand captured data. In our previous HASP application we proposed
building a complex sensor head composed of 25 LEDs covering wavelengths
from the blue to the infrared. Significant changes have been made to this
design that reduces the complexity of the sensor head and its fabrication. The
goal of our experiment is to enable our students to measure solar radiation in the
absence of the Earth’s atmosphere and compare it to simultaneously made
ground-based measurements.
Proposed Experiment: Measurement of the Extraterrestrial Constant
The calibration of sun photometers is critically dependent on the extraterrestrial
constant (ET), i.e. the intensity of sunlight at the top of the Earth’s atmosphere.
Our experiment will determine the value of ET at altitude while making
simultaneous intensity measurements on the ground. By employing the Langley
method we will determine the air mass for three separate wavelengths and
ERAU Hatchling I and PCC BrightStar 3
compare our results to published data. The detector head will employ the use
of six LEDs covering three distinct wavelengths and allow for a redundancy of
two. The use of LEDs as light sensors was pioneered by Forrest Mims III1 and has become the key instrument for his climate studies worldwide2,3.
The schematic representation below shows the signal flow through our LED
sensor head to the BX-24 microprocessor within BrightStar. The output of the
microprocessor is then passed to the Hatchling I onboard computer, described
later in this document.
Figure 1: BrightStar Signal Flow
There are two significant challenges presented by using LEDs as light sensors in
the near space environment found on the HASP platform:
• The measurement of ET is based on normal incidence of radiation.
• LED output is sensitive to temperature and hence the LEDs require heating.
In our previous HASP proposal, the sensor head called for a dome populated
with LEDs and was allowed to rotate with three degrees of freedom. The correct
1 F. M. Mims III, An Inexpensive and Accurate Student Sun Photometer with Light-Emitting Diodes as Spectrally Selective
Detectors, Proceedings of the Third Annual GLOBE Conference, 232-239, August 1998.
2 Brooks, David R., Forrest M. Mims III, Arlene S. Levine, Dwayne Hinton, The GLOBE/GIFTS Water Vapor Monitoring Project: An Educator's Guide with Activities in Earth Sciences. NASA Publication EG-2003-12-06-LARC, 2003.
3 Forrest M. Mims III, "LED Sun Photometry," Optics & Photonics News 20, 32-38 (2009)
http://www.opticsinfobase.org/abstract.cfm?URI=OPN-20-9-32
ERAU Hatchling I and PCC BrightStar 4
position of the sensor head was to be driven by servomotors that were
controlled by the output of four photocells arranged in an x-y pattern that
sensed the coordinates of maximum radiation and moved the LED platform
accordingly. This proved to be extremely complex to fabricate and was
abandoned for a simpler and more effective design. The new design calls for a
flat plate set at a pre-determined angle with respect to the y-axis. Figure 2 is our
proof-of-concept model that was used to finalize the circuit board design. The
final version will be considerably smaller owing to the use of vendor-fabricated
boards that adhere to Hatchling I’s bus specification. This will allow for
uniformity of the electrical and physical connections and simplicity of
integration within the payload structure.
Figure 2: Prototype Sensor Array
The output of each Op Amp was maximized by field testing the board and
determining the correct value of the feedback resistor that yielded the highest
voltage. The integration of the sensor board with the A/D circuitry and power
busses was then performed to evaluate signal integrity. Careful placement of
voltage lines and the addition of filtering capacitors further reduced the noise.
Finally, test integration with Hatchling I’s circuitry was performed. Those results
are discussed later in this document.
An electrical schematic is shown in the Preliminary Drawings section of this
document.
Op Amps
LEDs
ERAU Hatchling I and PCC BrightStar 5
Sensor Head Rotation
A single servo will drive the array in a plane orthogonal to the y-axis as shown in
Figure 3. To avoid twisting problems on the cable from the heater/LED platform,
rotation will be 180 degrees clockwise immediately followed by 180 degree
counterclockwise rotation. This constitutes a single cycle and will be repeated
throughout the measurement process. The platform will sit above the planar
exterior of the structure and still conform to a maximum overall height of 30 cm.
The mass of the sensor head and heater assembly does not present a problem
for the servo. We have cold tested the servo for 1 hour at -50 oC both loaded
and unloaded with no problems. The addition of a low temperature lubricant to
the servo drive mechanism will ensure continuous operation in near space conditions.
A cross-section of the measuring assembly can be found Figure 3. The mounting
plate that holds the sensor board and heater assembly is a picture frame design
that minimizes the mass. Materials under consideration at this time are
aluminum or Delran. The attachment of the sensor board to the frame will be
done with screws of the same material as the frame.
Figure 3: BrightStar Cross-Section (dimensions in inches)
ERAU Hatchling I and PCC BrightStar 6
The design of the electronic boards (trays #1 and #2 above) has since changed
and will instead interface directly with Hatchling I’s main PCB stack to simplify
integration.
Sensor Attitude
Since in our simplified design we are only rotating the platform in one plane we
need to establish an angle for the LEDs that will ensure orthogonal incidence of
the solar radiation. Realizing that this direction is a function of month, day, time
of day and geographic location, we chose to use date of launch and Ft.
Sumner, New Mexico as our starting point. While data collection will commence
with lift-off, the data of interest will be collected when the balloon has reached
float altitude. Assuming we reach float by 11:00 am on September 6th, 2010,
with solar noon occurring at ~11:55:33 am MST, a sufficient number of
measurements will have been made. Should the launch be delayed or
postponed until the next day, the variation in solar noon times from day to day is
only 30 seconds per day. As long as the exact geographic position of the
payload is known, we can apply the appropriate correction value of the angle
at which the array must be set. For a launch date of September 6, 2010 the
angle is equal to 63o with respect to the horizon.
Thermal Considerations
The responsiveness of LEDs used as detectors is affected by temperature. As a
result we have added a heater to the back of the sensor head (see Figure 4).
Environmental testing of the LED array was performed to determine the
effectiveness of the heater assembly. Since we will only be making
measurements during the balloon’s first 6 hours, this will allow us to stay within the
allocated payload power budget of which the heater required 50% of that power.
A novel circuit was employed that used Zener diodes along with software to
control the duty cycle. Additionally, a stored record of the sensor head’s
temperature during the flight will enable us to apply minimal corrections to the
LED output upon analysis of the data. In near space the mechanisms for
thermal transfer are limited to direct conduction. The key aspect of this heater
design is a conformal pad made of metal and coated with a thin electrically
insulating sheet. The pad conforms to the topology of the reverse side of the
circuit board while providing excellent thermal transfer. The environmental test
chamber was held at -55 oC and 0.3 atm. The sensor board temperature never
went below 15 oC over a 1-hour period. We will continue these tests over longer
time periods to look for possible failure modes. Heating of the sensor board is
only required for ~5 hours while measurements are being made.
ERAU Hatchling I and PCC BrightStar 7
Figure 4: BrightStar Sensor Array Heater
Calculation of ET
The idea of a Langley plot follows directly from the Lambert-Beer Law defining
the transmittance of the atmosphere:
I = Io exp(-t/cos!)
Where I0 = intensity of the solar radiation at the top of the atmosphere,
I = intensity at the Earth’s surface,
t = atmospheric optical thickness, and
! = solar zenith angle.
Since the voltage measured by the LED sensors is directly proportional to the intensity, the above equation can be written as:
V = V0 exp(-t/cos!)
Defining M = 1/cos! as the “air mass” yields:
Ln V = - M t Ln V0
Heating Pad
ERAU Hatchling I and PCC BrightStar 8
Plotting ln(V) versus “air mass” yields a typical Langley plot (shown in Figure 5), and the y-intercept gives the value of the extra terrestrial constant.
Figure 5: Langley Plot
ERAU Hatchling I As previously stated, the main objective of the Hatchling I satellite bus is to
provide a standard set of core satellite subsystems (power, computer, and
communications) for implementation in future satellite projects. As such, the
PCBs are being designed with CubeSat dimensions in mind and have a 10 cm
by 10 cm square footprint. A PC/104 computer bus connector is employed as
the main electrical bus for the entire satellite.
Structure
For the HASP 2010 launch a structure is being fabricated to accommodate the
PCC BrightStar payload and conform to HASP standards. Figure 6 below shows
an exploded view of the HASP 2010 ERAU Hatchling I BaloonSat with the integrated PCC BrightStar scientific payload.
ERAU Hatchling I and PCC BrightStar 9
Figure 6: Hatchling I Exploded View
The outer structure is an E-glass/foam composite fabricated at ERAU using pre-
preg. An aluminum plate inside the bottom of the foam structure (shown below
the PCBs) spreads the stress from the mounting hardware to prevent tear-out at
high loads. The structure was tested in this configuration (with dummy mass
inside) at ERAU using a shaker table in step-mode (single shock) and remained
attached after 30-G lateral and vertical shocks were applied.
Electrical Power Subsystem (EPS)
A system of regulators and switches governs the flow of electrical power from
HASP and within the BalloonSat. The 30 VDC from HASP is converted to 8.3, 5,
and 3 VDC with 85% efficiency for the systems onboard Hatchling I. Switches
controlled by the onboard computer (OBC) turn individual components on and
off. Inline capacitors reduce the ripple to ±20 mV. A breadboard prototype of
the design has been built and tested, and PCB design and fabrication is nearing
completion. A schematic is included in the Preliminary Drawings section. The
power budget is in the Payload Specifications section.
Top plate w/ PCC
servo and rotating
sensor platform
E-glass/foam
composite exoskeleton
HASP
mounting plate
Aluminum spars
and mounting hardware
Main PCB stack
ERAU Hatchling I and PCC BrightStar 10
Onboard Computer Subsystem (OBC)
The Onboard Computer subsystem is responsible for collecting the data from
sensors and packaging the data for transmission via the communications
subsystem. Additionally, the OBC has the responsibility of maintaining some
aspect of “thermal control” of the BalloonSat through the use of temperature
sensors, resistive contact heaters, and an automatic thermostat control in the
main function block. The OBC must interface with two transceivers (HASP’s
provided communication and Hatchling I’s own communication), a GPS
module, PCC BrightStar, and several temperature sensors and heaters
throughout the BalloonSat. Two ATMega644P microcontrollers (each with two
independent serial UART ports) have been selected to provide the four
necessary serial UART connections (two each for HASP and Hatchling I
communications). One microcontroller interfaces with the transceivers, enable
switches, and temperature sensors. The other microcontroller is responsible for
collecting data from BrightStar and the GPS module. The microcontrollers
connect via the Serial Peripheral Interface (SPI) Protocol. The microcontrollers
are interrupt-driven meaning that when they receive data the main function is halted and the data handling function is called.
A breadboard prototype of the design has been built, programmed, and tested
to ensure proper communication with the transceivers, GPS module, and PCC
BrightStar. PCB design and fabrication is nearing completion. A schematic is included in the Preliminary Drawings section.
Communications Subsystem (COMM)
In addition to utilizing the wireless communication provided by HASP, Hatchling I
employs its own communications subsystem for certification for future flights. The
COMM handles wireless communications between Hatchling I and our own
ground station, allowing for both real-time downlink of data as well as uplink of
commands. This is accomplished through the 70 cm amateur radio band. This
particular band allows for reasonably small antennas while still allowing us to
easily receive the packets on standard amateur radio equipment. It will be
operating on 445.925 MHz and is frequency modulated. The whole system
consists of a small transceiver and a TNC (Terminal Node Controller). The TNC
interfaces with the OBC through a 4800 baud full duplex serial port. The packets
are formatted in the internationally recognized APRS format and transmitted
using AFSK at 1200 baud. The TNC handles all the packet formatting, routing,
and outputs audio that the radio transmits. It is also able to receive audio from
the radio, decode the packets, and output the data as a serial stream. In short,
the COMM transmits everything it receives from the OBC, and forwards
everything it receives from the ground station to the OBC. A 6-inch antenna
extends below the plane of the HASP mounting plate.
The COMM has been tested in conjunction with the OBC and BrightStar to verify
functionality. Similar systems have been flown successfully on past ERAU
ERAU Hatchling I and PCC BrightStar 11
balloon missions. PCB design and fabrication is nearing completion. Link rates are shown in Payload Specification section.
Team Management
Organizations Hatchling I is being developed outside of class by engineering undergraduate
students at Embry-Riddle Aeronautical University. The team is led by student
project manager Seth Guberman, with assistance from faculty advisors Jack
Crabtree and Dr. Ron Madler and funding from the Arizona Space Grant
Consortium. The chart below shows the ERAU team’s organization.
Figure 7: ERAU Organization
The experimental subsystem is subcontracted to students at Pima Community
College Northwest Campus Science Department, led by Stacy Harrison and
faculty advisors Mike Sompogna, Anthony Pitucco, and Denise Meeks. The following chart shows their organization.
Project Manager
Seth Guberman
OBC
Lead Cody Blevins
Zach Grey
MEC
Lead Adam Ritchie
Bryce Fox
EPS
Lead Greg
Winkleman
Brittany Griffin
COMM
Lead Elijah Brown
THRM
Lead Zach Grey
Cody Blevins
EXP1
PCC BrightStar
Faculty Advisor Jack Crabtree
Faculty Advisor Dr. Ron Madler
ERAU Hatchling I and PCC BrightStar 12
Figure 8: PCC Organization
Contact Information The chart below gives phone and email contact information for the principal leads.
Table 1: Contact Information
Name Phone Email
Seth Guberman (928) 458-5148 [email protected]
Stacy Harrison (520) 390-8374 [email protected]
Jack Crabtree (928) 777-6916 [email protected]
Mike Sampogna (520) 206-2157 [email protected]
Timeline A timeline of milestones up to this point and in the future is shown for reference on the next page.
Project Manager
Stacy Harrison
Electronics
Zack J
Mike I
Peter S
Amy G
Software
Zack J
Peter S
Structure
Zack J
Kyle R
Thermo
Peter K
Amy G
Kyle R
Faculty Advisor Mike
Sampogna
Faculty Advisor Anthony Pitucco
Faculty Advisor Denise Meeks
Faculty Advisor Forrest M. Mims III
ERAU Hatchling I and PCC BrightStar 13
Table 2: Project Schedule and Milestones
Date Item
July 30, 2009 System Requirements Review
September 1, 2009 Begin Preliminary Design and
Breadboarding
October 1, 2009 Preliminary Design Review
October 24, 2009 PCC Data Stream Test,
Structural Design Frozen
November 1, 2009 Subsystem Testing
December 1, 2009 Critical Design Review, Begin
PCB Layouts
December 18, 2009 Application Deadline
January 15, 2010 Flight Subsystem Assembly
February 15, 2010 Final PCC Integration and Test
March 1, 2010 Thermal and Vaccuum Test
May 1, 2010 Submit Payload Integration
and Flight Operations Plans
Launch Personnel A number of the students involved in the project are graduating seniors. To
ensure the continued success of the project, younger members are being
trained for the summer integration and flight. Exact personnel have not yet
been decided, but it is estimated that between seven and ten members will be
present for each event. Expect more details in the upcoming Payload
Integration and Test Plan and Flight Operations Plan documents.
Payload Specifications Much care is being taken to adhere to the standards dictated by HASP for the small class payload to secure a position on the 2010 launch.
Weight Budget The weight of the Hatchling I BalloonSat with PCC BrightStar onboard, including
all cabling and mounting hardware shall not exceed 3 kg. Mass budgeting (Table 3) is taking place to meet this requirement.
ERAU Hatchling I and PCC BrightStar 14
Table 3: Mass Budget (in grams)
Component Allocation Estimate Measurement
Structure 600 500 426
COMM 300 280 274
EPS 200 125 105
OBC 200 125 122
GPS 150 50 36
PCC 600 600 988
Heaters 100 100 X
Cables 350 300 X
Subtotal 2500 2080 1951
Margin 500 920 1049
Total 3000 3000 3000
The measured values are for prototype units (breadboards, etc). The number of
heaters has not yet been decided and will be dictated by thermal testing.
However, they are lightweight resistive contact heaters and do not greatly
affect the overall mass. PCC BrightStar was under-budgeted from the outset,
but thanks to our 500 g margin that was not an issue.
Power Budget The incoming 30 VDC (0.5 A) electrical power from HASP is distributed as
needed by the Hatchling I EPS. Assuming 85% efficiency of our main regulators
(verified in test) that leaves 12.75 W for use by the BalloonSat and its subsystems.
Table 4: Power Budget
Component 3.3V (mA) 5V (mA) 8.3V (mA) Power (mW)
Linear Regulator
(1.7V drop)
48 0 0 81.6
GPS 48 0 0 158.4
OBC 0 40 0 200
COMM 0 400 0 2000
Relays (x5) 0 24 (x5) 0 120 (x5)
PCC 0 0 880 7304
Subtotal X X X 10344
Margin X X X 2406
Total X X X 12750
A margin of nearly 2.5 W is left for safety.
ERAU Hatchling I and PCC BrightStar 15
Other Specifications Other specifications requested by the HASP administration are given below in
Table 5.
Table 5: Miscellaneous Specifications
Specification Value
Footprint 15 cm x 15 cm
Height 26.9 cm
HASP Downlink 1200 baud
HASP Uplink 1200 baud
The HASP Downlink may be used simultaneously with or separate from the
onboard Hatchling I COMM. The external height of the structure including the
rotating sensor platform, but not the sensor head itself, is just under 27 cm. An
antenna for wireless communication will extend ~14 cm below the HASP
mounting plate. The overall height from the mounting plate to the top of the
sensor head will not exceed 30 cm. For more information refer to the structural
drawing in the Preliminary Drawings section.
Desired Position and Orientation No specific position is requested so long as a clear view of the sun (from the top
of the BaloonSat) without obstructions from HASP itself or any other payloads is
available. Of course a level platform (hopefully provided by HASP) is preferred
for the measurements made by BrightStar. The antenna should also have a clear line-of-sight path to the Earth below.
Integration Procedures We anticipate that the integration of Hatchling I to HASP will consist of fastening
the mounting plate to HASP itself and connecting the power and data cables to
the connections provided by HASP. The power-on command will be given to
verify that the Hatchling I systems and BrightStar respond appropriately. More
details will follow in the Payload Integration and Test Plan.
ERAU Hatchling I and PCC BrightStar 16
Functional Block Diagram Figure 9 shows the electrical connections within the Hatchling I BalloonSat.
Figure 9: Hatchling I Block Diagram
The thermal voltage required will be determined in testing at ERAU facilities later
and will likely consume the remainder of our power margin. If more power for
heating is needed, the Hatchling I COMM will be used less frequently, making
more power available to the heaters.
Preliminary Drawings For reference, this section provides the preliminary structural and electrical
schematics as they relate to previous topics.
Hatchling I
EPS
Hatchling I
OBC
HASP
COMM
Hatchling I
COMM
Hatchling I
Thermal
PCC
BrightStar
Hatchling I
GPS
BrightStar sensor electronics