rascal complied8 03format - umd · 2008. 8. 8. · rover mock-up full size model of flight rover...

Project TURTLE:Terrapin Undergraduate Rover for

Terrestrial Lunar Exploration

University of MarylandRASC-AL Presentation

June 9-11, 2008

Team TURTLE

June 9-11, 2008 University of Maryland Project TURTLE

2

Avionics• Andrew Ellsberry• Michael Levashov• Joseph Lisee*• Jacob Zwillinger

Loads, Structures, andMechanisms• Enrique Coello• Aaron Cox• Stuart Douglas• Ryan Levin• David McLaren*• Jessica Mayerovitch• Brian McCall• Omar Manning• Zohaib Hasnain

Crew Systems• James Briscoe• Sara Fields• Ali Husain• Jason Laing*• Adam Mirvis• Tiffany Russell

Power, Propulsion, andThermal• Jason Leggett• Aleksandar Nacev*• Ugonma Onukwubiri• Stephanie Petillo• Ali-Reza Shishineh

Systems Integration• Joshua Colver• David Gers• Madeline Kirk*• Thomas Mariano• Kanwarpal Chandhok

Mission Planning andAnalysis• David Berg• Hasan Oberoi• May Lam• Ryan Murphy• Matt Schaffer

* RASC-AL Presenters

Program Rationale

• Lunar exploration will become the focus of NASA's future human space program - Constellation Program

• Focus mainly on lunar outpost and infrastructure development

• Requires dedicated lander-based sortie missions for exploration beyond immediate region of outpost site

• System payload constraints limit additional payload for extended range rovers

• Project concept: develop a light-weight pressurized rover capable of independent launch and delivery using existing EELVs to augment exploration and science goals of Constellation sortie missions


3

TURTLE Project Goals

• Design the smallest practical pressurized rover to support Constellation sortie-class missions with independent delivery to moon

• Validate critical issues in habitability and crew operations by developing a full-scale mock-up of the rover cabin and external interfaces

• Develop a variant of the basic sortie rover to support Constellation outpost construction and operations

• Start the design and development process for a fully functional Earth simulation rover for near-term lunar analogue studies 4

TURTLE Overview• 4 wheels, independently

steered & powered• Range: 25 km radius around

lander over two three-day sorties

• Suitports provide astronaut ingress/egress

• External Platform– Folds in 3 configurations– Provides suitport access– External driving capabilities

• TURTLE total dimensions– Length: 3.45 m– Width: 3.24 m– Height: 2.93 m

• Total initial mass: 1750 kg*TURTLE Components* Initial mass does not include astronauts or suits, but does include consumables

June 9-11, 2008 5University of Maryland Project TURTLE

Concept of Operations (Transit)

Burn Delta V

Delta-IV Heavy to TLI

TLI to Low Lunar Parking Orbit 800 m/s

Transfer Descent 135 m/s

Retro Engine Braking 1725 m/s

Landing 80 m/s

Primary Descent Stage (LLO – 2 km)

Engine Separation Stage (2 km)

Landing Stage w/ Retro Engine Braking

(2 km - 1 m)

Rover Separation Stage (surface)

Trans-lunar InjectionLow Lunar

Parking Orbit Transfer

Descent


Honeycomb inserts in legs crush upon landing


7

Concept of Operations (Mission)Science Goals

• Deploy equipment for long-term data collection

• Collect data for the lunar base design

• Obtain samples for study on Earth

• Perform basic analysis of samples on the moon

• Increase understanding of lunar habitability

Sample Sortie Mission

TURTLE will autonomously rendezvous with crew who will land less than 10 km

away

Upon return, two other astronauts will board TURTLE for a second three day

mission

Nasa Image

Two crew members will board TURTLE for a

three day mission with three EVAs traveling up

to 25 km from base


8

Level One Requirements

• Launch on an existing EELV as a stand-alone addition to a Constellation sortie mission

• Capable of autonomously driving up to 10 km to rendezvous with the crew• Fully support two astronauts for a pair of three day missions plus 48 hours

contingency• Capable of traveling a 25 km radius from the lander with a total travel

distance of 100 km between two sortie missions• Accommodate crew size from 95th percentile American male to 5th

percentile American female• Support two-person EVAs without cabin depressurization• Have a maximum operating speed of 15 km/hr on flat, level terrain• Accommodate a 0.5 m obstacle at minimal velocity and a 0.1 m obstacle at

7.5 km/hr• Accommodate a 20° slope with positive static and dynamic margins

The following are excerpts from the 25 Level One Requirements initiallyprovided to highlight those with the largest design impacts


9

Rover VariationsThere are four rover variations to fulfill

separate goals and missions

Rover Mock-upFull size model of flight rover cabin and suitports for use as

a design tool

Field RoverFully functional Earth

based rover to test the concepts of the flight

rover

Outpost RoverA flight rover designed to support a lunar outpost

for multiple missions

Flight RoverThe baseline rover design that fits the requirements

listed above for one time use

Design

TestResults


10

Mock-up Rover

Testing Goals• Determine suitport functionality and ease of use• Confirm window placement and sizing• Determine most effective interior layout

– Bed, chairs, driving console, storage

Original Flight Design

Tested in Mockup

Modified Flight Design

Mobility System

Wheels• To clear 0.5 m obstacle,

wheels have 1 m diameter• Bekker’s Theory was used

to determine number of wheels, grousers, and wheel width

• Wheels are non-pneumatic Aluminum 2024


12

Number of wheels 4

Height 1 m

Width 0.3 m

Number of contact grousers 8

Grouser height 1.5 cm

Drawbar Pull vs Slope for 4, 6, 8 Wheels

Motors

• DC brushless motors (TRL 6) mounted to the strut of the suspension system

• The motors extend a drive shaft into a 5:1 parallel reduction gear train which is centered in the wheel

• Encased in aluminum housing for dust protectionPerformance Ratings Critical Ratings

Nominal Motor Torque 26 N-m Average Power Draw 0.821 kW

Max Motor RPM 540 rpm Max Power Draw 6.19 kW

Max Torque per Motor 62 N-m Acceleration 0.23 m/s²

Efficiency 0.91 Average Waste Heat 48.6 W

Total Mass 171 kg Total Length 22 cm


13

Steering and Braking

• Steering– A linear actuator (TRL 5) mounted on the

suspension strut controls the steering of each wheel with a maximum rotation of 60°

– Highest power draw from each actuator is estimated at 100 W

• Braking– Stopping distance is 4.34 m in 2.1 s from top

speed which is determined by crew sight lines– Magnetic braking from motors and friction

titanium carbide brakes (TRL 4)


14

Suspension & Stability• Independent, MacPherson struts (TRL 4)

– Required to absorb impact forces from:• Driving over 10 cm boulder at 7.5 kmph• Landing on one wheel, 1 m/s impact velocity

– Spring constant: 35 kN/m– Damping constant: 1 kN*s/m– Max 15 cm compression– System mass: 120 kg (for 4 wheels)

• Stability & performance– Static stability critical angles

• 37° longitudinal• 48° lateral

– 9.2 m turning radius at 15 kph, on level ground

– Pitch and roll angles < 3° during motion over bumpy terrain

Case Max Force

Settling Time

Landing 28 kN 0.1 s

Rock Hit 6.5 kN 0.1 s

MacPherson Strut

Reaction to Loads


Structures

Chassis• Aluminum Alloy 6061-T6 (TRL 9)• Loads (Safety Factor = 1.4)

– Takeoff: 6g axial, 2g lateral– Forces transferred from suspension– Temperature variation

• All members sized to resist buckling, bending, shear, and axial loads with > 15% MOS

• 90 separate circular, hollow members• Final mass: 163 kg

Chassis Design

Region Load Source

Critical Load Inner/Outer diameter (mm)

Safety Margin

Shock Tower Driving 180 Nm moment 16/28 0.45

Main Chassis Launch -35 kN axial force 34/52 0.25

Suitport Support Launch 2.3 kNm moment 36/62 0.23

Long. Strut Launch -20 kN axial force 22/42 0.16

Critical loads and structural sizes in chassis regions


Cabin: Pressure Shell• Graphite epoxy T300/934 (TRL 9)• Loads (safety factor = 3)

– Internal pressure– Thermal stress– External loads (drive, land, launch)

• Geometry– Cylindrical region: 2.43 m long,

1.83 m diameter– Semielliptical endcaps extend

0.325 m

• Two layers, enclosing chassis– Inner layer: resists loads– Outer layer: uniform 2 mm thickness to

protect against micrometeoroid strike

• Margin of safety: 1% (rear endcap)• Total mass 240 kg

Region FrontEndcap

RearEndcap

Cylinder

Thickness 10 mm 10 mm 8.4 mm

Sources of Extra Stress Window Suitports ---

Max Stress 190 MPa 198 MPa 190 MPa

Inner Shell: Stress from pressure, chassis loads


Cabin: Additional Structure

Driving Window Dimensions

Pane Glass type Thickness Purpose

Inner Fused silica 20 mm Resist pressure

Outer Alumino-silicate 13 mm

Heat, micro-meteoroid

shieldWindow Construction

• Fiberglass grated flooring (TRL 4)– Corrosion, fire, and impact resistant– Eight removable panels– 0.1 mm deflection under 360 N

load– Total mass: 33 kg

• Driving Window– FOV: 45° L/R, 20° down, 5° up– Two-pane system derived from

space shuttle design• Material TRL 9; System TRL 5

– Vitreloy frame molds to cabin shape

• Material TRL 8; System TRL 4– Total mass: 54 kg


Crew Systems


21

Cabin Interior Layout

1

2

3

4

5

6

6

8

7

1. First aid kit, AED, supplemental oxygen

2. Fire extinguishers

3. Food / food waste storage

4. Clothing storage

5. Suitports

6. Computers

7. Storage locker

8. Supplemental airlock

9. Beds (stowed)

9

9

Pros Cons•Excellent driver accessibility

•Good overhead space and legroom

•Limited passenger accessibility

•Laterally sliding driver’s seat necessary

Feedback from Testing

• Atmospheric composition– O2: 39% (partial pressure: 21.3 kPa / 3 psi)– N2: 61% (partial pressure: 33.9 kPa / 5 psi)– Allows zero-prebreathe EVA with R-factor =

1.14 for a suit pressure of 29.6 kPa / 4 psi(based on EMU)

• Seven distributors (20 cm × 12.1 cm each) for a total exit area of 1694 cm2

– Reduces flow velocity to 0.2 m/s at outlets– Promotes mixing, minimizing CO2 pooling– 60 W fan circulates 2.03 m3/min

• Atmospheric Maintenance– Six 4.6 kg LiOH canisters for CO2 adsorption

(TRL 9)– Activated charcoal filter for odor removal (TRL 9)– 0.5 µm filter for fine particulate control (TRL 9)– Oxygen and pressure sensors allow computer

control of regulators on O2 and N2 tanks

Particle and odor filtration

Flow distributors

Active LiOHcanister


22

Life Support Systems - Atmosphere• Cabin pressure: 55.2 kPa / 8 psi (Identical to LSAM)

• Nutrition– Water management

• Continuous re-supply from fuel cells (182 kg water needed, 252 kg provided)

• Microbial filter• 0.5 ppm iodine• Redundant water tanks

– Diet corresponds to World Health Organization recommendations for 95th percentile male with high physical activity level, representative of Skylab astronaut diet


23

Life Support Systems

Overhead Water

Storage

Wastewater Tank• Radiation

– As low as reasonably achievable– Potable water tank overhead for galactic cosmic radiation shielding– Critical solar particle events found to be likely to occur in only 0.4% of

missions and treated as a contingency scenario: seek shelter beneath rover or employ natural landforms

• Dramatically decreases volume and mass compared to airlock– Mass: 145 kg vs. ISS’s 6064 kg – Volume: 0.25 m3 vs. ISS’s 34 m3

• Opening mechanism: “garage door” movement (TRL 2)– Hinged door sweeps out 2 m3, current mechanism uses

less than 0.5 m3

• Connections (TRL 2)– Passive mechanisms: low power draw and easier repairs


24

Suitports

– Between suit and suitport• Two spring-loaded locks for each suit (locked when unloaded)

– Pneumatic-trigger locks between PLSS/PCS and PCS/suitport• Seals (TRL 4)

– Inflatable seals with isomeric materials at suit/suitport and PLSS/PCS connections– NASA Ames o-ring seal between PCS and suitport

• Designed for pressurized environments• PCS is tapered out and surrounded by o-ring• As pressure increases, o-ring rolls up ramp, making a more pressure tight seal

– Weather-strip style seal between suitport and shell for dust mitigation

“Garage Door” Style Suitport


25


26

External Driving Platform

• Ingress/egress: platform hangs perpendicular to surface• Three additional configurations: launch, internal driving, external driving • Platform thickness: 10 mm (Aluminum alloy 6061-T6)• 1.8 m wide × 1.2 m long• Adjustable components to accommodate all required astronaut geometries• Mass is approximately 30 kg including actuators

Internal Driving

External Driving

Ingress/ Egress

Avionics

Command & Data Handling• Internal Network (TRL 4)

– All major components are connected by an Avionics Full Duplex Ethernet (AFDX) network

– AFDX is an aerospace version of Ethernet, used by Boeing and Airbus and being considered by NASA

– Bandwidth of 1 Gbps– Fault tolerant and deterministic (real time)

• Main Computer: three next generation RAD 750

• Distributed Compute Units (DCU) – Field Programmable Gate Array (FPGA) based with AFDX

communication– Run the control loops for life critical systems– All systems connected to manual controls in case of DCU failure


Internal Network


TURTLE

Network

Crew Interfaces• Display: Honeywell DU-1310

– 14.1” LCD Monitor– 1050 x 1400 Resolution– Operated by passive touch screen– TRL 4+ (currently being space rated for CEV)

• Driving Controller – Two Axis Gimbal Joystick (TRL 9)

• Interior– Three DU-1310 (0.185 m2 display area) and joystick

• External– One vertical DU-1310 and joystick


Console & Control Layout

Driver’s Interface2x DU-1310

Alarm IndicatorAnd Backup Terminal

Lunar Imagery: NASA

Navigator’s InterfaceDU-1310

Controls:

Console:

Accelerate

TurnLeft

TurnRight

Brake

TurnLeft

Forward Reverse

AccelerateBrake

TurnRight


Navigation & Autonomy

• Capabilities– Autonomous rendezvous with crew or outpost– Determines rover position– Maps and navigates around obstacles

LIDAR Point CloudImage: Velodyne Acoustics, Inc.

• Position Determination (TRL 4)

– Initial satellite based fix (TRL 8)– Continuous odometry estimate

– Local map built with LIDAR

– Position updated with 30 m accuracy

• Obstacle Avoidance (TRL 4)

– LIDAR sensor (TRL 4) scans terrain– LIDAR generates a map of

surrounding obstacles

– Computer finds calculates a route through the obstacles

– Avoids 0.1 m or bigger obstacles at 7.5 kph


Communications

Deep SpaceNetwork (DSN)

S/Ka380,000 km

S/Ka3,000 km

Lunar RelaySatellite (LRS)

Ka Trunk to Earth


Ka-Band S-Band

Max Data Rate 120 Mbps 20 Mbps

Direction Transmit Two-Way

Antennas 53 cm Parabolic HGA

Omni/Parabolic HGA

Gain 40 dBi 0 dBi/20 dBi

System Power 50 250

RF Power 2 100

Optimal Receiver LRS LRS

Optimal Link Margin 9.4 3.0

Use While Moving No Yes

Usable Antennas 2 5

Trancievers 2 3

System Overview

Overview

• Three Proton Exchange Membrane (PEM) fuel cells• Three-fold redundancy: One fuel cell is able to

power all rover systems• Power requirements are broken into five stages as

shown below

Avg. Power Req’d. (W) Stage Length (hrs) Energy Req’d.

(kWhr) Transfer Stage 290 167 48

Descent & Landing Stage #1 1330 0.92 1.2

Descent & Landing Stage #2 1070 0.08 0.1

Standby Stage 430 220 92

Sortie Mission Stage 3240 190 622

Total — 578 764


35

Fuel Cells

• Supplied with cryogenic liquid oxygen and liquid hydrogen

• After reaction, potable water is stored for use by astronauts during the mission

• Modeled after an existing PEM fuel cell (TRL 3)


36

Power 13.2 kW

Voltage 48 V max (24 V most systems)

Amperage 300 A

Efficiency 60%

Fuel Tanks

• Boil-off effects from solar heating of the fuel tanks converts the liquid propellants into gases rendering them unusable

• Excess fuel, tank size, and perforated MLI insulation layer (TRL 7) requirements were determined for a desired usable fuel mass

• Redundancy, mass, and space restrictions were considered when choosing number and size of tanks


37

Number of Tanks

Mass of Fuel

Diameter Length Layers of MLI

Percent Extra Fuel

LOX 2 243 kg 46.4 cm 82 cm 1 2.9%

LH2 4 32.9 kg 50 cm 82 cm 2 10.8%

Thermal Control System

Overview

• Solar heating and internal component heat (813 W) raise the thermal equilibrium temperature to 330 K (beyond habitable regions)

• Two heat controlling methods used to maintain cabin temperature at 295 K– Passive: Aeroglaze A276 white paint (TRL 9)– Active: Helium gas heat exchanger (TRL 4)


39

Heat Transfer System


40

• Single phase helium gas exchange system was chosen for simplicity and robustness

• Heat is removed by an internal heat exchanger and then expelled through an external radiator

• The gas is compressed so that the efficiency is maximized without reaching unrealistic mass flow rates

• The coefficient of performance for this system is 2.2

Heat Exchangers• Internal heat exchanger

– Piping containing cold gas absorbs energy from the cabin air passed over it

– Film heat transfer coefficients of the moving gas were used to determine the necessary diameter (1 cm) and length (21 m) of thepipes

• External Radiator– Corrugated radiator design with a planar area of 8 m² maximizes

radiation area– Radiator has a cross section composed of equilateral right triangles

whose thickness (2 mm) and height (3.7 cm) were chosen by using the heat flux terms in the overall heat transfer system


41

External Radiator Design

System Overview

Technology Development

TRL 1-3 TRL 4-6• Suitport connections• Suitport mechanisms• Suit with detachable

PLSS• Lander leg

honeycomb inserts • Lander detachment

mechanisms• Fuel cells

• Science packages • Window• Flooring• Suitport seals• AFDX network• Wheels/Tires/Brakes• Motors/Gears/Actuators• Fuel Tanks• Active thermal control• Radiator• Laser ranging• Obstacle Avoidance• Honeywell displays• Position determination


• Components with TRL 1-3 require significant technology development programs for implementation on TURTLE

• Components with TRL 4-6 require some additional development and testing

• Other components are TRL 7-9 and require little additional development

Reliability

Component Rel. LOM

Suitport Systems .9998

Wheels .9900

Motors .9990

Suspension .9900

Avionics Hardware .9983

Software .9990

Fuel Tanks .9990

Thermal/Radiation System

.9980

Batteries .9990

Total .9723Loss of Mission: Reliability over 2 sorties

• Loss of Mission– Probability 1.4% during a

sortie– Only considered after TURTLE

rendezvous with astronauts

• Loss of Crew– Probability 0.4% during a

sortie

• Launch and Landing– Assumed 90% probability of

success



45

Scheduling and Cost

System Non-Recurring Recurring Total

($M)

Rover 1600 850 2450

Transit 850 990 1840

Lander 280 250 530

Science Package 25 78 103

Delta-IV - 2500 2500

Total 2800 4700 7400

Cost based on costing heuristic with four assumptions:

1) No DDT&E on the launch vehicle

2) Initial flight in 2020

3) 85% learning curve for TURTLE construction

4) Program length is ten missions

Total Cost: 7.4 billion

Rated at a CRL of 4 based on preliminary design readiness

Outpost Rover

Changes from Flight

• Original flight rover must be converted into a reusable rover to be incorporated into the lunar outpost architecture

• Must be able to withstand long term use with serviceable and replaceable parts

• Consumables and fuel must be replenished• Must account for long term dust and

radiation environment


47

Outpost CONOPS - Logistics• There will be two supplies of fuel, one on the rover and one at

the outpost for refueling– Gray waste water will be stored throughout a mission and then

transferred to the outpost to regenerate LOX and LH2

– Water from solid waste can also be used to regenerate fuel depending on outpost capabilities

• Food, clothing and LiOH canisters will be resupplied by shirt-sleeve transfer

• Atmospheric gases will be resupplied externally• Two possible methods for external refueling

– Replace tanks: easy with light tanks, but requires extra tanks– Umbilical: more complicated system to develop, but easier to use


48

Docking Options

• Outpost to Rover docking– Docking using the suitport hatch as

connection to a rigid docking structure at the outpost

– One astronaut would exit through the connecting suitport, aid in docking the rover, and then enter the outpost through an airlock or suitport


49

• Retractable docking– Retractable docking structure is depressurized and collapsed

when not in use– Extended and pressurized when docked to TURTLE’s suitport

Retractable Docking Option

Outreach


51

Technical Community Outreach– Preliminary Design Review

• December 2007– Baseline Design Review

• March 6, 2008• Industry professionals, several graduate students, aerospace faculty

– Critical Design Review• April 22, 2008• Includes mock-up and suitport demonstration• Approximately 30 visitors. Audience from NASA, industry, government

agencies, AIAA Space Automation and Robotics Technical Committee, UMD professors, graduate students, and family and friends

Outreach• 100% Team participation with 143 contact hours• 18 total events


52

Outreach: General Public

• UMD Open Houses– Four presentations in the

spring for prospective students and parents

– Focused on overview of TURTLE and design process

• Other Presentations– Aerospace Advisory Board– Aerospace Banquet– AIAA General Body Meeting– Space Systems Lab Tours

Aerospace Banquet Presentation


53

Outreach: General Public (Maryland Day)

MD day is a University-wide event with approx. 70,000 visitors

TURTLE display • Mock-up demos and display• Candy rovers• Celestia simulatorOther Activities• SGT/AIAA wind tunnel activity• Staffing aerospace table• Supporting lab activitiesTotal 22 team members helping with

aerospace engineering activities


54

Outreach: K-12th GradeThrough school visits and tours, 10 TURTLE team members spoke to

approximately 285 students and teachers• High School

– Four visits to science and engineering classes in MD/VA area• Middle School

– Interactive presentation at two local schools. Presentations were driven by questions and responses from the students

• Elementary School– A local elementary school toured the SSL and saw the early

stages of our mock-up. Team members led the tours.


55

AcknowledgementsThe TURTLE Team would like to thank Maryland Space Grant

Consortium for generously funding our rover mock-up, NASA/USRA for RASC-AL travel funds, and the Space Systems

Laboratory for mockup fabrication and testing support.

rascal complied8 03format - umd · 2008. 8. 8. · rover mock-up full size model of flight rover...

Documents