rascal complied8 03format - umd · 2008. 8. 8. · rover mock-up full size model of flight rover...
TRANSCRIPT
Project TURTLE:Terrapin Undergraduate Rover for
Terrestrial Lunar Exploration
University of MarylandRASC-AL Presentation
June 9-11, 2008
Team TURTLE
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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
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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
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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
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Honeycomb inserts in legs crush upon landing
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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
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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
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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
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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
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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
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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)
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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
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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
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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
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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
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Crew Systems
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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)
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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
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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
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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
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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
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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
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Internal Network
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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
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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
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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
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Communications
Deep SpaceNetwork (DSN)
S/Ka380,000 km
S/Ka3,000 km
Lunar RelaySatellite (LRS)
Ka Trunk to Earth
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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
Power
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
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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)
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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
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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)
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Heat Transfer System
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• 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
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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
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• 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
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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
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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
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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
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• 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
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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
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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
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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
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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.
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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.