Project TURTLE: Terrapin Undergraduate Rover for Terrestrial Lunar Exploration

University of Maryland RASC-AL Presentation June 9-11, 2008 Team TURTLE

Avionics Crew Systems Mission Planning and • Andrew Ellsberry •James Briscoe Analysis • Michael Levashov • Sara Fields •David Berg • Joseph Lisee* •AliHusain • Hasan Oberoi • Jacob Zwillinger • Jason Laing* •May Lam •AdamMirvis • Ryan Murphy Loads, Structures, and • Tiffany Russell • Matt Schaffer Mechanisms • Enrique Coello Power, Propulsion, and Systems Integration •Aaron Cox Thermal • Joshua Colver • Stuart Douglas • Jason Leggett •DavidGers •Ryan Levin • Aleksandar Nacev* • Madeline Kirk* • David McLaren* • Ugonma Onukwubiri •Thomas Mariano • Jessica Mayerovitch •StephaniePetillo • Kanwarpal Chandhok •Brian McCall • Ali-Reza Shishineh • Omar Manning • Zohaib Hasnain * RASC-AL Presenters

June 9-11, 2008 University of Maryland 2 Project TURTLE 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

June 9-11, 2008 University of Maryland 3 Project TURTLE 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 TURTLE Components • Total initial mass: 1750 kg* * Initial mass does not include astronauts or suits, but does include consumables

June 9-11, 2008 University of Maryland 5 Project TURTLE Concept of Operations (Transit)

Primary Descent Stage Trans-lunar Injection (LLO – 2 km) Low Lunar Parking Orbit Transfer Engine Separation Descent Stage (2 km)

Burn Delta V

Delta-IV Heavy to TLI Landing Stage w/ Retro Engine TLI to Low Lunar Parking Orbit 800 m/s Braking Honeycomb Transfer Descent 135 m/s inserts in legs (2 km - 1 m) Retro Engine Braking 1725 m/s crush upon landing Landing 80 m/s Rover Separation Stage (surface)

June 9-11, 2008 University of Maryland 6 Project TURTLE 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 Nasa Image TURTLE will autonomously Two crew members will Upon return, two rendezvous with crew who board TURTLE for a other astronauts will will land less than 10 km three day mission with board TURTLE for a away three EVAs traveling up second three day to 25 km from base mission

June 9-11, 2008 University of Maryland 7 Project TURTLE Level One Requirements

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

June 9-11, 2008 University of Maryland 8 Project TURTLE Rover Variations

There are four rover variations to fulfill separate goals and missions

Flight Rover Design Rover Mock-up The baseline rover design Test Full size model of flight rover that fits the requirements Results cabin and suitports for use as listed above for one time use a design tool

Field Rover Outpost Rover Fully functional Earth A flight rover designed to based rover to test the concepts of the flight support a lunar outpost rover for multiple missions

June 9-11, 2008 University of Maryland 9 Project TURTLE Mock-up Rover

Testing Goals • Determine suitport functionality and ease of use • Confirm window placement and sizing Original • Determine most effective interior layout Flight Design – Bed, chairs, driving console, storage Tested in Mockup

Modified Flight Design

June 9-11, 2008 University of Maryland 10 Project TURTLE 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

Number of wheels 4 Height 1 m Width 0.3 m Drawbar Pull vs Slope for 4, 6, 8 Number of contact grousers 8 Grouser height 1.5 cm Wheels June 9-11, 2008 University of Maryland 12 Project TURTLE 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 protection Performance 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

June 9-11, 2008 University of Maryland 13 Project TURTLE 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)

June 9-11, 2008 University of Maryland 14 Project TURTLE Suspension & Stability

• Independent, MacPherson struts (TRL 4) Reaction to Loads – Required to absorb impact forces from: Case Max Settling • Driving over 10 cm boulder at 7.5 kmph Force Time • Landing on one wheel, 1 m/s impact velocity Landing 28 kN 0.1 s – Spring constant: 35 kN/m Rock Hit 6.5 kN 0.1 s – 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 MacPherson Strut June 9-11, 2008 University of Maryland 15 Project TURTLE 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 Chassis Design • Final mass: 163 kg Critical loads and structural sizes in chassis regions Region Load Critical Load Inner/Outer Safety Source diameter (mm) 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

June 9-11, 2008 University of Maryland 17 Project TURTLE Cabin: Pressure Shell

• Graphite epoxy T300/934 (TRL 9) Region Front Rear Cylinder • Loads (safety factor = 3) Endcap Endcap – Internal pressure Thickness 10 mm 10 mm 8.4 mm – Thermal stress Sources of Window Suitports --- – External loads (drive, land, launch) Extra Stress •Geometry Max Stress 190 MPa 198 MPa 190 MPa – 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 Inner Shell: Stress from pressure, chassis loads June 9-11, 2008 University of Maryland 18 Project TURTLE Cabin: Additional Structure

• 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 Driving Window Dimensions • Material TRL 9; System TRL 5 Pane Glass type Thickness Purpose – Vitreloy frame molds to cabin Resist shape Inner Fused silica 20 mm pressure • Material TRL 8; System TRL 4 Heat, micro- – Total mass: 54 kg Alumino- Outer 13 mm meteoroid silicate shield Window Construction June 9-11, 2008 University of Maryland 19 Project TURTLE Crew Systems Cabin Interior Layout

1. First aid kit, AED, supplemental oxygen 9 2 2. Fire extinguishers 6 3. Food / food waste storage 7 3 5 4. Clothing storage 5. Suitports 8 4 6. Computers 6 9 7. Storage locker 1 8. Supplemental airlock 9. Beds (stowed) Pros Cons •Excellent driver accessibility •Limited passenger accessibility Feedback from Testing •Good overhead space and •Laterally sliding driver’s seat legroom necessary June 9-11, 2008 University of Maryland 21 Project TURTLE Life Support Systems - Atmosphere

• Cabin pressure: 55.2 kPa / 8 psi (Identical to LSAM) • Atmospheric composition Active LiOH –O: 39% (partial pressure: 21.3 kPa / 3 psi) canister Flow 2 distributors –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 Particle and – Six 4.6 kg LiOH canisters for CO2 adsorption (TRL 9) odor filtration – 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 June 9-11, 2008 University of Maryland 22 Project TURTLE Life Support Systems

•Nutrition – Water management Overhead • Continuous re-supply from fuel cells Water (182 kg water needed, 252 kg provided) Storage • 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 Wastewater •Radiation Tank – 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 June 9-11, 2008 University of Maryland 23 Project TURTLE Suitports

• 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 –Between suit andsuitport • 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 June 9-11, 2008 University of Maryland 24 Project TURTLE “Garage Door” Style Suitport

June 9-11, 2008 University of Maryland 25 Project TURTLE External Driving Platform

Internal Driving

External Driving

Ingress/ Egress

• 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

June 9-11, 2008 University of Maryland 26 Project TURTLE 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

June 9-11, 2008 University of Maryland 28 Project TURTLE Internal Network

TURTLE

Network

June 9-11, 2008 University of Maryland 29 Project TURTLE 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

June 9-11, 2008 University of Maryland 30 Project TURTLE Console & Control Layout

Controls: Forward Reverse Accelerate Brake

Turn Turn Turn Turn Left Right Left Right

Brake Accelerate

Console: Driver’s Interface Navigator’s Interface 2x DU-1310 DU-1310

Lunar Imagery: NASA Alarm Indicator And Backup Terminal June 9-11, 2008 University of Maryland 31 Project TURTLE Navigation & Autonomy

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

LIDAR Point Cloud Image: Velodyne Acoustics, Inc. • Position Determination (TRL 4) • Obstacle Avoidance (TRL 4) – Initial satellite based fix (TRL 8) – LIDAR sensor (TRL 4) scans terrain – Continuous odometry estimate – LIDAR generates a map of – Local map built with LIDAR surrounding obstacles – Position updated with 30 m – Computer finds calculates a route accuracy through the obstacles – Avoids 0.1 m or bigger obstacles at 7.5 kph June 9-11, 2008 University of Maryland 32 Project TURTLE Communications

System Overview Lunar Relay Deep Space Satellite (LRS) Network (DSN) Ka-Band S-Band Max Data Rate 120 Mbps 20 Mbps Direction Transmit Two-Way Ka Trunk to 53 cm Parabolic Omni/Parabolic Earth Antennas HGA HGA S/Ka 3,000 km Gain 40 dBi 0 dBi/20 dBi S/Ka System Power 50 250 380,000 km 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

June 9-11, 2008 University of Maryland 33 Project TURTLE 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 Energy Req’d. Avg. Power Req’d. (W) Stage Length (hrs) (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

June 9-11, 2008 University of Maryland 35 Project TURTLE Fuel Cells

• Supplied with cryogenic liquid oxygen and liquid hydrogen • After reaction, potable water is stored for use by astronauts during Power 13.2 kW the mission Voltage 48 V max (24 V most systems) • Modeled after an Amperage 300 A existing PEM fuel cell Efficiency 60% (TRL 3)

June 9-11, 2008 University of Maryland 36 Project TURTLE 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

Number of Mass Diameter Length Layers Percent Tanks of Fuel of MLI 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%

June 9-11, 2008 University of Maryland 37 Project TURTLE 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)

June 9-11, 2008 University of Maryland 39 Project TURTLE Heat Transfer System

• 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

June 9-11, 2008 University of Maryland 40 Project TURTLE 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 the pipes •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

External Radiator Design June 9-11, 2008 University of Maryland 41 Project TURTLE System Overview Technology Development

• Components with TRL 1-3 TRL 1-3 TRL 4-6 require significant • Suitport connections • Science packages technology development programs for implementation • Suitport mechanisms • Window on TURTLE •Suit with detachable • Flooring PLSS •Suitportseals • Components with TRL 4-6 • Lander leg •AFDX network require some additional honeycomb inserts • Wheels/Tires/Brakes development and testing • Lander detachment • Motors/Gears/Actuators mechanisms • Other components are TRL •Fuel Tanks •Fuel cells 7-9 and require little • Active thermal control additional development •Radiator •Laser ranging • Obstacle Avoidance • Honeywell displays • Position determination June 9-11, 2008 University of Maryland 43 Project TURTLE Reliability

• Loss of Mission Component Rel. LOM – Probability 1.4% during a Suitport Systems .9998 sortie Wheels .9900 – Only considered after TURTLE Motors .9990 rendezvous with astronauts Suspension .9900 • Loss of Crew Avionics Hardware .9983 – Probability 0.4% during a Software .9990 sortie Fuel Tanks .9990 • Launch and Landing Thermal/Radiation .9980 – Assumed 90% probability of System success Batteries .9990 Total .9723 Loss of Mission: Reliability over 2 sorties

June 9-11, 2008 University of Maryland 44 Project TURTLE Scheduling and Cost

Non- Total Cost based on costing heuristic with four System Recurring Recurring ($M) assumptions: Rover 1600 850 2450 1) No DDT&E on the launch vehicle Transit 850 990 1840 2) Initial flight in 2020 Lander 280 250 530 3) 85% learning curve for TURTLE construction Science 25 78 103 Package 4) Program length is ten missions Delta-IV - 2500 2500

Total 2800 4700 7400

Total Cost: 7.4 billion Rated at a CRL of 4 based on preliminary design readiness

June 9-11, 2008 University of Maryland 45 Project TURTLE 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

June 9-11, 2008 University of Maryland 47 Project TURTLE 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

June 9-11, 2008 University of Maryland 48 Project TURTLE 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 Retractable Docking Option • Retractable docking – Retractable docking structure is depressurized and collapsed when not in use – Extended and pressurized when docked to TURTLE’s suitport

June 9-11, 2008 University of Maryland 49 Project TURTLE Outreach Outreach

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

June 9-11, 2008 University of Maryland 51 Project TURTLE 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 Aerospace Banquet Presentation – Space Systems Lab Tours

June 9-11, 2008 University of Maryland 52 Project TURTLE 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 simulator Other Activities • SGT/AIAA wind tunnel activity • Staffing aerospace table • Supporting lab activities Total 22 team members helping with aerospace engineering activities June 9-11, 2008 University of Maryland 53 Project TURTLE Outreach: K-12th Grade

Through 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.

June 9-11, 2008 University of Maryland 54 Project TURTLE Acknowledgements

The 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.

June 9-11, 2008 University of Maryland 55 Project TURTLE