unar obility tudy eneral oncept urveyrobotics.estec.esa.int/hdpc/rd/rd2; lunar mobility study... ·...

D O C U M E N T

document title/ titre du document

UNAR OBILITY TUDY

ENERAL ONCEPT URVEY

prepared by/préparé par Paolo Massioni – Stefano Nebuloni reference/réference issue/édition 1 revision/révision 0 date of issue/date d’édition 9/9/2005 status/état Document type/type de document Technical Note Distribution/distribution

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ESTEC Keplerlaan 1 - 2201 AZ Noordwijk - The Netherlands Tel. (31) 71 5656565 - Fax (31) 71 5656040

LunarMobReport1.doc

Lunar Mobility Study issue 1 revision 0 -

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T A B L E O F C O N T E N T S

REFERENCES IV

1 INTRODUCTION ......................................................................................................................1 1.1 Aim of the study.................................................................................................................................1 1.2 Lunar rovers .......................................................................................................................................1

1.2.1 The LRV ....................................................................................................................................1 1.2.2 The Lunokhods ..........................................................................................................................2

1.3 Scenario overview..............................................................................................................................2

2 CONCEPT OVERVIEW ............................................................................................................4 2.1 Utility Truck.......................................................................................................................................4

2.1.1 1a. Carrying Utility Truck..........................................................................................................5 2.1.1.1 1a.1A 6-Wheel Utility Truck .................................................................................................6 2.1.1.2 1a.1B 4-Wheel Utility Truck .................................................................................................8 2.1.1.3 1a.2A Articulated Track Utility Truck.................................................................................11 2.1.1.4 1a.2B Elastic Track Utility Truck ........................................................................................12 2.1.1.5 1a.3A Walking Utility Truck ...............................................................................................13 2.1.1.6 1a.3B Frame-Walking Utility Truck....................................................................................16 2.1.1.7 1a.3C Wheg Walking Utility Truck.....................................................................................18 2.1.1.8 1a.4 Ski-Walking Utility Truck ...........................................................................................20 2.1.1.9 1a.5A Hopping Utility Truck ...............................................................................................21 2.1.1.10 1a.5B Hopping Utility Truck with Rockets .....................................................................23

2.1.2 1b. Towing Utility Truck .........................................................................................................23 2.1.2.1 1b.1 Wheeled Tractor...........................................................................................................25 2.1.2.2 1b.2 Tracked Tractor............................................................................................................25 2.1.2.3 1b.xA Wheeled Trailer.........................................................................................................25 2.1.2.4 1b.xB Sleight........................................................................................................................26 2.1.2.5 1b.xC Inflatable Wheels.......................................................................................................26 2.1.2.6 1b.xD Inflatable Sleight .......................................................................................................27 2.1.2.7 1b.xE Elastic Tracks ............................................................................................................27

2.2 Independent Mobility .......................................................................................................................27 2.2.1 2.1A Folding Wheels ...............................................................................................................28 2.2.2 2.1B Inflatable Wheels.............................................................................................................29 2.2.3 2.2A Articulated Track Module ...............................................................................................30 2.2.4 2.2B Elastic Track Module ......................................................................................................30 2.2.5 2.3A Walking Lander...............................................................................................................31 2.2.6 2.3B Walking Module..............................................................................................................32 2.2.7 2.3C Frame-Walking Lander ...................................................................................................33 2.2.8 2.3D Wheg-Walking Module...................................................................................................35 2.2.9 2.4A Ski-Walking Lander ........................................................................................................35 2.2.10 2.4B Ski-Walking Module .......................................................................................................36 2.2.11 2.5A Hopping Lander ..............................................................................................................37


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2.2.12 2.5B Hopping Lander with Rockets.........................................................................................38 2.2.13 2.5C Hopping Module..............................................................................................................39 2.2.14 2.5D Hopping Module with Rockets .......................................................................................40 2.2.15 2.6A Arm Roller ......................................................................................................................41 2.2.16 2.6B Rolling Baloon ................................................................................................................42 2.2.17 2.6C Rolling Sphere .................................................................................................................44

2.3 Infrastructure Based Mobility ..........................................................................................................44 2.3.1 3.1 Lunar Railroad ...................................................................................................................45 2.3.2 3.2 Lunar Cableway .................................................................................................................45

3 CONCLUSION........................................................................................................................47 3.1 Not appropriate systems...................................................................................................................49 3.2 Wheels, tracks, legs..........................................................................................................................49

3.2.1 Wheels......................................................................................................................................49 3.2.2 Tracks.......................................................................................................................................50 3.2.3 Legs..........................................................................................................................................50

3.3 Other means of transport..................................................................................................................50 3.4 Inflatable technology........................................................................................................................51


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REFERENCES RD1. The Apollo Lunar Roving Vehicle http://nssdc.gsfc.nasa.gov/planetary/lunar/apollo_lrv.html RD2. Bob Pedersen – My mark on the Moon

http://www.usfamily.net/web/k9eq/LRV/my-mark-on-the-moon.pdf

RD3. Soviet Lunar Missions http://nssdc.gsfc.nasa.gov/planetary/lunar/lunarussr.html

RD4. Human Spaceflight Vision (HSV) – CDF Study Report (CDF 23(A), January 2004) RD5. Architectural Design of the AROMA Reference System - ARO-KT-TN-E-0004 \pcnfs\pub\people\ljoudrie\LUNARMOB\AROMA\ARO-KT-TN-E-04_issue_2.pdf RD6. Heiken, Vaniman, French - Lunar Source Book (a user’s guide to the Moon), Cambridge University

Press. RD7. Engineering Support on Rover Locomotion for Exomars Rover Phase A, final report FR-

1011/2004/RCL RD8. Design of a day/night CMU-RI-TR-95-24, June 1995 RD9. NANOKHOD – Autonomous Systems Lab, EPFL http://asl.epfl.ch/index.html?content=research/systems/Nanokhod/nanokhod.php RD10. Nildeep Patel, Alex Ellery, Chris Welch, Andy Curley, Michael Van Winnendael

Elastic loop mobility system: the concept and future prospects for rover mobility on Mars – ASTRA 2002 http://technology.kingston.ac.uk/space/research/papers/nildeeppatel/ASTRA%20Paper_2002.pdf

RD11. Nildeep Patel, Alex Ellery, Chris Welch, Andy Curley

Elastic loop mobility system (ELMS): concept, innovation and performance evaluation for a mars robotic rover – IAC-03-IAA.1.1.05 http://technology.kingston.ac.uk/space/research/papers/nildeeppatel/IAF_2003_NildeepPatel.pdf

RD12. SCORPION – Bremen Robotics

http://ag47.informatik.uni-bremen.de/eng/project.php?id=4&details=ja RD13. NASA evaluates eight-legged Scorpion robot for future exploration http://www.nasa.gov/centers/ames/research/exploringtheuniverse/scorpion_robot.html

http://nssdc.gsfc.nasa.gov/planetary/lunar/apollo_lrv.html

http://www.usfamily.net/web/k9eq/LRV/my-mark-on-the-moon.pdf

http://nssdc.gsfc.nasa.gov/planetary/lunar/lunarussr.html

http://asl.epfl.ch/index.html?content=research/systems/Nanokhod/nanokhod.php

http://technology.kingston.ac.uk/space/research/papers/nildeeppatel/ASTRA Paper_2002.pdf

http://technology.kingston.ac.uk/space/research/papers/nildeeppatel/IAF_2003_NildeepPatel.pdf

http://ag47.informatik.uni-bremen.de/eng/project.php?id=4&details=ja

http://www.nasa.gov/centers/ames/research/exploringtheuniverse/scorpion_robot.html


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RD14. ROBOT III (Case Western Reserve University) http://neuromechanics.cwru.edu/news/igertnews3.htm RD15. HEXCRAWLER

http://www.parallax.com/html_pages/robotics/hexcrawler.asp RD16. SILO 4 - Industrial Automation Institute (IAI), Madrid

http://www.iai.csic.es/users/silo4/ RD17. ALDURO – Duisburg Essen University

http://www.mechatronik.uni-duisburg.de/robotics/alduro/welcome.html RD18. Walking Machines Catalogue

http://www.walking-machines.org/ RD19. DANTE II

\\131.176.25.16\pcnfs\section stuff\Library\Robotics\planetary robotics\Rovers\NASA-CMU Dante\DANTE2 descriptions and achievements.pdf

RD20. Giancarlo Genta, Marcello Chiaberge, Nicola Amati

Non Zoomorphic Rigid Frame Walking Micro-Rover for Uneven Ground: from a Demonstrator to an Engineering Prototype - Politecnico di Torino, Italy http://www.giancarlogenta.it/non_zoo.pdf

RD21. JIM – Carnegie Mellon University

http://www.roboticsclub.org/oldprojects/jim2/index.html RD22. WHEGSTM – Case Western Reserve University

http://biorobots.cwru.edu/projects/whegs/whegs.html RD23. MARS 3 Lander – NASA http://nssdc.gsfc.nasa.gov/database/MasterCatalog?sc=1971-049F RD24. Eric Hale, Nathan Schara, Joel Burdick, Paolo Fiorini

A Minimally Actuated Hopping Rover for Exploration of Celestial Bodies – California Institute of Technology and JPL \pcnfs\section stuff\Library\Robotics\planetary robotics\hopping robots\hopping_rover hale_icra2000.pdf

RD25. Garth Zeglin

The Bow Leg Hopping Robot – Carnegie Mellon University \pcnfs\section stuff\Library\Robotics\planetary robotics\hopping robots\Bow_Leg_Hopping CMU_Zeglin1999.pdf

RD26. AQUAROBOT – Hirose & Yoneda Robotics, Tokio

http://neuromechanics.cwru.edu/news/igertnews3.htm

http://www.parallax.com/html_pages/robotics/hexcrawler.asp

http://www.iai.csic.es/users/silo4/

http://www.mechatronik.uni-duisburg.de/robotics/alduro/welcome.html

http://www.walking-machines.org/

http://www.giancarlogenta.it/non_zoo.pdf

http://www.roboticsclub.org/oldprojects/jim2/index.html

http://biorobots.cwru.edu/projects/whegs/whegs.html

http://nssdc.gsfc.nasa.gov/database/MasterCatalog?sc=1971-049F


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http://www-robot.mes.titech.ac.jp/robot/walking/6legs/6legs_e.html

RD27. PARAWALKER – Hirose & Yoneda Robotics, Tokio

http://www-robot.mes.titech.ac.jp/robot/walking/parawalker/parawalker_e.html

RD28. Dinesh K. Pai Roderick A. Barman Scott K. Ralph Platonic Beasts: spherically symmetric multilimbed robots - University of British Columbia http://www.cs.rutgers.edu/~dpai/papers/PaBaRa95.pdf

RD29. Cableways

http://wwwrcamnl.wr.usgs.gov/sws/cableways/ RD30. Freyr Hardarson

Locomotion for difficult terrain – KTH, Stockholm. http://www.md.kth.se/~cas/publications/pubdata/Hardarson_1997_LDT.pdf RD31. Raibert, M.H.

Legged Robots That Balance, Cambridge, MIT Press, 1986.

http://www-robot.mes.titech.ac.jp/robot/walking/6legs/6legs_e.html

http://www-robot.mes.titech.ac.jp/robot/walking/parawalker/parawalker_e.html

http://www.cs.rutgers.edu/~dpai/papers/PaBaRa95.pdf

http://wwwrcamnl.wr.usgs.gov/sws/cableways/

http://www.md.kth.se/~cas/publications/pubdata/Hardarson_1997_LDT.pdf


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1 INTRODUCTION

1.1 Aim of the study This study will investigate possible concept designs for a system that would allow the automated unload, transport and assembly of modules of a lunar station. The features of the modules and the overall context are derived from the Lunar Exploration Study, a previous study developed by the ESTEC Concurrent Design Facilities team. The primary objective of such mission is to perform sustainable lunar exploration, in order to have the right knowledge to establish in the future a continuously inhabited base on the surface of the Moon. The core of the mission is the construction of a space station orbiting around the Moon. A number of manned vehicles will be sent on the surface; those vehicles (LEV) consist of a descent stage (DM, orbit to surface), an ascent stage (AM, surface to orbit) and a Habitation Module (HAB). The aim of this study is to show a survey of all the possible methods for moving the Habitation Modules (HAB) on the lunar surface. This survey is meant to be very wide, and will not discard a priori any option; some of the proposals can be unfeasible until a far future, some others are just ideas for new methods of mobility.

1.2 Lunar rovers Up to now, only two kind of mobility vehicles have been used on the surface of the Moon: - the Lunar Roving Vehicle (LRV) - the Lunokhod probes. These systems have successfully worked, and their lesson should be considered while designing any future mobility system on the Moon.

1.2.1 THE LRV The LRV [RD1.] is a sort of off-road jeep used by the astronauts of the Apollo 15, 16 and 17 missions. It had a mass of 210 kg, and it was designed for carrying two astronauts and some equipment and samples. It could carry a payload up to 490 kg, which is more than twice its empty weight, an uncommon performance even for Earth road vehicles [RD2.]. During its three missions, it proved to be reliable and it did not experience any problems. It had an autonomy of 92 km, but the astronauts were not allowed to go farther than 7.6 km from the lander for security reasons.


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1.2.2 THE LUNOKHODS The Lunokhod I and Lunokhod II [RD3.] are the only automated rovers sent on the surface on the Moon. They respectively arrived on the satellite in 1970 and 1973 as payload of the “Luna” Soviet Moon exploration program. The Lunokhod rovers had a mass of about 870 kg; they had 8 independently powered wheels, with independent suspensions, and they used a nuclear isotope decay heater for thermal preservation during the night. Both missions were successful; the rovers sent more than 100,000 pictures of the Moon and performed more than 500 tests on the soil.

1.3 Scenario overview - the descent modules have a 4 leg landing system; - the surface slope on the landing site is supposed to be less than 10 degrees; - the HAB modules are 7.6 m high from surface after landing; - the center of mass of the LEV is 9.15 m above surface; - the masses at landing are:

- 7400 kg (HAB module) - 5450 kg (2450 kg DM propellant + 3000 kg DM structure) - 9500 kg (Ascent);

- landing site is at worst 1 km from the building site; - the landing stage will endure a residual 1 m/s vertical velocity at landing.

Considering the constraints and requirements described above, several mobility system configurations have been taken into account in order to create a "trade-off tree" in which all possible solutions in terms of locomotion system and way of cargo transportation are shown.


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2.3A Walking Lander

2.3B Walking Module

2.3C Frame-Walking Lander

2.3D Wheg Walker

Legs

2.2A Articulated Track Module

2.2B Elastic Track Module

Tracks

3 Infrastructure Based

Mobility

2 Independent Mobility for each module

2.1A Folding Wheels 2.1B Inflatable

Wheels

Wheels Railroad

3.1 Lunar Railroad

Cableway

3.2 Lunar Cableway

2.4A Ski-Walking Lander

2.4B Ski-Walking Module

Skis

Accurate Landing (no mobility)Surface Mobility

Trailer

1b.x1 Wheeled Trailer

1b.x2 Sleight 1b.x3 Inflatable

Wheels 1b.x4 Inflatable

Sleight 1b.x5 Elastic Tracks

Tractor

1b.1 Wheeled Tractor

1b.2 Tracked Tractor

1a Carrying 1b Towing

Multiple

Single 1 Utility Truck (reusable vehicle)

Wheels

1a.1A 6-Wheel UT1a.1B 4-Wheel UT

Tracks

Legs

1a.2A Articulated Track UT

1b.2B Elastic Track UT

1a.3A Walking UT 1a.3B Frame-Walking

UT 1a.3C Wheg Walking

UT

1a.4 Ski-Walking UT

Skis

2.5A Hopping Lander

2.5B Hopping Lander with Rockets

2.5C Hopping Module

2.5D Hopping Module with Rockets

2.6A Arm Roller 2.6B Rolling Baloon 2.6C Rolling Sphere

Rolling

Hopping

1a.5A Hopping UT 1a.5B Hopping UT

with Rockets

Hopping


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2 CONCEPT OVERVIEW The mobility opportunities on the surface of the Moon can be sorted in 3 main groups: 1. Utility Trucks (UT); 2. Independent Mobility (IM); 3. Infrastructure-based Mobility (INF). The Utility Truck is reusable vehicle, which shall be able to transfer the cargo from its landing site to the final destination. Such a vehicle shall be able to dock the cargo and release it from the descent module. As the UT is supposed to execute many transfer missions in the range of several years (5-10), it shall be able to survive for the desired time in the lunar environment, thus requiring power and thermal systems adequately sized. The UT solution can be made up of either a single vehicle or a swarm of cooperative ones. The UT design may influence of the design of the modules in different ways, from details up to requiring the addition of passive means of locomotion. The Independent Mobility solution is instead based on making the modules able to move by themselves, each one independently from the others. This choice implies that significant fraction of the mass of the module will be dedicated to the locomotion system, thus reducing the mass of the payload. Such a system will not need to be reusable and will not imply a loading or unloading manoeuvre on a second vehicle; anyway the problem of the separation from the descent stage has still to be solved. A third option is the Infrastructure-based Mobility. This method shall require the preliminary construction of a permanent transport line from the landing site to the final destination. The transport line shall be reusable, and all the module arrivals shall take place in the same spot. A last approach to the problem could be no mobility at all, with the modules landing exactly in the correct place. This solution will not be investigated in this paper, but it should be considered as well as an option. The current assessment on the landing performances reports a 30 m of uncertainty on the landing position; this lack prevents executing a perfect docking between modules, so it has to be considered that additional components (mobility, extendable links, cables, etc.) will be needed.

2.1 Utility Truck The UT is a mobility solution very close to those used on the Earth; a cargo is loaded on a vehicle that transports it, and then it is unloaded after arrival. This option is convenient if the truck can be used more than once, and eventually the truck may become a “buggy” for the astronauts when the construction of the station is over. From a general survey of existing transport vehicles [RD4. p. 94], it can be forecast that the mass of the vehicle will be more or less the same of the payload. This means that the UT might require a whole launch for its sole deployment on the lunar surface.


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A main issue regarding the UT will be its ability to survive for a long time, in a stand-by condition, on the surface of the Moon; the dust and the extreme temperatures might be very problematic and might require complex systems to be dealt with. A first bifurcation on the design of a UT concept requires defining if the transport vehicle will be single or if the modules will be moved by a swarm of cooperative robots. The main reason that could drive the design towards the option of using multiple UT’s could be the static stability of the vehicle during loading and unloading [see 2.1.1]. The simplest solution is having a single UT, and it should be also the more efficient in terms of mass, because having multiple vehicles would lead to multiplying their subsystems. From now on, only single UT concepts will be investigated. Whenever for a certain concept the multiple UT option seems better than the single UT, this choice might be considered as well. The UT must be compatible with the cargo; this for example means that if the UT has to grip the module, the module shall have proper holds. The design of the UT might also require a significant part of the locomotion system to be already embedded in the module, obtaining an overall design that can be considered as a hybrid solution between the UT and the IM. This leads to a further sorting of the UT option: 1a. Carrying Utility Truck; 1b. Towing Utility Truck. The Carrying UT consists of a vehicle taking the whole load of the cargo on itself, providing all the means of transportation for it. This class of concept should imply a minimal impact on the module design. The Towing UT instead takes only a part of the cargo load on itself, or even no load at all. The cargo shall then have its own passive means of locomotion for sustaining the fraction of the weight that is not taken by the UT. This concept is called “towing” because, as the UT does not sustain the load of the cargo, it will just tow it. This class of concepts will have a significant influence on the module design.

2.1.1 1A. CARRYING UTILITY TRUCK The different concepts of Carrying UT can be sorted on their mean of locomotion: 1a.1 Wheels; 1a.2 Tracks; 1a.3 Legs; 1a.4 Skis; 1a.5 Hopping. An important matter that has to be solved about the Carrying UT is the static stability during loading (and unloading) operations. The cargo is expected to have a mass of the same order of


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magnitude of the vehicle; the projection of the centre of mass of the whole body (vehicle + cargo) must be always inside the stability polygon.

2.1.1.1 1a.1A 6-Wheel Utility Truck Description. This UT concept is derived from the HSV Utility Truck [RD4. p. 93] (Figure 1). It consists of a wheeled vehicle with a U-shaped chassis, with two robotic arms for loading operations. The empty space inside is used for hosting the cargo. Locomotion system. The UT has a 6-wheel locomotion system, with all wheels steering. The suspensions can be designed in many ways: more complex solutions will give more terrain adaptability. Also wheel-walking abilities may be included. Load/unload system. The vehicle has two arms (one on each side), which allow the grip of the module. The UT truck “embraces” and grips the descent stage on which the module is located, and then it can lift the cargo and lean it on itself. The same arms are used for unloading. Impact on cargo design. Very little impact on cargo design, only some holds for the robotic arms are needed. Nevertheless the shape of the descent stage must be compatible with the vehicle, in order to allow the mating manoeuvre. If this is not possible, another solution has to be found for granting the stability of the systems during loading (extensions to grip to the terrain, multiple UT’s). Steering abilities. Ackerman steering, crab steering, point turning. A variation on the design might have no steering wheels, with only skid steering and fewer motors. Slope/obstacle crossing. The vehicle should experience no peculiar problems, and the use of wheels has been already tested on the Moon. The design of the suspensions and a bigger wheel size can improve the performances. Stowage. This U-shaped vehicle has a width change mechanism on the short segment of the “U”. When stowed, the width of the vehicle is smaller than the width of a module, and so it can fit in the fairing. The vehicle can use the wheel steering abilities to obtain its final shape after deployment on the surface, otherwise other mechanisms have to be investigated. A backup solution could use inflatable wheels. Actuators/sensors. The vehicle will feature at least 2 motors per wheel (1 if the wheel is not steering), 3 motors for each arm, 6 motors for the docking mechanisms and 2 motors for locking the width change mechanism, for a total of 26. It will need as well one or more cameras for navigation. Notes. It needs a power source for recharging its batteries. Examples HSV Utility Track (concept) [RD4.]. This concept was developed for the same purpose of this study, which is assembling a station on the Moon. See Figure 1, Figure 2, Figure 3 and Figure 4.


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Figure 1: the HSV utility truck.

Figure 2: HSV utility truck, stowing configuration.

Figure 3: HSV utility truck, deployment.

Figure 4: HSV utility truck, cargo unload.

Vehicle mass: 5067 kg Cargo mass: 7600 kg Size: 7 x 6.4 x 2.1 m, 7 x 2.7 x 2.1 m (stowed) Wheel formula: 6 x 6 x 6 Range: 2 km Speed: 0.1 km/h (loaded), 1 km/h (unloaded) Power consumption: 1900 W Wheel size: 1.8 m (diameter) x 0.5 m (width) Final Considerations


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Pro: - use of wheels (already tested on the Moon) - good steering and control abilities - it can become a service vehicle after its nominal mission - it can carry other payloads (digging arms)

Con: - it constraints the descent module size, so that the mating operation might be possible.

2.1.1.2 1a.1B 4-Wheel Utility Truck Description. This concept is derived from the AROMA Utility Truck [RD5.] (Figure 5). It is quite similar to Concept 1a.1A, it still consists of a wheeled vehicle with a U-shaped chassis, with a robotic arm for loading operations. Locomotion system. The UT has a 4-wheel locomotion system, with backward wheels steering and walking. The forward wheels are very close to each other, making the vehicle a tricycle. Flexible wheels are used to increase the contact surface. Load/unload system. The vehicle has an arm, which can grip the module. For the original concept (AROMA) the cargo was supposed to be already on the ground, while the scenario for this study will see the module still mounted on the descent stage. Anyway, also for this concept a solution like the one of Concept 1a.1A can be used. Impact on cargo design. Very little impact on cargo design, same consideration as for Concept 1a.1A. Steering abilities. Ackerman steering. Slope/obstacle crossing. The use of only 3 points of contact on the ground gives low stability margins, so certain slopes can be a problem. Bigger wheels ensure better obstacle crossing abilities, while no complex suspensions can be made. Stowage. This U-shaped vehicle can be stowed with the two long segments of the “U” close to each other, reducing the encumbrance of the backward wheels. When stowed, the width of the vehicle is the same of a module, and so it can fit in the fairing. The vehicle can obtain its final shape with the use of a mechanism. A backup solution could use inflatable wheels. Actuators/sensors. The vehicle will feature at least 7 motors for the wheels, 3 motors for each arm, 6 motors for the docking mechanisms and 2 motors for the width change mechanism, for a total of 21. It will need as well one or more cameras for navigation. Notes. It needs a power source for recharging its batteries. Examples AROMA Utility Track (concept) [RD5. p. 50] This concept was developed for the realization of a station on Mars. See Figure 5, Figure 6 and Figure 7.


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Figure 5: AROMA utility truck.

Figure 6: AROMA utility truck, stowing configuration.


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Figure 7: AROMA utility truck, loaded.

Vehicle mass: 5700 kg Cargo mass: 8000 kg Size: 11 x 7.2 x 2.2 m, 11 x 5.4 x 2.2 m (stowed) Wheel formula: 4 x 4 x 2 x 2 Range: 37 km (batteries), 455 (fuel cells) Speed: 1 km/h (loaded), 10 km/h (unloaded) Power consumption: 32 kW (unloaded, 10 km/h), 8 kW (loaded, 1 km/h, on 20 degrees slope) Wheel size: 2 m (diameter) x 0.8 m (width) Lunar Rover Vehicle (FM) [RD1.][RD6.] The LRV (Figure 8) is the vehicle used on the Moon by the astronauts of the last Apollo missions. It was designed for carrying two people. Vehicle mass: 210 kg Cargo mass: 490 kg Size: 3.1 x 2.3 m Wheel formula: 4 x 4 x 4 Range: 92 km Speed: 10 km/h Power consumption: 0.75 kW (max) Wheel size: 0.82 m (diameter) x 0.23 m (width)

Figure 8: the LRV.

Final Considerations Pro:


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- use of wheels (already tested on the Moon) - good steering and control abilities - overall simplicity - it can become a service vehicle after its nominal mission - it can carry other payloads (digging arms) - simpler design than the 6-wheel concept (Concept 1a.1A)

Con: - less terrain adaptability and less stability than the 6-wheel design (Concept 1a.1A) - it constraints the descent module size, so that the mating operation might be possible.

2.1.1.3 1a.2A Articulated Track Utility Truck Description. This vehicle is a variation on Concepts 1a.1, with metal tracks instead of wheels. Locomotion system. The locomotion system is based on a two rows of metal articulated tracks at the side of the vehicle. Each track may contain 3 or more wheels. Load/unload system. Similar to Concepts 1a.1. Impact on cargo design. Little impact. Steering abilities. Skid steering. Slope/obstacle crossing abilities. The tracks can negotiate high slopes better than wheels [p .39] Stowage. A possible stowed configuration could be related to the possibility of keeping the two parallel tracks near while the vehicle is in the descending module; a deployment phase is thus necessary to be defined. Actuators/sensors. At least one motor per track is needed; the vehicle will also feature at least 3 motors for each robotic arm and 6 actuators for docking mechanism. Some other mechanisms are needed for deployment from stowing position. Navigation cameras will also be necessary. Notes. Many references [RD7. p. 39] [RD8.] [RD5. p.24] suggest not using tracks for planetary locomotion, due to reliability problems (the dust of the surface enters in the loops and may halt the track). Examples NANOKHOD (prototype) [RD9.] A very small rover for planetary exploration. It carries a drill. Vehicle mass: 2.55 kg Cargo mass: 1 kg Size: 0.22 x 0.16 x 0.06 m Power consumption: 2 W Final Considerations Pro - low numbers of actuators


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- low pressure on ground, low sinkage - high slope negotiation capabilities Con - limited maneuverability on rocky terrain [RD7. p. 40] - not reliable.

2.1.1.4 1a.2B Elastic Track Utility Truck Description. This vehicle is a variation on Concept 1a.2A, with elastic loop tracks (Figure 9). Locomotion system. The locomotion system is based on a couple of elastic tracks of high-strength material (metallic or fibre-reinforced composite). These tracks are continuous so that several sources of internal friction (and mechanical complexity as well) are eliminated. Each track is linked to two driving wheels (the ones actuated by motors) and with two load wheels, which have the task of transferring the load from the chassis of the vehicle to the elastic loop. The tracks also provide the spring suspension for the vehicle being the driving wheels not in contact with the ground. The lower section is stiffened longitudinally by the transverse curvature of the strip and it can uniformly distribute the vehicle load over a large footprint area without any additional support structure. The contact between the drive drums and the elastic loops is restricted to very small section in the "clean" upper part of the loop wheel which should be free from all the dirt, dust or any other debris picked up by the loop during its contact with the ground. Load/unload system. It requires at least two robotic arms for load and unload operations and docking manoeuvres. Impact on cargo design. Little impact on cargo design, holding points are required for load and unload operations. Steering abilities. This vehicle can perform skid-steering by rotating the two loops at different speeds. Slope/obstacle crossing abilities. The elastic loop mobility has the same advantages that conventional tracked mobility vehicles have, in terms of obstacle and soft terrain negotiation capability. Stowage. A possible stowed configuration could be related to the possibility of keeping the two parallel tracks near while the vehicle is in the descending module; a deployment phase is thus necessary to be defined. Actuators/sensors. Locomotion system requires at least 4 motors to drive the elastic loops; the vehicle will also feature at least 3 motors for each robotic arm and 6 actuators for docking mechanism. Navigation cameras will also be necessary. Notes. 35 degrees max slope climbing capacity has been tested (with grousers). Examples


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ELMS (Kingston University) (study) [RD10.] [RD11.] Study on a small elastic loop rover (Figure 9). A comparison between Nanokhod, ELMS and Sojourner is made using Finite Element models for elastic suspension systems and rigid multi-body dynamics simulator (ADAMS). Mass: 14 kg Locomotion system mass: 8 kg Wheel diameter: 0.1 m.

Figure 9: the elastic loop mobility system.

Final Considerations Pro - low numbers of actuators - simple locomotion system (no lubrication required) - high terrain negotiation capabilities - low pressure on the ground, low sinkage Con - limited maneuverability on rocky terrain [RD7. p. 40] - the friction is proportional to the load - the ratio between locomotion unit mass and total vehicle mass could be high.

2.1.1.5 1a.3A Walking Utility Truck Description. This vehicle is a variation on Concepts 1a.1, with legs instead of wheels. Locomotion system. The mobility is obtained with the use of legs, from 4 to 8. The more the legs, the better the stability of the vehicle. Each leg consists in a robotic arm with 2, 3 or more degrees of freedom, which end is suitable for pushing the ground. A 2-degree of freedom leg shall be able to move its end up/down and forward/backwards: a proper combination of these movements will generate a longitudinal step motion. 3-DOF (or more) legs will allow also lateral steps, giving more mobility abilities. The legs shall be able to sustain the weight of the vehicle and the cargo, and they can have all the same design [RD12.] or be specialized, for example mocking the shape of an arthropod (bio-mimicry) [RD14.]. The vehicle walks applying a coordinated movement of the legs (gait pattern); different fashions of these motions achieve different performances. Load/unload system. It requires at least 2 robotic arms for load and unload operations and docking manoeuvres. It can be questionable if two of the legs may perform this task, without the need of adding other 2 arms for this purpose. Impact on cargo design. Little impact on cargo design, holding points are required for load and unload operations.


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Steering abilities. The steering abilities depend on the number of degrees of freedom of the legs. 2-degree of freedom legs will allow only a sort of skid steering, while 3-degree ones will consent any movement (crab steering, point turning and curves with any turning radius). Slope/obstacle crossing abilities. The use of legs is supposed to ensure better abilities than wheels and tracks. The maximum height of negotiable obstacle depends on the length of the leg segments. Legs will not get stuck in sinking terrain. Stowage. Can be similar to Concepts 1a.1. The leg degrees of freedom should be considered also on this issue. The deployment from stowed configuration may be executed with the legs if they have lateral step ability. Actuators/sensors. Each leg will require as many motors as its degrees of freedom; the total number of motors for mobility can range from 12 (4 legs with 3 DOF or 6 legs with 2 DOF) to 36 (8 legs with 4 DOF). The motors located on the joints sustaining the vehicle weight shall be more powerful than the others. Other motors (2) are needed for locking mechanisms and for dockings (6). Also, two additional robotic arms may be needed. A contact/strain sensor is needed for each leg, and inclinometers might be needed for attitude control. Navigation cameras will also be necessary. Notes. The legs usually require more power than others locomotion means [RD13.]. Examples SCORPION (prototype) [RD12.] A prototype (Figure 10) of 8-leg rover for Mars exploration. Tested successfully on Earth on many soils (20 degrees slopes). Mass: 11.5 kg Size: 0.65 x 0.40 m Number of legs: 8 Degrees of freedom per leg: 3 Speed: 30 cm/s Power consumption: 150 W (maximum)

Figure 10: SCORPION.


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ROBOT III (prototype) [RD14.] A biomimetic 6-leg robot (Figure 11). Number of legs: 6 Degrees of freedom per leg: 5 (front), 4 (middle), 3 (rear)

Figure 11: ROBOT III.

HEXCRAWLER (Earth) [RD15.] Commercial hexapod robot. Vehicle mass: 1.8 kg Payload mass: 3.4 kg Size: 0.50 x 0.40 x 0.15 m Number of legs: 6 Degrees of freedom per leg: 2 SILO4 (Earth) [RD16.] Legged robot (Figure 12). Vehicle mass: 30 kg Payload mass: 15 kg Size: 0.30 x 0.30 x 0.31 m Number of legs: 4 Degrees of freedom per leg: 3 Speed: 2.5 cm/s

Figure 12: SILO4.

ALDURO (study, Earth) [RD17.] A legged car. Vehicle mass: 1600 kg Payload mass: 300 kg Size: 3.5 x 2.5 m Number of legs: 4 Degrees of freedom per leg: 3


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Power consumption: 40 kW (maximum)

Walking Machinespayload ratio vs payload mass

0.000.200.400.600.801.001.201.401.601.802.00

0 50 100 150 200 250 300 350

payload mass [kg]

payl

oad/

vehi

cle

Figure 13: payload ratio for walking machines; the data have been taken form [RD18.].

Final Considerations From the examples found (Figure 13), it seems that the payload/vehicle ratio is decreasing as the mass of the payload increases: the scaling of the system might render this method disadvantageous for massive cargoes. Pro - high terrain negotiation capabilities - will not get stuck for terrain sinkage Con - complexity, high number of motors - high power consumption - scalability questionable.

2.1.1.6 1a.3B Frame-Walking Utility Truck Description. This vehicle is a variation on Concept 1a.3A, with fewer degrees of freedom. Locomotion system. The mobility is obtained with the use of legs, typically 6 or 8. The legs are stiff vertical beams, and they are connected to a mobile frame, which can move up/down, forward/backward and rotate. The mobile frames are 2: half of the legs are attached under the first and the others under the second. The motion is obtained with an alternate motion of the two frames: while one is lowered and it sustains the weight of the robot, the other is lifted and moved forward or rotated for displacing the vehicle. A variation on this design could have only one of the two frames moving, thus reducing the number of actuators. Another variation may have all the legs


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having an independent degree of freedom in the vertical direction, allowing more adaptability to the terrain. Load/unload system. It requires at least 2 robotic arms for load and unload operations and docking manoeuvres. Impact on cargo design. Little impact on cargo design, holding points are required for load and unload operations. Steering abilities. Point turning, the ability to follow curves is to be defined. Slope/obstacle crossing abilities. It should be able to cross any obstacle smaller than the height that the ends of the legs reach while lifted. Stowage. Can be similar to Concepts 1a.1, with the difference that also the leg frames will need a width change mechanism. Actuators/sensors. Each leg frame will require at least 3 motors. Other motors are needed for locking mechanisms (2 to 6) and for docking (6). Also two robotic arms (6 motors) are needed. Inclinometers and navigation cameras will also be necessary. Notes. This design attempts to achieve the advantages of using legs instead of wheels, with a lesser complexity. Examples DANTE II (Earth) [RD19.] A frame-walker for volcano exploration (Figure 14). Total mass: 770 kg Payload mass: 130 kg Size: 3.7 x 2.3 x 3.7 m Number of legs: 8 Speed: 1 cm/s Power consumption: 2000 W (maximum) Maximum slope: 30 degrees Maximum step crossable: 1.3 m

Figure 14: DANTE II.

WALKIE 6 (prototype) [RD20.] A set of prototypes of rovers for planetary exploration (Figure 15). Vehicle mass: 3 kg Payload mass: 6 kg Size: 0.3 x 0.2 x 0.2 m Number of legs: 6 Speed: 0.4 cm/s Power consumption: 2 W (maximum) Maximum slope: 19 degrees Maximum step crossable: 0.12 m

Figure 15: WALKIE 6.


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JIM (prototype) [RD21.] A different shape of frame walker (Figure 16).

Figure 16: JIM.

Final Considerations Pro - high payload mass/total mass ratios - will not get stuck for terrain sinkage Con - it might require complex stowage mechanisms - inefficient (the motion is made of stop-and-go’s).

2.1.1.7 1a.3C Wheg Walking Utility Truck Description. This vehicle is a variation on Concepts 1a.1, with “whegs” (Figure 17) instead of wheels. Locomotion system. A wheg is a hybrid concept between a wheel and a leg. It is like a wheel composed only by 3 or 4 hooked flexible spokes, without the external circle. The vehicle has 6 or 8 whegs instead of wheels, and the rotation of all the whegs has to be coordinated in order to keep a relative phase consistent with a walking gait.

Figure 17: the functioning principle of the whegs.


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Load/unload system. Similar to Concepts 1a.1. Impact on cargo design. Little impact. Steering abilities. Skid steering, at the cost of losing the coordination of the gait. Slope/obstacle crossing abilities. The whegs are supposed to negotiate steps or slopes better than wheels without walking ability. According to the reference [RD22.], a wheg can negotiate a step as high as 1.5 times the radius of the wheg. Stowage. Can be similar to Concepts 1a.1. Actuators/sensors. At least one motor per wheg is needed; the vehicle will also feature at least 3 motors for each robotic arm and 6 actuators for docking mechanism. Other motors are needed for locking mechanisms for docking (6) and for two robotic arms (6 motors). Some other mechanisms are needed for deployment from stowing position. Navigation cameras will also be necessary. Notes. Examples WHEGSTM

[RD22.] A series of small biologically inspired robots (Figure 18). Length: 0.51 m Speed: 1,5 m/s

Figure 18: WHEGS II.

Final Considerations Pro - low numbers of actuators - fair terrain negotiability with overall simplicity Con - steering is a problem - vertical oscillations of the center of mass of the vehicle while walking.


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2.1.1.8 1a.4 Ski-Walking Utility Truck

Figure 19: the working principle of a ski-walker.

Description. It consists of a vehicle with two skis, with two robotic arms for loading and unloading operations. Locomotion system. The locomotion system is based on a couple of parallel flat skis with one degree of freedom each. Each ski is connected to the body of the vehicle by a couple of arms in a 4-beam articulate frame shape; the arms are actuated by motors and they can rotate leading the skis to move up and down in a vertical plane with respect to the body of the vehicle. In this way, while the skis are in contact with the ground, the vehicle can move forward, raised and sustained by this ski mechanism; at the end of this phase, the body of the vehicle rests on the ground while the skis recover the forward position for next step (Figure 19). The chassis is based on a rigid frame where the payload can be stored. Load/unload system. It requires at least two robotic arms for load and unload operations and docking manoeuvres. Impact on cargo design. Small impact on cargo design, holding points are required for load and unload operations. Steering abilities. This vehicle can perform point turning by opposite movements of the skis. This implies that skis skid during this phase. Slope/obstacle crossing abilities. Obstacle crossing is limited by the height that is reached while the body is suspended and held by the ski mechanism. Stowage. A possible stowed configuration could be related to the possibility of keeping the two parallel skis near while the vehicle is in the descending module; a deployment phase is thus necessary to be defined. Actuators/sensors. Locomotion system requires at least 4 motors to drive skis; the deployment system should require at least 2 actuators; the vehicle will also feature at least 3 motors for each robotic arm and 6 actuators for docking mechanism. Navigation cameras will also be necessary. Notes. Examples


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Prop-M Rover (FM) [RD7. p. 26][RD23.] A small ski-walking robot that took part in a Mars mission in 1971, carried by a lander (Figure 20). It was tethered to the lander by a cable for communication. The mission was a failure because the lander ceased communication soon after arrival. Mass: 4.5 kg Payload mass: 1.0 kg Dimensions: 0.25 m (length), 0.22 m (width).

Figure 20: PROP-M.

Final Considerations Pro - low numbers of actuators - simple locomotion system Con - limited capabilities in obstacle negotiation - low efficiency of steering system (especially on rough terrain)

2.1.1.9 1a.5A Hopping Utility Truck Description. This kind of robot has a system that permits the robot to jump and thus to move on the surface, flying over the obstacles. It is equipped with robotic arms necessary for the load/unload phase. Locomotion system. The locomotion system is made up of a mechanical system that can store energy and release it. In this way it can provide the force required for the robot to jump upwards and toward a desired direction, thus moving on the surface. Typically this system is based on one or more elastic elements (springs) and it is coupled with an actuated system which task is essentially to recharge the first one during the loiter time (time between the two jumps). The jump system could be continuous or “one-shot”. In the first case the motion consists in continuous jumps: the loiter time is less than the jump time and, during the motion, the time during which the vehicle is in contact with the ground is just that required for the thrust. Instead, if the time required for the elastic system to recharge is greater than fly time, the side movement cannot be continuous: in this case the efficiency of the mobility system is reduced, but a longer time could be spent for path planning or any other stationary activity. This system requires also an attitude control system, because it is necessary to keep the elastic element in contact with the ground during the thrust phase. The landing phase (the one necessary to stop the vehicle in both horizontal and vertical direction) is a critical situation for the stability of the vehicle, because side-forces on the ground could compromise the equilibrium of the system. Another aspect regarding the stability is related to the difference in height from the centre of mass and the point where the elastic element is connected to the body: if the first one is lower, stability (during ground contact) is increased.


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Load/unload system. To be defined (can be similar to Concepts 1a.1) Impact on cargo design. Little impact. Steering abilities. The robot is not able to turn while it is suspended over the surface. It cannot follow a curved line, but it can move zigzag. Slope/obstacle crossing abilities. Depending on the locomotion system and the environment characteristics, the vehicle can overcome obstacles even higher than the robot itself. Slope crossing abilities is mainly related to the standing system features (stability while on the ground). Stowage. To be defined (can be similar to Concepts 1a.1) Actuators/sensors needed. The locomotion system is simple and few actuators are required for the vehicle to be operative: at least one actuator for main locomotion system, at least 3 actuators (to be defined the type: reaction wheels, rockets, ...) for the attitude control. Cameras for navigation and attitude sensors (gyro, accelerometers) are required. The robotic arms require at least 3 motors each, holding mechanism requires 4 or more motors. Notes. This concept has still to be better defined, especially for the load/unload phase. Examples Hopper (JPL, CIT) (prototype) [RD24.] Prototypes of a hopping rovers for Mars exploration; they have one on-board camera and a single actuator that is enough to propel, steer and self-right the robot. Mass: 1.5 kg Hopping height: 0.85 m (at g = 9.8 m/s2) Bow Leg Hopping Robot (prototype) [RD25.] A bow legged prototype, with passive stabilizing body attitude. A detailed report describing the development of the robot is presented in the reference. Mass: 2.5 kg Leg length: 0.25 m Hopping height: 0.5 m (g = 3.4 m/s2) Final Considerations Pro - low number of actuators - it avoids many problems of surface navigation (obstacle negotiation, ...) - high efficiency Con - never tested except on Earth - low precision of side movement - it requires an attitude control system


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- the system could lift too much dust from the lunar surface - load/unload manoeuvre can be unfeasible.

2.1.1.10 1a.5B Hopping Utility Truck with Rockets Description. This concept is a variation on Concept 1a.5A; this UT still uses a mechanical device to jump, but it uses rockets to obtain horizontal transfer. Locomotion system. The mechanical energy storing system is simpler than in Concept 1a.5A, as it has to develop only a vertical force. A set of rockets (storable propellant or cold gas) accelerates the vehicle towards the desired direction while jumping. Load/unload system. To be defined (can be similar to Concepts 1a.1) Impact on cargo design. Little impact. Steering abilities. While flying, the rockets allow a variety of manoeuvres. The performances depend on the type of the rockets. Slope/obstacle crossing abilities. As Concept 1a.5A. Actuators/sensors needed. All the equipment needed for Concept 1a.5A, plus a set of rockets (at least 4). If the same rockets are used for attitude control, their minimum number grows to 8. Stowage. To be defined (can be similar to Concepts 1a.1) Notes. This concept has still to be better defined, especially for the load/unload phase. Final Considerations Pro - low number of actuators - it avoids many problems of surface navigation (obstacle negotiation, ...) - good maneuverability Con - never tested - it requires an attitude control system - it consumes propellant - load/unload manoeuvre can be unfeasible.

2.1.2 1B. TOWING UTILITY TRUCK This solution is made of a combination of a tractive vehicle (the UT), with active means of transport, and the module, which owns passive means of locomotion. The design of the UT can require that all the load of the module is sustained by its passive means, or that a part of the cargo is leaned on the tractor. The first class of concepts is derived from Configuration IV (Figure 21) of AROMA study [RD5. p. 30], while the second is derived from Configuration II (Figure 22) of the same reference.


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Figure 21: AROMA (Configuration IV) towing vehicle.

Figure 22: AROMA (Configuration II) towing vehicle.

The locomotion mean is independent from the choice of one configuration or the other, but a simple consideration would lead to prefer the first: actually, it is better to put the more load on the tractive elements, to achieve more grip to the soil and more tractive force. The same assertion would also push towards the carrying concepts instead of towing UT’s. Anyway the question is not easily solved, and the convenience on choosing a solution or the other will depend as well on the shape and size of the cargo module. Configuration II needs a robotic arm to load the cargo on it, and for equilibrium it can be inferred that it will need as well to dock to the LEV: so this solution becomes as complex as the 1a concepts if the module is not able to get off the descent module by itself. If the module instead can descend (for example, with air bags) by itself, the simplest Configuration IV can be enough. The choice between the two options shown above is left open and still to be better defined; anyway, it makes sense to investigate solutions which are significantly different from concept 1a, so it will be assumed that all the modules are able to descend by themselves with the use of air bags, thus reducing the complexity of the tractor (with the reduction of its mass). In facts, there are no reasons to investigate solutions of towing UT’s that are as complex as the carrying ones: the mass of the trucks will be the same, but for the towing ones there will be also the add-ons on the module to make the total mass budget. The 1b class of concepts is sorted on the base of the tractor active mean of transport: 1b.1 Wheeled Tractor; 1b.2 Tracked Tractor


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and on the module passive mean of transport: 1b.xA Wheeled Trailer; 1b.xB Sleight; 1b.xC Inflatable Wheels; 1b.xD Inflatable Sleight; 1b.xE Elastic Track. The concepts are made on combination of the two elements. Of course other means could be imagined for the tractors (i.e. legs), but as the towed cargo can have only passive means, it seems advisable not to use for traction devices more complex and efficient than the passive ones used by the cargo.

2.1.2.1 1b.1 Wheeled Tractor Description. The design is basically the same of Concepts 1a.1, modified for towing instead of carrying. The U-shaped chassis is no more needed and the robotic arm could be only one instead of two. The robotic arm is the tool that grips the module for towing. See Concepts 1a.1A or 1a.1B.

2.1.2.2 1b.2 Tracked Tractor Description. The design is basically the same of Concepts 1a.2, modified for towing instead of carrying (no U-shaped chassis, one robotic arm for towing). See Concepts 1a.2A or 1a.2B.

2.1.2.3 1b.xA Wheeled Trailer Description. The module has its own wheels, folded. Locomotion system. The module shall have 2 or 4 or more passive wheels. A passive steering ability may be added. Impact on cargo design. Some of the volume has to be used for hosting the wheels. Slope/obstacle crossing. Bigger wheels ensure better obstacle crossing abilities, while no complex suspensions can be made. Stowage. For preserving the structural cylindrical shape of the modules, the wheels should be kept attached to the bases of the cylinder while stowed. Notes. The descent from the landing stage has to be better defined. Examples Aroma, configuration II (concept) [RD5. p. 60] Final Considerations Pro - overall simplicity


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Con - the unload from LEV phase may be complex.

2.1.2.4 1b.xB Sleight Description. The module can extend skis for passive locomotion. Locomotion system. Extendable skis shall support the weight of the module. The number is to be defined. Impact on cargo design. Some of the volume has to be used for hosting the skis. Slope/obstacle crossing. Questionable. Stowage. The skis will occupy little space on the external surface of the module. Notes. The descent from the landing stage has to be better defined. Final Considerations Pro - overall simplicity - small volume needed Con - the unload from LEV phase may be complex - terrain negotiability is questionable.

2.1.2.5 1b.xC Inflatable Wheels Description. The module has its own inflatable wheels. Locomotion system. The module shall have 2, 4 or more passive inflatable wheels. Impact on cargo design. Some of the volume has to be used for hosting the wheels. Slope/obstacle crossing. Bigger wheels ensure better obstacle crossing abilities, while no complex suspensions can be made. Stowage. No special problems foreseen. Notes. The wheels can be designed for being used as air bags as well. Examples HSV [RD4. p. 97] A concept involving the use of inflatable wheels and a towing vehicle is shown. Final Considerations Pro - overall simplicity - stowage simplicity


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Con - the unload from LEV phase may be complex.

2.1.2.6 1b.xD Inflatable Sleight Description. The module is surrounded by a big air bag, and it is towed letting the ground slip under it. Locomotion system. The air bag shall be inflated at low pressure and have a big contact surface on the ground, in order to reduce the friction (to be confirmed). It has to be ensured that the fabric of the air bag shall not break during the transport. Impact on cargo design. Some of the volume has to be used for hosting the air bag. Slope/obstacle crossing. To be defined. Stowage. No special problems foreseen. Notes. The air bag can be used for descending from the landing stage as well. Final Considerations Pro - overall simplicity - stowage simplicity Con - the unload from LEV phase may be complex - the resistance of the air bag is questionable.

2.1.2.7 1b.xE Elastic Tracks Description. The module has a set of elastic tracks around itself. Locomotion system. The module uses tracks like those of Concept 1a.2B for passive locomotion. Notes. The concept has to be better defined.

2.2 Independent Mobility The IM solution requires the mobility system to be embedded in the cargo modules delivered to the Moon. This choice may be advantageous for a small number of modules, as the total mass of the mobility systems might be smaller than the mass of one UT. The IM solution will imply mayor changes in the module design, but shall not use a significant part of the internal volume of the cargo, as it is supposed to be bound to other purposes. The mobility systems used may be similar to those used for the UT’s, or have a completely different approach. The IM options can be sorted as follows by the mean on locomotion: 2.1 Wheels; 2.2 Tracks; 2.3 Legs;


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2.4 Skis; 2.5 Hopping; 2.6 Rolling. The IM requires also finding out a way to unload the cargo from the landing stage. All the designs will also need a mechanism to dock or mate to the other modules; the design of these machineries will depend on the station design.

2.2.1 2.1A FOLDING WHEELS Description. The module has its own tractive wheels as means of transport. Locomotion system. The module can have 4 or 6 wheels (or more); 2 or 4 steering. Walking abilities might be useful, both for locomotion and for stowage. It is advisable to use the biggest wheel size possible to improve the obstacle crossing ability, as no complex suspensions can be designed without compromising the module design. Load/unload system. To be defined. A solution could be making the module fall down with the use of the wheel deployment mechanisms, and absorb the impact with an air-bag; as the falling position cannot be predicted, it is advisable that the wheel deployment mechanism should be able to turn the module in the right position as well. Impact on cargo design. Some of the volume has to be used for hosting the wheels. Steering abilities. Skid steering or Ackerman steering; depending on the design, the performances may vary. Slope/obstacle crossing. Bigger wheels ensure better obstacle crossing abilities, while no complex suspensions can be made. Stowage. For preserving the structural cylindrical shape of the modules, the wheels should be kept attached to the bases of the cylinder while stowed. Actuators/sensors. The vehicle will feature at least 4 to 8 motors for the wheels and 8 motors for the wheel deployment system (locking mechanisms may be needed). Cameras needed for navigation. Notes. It could be self power supplied if the module has body mounted solar panels. Examples AROMA Mobile Pressurized Laboratory (concept) [RD5. p. 67] It consists of a pressurized 4-wheel vehicle for Mars exploration (Figure 23). It has some similarities with the concept shown above, as it can be considered as an habitation module provided with mobility. Total mass: 7000 kg Size: 9.5 x 3.6 x 3.8 m, 11 x 5.4 x 2.2 m (stowed) Wheel formula: 4 x 4 (x 4, optional)


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Range: ? Speed: 5 km/h Power consumption: ? Wheel size: 3.8 m (diameter) x 0.75 m (width)

Figure 23: AROMA mobile lab.

Final Considerations Pro: - use of wheels (already tested on the Moon) - overall simplicity

Con: - complex deployment mechanism - it requires space for stowing the wheels - different cargoes require different wheel design - the unload from descent stage may be problematic.

2.2.2 2.1B INFLATABLE WHEELS Description. This concept is a variation on Concept 2.1A: the wheels are not folded but inflatable. Locomotion system. The module can have 4 or 6 wheels (or more); 2, 4 or no steering wheels. Load/unload system. To be defined. As for Concept 2.1A, an air-bag could be used. Impact on cargo design. Some of the volume has to be used for hosting the inflatable parts and the related machinery. Steering abilities. Skid steering or Ackerman steering; depending on the design, the performances may vary. Slope/obstacle crossing. The only way to improve the performances is making big wheels. Stowage. No problems thanks to the inflatable parts. Actuators/sensors. The vehicle will feature at least 4 motors for the wheels, valves and gas tanks for the inflatable parts. Some motors could be needed as well for wheel deployment (the axle of the wheels have to come out from the module external surface). Cameras needed for navigation. Notes. It could be self power supplied if the module has body mounted solar panels. Final Considerations Pro: - use of wheels (already tested on the Moon) - overall simplicity - reduced mass and encumbrance

Con: - different cargoes require different wheel design - the unload from descent stage may be problematic.


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2.2.3 2.2A ARTICULATED TRACK MODULE Description. This vehicle is a variation on Concept 1a.2A; it has its own articulated track as a mean of transport. Locomotion system. The locomotion system is based on a two rows of metal articulated tracks at the side of the vehicle. Each track may contain 3 or more wheels. Load/unload system. Similar to Concepts 2.1A. The position of the moving module (vertical, horizontal) is to be defined. Impact on cargo design. Little or no impact on Descent Module design, considerable impact on module design, being the mobility system installed on. Steering abilities. Skid steering. Slope/obstacle crossing abilities. The tracks can negotiate high slopes better than wheels [RD7. p. 39]. Stowage. A possible stowed configuration could be related to the possibility of keeping the two parallel tracks near while the vehicle is in the Descent Module; a deployment phase is thus necessary to be defined. Actuators/sensors. At least one motor per track is needed; some other mechanisms are needed for deployment from stowing position. Navigation cameras will also be necessary. Notes. Many references [RD7. p. 39] [RD8.] [RD5. p.24] suggest not using tracks for planetary locomotion, due to reliability problems (the dust of the surface enters in the loops and may halt the track). Examples See Concept 1a.2A Final Considerations Pro - low pressure on ground, low sinkage - high slope negotiation capabilities Con - limited maneuverability on rocky terrain [RD7. p. 40] - not reliable - the impact on the module design is considerable - the stowage of the tracks could be complex.

2.2.4 2.2B ELASTIC TRACK MODULE Description. This vehicle is a variation on Concept 2.2A, with elastic tracks. Locomotion system. The principle of the locomotion system is the same as the one described for Concept 1a.2B. The position of the moving module (vertical, horizontal) is to be defined. Load/unload system. Impact on cargo design. Little or no impact on Descent Module design, considerable impact on module design, being the mobility system installed on.


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Steering abilities. The vehicle can perform skid-steering by rotating the two loops at different speeds. Slope/obstacle crossing abilities. The elastic loop mobility has the same advantages that conventional tracked mobility vehicles have, in terms of obstacle and soft terrain negotiation capability. Stowage. A possible stowed configuration could be related to the possibility of keeping the two parallel tracks attached to the module surface while the vehicle is in the Descent Module; a deployment phase is thus necessary to be defined. Actuators/sensors. Locomotion system requires at least 4 motors to drive the elastic loops; some other mechanisms are needed for deployment from stowing position. Navigation cameras will also be necessary. Notes. Examples See Concept 1a.2A Final Considerations Pro - low pressure on ground, low sinkage - high slope negotiation capabilities - simple locomotion system (no lubrication required) Con - never tested - limited maneuverability on rocky terrain [RD7. p. 40] - the impact on the module design is considerable - the stowage of the tracks could be complex.

2.2.5 2.3A WALKING LANDER Description. This vehicle uses the same locomotion system as Concept 1a.3A, embedded in the descent stage. Locomotion system. The same as Concept 1a.3A The legs of the Descent Module are replaced by mobile ones. A central symmetry (instead of axial) may be preferable for the disposition of the legs. Load/unload system. Absent: load and unload phases do not exist. Impact on cargo design. No impact on cargo design, significant impact on Descent Module design. The landing has to be sustained by the same legs that will be used for walking, so they have to be completely re-designed. Steering abilities. Same as Concept 1a.3B. Slope/obstacle crossing abilities. Same as Concept 1a.3B. Stowage. The device replaces the landing legs, so the stowage should not be a problem. Actuators/sensors. Each leg will require as many motors as its degrees of freedom; the total number of motors for mobility can range from 12 (4 legs with 3 DOF or 6 legs with 2 DOF) to 36


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(8 legs with 4 DOF). The motors located on the joints that sustain the vehicle weight shall be more powerful than the others. Other motors may be needed for locking mechanisms used during the landing. A contact/strain sensor is needed for each leg, and inclinometers might be needed for attitude control. Navigation cameras will also be necessary. Notes. The feasibility of this concept is questionable, it has to be defined if robotic legs with many degrees of freedom can sustain the landing. Examples AQUAROBOT (prototype, Earth) [RD26.] A hexapod walker with central symmetry (Figure 24).

Figure 24: AQUAROBOT.

Final Considerations Pro - will not get stuck for terrain sinkage - high terrain negotiability - it uses for mobility a part which was already necessary (although it needs to be redesigned) Con - the necessity to sustain the landing may render the concept unfeasible - reliability is questionable - low payload mass/total mass ratio is expected.

2.2.6 2.3B WALKING MODULE Description. This concept is a variation on Concept 2.3B, with the locomotion system embedded in the module (not in the descent stage). Locomotion system. The same as Concept 1a.3B. The habitation module has 4 or 6 legs, which are used for mobility. Load/unload system. The system could be designed so that the module might be able to get down from the descent stage with the legs themselves. Otherwise, other systems could be used (air-bags). Impact on cargo design. A significant impact on cargo design, the legs will require a great part of the mass of the module. Steering abilities. Same as Concept 1a.3B.


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Slope/obstacle crossing abilities. Same as Concept 1a.3B. Stowage. The legs shall be designed so that they can be folded. Actuators/sensors. Each leg will require as many motors as its degrees of freedom; the total number of motors for mobility can range from 12 (4 legs with 3 DOF or 6 legs with 2 DOF) to 36 (8 legs with 4 DOF). The motors located on the joints that sustain the vehicle weight shall be more powerful than the others. A contact/strain sensor is needed for each leg, and inclinometers might be needed for attitude control. Navigation cameras will also be necessary. Notes. Examples See Concept 2.3B Final Considerations Pro - will not get stuck for terrain sinkage - high terrain negotiability Con - excessive mass (to b confirmed) - deployment is still to be defined.

2.2.7 2.3C FRAME-WALKING LANDER

Figure 25: stowed configuration (left) and operational configuration (right) of Concept 2.3C.

Description. This vehicle uses the same locomotion system as Concept 1a.3B, embedded in the descent stage (Figure 25). Locomotion system. The same as Concept 1a.3B. The legs used for the landing become a fixed frame of legs: with the addition of a single mobile frame under the Descent Module, the vehicle is granted full mobility. Load/unload system. Absent: load and unload phases do not exist.


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Impact on cargo design. No impact on cargo design, significant impact on Descent Module design. Steering abilities. Point turning, the ability to follow curves is to be defined. Slope/obstacle crossing abilities. It should be able to cross any obstacle smaller than the height that the ends of the legs reach while lifted. Stowage. The device occupies the volume around the nozzle, it has to be confirmed that it can be stowed. Actuators/sensors. The mobile leg frame will require at least 3 actuators; 6 (using a Stewart platform for example) will grant a full 6 degrees of freedom mobility. Other motors are needed for locking mechanisms (2 to 6) and for docking (6). Also two robotic arms (6 motors) are needed. Inclinometers and navigation cameras will also be necessary. Notes. This design has a low impact on the whole mission, as it uses for mobility a part which was already designed (the legs of the descent stage) without any need of changes on them. Examples PARAWAKER (prototype, Earth) [RD27.] A frame walker, with a very simple design (Figure 26). It uses a Stewart platform. Total mass: 50 kg Size: 1.25 x 1.50 x 1.20 m Number of legs: 6

Figure 26: PARAWALKER.

Final Considerations Pro - high payload mass/total mass ratios - will not get stuck for terrain sinkage - it uses for mobility a part which was already designed Con - inefficient (the motion is made of stop-and-go’s). - volume for stowage is to be defined.


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2.2.8 2.3D WHEG-WALKING MODULE Description. This vehicle is a variation on Concept 2.1A, with the locomotion system described in Concept 1a.3C, that is “whegs” instead of wheels. Locomotion system. Same as Concept 2.1A, but the wheels are substituted by whegs. Slope/obstacle crossing abilities. The whegs are supposed to negotiate steps or slopes better than wheels without walking ability. Stowage. Same as Concept 2.1A. It has to be defined if the whegs are more easily stowable. Notes. Examples See Concept 1a.3C Final Considerations Pro: - fair terrain negotiability with overall simplicity - low encumbrance of the whegs

Con: - complex deployment mechanism - different cargoes require different wheel design - the unload from descent stage may be problematic.

2.2.9 2.4A SKI-WALKING LANDER

Figure 27: ski-walking lander concept (2.4A).

Description. The lander has a pair of skis that allow the mobility of the whole system (Figure 27). The skis are stowed in the Descent Module and deployed after the landing. Locomotion system. The principle of the locomotion system is the same as the one described for Concept 1a.4. The main different aspect is that during the rest phase, the vehicle is sustained by the 4 supporting legs of the Descent Module, keeping the module high over the surface.


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Load/unload system. Absent: load and unload phases do not exist. Impact on cargo design. Small impact on cargo design; little impact on Descent Module design being the mobility system installed on. Steering abilities. This vehicle can perform point turning by opposite movements of the skis. This implies that skis skid during this phase. Slope/obstacle crossing abilities. Obstacle crossing is limited by the height that skis reach while moving forward (during the rest phase of the body vehicle); obstacle negotiation may not be easy, relating to the necessity of static stability (one edge of the ski might be in on a rock, while the other side is in contact with the ground) Stowage. To be defined. Actuators/sensors. Locomotion system requires at least 4 motors to drive skis; the deployment system should require at least 2 actuators. Navigation cameras will also be necessary. Notes. Final Considerations Pro - low numbers of actuators - simple locomotion system - limited impact on vehicle design - it uses for mobility a part which was already designed Con - limited capabilities in obstacle negotiation (due to static stability) - low efficiency of steering system (especially on rough terrain)

2.2.10 2.4B SKI-WALKING MODULE

Figure 28: Concept 2.4B.

Description. After having been detached and unloaded by the Descent, the module has a pair of skis that allow the mobility on the surface (Figure 28); the locomotion system is integrated in the module. Locomotion system. The principle of the locomotion system is the same as the one described for Concept 1a.4. Both horizontal and vertical position during walking may be considered. Load/unload system. To be defined. As for Concept 2.1A, an air-bag could be used for unload.


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Impact on cargo design. Small impact on Descent Module design; little impact on the module design being the mobility system installed on. Steering abilities. The vehicle can perform point turning by opposite movements of the skis. This implies that skis skid during this phase. Slope/obstacle crossing abilities. Obstacle crossing is limited by the height that skis reach while moving forward (during the rest phase of the body vehicle); obstacle negotiation may not be easy, relating to the necessity of static stability (one edge of the ski might be in on a rock, while the other side is in contact with the ground) Stowage. To be defined. Actuators/sensors. Locomotion system requires at least 4 motors to drive skis; the deployment system of the skis should require at least 2 actuators. Navigation cameras will also be necessary. Notes. Final Considerations Pro - low numbers of actuators - simple locomotion system - limited impact on vehicle design - the mass of the moving system is lower Con - limited capabilities in obstacle negotiation (due to static stability) - low efficiency of steering system (especially on rough terrain)

2.2.11 2.5A HOPPING LANDER Description. The vehicle landed on the surface, made of both the Descent Module and the Habitation Module, has a system that permits to jump moving on the surface; remaining the module attached to the descent vehicle, there is no need to unload it. The locomotion system is integrated in the landing system; this means that the legs needed for landing phase and support will be used for the mobility system as well. It is equipped with a robotic arm, necessary for docking and mating operations. Locomotion system. Equal to Concept 1a.5A. Load/unload system. Absent: load and unload phases do not exist. Impact on cargo design. Strong impact on descent vehicle design: the mobility system has to be installed onboard. Little or no impact on module design. Steering abilities. Same as Concept 1a.5A. Slope/obstacle crossing. Same as Concept 1a.5A. Stowage. To be defined. Actuators/sensors. At least 1 actuator for main locomotion system, 3 actuators for attitude control. Cameras for navigation and attitude sensors are required (the LEV should have them anyway); the robotic arm requires at least 3 actuators. Notes.


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Examples See Concept 1a.5A Final Considerations Pro - low number of actuators - it avoids many problems of surface navigation (obstacle negotiation, ..) - no load/unload phases Con - never tested except on Earth - low precision of side movement - it requires an attitude control system - the mass of the moving system is higher than that of the hopping module.

2.2.12 2.5B HOPPING LANDER WITH ROCKETS Description. This concept is a variation on Concept 2.5A; the vehicle still uses a mechanical device to jump, but it uses rockets to obtain horizontal transfer. Locomotion system. The mechanical energy storing system is simpler than in Concept 1a.5A, as it has to develop only a vertical force. A set of rockets (storable propellant or cold gas) accelerates the vehicle towards the desired direction while jumping. Load/unload system. Absent: load and unload phases do not exist. Impact on cargo design. Strong impact on descent vehicle design: the mobility system has to be installed onboard. Little or no impact on module design (rockets could be installed on the surface of the module, taking advantage of the dimension of the system, if these rockets provide also attitude control). Steering abilities. While suspended over the surface, the rockets can modify the trajectory, depending on the characteristics of the rockets. Slope/obstacle crossing. Same as Concept 1a.5A. Stowage. To be defined. Actuators/sensors. All the equipment which is needed for Concept 1a.5A, plus a set of rockets (at least 4). If the same rockets are used for attitude control, their minimum number grows to 8 and other attitude actuators may not be necessary any more. Notes. Final Considerations Pro - low number of actuators - it avoids many problems of surface navigation (obstacle negotiation, ..) - no load/unload phases - good maneuverability


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Con - never tested - it requires an attitude control system - it consumes propellant - the mass of the moving system is higher

2.2.13 2.5C HOPPING MODULE Description. After having been detached and unloaded by the Descent Module, which is left at landing site, the payload module can move alone, having its own mobility system that permits to jump moving on the surface. It is equipped with a robotic arm, necessary for docking and mating operations. Locomotion system. Equal to Concept 1a.5A. Load/unload system. One possible solution could use air-bags, but it is necessary to make sure that the mechanical locomotion system will be in contact with the ground after the fall; otherwise an up-right system has to be considered. A second solution could even be that the module itself jump down the DM support. Impact on cargo design. Little or no impact on descent vehicle design. Strong impact module design: the mobility system and attitude control system have to be installed onboard. Steering abilities. Same as Concept 1a.5A. Slope/obstacle crossing. Same as Concept 1a.5A. Stowage. The mobility system has to be stowed in the module structure. Actuators/sensors. At least 1 actuator for main locomotion system, 3 actuators for attitude control. Cameras for navigation and attitude sensors are required; the robotic arm requires at least 3 actuators. A number to be defined of actuators for mobility system deployment. Notes. Examples See Concept 1a.5A. Final Considerations Pro - low number of actuators - it avoids many problems of surface navigation (obstacle negotiation, ..) - the mass of the moving system is lower Con - never tested except on Earth - low precision of side movement - it requires an attitude control system - the impact on module design could be too strong


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2.2.14 2.5D HOPPING MODULE WITH ROCKETS Description. This concept is a mixed solution of Concept 2.5B and Concept 2.5C; the module, having been detached by the Descent Module, has its own mobility system; it still uses a mechanical device to jump, but it uses rockets to obtain horizontal transfer. It is equipped with a robotic arm, necessary for docking and mating operations. Locomotion system. Equal to Concept 2.5B. Load/unload system. Same as Concept 2.5C. Impact on cargo design. Little or no impact on descent vehicle design. Strong impact on module design: the mobility system and attitude control system have to be installed onboard. Steering abilities. While suspended over the surface, the rockets can modify the trajectory, depending on the characteristics of the rockets. Slope/obstacle crossing. Same as Concept 1a.5A. Stowage. To be defined. Actuators/sensors. All the equipment which is needed for Concept 1a.5A, plus a set of rockets (at least 4). If the same rockets are used for attitude control, their minimum number grows to 8 and other attitude actuators may not be necessary any more. Notes. Final Considerations Pro - low number of actuators - it avoids many problems of surface navigation (obstacle negotiation, ..) - good maneuverability - the mass of the moving system is lower Con - never tested - it requires an attitude control system - it consumes propellant


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2.2.15 2.6A ARM ROLLER

Figure 29: two possible designs of Concept 2.6A.

Description. This system is based on the possibility of letting the modules roll on the surface of the Moon, controlled by a set of coordinated robotic arms. Being the shape of the modules cylindrical, the basic idea is to obtain the mobility of this element by letting them roll in a horizontal position. In order to preserve and protect the surface of the module and the payload it brings and in order to control them, a pair of inflatable wheels is fixed at the module edges. Locomotion system. It is constituted by a couple of inflatable wheels and a set of robotic arms which control the motion of the system. The robotic arms (at least 3 of them are required) are mounted on the surface of the module, so that pushing back or forward (in relation to the direction of the mean motion of the module) they can control the rotating speed of the module. They are mounted on the same circumference, kept at the same angular distance one to another, so that while rolling, they can operate one after the other. If necessary, they can also be used to brake the system. Load/unload system. To be defined. As for Concept 2.1A, an airbag could be used: in this case the upper inflated wheel will work as an airbag. Impact on cargo design. Some of the volume might be used for hosting the inflatable parts and for the robotic arm storage. This solution is better applicable to cylinders with height at least of the same order of magnitude of the diameter. Steering abilities. Partially deflating one of the two wheels, the curvature radius of the trajectory can be varied; the performance of this system depends on the ratio between the wheel diameter and the module diameter and on the height of the module. Fine positioning manoeuvres are either unfeasible or very long.


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Slope/obstacle crossing. Bigger wheels allow negotiating higher obstacles; it has to be considered the fact that rocks that could be encountered on the way do not touch the module surface while passing over them. Stowage. Inflatable parts do not have special problems; robotic arms might be better stowed in a way that the global cylindrical shape of the module is not modified. Actuators/sensors. A number to be defined of actuators and sensors for robotic arms is required. Cameras needed for navigation. Additional subsystems like compressed air reservoirs and valves have to be considered too. Notes. It could be self power supplied if the module has body mounted solar panels. Examples HSV [RD4. p. 97] A concept involving the use of inflatable wheels and a towing vehicle is shown. The Platonic Beast [RD28.] A small rolling robot with four arms (Figure 30).

Figure 30: the Platonic Beast.

Final Considerations Pro: - use of wheels (already tested on the Moon) - reduced mass and encumbrance

Con: - different cargoes require different wheel design - not all the shapes of modules are suitable for this concept - the unload from descent stage may be problematic.

2.2.16 2.6B ROLLING BALOON Description. This concept is a variation on Concept 2.6A. The module rolls with the use of inflatable wheels, but the thrust is given by inflating balloons instead of arms. Locomotion system. The module has couple of inflatable wheels on its bases, and its entire lateral surface is covered with air bags (the number is to be defined). Each air bag covers a sector of the cylinder lateral surface. Inflating an air bag that is actually under the module will make it roll towards one side, and it can be deflated afterwards.


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Figure 31: Concept 2.6B.

Load/unload system. The air bags could be used for descending as well. Impact on cargo design. Some of the volume might be used for hosting the inflatable parts and all the related machinery. Steering abilities. Deflating one of the two big wheels, the curvature radius of the trajectory can be varied; the performance of this system depends on the ratio between the wheel diameter and the module diameter and on the height of the module. Fine positioning manoeuvres are either unfeasible or very long. Slope/obstacle crossing. Bigger wheels allow negotiating higher obstacles; anyway the performances are to be defined. Stowage. Inflatable parts do not have special problems. Actuators/sensors. Cameras needed for navigation. Gas tanks, compressors and valves have to be included. Notes. Examples HSV [RD4. p. 97] A concept involving the use of inflatable wheels and a towing vehicle is shown. Final Considerations Pro: - small mass and encumbrance

Con: - never tested - not all the shapes of modules are suitable for this concept - the terrain negotiation ability is questionable.


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2.2.17 2.6C ROLLING SPHERE Description. The module is supported in the center of a big inflatable sphere that rolls on the surface; an eccentric mass is located on the top of a beam that is connected to the module and it is moved in order to control the movement of the sphere. Locomotion system. The locomotion system is based on the possibility of letting the resulting weight force of the system not falling in the contact point of the sphere: in this way a net torque and a net force (provided the sphere has enough grip on the ground) would act on the system, letting it rotate. The beam has two angular degrees of freedom, so that it can be positioned in every point of the surface of the sphere. Load/unload system. To be defined. The sphere itself could be used for unloading the system. Impact on cargo design. Some of the volume might be used for hosting the inflatable parts, the beams and the driving mechanism. Steering abilities. It can roll towards all the direction and perform point turnings. Slope/obstacle crossing. Depending on the radius of the sphere and mechanical characteristics of the system. Stowage. Inflatable parts do not have special problems. The beam, mass and its motion system are to be defined Actuators/sensors. At least two actuators and sensors for beam. Cameras needed for navigation. Additional subsystems like compressed air reservoirs and valves have to be considered too. Notes. Many points concerning mobility systems are not defined. Final Considerations Pro: - reduced mass and encumbrance

Con: - never tested - the control of the system might be difficult - the deployment of the sphere could be complex - the architecture of the locomotion system is complex.

2.3 Infrastructure Based Mobility The INF solution requires the presence of an infrastructure located on the surface of the Moon which task is to unload the cargo from the landing point, to load it on the mobility system that is part of the structure, to transport it and eventually to unload it to the target point. This possibility has been taken into account in relation to the possibility of building a permanent station on the Moon, which is at the moment a very long-term project for far future. Actually the infrastructure mobility system could be convenient just in case of large number of transported cargo and for providing high frequency service to the station. More that one dedicated launch would be required for the delivery of the main infrastructure; furthermore it would be necessary to


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have something that would take care of assembling and building up the mobility system (for instance a “light mobility system” might be the solution for this problem). This system would not affect cargo design in a significant way, being necessary just holds or hooks for load/unload operations or for transportation; the mean of locomotion is provided by the INF itself. Two options have been taken considered: 3.1 Lunar Railroad; 3.2 Lunar Cableway.

2.3.1 3.1 LUNAR RAILROAD Description. This concept takes inspiration from earth railroad system: it is constituted by two stations (necessary for load and unload, one in proximity of landing site, the other near the station) connected by the transportation line through which the payload is moved. Locomotion system. Mean of transportation (similar to a train) moving on railroad. Load/unload system. To be defined; it could be a system like a crane with a robotic arm for loading and unloading operations or docking. Impact on cargo design. Little or no impact. Steering abilities. The path of the transportation line would be defined a priori so steering concept does not exist. Slope/obstacle crossing abilities. This problem would regard just the transportation line deployment and assembly; once it is operative, obstacles could not affect movement any more. Actuators/sensors needed. At least one motor for main locomotion system; a number to be defined of actuators and sensors for robotic arms. Stowage. To be defined. Notes. Final Considerations Pro - high efficiency in transportation - problems of surface navigation are avoided Con - the mass of the system would be many times the mass of a single cargo - it requires dedicated launches - it requires an assembly system

2.3.2 3.2 LUNAR CABLEWAY Description. This concept takes inspiration from earth cableway system: it is constituted by at least two main supports where the cable is anchored and a cable car that can run on it. The supports are constituted by an A-frame (a structure made of pillars for supporting loads) and an anchor that is necessary for A-frame equilibrium. The cargo is loaded on the cable car. Locomotion system. Cable car on a cableway.


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Load/unload system. To be defined; it could be a system like a crane with a robotic arm for loading and unloading operations or docking. Impact on cargo design. Little or no impact. Steering abilities. The path of the transportation line would be defined a priori so steering concept does not exist. Slope/obstacle crossing abilities. The cable is suspended over the surface so that collision with the ground or with obstacles during movement are avoided. Actuators/sensors needed. At least one motor for main locomotion system of the cable car; a number to be defined of actuators and sensors for robotic arms. Stowage. To be defined. Notes. Examples [RD29.] Earth cableways. Final Considerations Pro - high efficiency in transportation - problems of surface navigation are avoided Con - the mass of the system would be many times the mass of a single cargo - it requires dedicated launches - it requires an assembly system (and cable deployment).


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3 CONCLUSION At this stage of the work it is not possible yet to define which is the best mobility system, that would satisfy the mission requirements and perfectly fit to lunar environment. The concepts have been arranged in a table, in order to have a rough classification of them, based on the general considerations that have been presented in this document. This classification is made through three different levels:

1. interesting and feasible 2. possible in the future 3. not appropriate;

The first group regards ideas of projects or work that have been already tested (on Earth or on the Moon) or that seem to be technically feasible and appropriate for the purpose of the system; these are the concept that should be investigated more deeply in order to get a clearer view of their more detailed aspects. In the second group, concepts that might be possible in the future have been inserted; technical issues and ideas that have few in common with prototype already tested are the main points that cause them to be receded. Eventually in the third group the concepts that are evidently not appropriated for the problem have been put in.


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Concept evaluation

Mean of

locomotion Interesting and

feasible Possible in the

future Not appropriate 6-Wheel UT 4-Wheel UT Wheeled Tractor Folding Wheels

Wheels

Inflatable Wheels Articulated Track UT Tracked Tractor Elastic Track UT Elastic Track Module Tracks

Articulated Track Module

Frame-Walking UT Walking UT Frame-Walking Lander Wheg Walking UT Walking Lander Walking Module

Legs

Wheg Walker Hopping UT Hopping UT with

Rockets

Hopping Lander Hopping Lander with

Rockets

Hopping Module

Hopping

Hopping Module with Rockets

Ski-Walking UT Ski-Walking Lander Skis Ski-Walking Module Arm Roller Lunar RailroadRolling Baloon Lunar Cableway Rolling Sphere Flying Systems Other

Drilling/Screwing Systems


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3.1 Not appropriate systems Some of the concept shown in Chapter 2 are evidently not applicable to the proposed scenario. Some of them are too futuristic, like the cableway or the railroad, while the rolling sphere concept is just a not well-defined idea of mobility. Other means of locomotion, not mentioned before, that are absolutely to be rejected, are all the systems involving flying machines: on the Moon the flight is impossible due to the absence of atmosphere.

3.2 Wheels, tracks, legs The most used means of transport for Earth locomotion are wheels, tracks and legs. Wheels and tracks are used by vehicles, while the legs are the transportation system of living beings. An interesting comparison among the three methods is shown in [RD30.] (Figure 32).

Figure 32: evaluation of locomotion systems, from [RD30.]

3.2.1 WHEELS Wheels are the most energy efficient and probably the most studied locomotion system. The advantages in the use of wheels are smoothness and speed in even or almost even terrain, simplicity, and a good payload mass/ vehicle mass ratio. The problems of wheels are in the negotiation of obstacles and rough terrains: the wheels have troubles with steps higher than the radius, and may experience slippage and sinkage on loose surfaces. The use of appropriate suspensions (like the “rocker-bogie” and body averaging system) may reduce the problems due to terrain unevenness, while grousers and flexible wheels may contribute to reduce slippage and sinkage [RD7.]. The wheel technology is mature, reliable and already tested on celestial bodies,


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and so all the concepts involving wheels can be considered feasible; the main issue on their design will be on their loading and unloading functions, and not on the locomotion system.

3.2.2 TRACKS Tracks are used on Earth for locomotion on muddy and loose terrains, where it is necessary to increase the contact surface. The technology is simple and mature in this case as well, but only for Earth applications and not or space. The tracks would be unreliable on the Moon, as the soil tends to enter in the loop, reducing the efficiency of the system and eventually jamming the track [RD7. p. 39]. The elastic loop mobility attempt to reduce the problem of the dust entering the gears thanks to the fact that the wheels are far from the surface; anyway, the experience of the astronauts on the Moon has shown that the dust can be easily lifted from the soil and remain floating for a long time; moreover, the dust adheres electrostatically to everything that comes in contact with the soil, forming a thin layer of dust [RD6. p. 478]. So it seems better to reject the concept involving the use of tracks, but it is not to be excluded that in the near future a there will be an improvement in the track technology that could change this statement.

3.2.3 LEGS It has been estimated that only half of Earth’s surface is accessible to wheels and tracks [RD30.], while almost any location is reachable with the use of legs. For what concerns robotics, the use of legs is still a young concept, which implies a higher level of complexity than wheels and tracks. As stated in [RD31.], “one reason legs provide better mobility in rough terrain than do wheels or tracks is that they can use isolated footholds that optimize support and traction, whereas a wheel requires a continuous path of support. As a consequence, the mobility of a legged system is generally limited by the best footholds in the reachable terrain and a wheel is limited by the worst terrain”. Nevertheless, legged systems seems to be unfeasible by now because of their excessive mass; the complexity and high number of actuators make usually the vehicles to weight much more than the payload (Figure 13). An exception to this is made by the frame walkers, which have a simpler design but also smaller agility; by now, they seem to be the only legged feasible concept.

3.3 Other means of transport Hopping systems are both aimed to reduce the interactions between the soil and the vehicle, and to minimize the number of actuators. The hopping technology still seems not well developed for applications, especially for heavy load transportations; existing hopping robots are only a few kilograms in mass, and the scalability of the system is questionable. Ski-walking systems have a very simple mean of transport, with no technological problems. They have already been tested on the Earth, and they have the same level of reliability than wheels and tracks. Their performances on rough terrain can be unsatisfactory. Rolling systems are quite new, and they have very few references [RD4.] [RD28.]. Anyway they require no new technology, as the locomotion system is the same of the wheel, and they can be considered feasible, although their performances are questionable.


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3.4 Inflatable technology Many of the concepts shown involve the use of inflatable parts. This method is definitely tempting because of the great saving of mass and volume that can result from that, but the actual applicability of these systems to the problem has to be confirmed. Inflating parts require the preservation and storage of a compressed gas, inside tanks or rubber/tissue balloons; the leakages will prevent any long-term use of inflatable parts, thus making unfeasible any utility truck with them. And also for short-term use, it has to be confirmed that inflatable parts can actually resist their working time without breaking: the safety and reliability of those systems is still questionable, especially in an environment like the surface of the Moon, where the temperature usually shifts from –110°C to +130°C. It is anyway encouraging that air bags have been successfully used for the landing of the latest Mars probes.

3.5 Final considerations The table shown in Figure 32 can be completed as follows:

Wheels Tracks Legs Skis Hopping Rolling Soft ground o + o + - o Rough ground + o ++ o + o Speed + o - - + - Agility + o + - + - Stability o + + + - o Adaptability o - + - + - Complexity + + - ++ o + Payload + + - + ? + Efficiency + o - - ? o Reliability + -- - + ? ? Fault tolerance o o + - ? ? Environmental effects o - + - - o

The first three rows are the same of Figure 32, but for the “reliability” of the tracks, which is now evaluated as negative for the reasons stated in Paragraph 3.2.2. The final choice of the system cannot be made without any specification of the context where the system is going to operate. For almost flat, non-problematic terrains, the solution will be simple and light-weight; on the contrary, if the necessity leads towards steep slopes, loose terrain and high obstacles, the solution will be more complex and heavy.

unar obility tudy eneral oncept urveyrobotics.estec.esa.int/hdpc/rd/rd2; lunar mobility study... ·...

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