Jekan Thanga

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Chapters

• Thangavelautham, J. (2018). Degradation in PEM Fuel Cells and Mitigation Strategies Using System Design and Control. In Proton Exchange Membrane Fuel Cell(p. 28). London, UK: IntechOpen.
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  The rapid miniaturization of electronics, sensors, actuators and communication devices have reduced the cost of field sensors and enabled more functionality in ever smaller packages. The technology has advanced to enable deployment of hundreds if not thousands of sensor modules in the field. Networks of field sensors have emerging applications in environmental monitoring, particularly climate change, air, water and soil quality measurement, in disaster monitoring, security and agriculture. Current power supply technologies such as chemical batteries limit potential applications due to their low specific energy. A promising alternative in warmer, drier climates included photovoltaics. Photovoltaics require large, bulky panels and are impacted by daily and seasonal variation in solar insolation that requires coupling to a backup power source. Polymer Electrolyte Membrane (PEM) fuel cells are a promising alternative, because they are clean, quiet and operate at high efficiencies. However, challenges remain in achievinglong lives due to factors such as catalyst degradation and hydrogen storage. In this chapter, we present a design framework for high-energy fuel cell power supplies applied to field sensor networks. The aim is to achieve long operational lives by effectively controlling degradation and utilizing high-energy density fuels such as lithium hydride to produce hydrogen. Lithium hydride in combination with fuel-cell wastewater or ambient humidity can achieve fuel specific energy of 5000 Wh/kg. Using this design framework,we identify operating conditions to maximize the life of the power supply, meet the required power output and minimize fuel consumption. The results of the study show the proposed PEM fuel cell hybrid system fueled using lithium hydride offer at least a three to five fold reduction in mass compared to state-of-the-art batteries.

Journals/Publications

• Robinson, M., Thangavelautham, J., Anderson, B., Deran, A., Lawrence, S., Wagner, R., Ridenoure, R., Williams, B., Dunham, D., Babuscia, A., Cheung, K., & Genova, A. (2018). Swirl: Unravelling an Enigma. Planetary and Space Sciences Special Issue, 14.
• Thangavelautham, J. (2019). Motion Planning on an Asteroid Surface with Irregular Gravity Fields. AAS GNC Conference.
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  There are thousands of asteroids in near-Earth space and millions in the MainBelt. They are diverse in physical properties and composition and are timecapsules of the early solar system. This makes them strategic locations forplanetary science, resource mining, planetary defense/security and asinter-planetary depots and communication relays. However, asteroids are achal-lenging target for surface exploration due it its low but highly nonlineargravity field. In such conditions, mobility through ballistic hopping possessmultiple advantages over conventional mobility solutions and as such hop-pingrobots have emerged as a promising platform for future exploration of asteroidsand comets. They can traverse large distances over rough terrain with theexpenditure of minimum energy. In this paper we present ballistic hoppingdynamics and its motion planning on an asteroid surface with highly nonlineargravity fields. We do it by solving Lambert's orbital boundary val-ue problemin irregular gravity fields by a shooting method to find the initial velocityrequired to intercept a target. We then present methods to localize the hoppingrobot using pose estimation by successive scan matching with a 3D laserscanner. Using the above results, we provide methods for motion planning on theasteroid surface over long distances. The robot will require to performmultiple hops to reach a desired goal from its initial position while avoidingobstacles. The study is then be extended to find optimal tra-jectories to reacha desired goal by visiting multiple waypoints.[Journal_ref: ]
• Asphaug, E., Thangavelautham, J., Klesh, A., Chandra, A., Nallapu, R., Raura, L., Herreras-Martinez, M., & Schwartz, S. (2017). A cubesat centrifuge for long duration milligravity research. Nature Microgravity, 5.
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  We advocate a low-cost strategy for long-duration research into the ‘milligravity’ environment of asteroids, comets and smallmoons, where surface gravity is a vector field typically less than 1/1000 the gravity of Earth. Unlike the microgravity environment ofspace, there is a directionality that gives rise, over time, to strangely familiar geologic textures and landforms. In addition toadvancing planetary science, and furthering technologies for hazardous asteroid mitigation and in situ resource utilization,simplified access to long-duration milligravity offers significant potential for advancing human spaceflight, biomedicine andmanufacturing. We show that a commodity 3U (10 × 10 × 34 cm3) cubesat containing a laboratory of loose materials can be spun to1 r.p.m. = 2π/60 s−1 on its long axis, creating a centrifugal force equivalent to the surface gravity of a kilometer-sized asteroid. Wedescribe the first flight demonstration, where small meteorite fragments will pile up to create a patch of real regolith under realisticasteroid conditions, paving the way for subsequent missions where landing and mobility technology can be flight-proven in theoperational environment, in low-Earth orbit. The 3U design can be adapted for use onboard the International Space Station to allowfor variable gravity experiments under ambient temperature and pressure for a broader range of experiments.
• Lightholder, J., Thoesen, A., Adamson, E., Jakubowski, J., Nallapu, R., Smallwood, S., Raura, L., Klesh, A., Asphaug, E., & Thangavelautham, J. (2017). Asteroid Origins Satellite 1: An On-orbit CubeSat Centrifuge Science Laboratory. Acta Astronautica, 133, 14.
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  Exploration of asteroids, comets and small moons (small bodies) can answer fundamental questions relating to the formation of the solar system, the availability of resources, and the nature of impact hazards. Near-earthasteroids and the small moons of Mars are potential targets of human exploration. But as illustrated by recent missions, small body surface exploration remains challenging, expensive, and fraught with risk. Despite their small size, they are among the most extreme planetary environments, with low and irregular gravity, loosely bound regolith, extreme temperature variation, and the presence of electrically charged dust. Here we describethe Asteroid Origins Satellite (AOSAT-I), an on-orbit, 3U CubeSat centrifuge using a sandwich-sized bed of crushed meteorite fragments to replicate asteroid surface conditions. Demonstration of this CubeSat willprovide a low-cost pathway to physical asteroid model validation, shed light on the origin and geophysics of asteroids, and constrain the design of future landers, rovers, resource extractors, and human missions. AOSAT-Iwill conduct scientific experiments within its payload chamber while operating in two distinct modes: (1) as a nonrotating microgravity laboratory to investigate primary accretion, and (2) as a rotating centrifuge producingartificial milligravity to simulate surface conditions on asteroids, comets and small moons. AOSAT-I takes advantage of low-cost, off-the-shelf components, modular design, and the rapid assembly and instrumentationof the CubeSat standard, to answer fundamental questions in planetary science and reduce cost and risk of future exploration.
• Thangavelautham, J. (2017). The Design of Long-Life, High-Efficiency PEM Fuel Cell Power Supplies for Low Power Sensor Networks. International Journal of Hydrogen Energy, 19.
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  Field sensor networks have important applications in environmentalmonitoring, particularly climate change, air, water and soil quality, indisaster monitoring and in border security. The reduced cost of electronics,sensors and actuators make it possible to deploy hundreds if not thousands of these sensor modules. However power technology have not kept up. Current power supply technologies such as batteries limit many applications due to their low specific energy. Photovoltaics typically requires large bulky panels and is dependent on varying solar insolation and therefore requires backup power sources. Polymer Electrolyte Membrane (PEM) fuel cells are a promising alternative, because they are clean, quiet and operate at high efficiency. However challenges remain in achieving long lives due to factors such as catalyst degradation and hydrogen storage. In this work, we devise a framework for designing fuel cells power supplies for field sensor networks to achieve long lives and utilize lithium hydride hydrogen storage technology that offers high energy density of up to 5,000 Wh/kg. Using this design framework, we identify operating conditions to maximize the life of the power supply, meet the required power output and minimize fuel consumption. We devise a series of controllers to achieve this capability and demonstrate it using a bench-top experiment that operated for 5,000 hours. The laboratory experiments point towards a pathway to design and scale these fuel cell power supplies for various field applications. Our studies show the proposed PEM fuel cell hybrid system fueled using lithium hydride offers at least a 3 fold reduction in mass compared to state of the art batteries and 3-5 fold reduction in mass compared to current fuel cell technologies.
• Thangavelautham, J., Law, K., Fu, T., El Samid, N. A., Smith, A., & D'Eleuterio, G. (2017). Autonomous Multirobot Excavation for Lunar Applications. Robotica, 33.
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  In this paper, a control approach called Artificial Neural Tissue (ANT) is applied to multirobot excavation for lunar base preparation tasks including clearing landing pads and burying of habitat modules. We show for the first time, a team of autonomous robots excavating a terrain to match a given three-dimensional (3D) blueprint. Constructing mounds around landing pads will provide physical shielding from debris during launch/landing. Burying a human habitat modules under 0.5 m of lunar regolith is expected to provide both radiation shielding and maintain temperatures of−25 ◦21 C. This minimizes base life-support complexity and reduces launch mass. ANT is compelling for a lunar mission because it does not require a team of astronauts for excavation and it requires minimal supervision. The robot teams are shown to autonomously interpret blueprints, excavate andprepare sites for a lunar base. Because little pre-programmed knowledge is provided, the controllers discover creative techniques. ANT evolves techniques such as slot-dozing that would otherwise require excavation experts. This is critical in making an excavation mission feasible when it is prohibitively expensive to send astronauts. The controllers evolve elaborate negotiation behaviors to work in close quarters. These and other techniques such as concurrent evolution of the controller and team size are shown to tackle problem of antagonism, when too many robots interfere reducing the overall efficiency or worse, resulting in gridlock. Although many challenges remain with this technology, our work shows a compelling pathway for field testing this approach.

Proceedings Publications

• Kalita, H., Asphaug, E., & Thangavelautham, J. (2018, 01). Mobility and Science operations On An Asteroid Using a Hopping Small Spacecraft on Stilts. In AAS GNC Conference.
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  There are thousands of asteroids in near-Earth space and millions in the MainBelt. They are diverse in physical properties and composition and are timecapsules of the early solar system. This makes them strategic locations forplanetary science, resource mining, planetary defense/security and asinterplanetary depots and communication relays. Landing on a small asteroid andmanipulating its surface materials remains a major unsolved challenge fraughtwith high risk. The asteroid surface may contain everything from hard bouldersto soft regolith loosely held by cohesion and very low-gravity. Upcomingmissions Hayabusa II and OSIRIS-REx will perform touch and go operations tomitigate the risks of landing on an asteroid. This limits the contact time andrequires fuel expenditure for hovering. An important unknown is the problem ofgetting stuck or making a hard impact with the surface. The SpacecraftPenetrator for Increasing Knowledge of NEOs (SPIKE) mission concept willutilize a small-satellite bus that is propelled using a xenon-fueled ion engineand will contain an extendable, low-mass, high-strength boom with a tipcontaining force-moment sensors. SPIKE will enable contact with the asteroidsurface, where it will perform detailed regolith analysis and seismology aswell as penetrometry, while keeping the main spacecraft bus at a safe distance.Using one or more long stilts frees the spacecraft from having to hover abovethe asteroid and thus substantially reduces or eliminates fuel use when doingscience operations. This enables much longer missions that include a series ofhops to multiple locations on the small-body surface.[Journal_ref: ]
• Kalita, H., Vance, L., Reddy, V., & Thangavelautham, J. (2019, 01). Use of Laser Beams to Configure and Command Spacecraft Swarms. In AAS GNC Conference.
• Bouskela, A., Chandra, A., Shakarayev, S., & Thangavelautham, J. (2019, 01). Attitude Control of an Inflatable Sailplane for Mars Exploration. In AAS GNC Conference.
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  Exploration of Mars has been made possible using a series of landers, roversand orbiters. The HiRise camera on the Mars Reconnaissance Orbiter (MRO) hascaptured high-resolution images covering large tracts of the surface. However,orbital images lack the depth and rich detail obtained from in-situexploration. Rovers such as Mars Science Laboratory and upcoming Mars 2020carry state-of-the-art science laboratories to perform in-situ exploration andanalysis. However, they can only cover a small area of Mars through the courseof their mission. A critical capability gap exists in our ability to image,provide services and explore large tracts of the surface of Mars required forenabling a future human mission. A promising solution is to develop areconnaissance sailplane that travels tens to hundreds of kilometers per sol.The aircraft would be equipped with imagers that provide that in-situ depth offield, with coverage comparable to orbital assets such as MRO. A majorchallenge is that the Martian carbon dioxide atmosphere is thin, with apres-sure of 1% of Earth at sea level. To compensate, the aircraft needs to flyat high-velocities and have sufficiently large wing area to generate therequired lift. Inflatable wings are an excellent choice as they have the lowestmass and can be used to change shape (morph) depending on aerodynamic orcon-trol requirements. In this paper, we present our design of an inflatablesail-plane capable of deploying from a 12U CubeSat platform. A pneumaticde-ployment mechanism ensures highly compact stowage volumes and minimizescomplexity.[Journal_ref: ]
• Chandra, A., & Thangavelautham, J. (2019, 01). De-orbiting Small Satellites Using Inflatables. In Space Traffic Management Conference.
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  Small-satellites and CubeSats offer a low-cost pathway to access Low EarthOrbit at altitudes of 450 km and lower thanks to miniaturization andadvancement in reliability of commercial electronics. However, at these lowaltitudes, atmospheric drag has a critical effect on the satellite resulting innatural deorbits within months. As these small systems further increase inreliability and radiation tolerance they will be able readily access higherorbits at altitudes of 700 km and higher, where atmospheric drag has little tono effect. This requires alternative technologies to either de-orbit thesesmall spacecrafts at the end of life or move them to a safe parking orbit. Useof propulsion and de-orbit mechanisms have been proposed, however they requireactive control systems to be trigged. Other typical de-orbit mechanism relieson complex mechanisms with many moving parts. In this work, we analyze thefeasibility of using inflatable de-orbit devices that are triggered passivelywhen a spacecraft is tumbling. Inflatables have already been proposed ashypersonic deccelerators that would carry large payload to the Martian surface.However, these systems are quite complex and need to withstand high-forces,temperature and enable survival of a critical payload. Furthermore, inflatableshave been proposed as communication antennas and as structures using a class ofsublimates that turn into gas under the vacuum of space. These inflatablessystem are relatively simple and does not require a specialized inflationsystem.[Journal_ref: ]
• Chandra, A., & Thangavelautham, J. (2019, 02). Modular Inflatable Composites for Space Telescopes. In IEEE Aerospace.
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  There is an every-growing need to construct large space telescopes andstructures for observation of exo-planets, main-belt asteroids and NEOs. Spaceobservation capabilities can significant enhanced by large-aperture structures.Structures extending to several meters in size could potentially revolutionizeobservation enabling technologies. These include star-shades for imagingdistant objects such as exo-planets and high-resolution large aperturetelescopes. In addition to size, such structures require controllable precisionsurfaces and high packing efficiencies. A promising approach to achieving highcompaction for large surface areas is by incorporating compliant materials orgossamers. Gossamer structures on their own do not meet stiffness requirementsfor controlled deployment. Supporting stiffening mechanisms are required tofully realize their structural potential. The accuracy of the 'active' surfaceconstructed out of a gossamer additionally also depends on the load bearingstructure that supports it. This paper investigates structural assembliesconstructed from modular inflatable membranes stiffened pneumatically usinginflation gas. These units assembled into composites can yield desirablecharacteristics. We present the design of large assemblies of these modularelements.[Journal_ref: ]
• Chandra, A., Kalita, H., Furfaro, R., & Thangavelautham, J. (2019, 01). End to End Satellite Servicing and Space Debris Management. In Space Traffic Management Conference.
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  There is growing demand for satellite swarms and constellations for globalpositioning, remote sensing and relay communication in higher LEO orbits. Thiswill result in many obsolete, damaged and abandoned satellites that will remainon-orbit beyond 25 years. These abandoned satellites and space debris maybeeconomically valuable orbital real-estate and resources that can be reused,repaired or upgraded for future use. Space traffic management is critical torepair damaged satellites, divert satellites into warehouse orbits andeffectively de-orbit satellites and space debris that are beyond repair andsalvage. Current methods for on-orbit capture, servicing and repair require alarge service satellite. However, by accessing abandoned satellites and spacedebris, there is an inherent heightened risk of damage to a servicingspacecraft. Sending multiple small-robots with each robot specialized in aspecific task is a credible alternative, as the system is simple andcost-effective and where loss of one or more robots does not end the mission.In this work, we outline an end to end multirobot system to capture damaged andabandoned spacecraft for salvaging, repair and for de-orbiting. We analyze thefeasibility of sending multiple, decentralized robots that can workcooperatively to perform capture of the target satellite as a first step,followed by crawling onto damage satellites to perform detailed mapping. Afterobtaining a detailed map of the satellite, the robots will proceed to eitherrepair and replace or dismantle components for salvage operations. Finally, theremaining components will be packaged with a de-orbit device for acceleratedde-orbit.[Journal_ref: ]
• Chandra, A., Thangavelautham, J., & Babuscia, A. (2018, 11). Composite Inflatable Antennas for Small-Satellite and Backup Communication. In 24th Ka-band and Broadband Communications Conference.
• Chandra, A., Wilburn, G., & Thangavelautham, J. (2019, 01). Advanced Inflatable De-Orbit Solutions for Derelict Satellites and Orbital Debris. In Space Traffic Management Conference.
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  The exponential rise in small-satellites and CubeSats in Low Earth Orbit(LEO) poses important challenges for future space traffic management. Ataltitudes of 600 km and lower, aerodynamic drag accelerates de-orbiting ofsatellites. However, placement of satellites at higher altitudes required forconstellations pose important challenges. The satellites will require on-boardpropulsion to lower their orbits to 600 km and let aerodynamic drag take-over.In this work we analyze solutions for de-orbiting satellites at altitudes of upto 3000 km. We consider a modular robotic de-orbit device that has stowedvolume of a regular CubeSat. The de-orbit device would be externally directedtowards a dead satellite or placed on one by an external satellite servicingsystem. Our solutions are intended to be simple, high-reliability devices thatoperate in a passive manner, requiring no active electronics or utilizeexternal beamed power in the form of radio frequency, microwave or laser tooperate. Utilizing this approach, it is possible for an external, even groundbased system to direct the de-orbit of a spacecraft. The role of an externalsystem to direct the de-orbit is important to avoid accidental collisions. Someform of propulsion is needed to lower the orbit of the dead satellite ororbital debris. We considered green (non-toxic) propulsion methods includingsolar radiation pressure, solar-thermal propulsion using water steam,solar-electrolysis propulsion using water and use of electrodynamic tethers.Based on this trade-study we identify multiple solutions that can be used tode-orbit a spacecraft or orbital debris.[Journal_ref: ]
• Kalita, H., Furfaro, R., & Thangavelautham, J. (2018, 08). Satellite Capture and Servicing Using Networks of Tethered Robots Supported by Ground Surveillance. In Advanced Maui Optical and Space Surveillance Technologies Conference.
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  There is ever growing demand for satellite constellations that perform globalpositioning, remote sensing, earth-imaging and relay communication. In thesehighly prized orbits, there are many obsolete and abandoned satellites andcomponents strewn posing ever-growing logistical challenges. This increaseddemand for satellite constellations pose challenges for space trafficmanagement, where there is growing need to identify the risks probabilities andif possible mitigate them. These abandoned satellites and space debris maybeeconomically valuable orbital real-estate and resources that can be reused,repaired or upgraded for future use. On-orbit capture and servicing of asatellite requires satellite rendezvous, docking and repair, removal andreplacement of components. Launching a big spacecraft that perform satellitesservicing is one credible approach for servicing and maintainingnext-generation constellations. By accessing abandoned satellites and spacedebris, there is an inherent heightened risk of damage to a servicingspacecraft. Under these scenarios, sending multiple, small-robots with eachrobot specialized in a specific task is a credible alternative, as the systemis simple and cost-effective and where loss of one or more of robot does notend the mission. Eliminating the need for a large spacecraft or positioning thelarge spacecraft at safe distance to provide position, navigation and trackingsupport simplifies the system and enable the approach to be extensible with thelatest ground-based sensing technology. In this work, we analyze thefeasibility of sending multiple, decentralized robots that can workcooperatively to perform capture of the target satellite as first steps toon-orbit satellite servicing.[Journal_ref: ]
• Kalita, H., Morad, S., & Thangavelautham, J. (2018, 05). Path Planning and Navigation Inside Off-World Lava Tubes and Caves. In IEEE ION PLANS.
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  Detailed surface images of the Moon and Mars reveal hundreds of cave-likeopenings. These cave-like openings are theorized to be remnants of lava-tubesand their interior maybe in pristine conditions. These locations may have wellpreserved geological records of the Moon and Mars, including evidence of pastwater flow and habitability. Exploration of these caves using wheeled roversremains a daunting challenge. These caves are likely to have entrances withcaved-in ceilings much like the lava-tubes of Arizona and New Mexico. Thus, theentrances are nearly impossible to traverse even for experienced human hikers.Our approach is to utilize the SphereX robot, a 3 kg, 30 cm diameter robot withcomputer hardware and sensors of a smartphone attached to rocket thrusters.Each SphereX robot can hop, roll or fly short distances in low gravity, airlessor low-pressure environments. Several SphereX robots maybe deployed to minimizesingle-point failure and exploit cooperative behaviors to traverse the cave.There are some important challenges for navigation and path planning in thesecave environments. Localization systems such as GPS are not available nor arethey easy to install due to the signal blockage from the rocks. These caves aretoo dark and too large for conventional sensor such as cameras and miniaturelaser sensors to perform detailed mapping and navigation. In this paper, weidentify new techniques to map these caves by performing localized, cooperativemapping and navigation.[Journal_ref: ]
• Kalita, H., Vance, L., Reddy, V., & Thangavelautham, J. (2019, 01). Laser Communication and Coordination Control of Spacecraft Swarms. In Space Traffic Management.
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  Swarms of small spacecraft offer whole new capabilities in Earth observation,global positioning and communications compared to a large monolithicspacecraft. These small spacecrafts can provide bigger apertures that increasegain in communication antennas, increase area coverage or effective resolutionof distributed cameras and enable persistent observation of ground or spacetargets. However, there remain important challenges in operating large numberof spacecrafts at once. Current methods would require a large number of groundoperators monitor and actively control these spacecrafts which poses challengesin terms of coordination and control which prevents the technology from scaledup in cost-effective manner. Technologies are required to enable one groundoperator to manage tens if not hundreds of spacecrafts. We propose to utilizelaser beams directed from the ground or from a command and control spacecraftto organize and manage a large swarm. Each satellite in the swarm will have acustomized "smart skin" con-taining solar panels, power and control circuitryand an embedded secondary propulsion unit. A secondary propulsion unit mayinclude electrospray pro-pulsion, solar radiation pressure-based system,photonic laser thrusters and Lorentz force thrusters. Solar panels typicallyoccupy the largest surface area on an earth orbiting satellite. A laser beamfrom another spacecraft or from the ground would interact with solar panels ofthe spacecraft swarm. The laser beam would be used to select a 'leader' amongsta group of spacecrafts, set parameters for formation-flight, includingseparation distance, local if-then rules and coordinated changes in attitudeand position.[Journal_ref: ]
• Martinez, J., & Thangavelautham, J. (2019, 01). Propelling Interplanetary Spacecraft Utilizing Water-Steam. In AAS GNC Conference.
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  Water has been identified as a critical resource both to sustain human-lifebut also for use in propulsion, attitude-control, power, thermal and radiationpro-tection systems. Water may be obtained off-world through In-Situ ResourceUtilization (ISRU) in the course of human or robotic space exploration thatreplace materials that would otherwise be shipped from Earth. Water has beenhighlighted by many in the space community as a credible solution foraffordable/sustainable exploration. Water can be extracted from the Moon,C-class Near Earth Objects (NEOs), surface of Mars and Martian Moons Pho-bosand Deimos and from the surface of icy, rugged terrains of Ocean Worlds.However, use of water for propulsion faces some important techno-logicalbarriers. A technique to use water as a propellant is to electrolyze it intohydrogen and oxygen that is then pulse-detonated. High-efficiency elec-trolysisrequires use of platinum-catalyst based fuel cells. Even trace ele-ments ofsulfur and carbon monoxide found on planetary bodies can poison these cellsmaking them unusable. In this work, we develop steam-based propulsion thatavoids the technological barriers of electrolyzing impure water as propellant.Using a solar concentrator, heat is used to extract the water which is thencondensed as a liquid and stored. Steam is then formed using the solar thermalreflectors to concentrate the light into a nanoparticle-water mix. This solarthermal heating (STH) process converts 80 to 99% of the in-coming light intoheat.[Journal_ref: ]
• Morad, S., Kalita, H., & Thangavelautham, J. (2018, 05). Planning and Navigation of Climbing Robots in Low-Gravity Environments. In IEEE IONS Conferences.
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  Advances in planetary robotics have led to wheeled robots that have beamedback invaluable science data from the surface of the Moon and Mars. However,these large wheeled robots are unable to access rugged environments such ascliffs, canyons and crater walls that contain exposed rock-faces and aregeological time-capsules into the early Moon and Mars. We have proposed theSphereX robot with a mass of 3 kg, 30 cm diameter that can hop, roll and flyshort distances. A single robot may slip and fall, however, a multirobot systemcan work cooperatively by being interlinked using spring-tethers and work muchlike a team of mountaineers to systematically climb a slope. We consider a teamof four or more robots that are interlinked with tethers in an 'x'configuration. Each robot secures itself to a slope using spiny grippingactuators, and one by one each robot moves upwards by crawling, rolling orhopping up the slope. In this paper, we present a human devised autonomousclimbing algorithm and evaluate it using a high-fidelity dynamics simulator.The climbing surfaces contain impassable obstacles and some loosely held rocksthat can dislodge. Under these conditions, the robots need to autonomously map,plan and navigate up or down these steep environments. Autonomous mapping andnavigation capability is evaluated using simulated lasers, vision sensors. Thehuman devised planning algorithm uses a new algorithm called bounded-leg A*.Our early simulation results show much promise in these techniques and ourfuture plans include demonstration on real robots in a controlled laboratoryenvironment and outdoors in the canyons of Arizona.[Journal_ref: ]
• Morad, S., Kalita, H., Reddy, V., Furfaro, R., Asphaug, E., & Thangavelautham, J. (2018, 08). On-Orbit Smart Camera System to Observe Illuminated and Unilluminated Space Objects. In Advanced Maui Optical and Space Surveillance Technologies Conference,.
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  The wide availability of Commercial Off-The-Shelf (COTS) electronics that canwithstand Low Earth Orbit conditions has opened avenue for wide deployment ofCubeSats and small-satellites. CubeSats thanks to their low developmental andlaunch costs offer new opportunities for rapidly demonstrating on-orbitsurveillance capabilities. In our earlier work, we proposed development ofSWIMSat (Space based Wide-angle Imaging of Meteors) a 3U CubeSat demonstratorthat is designed to observe illuminated objects entering the Earth'satmosphere. The spacecraft would operate autonomously using a smart camera withvision algorithms to detect, track and report of objects. Several CubeSats cantrack an object in a coordinated fashion to pinpoint an object's trajectory. Anextension of this smart camera capability is to track unilluminated objectsutilizing capabilities we have been developing to track and navigate to NearEarth Objects (NEOs). This extension enables detecting and tracking objectsthat can't readily be detected by humans. The system maintains a dense star mapof the night sky and performs round the clock observations. Standard opticalflow algorithms are used to obtain trajectories of all moving objects in thecamera field of view. Through a process of elimination, certain stars maybeoccluded by a transiting unilluminated object which is then used to firstdetect and obtain a trajectory of the object. Using multiple cameras observingthe event from different points of view, it may be possible then to triangulatethe position of the object in space and obtain its orbital trajectory. In thiswork, the performance of our space object detection algorithm coupled with aspacecraft guidance, navigation, and control system is demonstrated.[Journal_ref: ]
• Nallapu, R., & Thangavelautham, J. (2019, 01). Attitude Control of Spacecraft Swarms for Visual Mapping of Planetary Bodies. In AAS GNC Conference.
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  Planetary bodies such as asteroids, comets, and planetary moons arehigh-value science targets as they hold important information about theformation and evolution of our solar system. However, due to their low-gravity,variable sizes and shapes, dedicated orbiting spacecraft missions around thesetarget bodies is difficult. Therefore, many planetary bodies are observedduring flyby encounters, and consequently, the mapping coverage of the targetbody is limited. In this work, we propose the use of a spacecraft swarm toprovide complete surface maps of a planetary body during a close encounterflyby. With the advancement of low-cost spacecraft technology, such a swarm canbe realized by using multiple miniature spacecraft. The design of a swarmmission is a complex multi-disciplinary problem. To get started, we propose theIntegrated Design Engineering & Automation of Swarms (IDEAS) software. In thiswork, we will introduce the development of the Automated Swarm Designer moduleof the software and apply it to total surface mapping of asteroid 433 Erosthrough flybys.[Journal_ref: ]
• Nallapu, R., & Thangavelautham, J. (2019, 01). Spacecraft Swarm Attitude Control for Small Body Surface Observation. In AAS GNC Conference.
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  Understanding the physics of small bodies such as asteroids, comets, andplanetary moons will help us understand the formation of the solar system, andalso provide us with resources for a future space economy. Due to thesereasons, missions to small bodies are actively being pursued. However, thesurfaces of small bodies contain unpredictable and interesting features such ascraters, dust, and granular matter, which need to be observed carefully beforea lander mission is even considered. This presents the need for a surveillancespacecraft to observe the surface of small bodies where these features exist.While traditionally, the small body exploration has been performed by a largemonolithic spacecraft, a group of small, low-cost spacecraft can enhance theobservational value of the mission. Such a spacecraft swarm has the advantageof providing longer observation time and is also tolerant to single pointfailures. In order to optimize a space-craft swarm mission design, we proposedthe Integrated Design Engineering & Automation of Swarms (IDEAS) software whichwill serve as an end-to-end tool for theoretical swarm mission design. Thecurrent work will focus on developing the Automated Swarm Designer module ofthe IDEAS software by extending its capabilities for exploring surface featureson small bodies while focusing on the attitude behaviors of the spacecraft inthe swarm. We begin by classifying space-craft swarms into 5 classes based onthe level of coordination. In the current work, we design Class 2 swarms, whosespacecraft operate in a decentralized fashion but coordinate for communication.We demonstrate the Class 2 swarm in 2 different configurations, based on theroles of the participating spacecraft.[Journal_ref: ]
• Thangavelautham, J. (2019, 02). A Milli-Newton Propulsion System for the Asteroid Mobile Imager and Geologic Observer (AMIGO). In IEEE Aerospace.
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  Exploration of small bodies, namely comets and asteroids remain a challengingendeavor due to their low gravity. The risk is so high that missions such asHayabusa II and OSIRIS-REx will be performing touch and go missions to obtainsamples. The next logical step is to perform longer-term mobility on thesurface of these asteroid. This can be accomplished by sending small landers ofa 1 kg or less with miniature propulsion systems that can just offset the forceof asteroid gravity. Such a propulsion system would ideally be used to hop onthe surface of the asteroid. Hopping has been found to be most efficient formof mobility on low-gravity. Use of wheels for rolling presents substantialchallenges as the wheel can't gain traction to roll. The Asteroid Mobile Imagerand Geologic Observer (AMIGO) utilizes 1 kg landers that are stowed in a 1UCubeSat configuration and deployed, releasing an inflatable that is 1 m indiameter. The inflatable is attached to the top of the 1U lander, enabling highspeed communications and a means of easily tracking lander from an overheadmothership. Milligravity propulsion is required for the AMIGO landers toperform ballistic hops on the asteroid surface. The propulsion system is usedto navigate the lander across the surface of the asteroid under the extremelylow gravity while taking care to not exceed escape velocity.Although theconcept for AMIGO missions is to use multiple landers, the more surface areaevaluated by each lander the better. Without a propulsion system, each AMIGOwill have a limited range of observable area. The propulsion system also servesas a rough attitude control system (ACS), as it enables pointing and regulationover where the lander is positioned via an array of MEMS thrusters.[Journal_ref: ]
• Thangavelautham, J., & Kalita, H. (2019, 01). Coordination and Control of Multiple Climbing Robots in Transport of Heavy Loads through Extreme Terrain. In AIAA SciTech.
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  The discovery of ice deposits in the permanently shadowed craters of thelunar North and South Pole Moon presents an important opportunity for In-SituResource Utilization. These ice deposits maybe the source for sustaining alunar base or for enabling an interplanetary refueling station. These icedeposits also preserve a unique record of the geology and environment of theirhosts, both in terms of impact history and the supply of volatile compounds,and so are of immense scientific interest. To date, these ice deposits havebeen studied indirectly and by remote active radar, but they need to beanalyzed in-situ by robotic systems that can study the depths of the deposits,their purity and composition. However, these shadowed craters never seesunlight and are one of the coldest places in the solar system. NASA JPLproposed use of solar reflectors mounted on crater rims to project sunlightinto the crater depths for use by ground robots. The solar reflectors wouldheat the crater base and vehicles positioned at the base sufficiently tosurvive the cold-temperatures. Our approach analyzes part of the logistics ofthe approach, with teams of robots climbing up and down to the crater to accessthe ice deposits. The mission will require robots to climb down extremeenvironments and carry large structures, including instruments andcommunication devices.[Journal_ref: ]
• Thangavelautham, J., Asphaug, E., & Schwartz, S. (2019, 02). An On-Orbit CubeSat Centrifuge for Asteroid Science and Exploration. In IEEE Aerospace.
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  There are thousands of asteroids in near-Earth space and millions expected inthe Main Belt. They are diverse in their physical properties and compositions.They are also time capsules of the early Solar System making them valuable forplanetary science, and are strategic for resource mining, planetarydefense/security and as interplanetary depots. But we lack direct knowledge ofthe geophysical behavior of an asteroid surface under milligravity conditions,and therefore landing on an asteroid and manipulating its surface materialremains a daunting challenge. Towards this goal we are putting forth plans for a 12U CubeSat that will bein Low Earth Orbit and that will operate as a spinning centrifuge on-orbit. Inthis paper, we will present an overview of the systems engineering andinstrumentation design on the spacecraft. Parts of this 12U CubeSat willcontain a laboratory that will recreate asteroid surface conditions bycontaining crushed meteorite. The laboratory will spin at 1 to 2 RPM during theprimary mission to simulate surface conditions of asteroids 2 km and smaller,followed by an extended mission where the spacecraft will spin at even higherRPM. The result is a bed of realistic regolith, the environment that landersand diggers and maybe astronauts will interact with. The CubeSat is configuredwith cameras, lasers, actuators and small mechanical instruments to bothobserve and manipulate the regolith at low simulated gravity conditions. Aseries of experiments will measure the general behavior, internal friction,adhesion, dilatancy, coefficients of restitution and other parameters that canfeed into asteroid surface dynamics simulations. Effective gravity can bevaried, and external mechanical forces can be applied.[Journal_ref: ]
• Vance, L., & Thangavelautham, J. (2019, 01). An Autonomous Passive Navigation Method for Nanosatellite Exploration of the Asteroid Belt. In AAS GNC Conference.
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  There are more than 750,000 asteroids identified in the main belt. Theseasteroids are diverse in composition and size. Some of these asteroids can betraced back to the early solar system and can provide insight into the originsof the so-lar system, origins of Earth and origins of life. Apart from beingimportant tar-gets for science exploration, asteroids are strategically placeddue to their low-gravity well, making it low-cost to transport material ontoand way from them. They hold valuable resources such as water, carbon, metalsincluding iron, nickel and platinum to name a few. These resources maybe usedin refueling depots for interplanetary spacecraft and construction material forfuture space colonies, communication relays and space telescopes. The costs ofgetting to the main asteroid belt, combined with large numbers of objects to beexplored encourage the application of small spacecraft swarms. The size andcapability of the result-ing nano-spacecraft can make detection from Earthdifficult. This paper dis-cusses a method by which a spacecraft can establishephemeris autonomously using line of sight measurements to nearby asteroidswith Extended Kalman Filtering techniques, without knowing accurate ephemerisof either the asteroids or the spacecraft initially. A description of thefilter implementation is followed by examples of resultant performance.[Journal_ref: ]
• Vance, L., & Thangavelautham, J. (2019, 01). Evaluation of Mother-Daughter Architectures for Asteroid Belt Exploration. In AIAA SciTech Conference.
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  This paper examines the effectiveness of an asteroid exploration architecturecomprised of multiple nanosatellite sized spacecraft deployed from a singlemother ship into a heliocentric orbit in the main asteroid belt where themothership is ideally located in region of high density. Basic missionrequirements associated with a Mother-Daughter architecture are establishedutilizing a relatively large number (10-20) daughter spacecraft distributedfrom a mothership within the asteroid belt for the purpose of executing sampleand return missions. A number of trade analyses are performed to establishsystem performance to changes in initial orbit, delta-V capability and maximumsmall spacecraft flight time. The balance between the initial delta-V burn andasteroid velocity matching are also examined, with a goal of minimizing theamount of fuel needed in the small spacecraft. Preliminary requirements for thesystem are established using these results, and a conceptual design ispresented for comparison to other asteroid exploration techniques. Preliminaryresults indicate that the aforementioned concept of a mothership with smallspacecraft is viable and should be considered as an alternative approach tofirst order surveying of the asteroid belt.[Journal_ref: ]
• Wilburn, G., Kalita, H., Chandra, A., Schwartz, S., Asphaug, E., & Thangavelautham, J. (2019, 01). Guidance, Navigation and Control of Asteroid Mobile Imager and Geologic Observer (AMIGO). In AAS GNC Conference.
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  The science and origins of asteroids is deemed high priority in the PlanetaryScience Decadal Survey. Major scientific goals for the study of planetesimalsare to decipher geological processes in SSSBs not determinable frominvestigation via in-situ experimentation, and to understand how planetesimalscontribute to the formation of planets. Ground based observations are notsufficient to examine SSSBs, as they are only able to measure what is on thesurface of the body; however, in-situ analysis allows for further, close upinvestigation as to the surface characteristics and the inner composure of thebody. To this end, the Asteroid Mobile Imager and Geologic Observer (AMIGO) anautonomous semi-inflatable robot will operate in a swarm to efficientlycharacterize the surface of an asteroid. The stowed package is 10x10x10 cm(equivalent to a 1U CubeSat) that deploys an inflatable sphere of ~1m indiameter. Three mobility modes are identified and designed: ballistic hopping,rotation during hops, and up-righting maneuvers. Ballistic hops provide theAMIGO robot the ability to explore a larger portion of the asteroid's surfaceto sample a larger area than a stationary lander. Rotation during the hopentails attitude control of the robot, utilizing propulsion and reaction wheelactuation. In the event of the robot tipping or not landing up-right, acombination of thrusters and reaction wheels will correct the robot's attitude.The AMIGO propulsion system utilizes sublimate-based micro-electromechanicalsystems (MEMS) technology as a means of lightweight, low-thrust ballistichopping and coarse attitude control. Each deployed AMIGO will hop across thesurface of the asteroid multiple times.[Journal_ref: ]
• Babuscia, A., Sauder, J., Chandra, A., & Thangavelautham, J. (2017, 03). Inflatable Antenna for CubeSats: A New Spherical Design for Increased X-band Gain. In IEEE Aerospace Conference, 10.
• Fleetwood, G., & Thangavelautham, J. (2017, 07). An Information Theoretic Approach to Sample Acquisition and Perception in Planetary Robotics. In Adaptive Hardware Conference, 10.
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  An important and emerging component of planetary exploration is sample retrieval and return to Earth. Obtaining and analyzing rock samples can provide unprecedented insight into the geology, geo-history and prospects for finding past life and water. Current methods of exploration rely on mission scientists to identify objects of interests and this presents major operational challenges. Finding objects of interests will require systematic and efficient methods to quickly and correctly evaluate the importance of hundreds if not thousands of samples so that the most interesting are saved for further analysis by the mission scientists. In this paper, we propose an automated information theoretic approach to identify shapes of interests using a library of predefined interesting shapes. These predefined shapes maybe human input or samples that are then extrapolated by the shape matching system using the Superformula to judge the importance of newly obtained objects. Shape samples are matched to a library of shapes using the eigenfaces approach enabling categorization and prioritization of the sample. The approach shows robustness to simulated sensor noise of up to 20%. The effect of shape parameters and rotational angle on shape matching accuracy has been analyzed. The approach shows significant promise and efforts are underway in testing the algorithm with real rock samples.
• Gankidi, P., & Thangavelautham, J. (2017, March). FPGA Accelerated Q learning in autonomous rovers for planetary exploration. In IEEE Aerospace Conference, 8.
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  Autonomous control systems onboard planetary rovers and spacecraft benefit from having cognitive capabilities like learning so that they can adapt to unexpected situations in-situ. Q-learning is a form of reinforcement learning and it has been efficient in solving certain class of learning problems. However, embedded systems onboard planetary rovers and spacecraft rarely implement learning algorithms due to the constraints faced in the field, like processing power, chip size, convergence rate and costs due to the need for radiation hardening. These challenges present a compelling need for a portable, low-power, area efficient hardware accelerator to make learning algorithms practical onboard space hardware. This paper presents a FPGA implementation of Q-learning with Artificial Neural Networks (ANN). This method matches the massive parallelism inherent in neural network software with the fine-grain parallelism of an FPGA hardware thereby dramatically reducing processing time. Mars Science Laboratory currently uses Xilinx-Space-grade Virtex FPGA devices for image processing, pyrotechnic operation control and obstacle avoidance. We simulate and program our architecture on a Xilinx Virtex 7 FPGA. The architectural implementation for a single neuron Q-learning and a more complex Multilayer Perception (MLP) Q-learning accelerator has been demonstrated. The results show up to a 43-fold speed up by Virtex 7 FPGAs compared to a conventional Intel i5 2.3 GHz CPU. Finally, we simulate the proposed architecture using the Symphony simulator and compiler from Xilinx, and evaluate the performance and power consumption.
• Hernandez, V., Aaditya, R., Herreras-Martinez, M., Thangavelautham, J., & Asphaug, E. (2017, 08). On-Orbit Demonstration of the Space Weather and Meteor Impact Monitoring Network. In Small Satellite Conference, 8.
• Hernendas-Martinez, M., Uglietta, J., Lozes, K., & Thangavelautham, J. (2017, 2). Entry, Descent and Landing System for CubeSat Missions to the Moon and Small-bodies. In AAS GNC Conference, 10.
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  CubeSats are emerging as low-cost platforms to perform space exploration. CubeSats are compelling because they can exploit unutilized mass and vol-ume aboard a large interplanetary spacecraft that would otherwise be ballast. Current CubeSat designs envision flyby or orbiting spacecraft, however, rare-ly do they envision landers. The ability to drop CubeSat-sized surface pay-loads from a flyby spacecraft opens entirely new exploration capabilities. We focus on developing drop-off payloads for deployment onto the surface of a planet or moon with an atmosphere. These surface probes would need to survive high-velocity (2-5 km/s) entry. Reentry of spacecraft components namely flight recorders through the Earth’s atmosphere have been shown by the Aerospace Corporation using the ReEntry Breakup Recorder (REBR) platform. Our application is towards safely landing an entire 6U, 36 cm × 24 cm × 12 cm CubeSat. Our proposed technology consists of an inflatable entry system that has a low-ballistic coefficient and is of low-cost and low-complexity. The technology can be a pathway towards testing larger landing platforms. The inflatable entry system contains multiple redundant bladders (cells) made of Vectran®, where even if one or a few are damaged, the sys-tem can maintain its shape. The bags are inflated using a solid-state chemical generator to produce nitrogen. The layers are hardened using a heat curing resin. The entry system will be slowed down using a subsonic parachute and crumple upon impact and absorb the brunt of the impact energy. In this pa-per, we perform a preliminary trade study and analyze both the challenges and opportunities with the proposed inflatable EDL system.
• Kalita, H., & Thangavelautham, J. (2017, 07). Multirobot Cliff Climbing on Low-Gravity Environments. In Adaptive Hardware Conference, 10.
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  Exploration of extreme environments, including caves, canyons and cliffs onlow-gravity surfaces such as the Moon, Mars and asteroids can provide insightinto the geological history of the solar system, origins of water, life andprospect for future habitation and resource exploitation. Current methods ofexploration utilize large rovers that are unsuitable for exploring theseextreme environments. In this work, we analyze the feasibility of small,low-cost, reconfigurable multirobot systems to climb steep cliffs and canyonwalls. Each robot is a 30-cm sphere covered in microspines for gripping ontorugged surfaces and attaches to several robots using a spring-tether. Even ifone robot were to slip and fall, the system would be held up with multipleattachment points much like a professional alpine climber. We analyzed andperformed detailed simulations of the design configuration space to identify anoptimal system design that trades off climbing performance with risk offalling. Our results identify a system of 4 robots is best suited when enablingsingle-robot climbs, while a system of 6 robots are suited when two robotsclimb simultaneously. The results show a pathway towards demonstration of thesystem on real robots.[Journal_ref: ]
• Kalita, H., Nallapu, R., & Thangavelautham, J. (2017, 02). GNC of the SphereX Robot for Extreme Environment Exploration on Mars. In AAS GNC Conference, 8.
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  Wheeled ground robots are limited from exploring extreme environments such as caves, lava tubes and skylights. Small robots that can utilize unconventional mobility through hopping, flying or rolling can overcome these limitations. Mul-tiple robots operating as a team offer significant benefits over a single large ro-bot, as they are not prone to single-point failure, enable distributed command and control and enable execution of tasks in parallel. These robots can complement large rovers and landers, helping to explore inaccessible sites, obtaining samples and for planning future exploration missions. Our robots, the SphereX, are 3-kg in mass, spherical and contain computers equivalent to current smartphones. They contain an array of guidance, navigation and control sensors and electronics. SphereX contains room for a 1-kg science payload, including for sample return. Our work in this field has recognized the need for miniaturized chemical mobility systems that provide power and propulsion. Our research explored the use of miniature rockets, including solid rockets, bi-propellants including RP1/hydrogen-peroxide and polyurethane/ammonium-perchlorate. These propulsion options provide maximum flight times of 10 minutes on Mars. Flying, especially hovering consumes significant fuel; hence, we have been developing our robots to perform ballistic hops that enable the robots to travel efficiently over long distances. Techniques are being developed to enable mid-course correction during a ballistic hop. Using multiple cameras, it is possible to reconstitute an image scene from motion blur. Hence our approach is to enable photo mapping as the robots travel on a ballistic hop. The same images would also be used for navigation and path planning. Using our proposed design approach, we are developing low-cost methods for surface exploration of planetary bodies using a network of small robots.
• Kalita, H., Nallapu, R., & Thangavelautham, J. (2017, 02). Guidance, Navigation and Control of Multirobot Systems in Cooperative Cliff Climbing. In AAS GNC Conference, 14.
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  The application of GNC devices on small robots is a game-changer that enables these robots to be mobile on low-gravity planetary surfaces and small bodies. Use of reaction wheels enables these robots to roll, hop, summersault and rest on precarious/sloped surfaces that would otherwise not be possible with conven-tional wheeled robots. We are extending this technology to enable robots to climb off-world canyons, cliffs and caves. A single robot may slip and fall, however, a multirobot system can work cooperatively by being interlinked using spring-tethers and work much like a team of mountaineers to systematically climb a slope. A multirobot system as we will show in this paper can climb sur-faces not possible with a single robot alone. We consider a team of four robots that are interlinked with tethers in an 'x' configuration. Each robot secures itself to a slope using spiny gripping actuators, and one by one each robot moves up-wards by crawling, rolling or hopping up the slope. If any one of the robots loses grip, slips or falls, the remaining robots will be holding it up as they are anchored. This distributed controls approach to cliff climbing enables the system to reconfigure itself where possible and avoid getting stuck at one hard to reach location. Instead, the risk is distributed and through close cooperation, the robots can identify multiple trajectories to climb a cliff or rugged surface. The benefits can also be realized on milligravity surfaces such as asteroids. Too fast a jump can result in the robot flying off the surface into space. Having multiple robots anchored to the surface keeps the entire system secure. Our work combines dynamics and control simulation to evaluate the feasibility of our approach. The simulation results show a promising pathway towards advanced development of this technology on a team of real robots.
• Kalita, H., Schwartz, S., Asphaug, E., & Thangavelautham, J. (2017, 09). Network of Nano-Landers for In-Situ Characterization of Asteroid Impact Studies. In International Astronautic Congress.
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  Exploration of asteroids and comets can give insight into the origins of thesolar system and can be instrumental in planetary defence and in-situ resource utilization (ISRU). Asteroids, due to their low gravity are a challenging target for surface exploration. Current missions envision performing touch-and-go operations over an asteroid surface. In this work, we analyse the feasibility of sending scores of nano-landers, each 1 kg in mass and volume of 1U, or 1000 cm3. These landers would hop, roll and fly over the asteroid surface. The landers would include science instruments such as stereo cameras, hand-lens imagers and spectrometers to characterize rock composition. A network of nano-landers situated on the surface of an asteroid can provide unique and very detailed measurements of a spacecraft impacting onto an asteroid surface. A full-scale, artificial impact experiment onto an asteroid can help characterize its composition and geology and help in the development of asteroid deflection techniques intended for planetary defence. Scores of nano-landers could provide multiple complementary views of the impact, resultant seismic activity and trajectory of the ejecta. The nano-landers can analyse the pristine, unearthed regolith shielded from effects of UV and cosmic rays and that may be millions of years old. Our approach to formulating this mission concepts utilizes automated machine learning techniques in the planning and design of space systems. We use a form of Darwinian selection to select and identify suitable number of nano-landers, the on-board instruments and control system to explore and navigate the asteroid environment. Scenarios are generated in simulation and evaluated against quantifiable mission goals such as area explored on the asteroid and amount of data recorded from the impact event.
• Nallapu, R., & Thangavelautham, J. (2017, 02). Precise Pointing of Cubesat Telescopes: Comparison Between Heat and Light Induced Attitude Control Methods. In AAS GNC Conference, 8.
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  CubeSats are emerging as low-cost tools to perform astronomy, exoplanetsearches and earth observation. These satellites can target an object forscience observation for weeks on end. This is typically not possible on largermissions where usage time is shared. The problem of designing an attitudecontrol system for CubeSat telescopes is very challenging because currentchoice of actuators such as reaction-wheels and magnetorquers can induce jitter on the spacecraft due to moving mechanical parts and due to externaldisturbances. These telescopes may contain cryo-pumps and servos that introduce additional vibrations. A better solution is required. In our paper, we analyze the feasibility of utilizing solar radiation pressure (SRP) and radiometric force to achieve precise attitude control. Our studies show radiometric actuators to be a viable method to achieve precise pointing. The device uses 8 thin vanes of different temperatures placed in a near-vacuum chamber. These chambers contain trace quantities of lightweight, inert gasses like argon. The temperature gradient across the vanes causes the gas molecules to strike the vanes differently and thus inducing a force. By controlling these forces, it's possible to produce a torque to precisely point or spin a spacecraft. We present a conceptual design of a CubeSat that is equipped with these actuators. We then analyze the potential slew maneuver and slew rates possible with these actuators by simulating their performance. Our analytical and simulation results point towards a promising pathway for laboratory testing of this technology and demonstration of this technology in space.
• Nallapu, R., Asphaug, E., & Thangavelautham, J. (2017, 02). Control of a Bucket-Wheel for Surface Mining of Asteroids and Small-Bodies. In AAS GNC Conference, 8.
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  Near Earth Asteroids (NEAs) are thought to contain a wealth of resources,including water, iron, titanium, nickel, platinum and silicates. Future spacemissions that can exploit these resources by performing In-Situ ResourceUtilization (ISRU) gain substantial benefit in terms of range, payload capacityand mission flexibility. Compared to the Moon or Mars, the milligravity on some asteroids demands a fraction of the energy for digging and accessing hydrated regolith just below the surface. However, asteroids and small-bodies, because of their low gravity present a major challenge in landing, surface excavation and resource capture. These challenges have resulted in adoption of a "touch and go techniques", like the upcoming Osiris-rex sample-return mission. Previous asteroid excavation efforts have focused on discrete capture events (an extension of sampling technology) or whole-asteroid capture and processing. This paper analyzes the control of a bucket-wheel design for asteroid or small-body excavation. Our study focuses on system design of two counter rotating bucket-wheels that are attached to a hovering spacecraft. Regolith is excavated and heated to 1000 C to extract water. The water in turn is electrolyzed to produce hydrogen and oxygen for rocket fuel. We analyze control techniques to maximize traction of the bucket-wheels on the asteroid surface and minimize lift-off the surface, together with methods to dig deeper into the asteroid surface. Our studies combine analytical models, with simulation and hardware testing. For initial evaluation of material-spacecraft dynamics and mechanics, we assume lunar-like regolith for bulk density, particle size and cohesion. Our early studies point towards a promising pathway towards refinement of this technology for demonstration aboard a future space mission.
• Nallapu, R., Sumit, S., Asphaug, E., & Thangavelautham, J. (2017, 02). Attitude Control of the Asteroid Origins Satellite 1 (AOSAT 1). In AAS GNC Conference, 8.
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  Exploration of asteroids and small-bodies can provide valuable insight intothe origins of the solar system, into the origins of Earth and the origins ofthe building blocks of life. However, the low-gravity and unknown surfaceconditions of asteroids presents a daunting challenge for surface exploration,manipulation and for resource processing. This has resulted in the loss ofseveral landers or shortened missions. Fundamental studies are required toobtain better readings of the material surface properties and physical modelsof these small bodies. The Asteroid Origins Satellite 1 (AOSAT 1) is a CubeSatcentrifuge laboratory that spins at up to 4 rpm to simulate the milligravityconditions of sub 1 km asteroids. Such a laboratory will help to de-riskdevelopment and testing of landing and resource processing technology forasteroids. Inside the laboratory are crushed meteorites, the remains ofasteroids. The laboratory is equipped with cameras and actuators to perform aseries of science experiments to better understand material properties andasteroid surface physics. These results will help to improve our physics modelsof asteroids. The CubeSat has been designed to be low-cost and contains 3-axismagnetorquers and a single reaction-wheel to induce spin. In our work, we first analyze how the attitude control system will de-tumble the spacecraft after deployment. Further analysis has been conducted to analyze the impact and stability of the attitude control system to shifting mass (crushed meteorites) inside the spacecraft as its spinning in its centrifuge mode. AOSAT 1 will be the first in a series of low-cost CubeSat centrifuges that will be launched setting the stage for a larger, permanent, on-orbit centrifuge laboratory for experiments in planetary science, life sciences and manufacturing.
• Nallapu, R., Tallapragada, A., & Thangavelautham, J. (2017, 03). Radiometric Actuators for Spacecraft Attitude Control. In IEEE Aerospace Conference, 10.
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  CubeSats and small satellites are emerging as low-cost tools to performastronomy, exoplanet searches and earth observation. These satellites can bededicated to pointing at targets for weeks or months at a time. This istypically not possible on larger missions where usage is shared. Currentsatellites use reaction wheels and where possible magneto-torquers to controlattitude. However, these actuators can induce jitter due to various sources. Inthis work, we introduce a new class of actuators that exploit radiometricforces induced by gasses on surface with a thermal gradient. Our work showsthat a CubeSat or small spacecraft mounted with radiometric actuators canachieve precise pointing of few arc-seconds or less and avoid the jitterproblem. The actuator is entirely solid-state, containing no moving mechanicalcomponents. This ensures high-reliability and long-life in space. A preliminarydesign for these actuators is proposed, followed by feasibility analysis of theactuator performance.[Journal_ref: ]
• Rabade, S., & Thangavelautham, J. (2017, 02). Combined Thermal Control and GNC: An Enabling Technology for CubeSat Surface Probes and Small Robots. In AAS GNC Conference, 10.
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  Advances in GNC, particularly from miniaturized control electronics,reaction-wheels and attitude determination sensors make it possible to design surface probes and small robots to perform surface exploration and science on low-gravity environments. These robots would use their reaction wheels to roll, hop and tumble over rugged surfaces. These robots could provide 'Google Streetview' quality images of off-world surfaces and perform some unique science using penetrometers. These systems can be powered by high-efficiency fuel cells that operate at 60-65 % and utilize hydrogen and oxygen electrolyzed from water. However, one of the major challenges that prevent these probes and robots from performing long duration surface exploration and science is thermal design and control. In the inner solar system, during the day time, there is often enough solar-insolation to keep these robots warm and power these devices, but during eclipse the temperatures falls well below storage temperature. We have developed a thermal control system that utilizes chemicals to store and dispense heat when needed. The system takes waste products, such as water from these robots and transfers them to a thermochemical storage system. These thermochemical storage systems when mixed with water (a waste product from a PEM fuel cell) releases heat. Under eclipse, the heat from the thermochemical storage system is released to keep the probe warm enough to survive. In sunlight, solar photovoltaics are used to electrolyze the water and reheat the thermochemical storage system to release the water. Our research has showed thermochemical storage systems are a feasible solution for use on surface probes and robots for applications on the Moon, Mars and asteroids.
• Raura, L., Warren, A., & Thangavelautham, J. (2017, March). Spherical Planetary Robot for Rugged Terrain Traversal. In IEEE Aerospace, 10.
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  Wheeled planetary rovers such as the Mars Exploration Rovers (MERs) and Mars Science Laboratory (MSL) have provided unprecedented, detailed images of the Mars surface. However, these rovers are large and are of high-cost as they need to carry sophisticated instruments and science laboratories. We propose the development of low-cost planetary rovers that are the size and shape of cantaloupes and that can be deployed from a larger rover. The rover named SphereX is 2 kg in mass, is spherical, holonomic and contains a hopping mechanism to jump over rugged terrain. A small low-cost rover complements a larger rover, particularly to traverse rugged terrain or roll down a canyon, cliff or crater to obtain images and science data. While it may be a one-way journey for these small robots, they could be used tactically to obtain high-reward science data. The robot is equipped with a pair of stereo cameras to perform visual navigation and has room for a science payload. In this paper, we analyze the design and development of a laboratory prototype. The results show a promising pathway towards development of a field system.
• Ravindra, A., Nallapu, R., Warren, A., Babuscia, A., Vasco, J., & Thangavelautham, J. (2017, 06). An Experimental Platform for Multi-spacecraft Phase-Array Communications. In IEEE Cognitive Communications for Aerospace Applications Workshop, 4.
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  The emergence of small satellites and CubeSats for interplanetary explorationwill mean hundreds if not thousands of spacecraft exploring every corner of thesolar-system. Current methods for communication and tracking of deep spaceprobes use ground based systems such as the Deep Space Network (DSN). However,the increased communication demand will require radically new methods to easecommunication congestion. Networks of communication relay satellites located atstrategic locations such as geostationary orbit and Lagrange points arepotential solutions. Instead of one large communication relay satellite, wecould have scores of small satellites that utilize phase arrays to effectivelyoperate as one large satellite. Excess payload capacity on rockets can be usedto warehouse more small satellites in the communication network. The advantageof this network is that even if one or a few of the satellites are damaged ordestroyed, the network still operates but with degraded performance. Thesatellite network would operate in a distributed architecture and somesatellites maybe dynamically repurposed to split and communicate with multipletargets at once. The potential for this alternate communication architecture issignificant, but this requires development of satellite formation flying andnetworking technologies. Our research has found neural-network controlapproaches such as the Artificial Neural Tissue can be effectively used tocontrol multirobot/multi-spacecraft systems and can produce human competitivecontrollers. We have been developing a laboratory experiment platform calledAthena to develop critical spacecraft control algorithms and cognitivecommunication methods. We briefly report on the development of the platform andour plans to gain insight into communication phase arrays for space.[Journal_ref: ]
• Schwartz, S., Ichikawa, S., Nallapu, R., Asphaug, E., & Thangavelautham, J. (2017, 02). Optical Navigation for Interplanetary CubeSats. In AAS GNC Conference, 8.
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  CubeSats and small satellites are emerging as low-cost tools for performingscience and exploration in deep space. These new classes of satellite exploitthe latest advancement in miniaturization of electronics, power systems, andcommunication technologies to promise reduced launch cost and development cadence. JPL's MarCO CubeSats, part of the Mars Insight mission, will head on an Earth escape trajectory to Mars in 2018 and serve as communication relays for the Mars Insight Lander during Entry, Descent and Landing. Incremental advancements to the MarCO CubeSats, particularly in propulsion and GNC, could enable these spacecraft to get to another planet or to Near Earth Objects. This can have substantial science return with the right science instrument. We have developed an interplanetary CubeSat concept that includes onboard green monopropellant propulsion system and that can get into a capture orbit around a neighboring planet or chase a small-body. One such candidate is the Martian moon Phobos. Because of the limits of current CubeSat hardware and lack of an accurate ephemeris of Phobos, there will be a 2 to 5 km uncertainty in distance between the spacecraft and Phobos. This presents a major GNC challenge when the CubeSat first attempts to get into visual range of the moon. One solution tothis challenge is to develop optical navigation technology that enables theCubeSat to take epicyclic orbits around the most probable location of thetarget, autonomously search and home-in on the target body. In worst-casescenarios, the technology would narrow down the uncertainty of the small-body location and then use optical flow, a computer vision algorithm to trackmovement of objects in the field of view. A dimly lit small-body can bedetected by the occlusion of one or more surrounding stars. Our studies present preliminary simulations that support the concept.
• Sonawane, N., & Thangavelautham, J. (2017, 02). Precision Pointing of Antennas in Space Using Arrays of Shape Memory Alloy Based Linear Actuators. In AAS GNC Conference, 10.
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  Space systems such as communication satellites, earth observation satellites and space telescopes require precise pointing to observe fixed targets over prolonged time. These systems typically use reaction-wheels to slew the spacecraft and gimballing systems containing motors to achieve precise pointing. Motor based actuators have limited life as they contain moving parts that require lubrication in space. Alternate methods have utilized piezoelectric actuators. This paper presents Shape memory alloys (SMA) actuators for control of a deployable antenna placed on a satellite. The SMAs are operated as a series of distributed linear actuators. These distributed linear actuators are not prone to single point failures and although each individual actuator is imprecise due to hysteresis and temperature variation. The system as a whole achieves reliable results. The SMAs can be programmed to perform a series of periodic motion and operate as a mechanical guidance system that is not prone to damage from radiation or space weather. Efforts are focused on developing a system that can achieve one degree pointing accuracy at first, with an ultimate goal of achieving a few arc seconds accuracy. Bench top models of the actuator system has been developed and working towards testing the system under vacuum. A demonstration flight of the technology is planned aboard a CubeSat.
• Thangavelautham, J., Rhoden, A., & Jones, D. (2017, 02). The Opportunities and Challenges of GN&C on a Europa CubeSat to Search for Plumes, Surface Fractures and Landing Sites. In AAS GNC Conference, 8.
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  Jupiter’s moon Europa is the target of NASA’s planned Europa Mission. The mission hopes to provide the most detailed view yet of the surface and subsurface of Europa and answer some fundamental questions, including whether Europa has a liquid-water ocean beneath a thick ice shelf, and if these conditions may harbor life. It is envisioned the multiple flyby mission would be only the first in a series of missions that could culminate into a sur-face landing mission. NASA JPL has sought proposals for CubeSats that could be carried by the main spacecraft and which would be released during the flybys. A CubeSat could significantly complement the capabilities of the multiple-flyby spacecraft. It could perform high-risk, high-payoff science missions at low altitudes. A CubeSat could provide unique science data that could not be obtained by the mothership by doing a low-altitude flyby and impact mission. A CubeSat could also perform landing site reconnaissance in preparation for a future surface lander mission. All of these capabilities depend on advances in guidance, navigation and control for use in the Jovian system. Three factors make a CubeSat concept challenging, including the high radiation in the vicinity of Europa, the low solar insolation of 50 W/m2 and extremely low temperatures of -230 oC. Coupled with these challenges, Europa lacks an atmosphere sufficient for aero-braking. Our concept is fo-cused on having the CubeSat separate from the mothership, 10 hours before a close flyby of Europa lasting 20 minutes. The CubeSat would use its onboard propulsion to attain altitudes of 3 to 12 km above the moon’s sur-face travelling at 4-5 km/s. Using the onboard optical navigation techniques, the CubeSat would navigate along Europa’s shadowed surface fractures to obtain detailed images of nearby features at 0.3 to 2 m/pixel. The notional spacecraft has the capacity to sample for and analyze potential plume sam-ples, and this option could be utilized to get first answers about potential plume content. The mission concept culminates with the CubeSat impacting the Europa surface. The artificial impact plume created would be analyzed by the array of instruments onboard the Europa Mission spacecraft for mate-rial composition. Advances in GNC are required to handle the unique light-ing, low temperature and high velocity conditions of the mission concept. Our early feasibility work shows a development pathway towards advancing the requisite technology towards technical feasibility.
• Xinchen, G., & Thangavelautham, J. (2017, 03). Novel Use of Photovoltaics for Backup Spacecraft Laser Communication System. In IEEE Aerospace Conference, 10.
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  Communication with a spacecraft is typically performed using Radio Frequency (RF). RF is a well-established and well-regulated technology that enables communication over long distances as proven by the Voyager 1 & II missions. However, RF requires licensing of very limited radio spectrum and this poses a challenge in the future, particularly with spectrum time-sharing. This is of aconcern for emergency communication when it is of utmost urgency to contact the spacecraft and maintain contact, particularly when there is a major mission anomaly or loss of contact. For these applications, we propose a backup laser communication system where a laser is beamed towards a satellite and the onboard photovoltaics acts as a laser receiver. This approach enables a laser ground station to broadcast commands to the spacecraft in times of emergency. Adding an actuated reflector to the laser receiver on the spacecraft enables two-way communication between ground and the spacecraft, but without the laser being located on the spacecraft. In this paper, we analyze the feasibility of the concept in the laboratory and develop a benchtop experiment to verify the concept. We have also developed a preliminary design for a 6U CubeSat-based demonstrator to evaluate technology merits

Others

• Thangavelautham, J. (2018, August). Sustainable and Green Power Sources for Long Duration Environment Monitoring. Encyclopedia of Renewable and Sustainable Materials by Elsevier.