arXiv subjects

Jekan Thangavelautham

Publications and source records attributed to Jekan Thangavelautham.

54 records · Page 3Linked to original sources

arXiv2017

The Design of Long-Life, High-Efficiency PEM Fuel Cell Power Supplies for Low Power Sensor Networks

Field sensor networks have important applications in environmental monitoring, particularly climate change, air, water and soil quality, in disaster 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.

physics.app-ph↗

arXiv2017

An Information Theoretic Approach to Sample Acquisition and Perception in Planetary Robotics

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.

cs.RO↗

arXiv2017

Multirobot Cliff Climbing on Low-Gravity Environments

Exploration of extreme environments, including caves, canyons and cliffs on low-gravity surfaces such as the Moon, Mars and asteroids can provide insight into the geological history of the solar system, origins of water, life and prospect for future habitation and resource exploitation. Current methods of exploration utilize large rovers that are unsuitable for exploring these extreme environments. In this work, we analyze the feasibility of small, low-cost, reconfigurable multirobot systems to climb steep cliffs and canyon walls. Each robot is a 30-cm sphere covered in microspines for gripping onto rugged surfaces and attaches to several robots using a spring-tether. Even if one robot were to slip and fall, the system would be held up with multiple attachment points much like a professional alpine climber. We analyzed and performed detailed simulations of the design configuration space to identify an optimal system design that trades off climbing performance with risk of falling. Our results identify a system of 4 robots is best suited when enabling single-robot climbs, while a system of 6 robots are suited when two robots climb simultaneously. The results show a pathway towards demonstration of the system on real robots.

cs.RO↗

arXiv2017

An Experimental Platform for Multi-spacecraft Phase-Array Communications

The emergence of small satellites and CubeSats for interplanetary exploration will mean hundreds if not thousands of spacecraft exploring every corner of the solar-system. Current methods for communication and tracking of deep space probes use ground based systems such as the Deep Space Network (DSN). However, the increased communication demand will require radically new methods to ease communication congestion. Networks of communication relay satellites located at strategic locations such as geostationary orbit and Lagrange points are potential solutions. Instead of one large communication relay satellite, we could have scores of small satellites that utilize phase arrays to effectively operate as one large satellite. Excess payload capacity on rockets can be used to warehouse more small satellites in the communication network. The advantage of this network is that even if one or a few of the satellites are damaged or destroyed, the network still operates but with degraded performance. The satellite network would operate in a distributed architecture and some satellites maybe dynamically repurposed to split and communicate with multiple targets at once. The potential for this alternate communication architecture is significant, but this requires development of satellite formation flying and networking technologies. Our research has found neural-network control approaches such as the Artificial Neural Tissue can be effectively used to control multirobot/multi-spacecraft systems and can produce human competitive controllers. We have been developing a laboratory experiment platform called Athena to develop critical spacecraft control algorithms and cognitive communication methods. We briefly report on the development of the platform and our plans to gain insight into communication phase arrays for space.

cs.RO↗

arXiv2017

A Cubesat Centrifuge for Long Duration Milligravity Research

We advocate a low-cost strategy for long-duration research into the 'milligravity' environment of asteroids, comets and small moons, where surface gravity is a vector field typically less than 1/1000 the gravity of Earth. Unlike the microgravity environment of space, there is a directionality that gives rise, over time, to strangely familiar geologic textures and landforms. In addition to advancing 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 and manufacturing. We show that a commodity 3U ($10\times10\times34$ cm$^3$) cubesat containing a laboratory of loose materials can be spun to 1 rpm = $2π/60$ s$^{-1}$ on its long axis, creating a centrifugal force equivalent to the surface gravity of a kilometer-sized asteroid. We describe the first flight demonstration, where small meteorite fragments will pile up to create a patch of real regolith under realistic asteroid conditions, paving the way for subsequent missions where landing and mobility technology can be flight-proven in the operational environment, in Low-Earth Orbit (LEO). The 3U design can be adapted for use onboard the International Space Station (ISS) to allow for variable gravity experiments under ambient temperature and pressure for a broader range of experiments.

astro-ph.IM↗

arXiv2017

Guidance, Navigation and Control of Multirobot Systems in Cooperative Cliff Climbing

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.

cs.RO↗

arXiv2017

Control of a Bucket-Wheel for Surface Mining of Asteroids and Small-Bodies

Near Earth Asteroids (NEAs) are thought to contain a wealth of resources, including water, iron, titanium, nickel, platinum and silicates. Future space missions that can exploit these resources by performing In-Situ Resource Utilization (ISRU) gain substantial benefit in terms of range, payload capacity and 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.

eess.SY↗

arXiv2017

Spherical Planetary Robot for Rugged Terrain Traversal

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.

cs.RO↗

arXiv2017

Novel Use of Photovoltaics for Backup Spacecraft Laser Communication System

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 a concern 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

astro-ph.IM↗

arXiv2017

Hybrid Fuel Cells Power for Long Duration Robot Missions in Field Environments

Mobile robots are often needed for long duration missions. These include search and rescue, sentry, repair, surveillance and entertainment. Current power supply technology limit walking and climbing robots from many such missions. Internal combustion engines have high noise and emit toxic exhaust while rechargeable batteries have low energy densities and high rates of self-discharge. In theory, fuel cells do not have such limitations. In particular Proton Exchange Membrane (PEMs) can provide very high energy densities, are clean and quiet. However, PEM fuel cells are found to be unreliable due to performance degradation. This can be mitigated by protecting the fuel cell in a fuel-cell battery hybrid configuration using filtering electronics that ensure the fuel cell is isolated from electrical noise and a battery to isolate it from power surges. Simulation results are presented for a HOAP 2 humanoid robot that suggests a fuel cell powered hybrid power supply superior to conventional batteries.

cs.RO↗

arXiv2017

GNC of the SphereX Robot for Extreme Environment Exploration on Mars

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.

cs.RO↗

arXiv2017

FPGA Architecture for Deep Learning and its application to Planetary Robotics

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.

cs.LG↗

arXiv2017

Radiometric Actuators for Spacecraft Attitude Control

CubeSats and small satellites are emerging as low-cost tools to perform astronomy, exoplanet searches and earth observation. These satellites can be dedicated to pointing at targets for weeks or months at a time. This is typically not possible on larger missions where usage is shared. Current satellites use reaction wheels and where possible magneto-torquers to control attitude. However, these actuators can induce jitter due to various sources. In this work, we introduce a new class of actuators that exploit radiometric forces induced by gasses on surface with a thermal gradient. Our work shows that a CubeSat or small spacecraft mounted with radiometric actuators can achieve precise pointing of few arc-seconds or less and avoid the jitter problem. The actuator is entirely solid-state, containing no moving mechanical components. This ensures high-reliability and long-life in space. A preliminary design for these actuators is proposed, followed by feasibility analysis of the actuator performance.

physics.space-ph↗

arXiv2017

Precision Pointing of Antennas in Space Using Arrays of Shape Memory Alloy Based Linear Actuators

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.

astro-ph.IM↗

arXiv2017

Precise Pointing of Cubesat Telescopes: Comparison Between Heat and Light Induced Attitude Control Methods

CubeSats are emerging as low-cost tools to perform astronomy, exoplanet searches and earth observation. These satellites can target an object for science observation for weeks on end. This is typically not possible on larger missions where usage time is shared. The problem of designing an attitude control system for CubeSat telescopes is very challenging because current choice of actuators such as reaction-wheels and magnetorquers can induce jitter on the spacecraft due to moving mechanical parts and due to external disturbances. 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.

astro-ph.IM↗

arXiv2017

Combined Thermal Control and GNC: An Enabling Technology for CubeSat Surface Probes and Small Robots

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.

eess.SY↗

arXiv2017

Attitude Control of the Asteroid Origins Satellite 1 (AOSAT 1)

Exploration of asteroids and small-bodies can provide valuable insight into the origins of the solar system, into the origins of Earth and the origins of the building blocks of life. However, the low-gravity and unknown surface conditions of asteroids presents a daunting challenge for surface exploration, manipulation and for resource processing. This has resulted in the loss of several landers or shortened missions. Fundamental studies are required to obtain better readings of the material surface properties and physical models of these small bodies. The Asteroid Origins Satellite 1 (AOSAT 1) is a CubeSat centrifuge laboratory that spins at up to 4 rpm to simulate the milligravity conditions of sub 1 km asteroids. Such a laboratory will help to de-risk development and testing of landing and resource processing technology for asteroids. Inside the laboratory are crushed meteorites, the remains of asteroids. The laboratory is equipped with cameras and actuators to perform a series of science experiments to better understand material properties and asteroid surface physics. These results will help to improve our physics models of asteroids. The CubeSat has been designed to be low-cost and contains 3-axis magnetorquers 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.

eess.SY↗

arXiv2017

Automated Design of CubeSats and Small Spacecrafts

The miniaturization of electronics, sensors and actuators has enabled the growing use of CubeSats and sub-20 kg spacecraft. Their reduced mass and volume has the potential to translate into significant reductions in required propellant and launch mass for interplanetary missions, earth observation and for astrophysics applications. There is an important need to optimize the design of these spacecraft to better ascertain their maximal capabilities by finding optimized solution, where mass, volume and power is a premium. Current spacecraft design methods require a team of experts, who use their engineering experience and judgement to develop a spacecraft design. Such an approach can miss innovative designs not thought of by a human design team. In this work we present a compelling alternative approach that extends the capabilities of a spacecraft engineering design team to search for and identify near-optimal solutions using machine learning. The approach enables automated design of a spacecraft that requires specifying quantitative goals, requiring reaching a target location or operating at a predetermined orbit for a required time. Next a virtual warehouse of components is specified that be selected to produce a candidate design. Candidate designs are produced using an artificial Darwinian approach, where fittest design survives and reproduce, while unfit individuals are culled off. Our past work in space robotic has produced systems designs and controllers that are human competitive. Finding a near-optimal solution presents vast improvements over a solution obtained through engineering judgment and point design alone. The approach shows a credible pathway to identify and evaluate many more candidate designs than it would be otherwise possible with a human design team alone.

astro-ph.IM↗