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

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.

Read this paper on arXiv…

R. Nallapu, E. Asphaug and J. Thangavelautham
Thu, 2 Feb 17

Comments: 8 pages, 7 figures in 40th AAS Conference on Guidance, Navigation and Control

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

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.

Read this paper on arXiv…

S. Rabade and J. Thangavelautham
Wed, 1 Feb 17

Comments: 12 pages, 15 figures in Proceedings of the 40th Annual AAS Guidance, Navigation and Control Conference 2017

Attitude Control of the Asteroid Origins Satellite 1 (AOSAT 1) [CL]

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.

Read this paper on arXiv…

R. Nallapu, S. Shah, E. Asphaug, et. al.
Wed, 1 Feb 17

Comments: 12 pages, 8 figures in Proceedings of the 40th Annual AAS Guidance, Navigation and Control Conference 2017

Automated Design of CubeSats and Small Spacecrafts [CL]

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.

Read this paper on arXiv…

H. Kalita and J. Thangavelautham
Tue, 10 Jan 17

Comments: 6 pages, 11 figures, Proceedings of the International Astronautical Congress, 2016

An In Situ Measurement System for Characterizing Orbital Debris [CL]

This paper presents the development of an in situ measurement system known as the Debris Resistive Acoustic Grid Orbital Navy/NASA Sensor (DRAGONS). The DRAGONS system is designed to detect impacts caused by particles ranging from 50 micrometers to 1 mm at both low-earth and geostationary orbits. DRAGONS utilizes a combination of low-cost sensor technologies to facilitate accurate measurements and approximations of the size, velocity, and angle of impacting micrometeoroids and orbital debris (MMOD). Two thin layers of kapton sheets with resistive traces are used to detect the changes in resistance that are directly proportional to the impacting force caused by the fast traveling particles. Four polyvinylidene fluoride-based sensors are positioned in the back of each kapton sheet to measure acoustic strain caused by an impact. The electronic hardware module that controls all operations employs a low-power, modular, and compact design that enables it to be installed as a low-resource load on a host satellite. Laboratory results demonstrate that in addition to having the ability to detect an impact event, the DRAGONS system can determine impact location, speed, and angle of impact with a mean error of 1.4 cm, 0.2 km/s, and 5{\deg}. The DRAGONS system could be deployed as an add-on subsystem of a payload to enable a real-time, in-depth study of the properties of MMOD.

Read this paper on arXiv…

M. Tsao, H. Ngo, R. Corsaro, et. al.
Wed, 14 Dec 16

Comments: 15 pages

GTOC8: Results and Methods of ESA Advanced Concepts Team and JAXA-ISAS [CL]

We consider the interplanetary trajectory design problem posed by the 8th edition of the Global Trajectory Optimization Competition and present the end-to-end strategy developed by the team ACT-ISAS (a collaboration between the European Space Agency’s Advanced Concepts Team and JAXA’s Institute of Space and Astronautical Science). The resulting interplanetary trajectory won 1st place in the competition, achieving a final mission value of $J=146.33$ [Mkm]. Several new algorithms were developed in this context but have an interest that go beyond the particular problem considered, thus, they are discussed in some detail. These include the Moon-targeting technique, allowing one to target a Moon encounter from a low Earth orbit; the 1-$k$ and 2-$k$ fly-by targeting techniques, enabling one to design resonant fly-bys while ensuring a targeted future formation plane% is acquired at some point after the manoeuvre ; the distributed low-thrust targeting technique, admitting one to control the spacecraft formation plane at 1,000,000 [km]; and the low-thrust optimization technique, permitting one to enforce the formation plane’s orientations as path constraints.

Read this paper on arXiv…

D. Izzo, D. Hennes, M. Martens, et. al.
Wed, 3 Feb 16

Comments: Presented at the 26th AAS/AIAA Space Flight Mechanics Meeting, Napa, CA