Space Systems Research Group
Current research highlights:
Optimal Orbit Design for Ground Surveillance Missions Using Genetic Algorithms The problem of visiting a given set of locations on the surface of Earth within a given time frame is considered. Solutions to this problem in literature require thrusters to continuously maneuver the satellite from one location to another. A natural solution is a set of orbit(s) that enables the spacecraft to satisfy the mission requirements without the use of propulsion. Optimization of a penalty function is performed to find natural solutions. This penalty function depends on the mission objectives, which in this study are assumed to be: maximum observation time for each location and maximum resolution. The penalty function poses multi minima and a Genetic Algorithm technique is used to solve this problem. In the case that there is no single orbit satisfying the mission requirements, then a multi-orbit solution is proposed. In a multi-orbit solution, the set of target sites is split into two groups. Then the developed algorithm is used to search for a natural solution for each group. The satellite has to be maneuvered between the two solution orbits. A new formulation is developed to solve the general orbit transfer problem using Genetic Algorithms. The developed formulation guarantees that the satellite will be transferred exactly to the final orbit even if the solution is non-optimal. Results demonstrated the feasibility of finding natural solutions for many case studies.
Spacecraft Interaction Studies for a 20-kW Bismuth-fueled Hall Thruster: As part of the Presidential Early Career Award for Scientists and Engineers L. Brad King received a five-year, $500,000 grant to continue his research on high-powered ion propulsion engines which someday could be used for manned space missions to Mars. Ion propulsion engines currently rely on xenon gas for fuel. However, xenon’s price tag—about $3,200 a pound—gives new meaning to the cliche “skyrocketing energy costs.” In his state-of the-art lab at Michigan Tech, King is experimenting with an alternative fuel that could slash the cost of ion propulsion. Bismuth, a brittle white metal, goes for about $3.60 a pound and is much easier to handle and store. He has developed the critical system that enables bismuth to be used as a propellant—something that could greatly reduce the cost of space travel.
Self-regenerating Nanotips as Indestructable Field Emission Cathodes for Low-power Electric Propulsion: Field-emission cathodes have recently received much interest for use as zero-flow “cold” electron emitters for sub-100-W EP Thrusters. Field emission cathodes rely on Fowler-Nordheim emission from very sharp (10-nm-radius) electrode tips. The lifetime of microfabricated field emitters is, so far, incompatible with EP applications. Because of the fragility of the nanometer-sized tips, the structures are susceptible to damage that blunts the tip and destroys the device functionality. Recent efforts have attempted to extend lifetime by reducing tip wear. The goal of research is to develop field-emission cathodes for use in EP that solve the tip degradation probel not through attempts to minimize tip wear, but instead by incorporating self-assembling nanostructures that can repeatedly re-generate damaged emitter tips. The proposed structures are created by forming an ion-emitting Taylor cone from a low-melting-temperature liquid metal in a method identical to a FEEP thruster. Studies have shown that if the ion emission current is extinguished by cooling and quenching the liquid metal, a nanometer-scale protrusion forms at the apex of the cone. By reversing the polarity of the extraction electrode, the now-solidified Taylor cone/protrusion structure exhibits stable Fowler-Nordheim emission of the electrons. The technique provides a mechanism to heal damaged or destroyed emitters: by re-melting the cone and repeating the ion-emission/quenching cycle, the functionality of the cathode is restored. Work proposed here will examine the fundamental operating characteristics of quenched liquid-metal-ion sources operated as cathodes in environments representative of EP thrusters. Architectures to be examined include cones formed on single needle emitters, on the ends of micro-machined capillaries fabricated from bulk metal, and on metal-coated macroporous silicon.
Nanosatellite for Space Situational Awareness: Michigan Tech’s Enterprise curriculum for undergraduate design will develop a nanosatellite in a balanced research and educational program. Undergraduates organized into a 50-member virtual business, the proposed effort will develop and fabricate a flight-quality vehicle for space situational awareness. Working closely with industry partner Raytheon, the team will integrate a psce sensor suite, delivered by Raytheon at no cost, capable of tracking, ranging, and imaging space targets from a three-axis stabilized nanosatellite platform. Sensor capabilities will be evaluated by tracking 1) a nanosta-deployed imaging target, 2) the primary launch vehicle payload, 3) in-space targets of opportunity such as satellites, the Space Shuttle and the ISS, and 4) ground-launched targets of opportunity to evaluate plume tracking ability.
