Doctor of engineering

Astronautics

I have been studying advanced space propulsions, especially, electric propulsion, for using as a deep space probe.
I have been investigating the mechanism of plasma production and loss in order to improve the thrust performance of these propulsion.

Research Interests

• Improvement of an ion engine performance
  keyword : Electric propulsion, plasma, measurement
  2005.04.
• Hall thrusters are a class of electric propulsion device in which a propellant gas is ionized and accelerated to produce thrust. They offer an attractive combination of high thrust efficiency (exceeding 50%) and specific impulse (~1,000-3,000 s). In comparison to chemical rockets, the high specific impulse is attractive for large delta V missions such as satellite positioning and station-keeping, and space exploration. Hall thrusters also have a higher thrust density than ion thrusters due to the existence of electrons in the ion acceleration zone. In addition, the lack of grids is attractive owing to the potential for reduced failures. Since the 1970s over 200 Hall thrusters have been operated in space. A key requirement for the practical use of Hall thrusters is the ability to operate for long durations, for example a Hall thruster used for north-south station keeping (NSSK) of a commercial spacecraft will have to operate for over 5,000 hours over the course of its mission. The primary life-limiter for Hall thrusters is acceleration channel wall erosion. A thruster is generally considered to have reached end of life when the channel is fully eroded and the underlying magnetic yoke becomes exposed. The physical mechanism causing the erosion is sputtering of the channel material due to bombardment by energetic particles, primarily propellant ions having undergone radial acceleration. In addition to causing channel erosion and associated lifetime concerns, sputtered particles can redeposit on spacecraft components such as solar-arrays, thereby degrading their performance and potentially compromising spacecraft operation.
  Ideally, the problems of lifetime and redeposition would be addressed with both numerical modeling and experimental measurement. Research in the former area is underway but the fidelity of current models tends to be limited by the accuracy in modeling the fluxes of ions to the channel walls (angular and energy distributions) and lack of knowledge of the sputter yields of the wall channel materials (especially at the needed low ion energies). Experimental lifetime measurements are also very challenging. With proposed thrust durations now as long as 5-10+ years, ground-based life tests over the full thruster duration are becoming increasingly expensive and limiting in terms of technology insertion schedules. And, even when such tests are performed, it is hard to infer the effect of varying thruster operating parameters such as voltage and mass flow rate. What is needed, therefore, is a method of quantitatively measuring thruster erosion rates non-intrusively in real- or near real-time, for example by in situ measurement of the eroded wall material (as we demonstrate here). Such measurements would be dramatically faster (and cheaper) than full life testing, and would readily allow the study of the effects of operating conditions and thruster design changes on erosion.
• An energy balance in inductively coupled radio frequency electrothermal thruster using water as a propellant was investigated with the objective of improving the thrust performance. Absorption efficiency was estimated by means of an I-V sensor and thrust efficiency was estimated by means of a thrust stand. The absorption efficiency using water is 0.75, which is worse than that using argon. This is because the number density using water is less than that of argon due to the low ionization coefficient and the loss of dissociation. The thrust efficiency using water is 0.05. The left energy would be dispersed as heat loss, frozen flow loss and nozzle loss. Overall, the thrust performance, thrust, specific impulse and thrust efficiency are 3.6 mN, 340 sec, and 0.05, respectively, at mass flow rate =1.1 mg/s, and Incident power = 100 W.
• Physics inside Hall thruster
  keyword : Hall thruster
  2004.04.
• Development of a miniature microwave discharge ion thruster
  keyword : Space propulsion, electric propulsion, Ion beam source, ion thruster
  2004.04.

Academic Activities Awards

• The demand for mN class miniature propulsion systems for small satellites is expected to grow in the future, due to their relatively low cost and short development time, among other reasons . Until recently, size restrictions have limited the capacity of the available propulsion systems, and this has restricted the capability of small satellites. One of the candidates for mN class miniature propulsion systems is a miniature ion thruster, since an ion thruster produces high thrust efficiency (over 50%) with a specific impulse of 3,000-8,000 sec .He developed a miniature microwave discharge ion thruster. This performance is competitive with that of the thruster developed by Wirz et al., which has hither to shown the best performance in this class of miniature thruster.This will contribute to expand the range and capabilities of small satellites; missions such as Mars exploration would become possible, as would satellite self-disposal. Miniature ion thrusters can also be used for precise high-stability attitude and position control in large spacecraft, as well as for primary propulsion of microsatellites.
• Dependence of Thruster Configuration on Thrust Performance in Miniature Ion Thruster
• Laser-Based Sensor for Real Time Sputter Monitoring and End Point Detection in Ion Beam Etch Systems