Published and presented at the 2005 IEPC, 2009 IEPC, and pending publication to the AIAA Journal of Propulsion and Power, this paper details the work to develop the smallest possible RF ion thruster. At the time of the IEPC 2009 conference, it was the smallest functional RF ion thruster in the world and the smallest ever produced at the SSPL at PSU. Stable operation, reliable ignition, consistent performance over an increased range, and notable efficiency were all achieved. Comprehensive performance analysis was completed in preparation for a system level qualification. The paper was well received at the IEPCs and the associated thesis work was awarded the 2009 Wolk Thesis Award from PSU. Thomas Trudel (Lead R&D Eng. and Founder) was the lead researcher on the project for 3 years.
DESIGN OVERVIEW
At 1 cm in diameter the MRIT was the smallest RF ion thruster in the world with published performance data as of 2009. The size of the thruster (seen here compared to a quarter) is notable due to the unique challenges to operating an ion thruster at this scale. Poor surface area-to-volume ratio leads to efficiency losses and manufacturing the required components at this scale can be exceedingly difficult. The MRIT solved these problems and produced respectable performance for a thruster of this size. Finally, a vacuum system capable of reaching 10^-6 torr was built from the ground up to provide a suitable environment for thruster testing. All on a budget under $15,000.
PERFORMANCE CHARACTERIZATION
The MRIT system was extensively characterized to determine the thrust (57uN), Isp (5174s), mass efficiency (64.1%), electrical efficiency (10.7%), and total efficiency (11.7%) among many other standard performance characteristics. For a thruster of this size these values are very respectable. The performance characterization on this iteration of the MRIT was the most comprehensive and rigorous performed to date. The calculations required to generate this data are indicative of a strong understanding of aerospace propulsion fundamentals, data analysis, and statistics.
SUSTAINED OPERATION
A wise man once said, "it is easy to make an ion plasma...it is hard to get it to go where you want." Establishing consistent operation of the MRIT was a major milestone for the project. There are many nuances to ion thruster design and at this time literature on the subject was limited. With minimal resources and budget, unique solutions to propellant isolator, ion optics, and electronics design were required. Ultimately, a start up procedure was created that resulted in 100+ sequential thruster firings and 50+ hours of continuous operation.