Lifetime Investigations of Micro-Cathode and Matrix Arc Thrusters

Abstract

The Microcathode arc thruster (µCAT) is a pulsing electric propulsion device that has been developed for small space-based satellites. These thrusters generate an electric arc between a cathode and an anode to form a cathode plasma plume. Within this plume, ion particles are expelled, and this expulsion is the mechanism that creates micronewton thrust. The matrix thruster is another version of the µCAT, but it was designed with multiple cathodes or anodes to increase the lifetime or thrust. Their low mass, low volume, and low power requirements should allow these thrusters to be the optimal thrusters of choice for small satellites. The µCAT has been tested on a US Naval Academy satellite, but there are concerns about the total number pulses, or lifetime that can be achieved. The goal of this research was to investigate the factors that influence the lifetime.  

Confirming that the test version of these thrusters produced thrust was the first step of this research. Major modifications had to be made to the inhouse thrust experiment apparatus, but it was confirmed that thrust was being produced in the 1-3 micronewton range. In addition to thrust tests, prior to working on the lifetime experiments, a set of tests were conducted to determine how the arc current and the temperature of the thruster’s cathode were impacted by the power inputs. 

Lifetime tests were conducted on the µCAT to review how the arc current, the pulsing frequency, the input voltage, the cathode temperature, the gap distance between the cathode and anode, and the various other power inputs impact the total number of pulses. The results indicate that the lifetime had a negative relationship with the arc current, the cathode temperature, and the voltage. An optimal gap distance was determined to be at 3 millimeters, which produced about 1.3 million pulses. The pulsing frequency did not have a relationship to the lifetime, so lifetime tests could be sped up by increasing the pulsing rate. The data also suggested an accelerated lifetime procedure could be created by heating the cathode to temperatures to just under 225 degrees Celsius. The temperature of the cathode on average was 146 degrees Celsius. 

A lifetime test on the matrix thruster yielded over 2 million pulses, which was the highest number of pulses observed for this class of thruster. Replicating this result has proven challenging. Possible reasons for this measurement, and the challenges to replicating it, involve the pulsing frequency and an inability to build the thruster to consistent dimensions. The matrix thruster does offer an advantage of using up more cathode material as well as the potential for reducing failures through cathode redundancy, thus further studies on the matrix thruster are worthwhile.