Orbital performance measurements of Air Force Electric Propulsion Space Experiment ammonia arcjet

During the Electric Propulsion Space Experiment mission eight firings of the 26-kW ammonia arcjet were performed. Data from onboard systems, including an accelerometer and global positioning system unit, are used to determine thruster performance. In addition, ground-based tracking is used to determine velocity change during these firings. The mean values of thrust, specific impulse, and thrust efficiency are estimated to be 1.93 +/- 0.06 N, 786.2 +/- 43.0 s, and 0.267 +/- 0.021, respectively. This measured performance is lower than expected based on ground test. The most likely cause of this discrepancy is error in onboard measurement of discharge power due to a 6% drift in the power processing unit current shunt. At the corrected power, performance falls within the expected envelope.