Development and demonstration of a 600-second mission-average I(sp) arcjet

Abstract

Recent advanced development has resulted in a 550-h demonstration of a hydrazine arcjet at a missionaverage special impulse 7sp of greater than 600 s. The laboratory-type arcjet thruster was operated at 1800 W through a flow rate schedule consistent with a flight application. The thruster demonstrated stable, high-efficiency operation for the duration of the test. The development effort leading to the demonstration addressed the operational and life issues associated with achieving high performance. As a result of the development activity, a wide range of performance was also achieved. Performance levels of greater than 575 s at 1000 W and greater than 675 s at 2000 W were demonstrated. The problems encountered with extending low-power arcjet performance are discussed. Increased thruster component temperatures caused new life issues to be identified, along with low propellant flow rate stability limits. The elevated temperatures caused significant changes in the electrode geometry for a thruster based on the state-of-the-art tungsten anode designs. Three paths to solving the problem were attempted, including lowering the operating temperature through improved heat rejection, mechanical design changes to reduce thermal stresses, and higher strength materials selection. The success of this program provides substantial evidence that an arcjet capable of greater than 600-s mission-average specific impulse will be available in the near term for flight qualification and application.