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space, starting with the Meteor I in 1969-1970.7.8 More recently, eight SPT-100 thrusters were flown on the Russian A cyclic endurance test of the Russian 1.35 kW Stationary GALS television satellite to perform both north-south and Plasma Thruster SPT-100 is described. The endurance test east-west station-keeping functions. 9 was performed for 6,925 on/off cycles and 5,730.3 hours of operation at an input power to the thruster of 1.35 kW. In 1991 a team of electric propulsion specialists Each cycle was approximately 50 minutes of thruster onvisited the former U.S.S.R. to experimentally evaluate the time and 23 minutes of thruster off-time. Thruster efficiency performance of a 1.35-kW SPT at the Scientific Research 1,000 hours. The efficiency increased slowly over the next Bureau "Fakel" in Kaliningrad, Russia. 10-1 1 The 1,000 hours and then slowly decreased to 45% by the end of evaluation verified that the actual performance of the thruster the wear test. The unused cathode ignitor and radiation was close to the claimed performance of 50% efficiency at a shieldswerefoundto erode anunexpectedy highrate. A specific impulse of 1600 s. 10 Studies indicate that for shields were found to erode at an unexpectedly high north/south station keeping and Earth orbit raising short between the cathode emitter and cathode ignitor applications of electric propulsion, the optimum specific occurred at cycle 5,316; the short was cleared without impulse is in the range of 1.000-2.000 sec. 12 The opening the vacuum tank but the short reoccurred at cycle combination of the flight heritage of the SPT-70 and the 6,344. The vacuum chamber was opened after the thruster availability of thrusters and thruster data led to substantial had accumulated 6,346 cycles and 5,250 hours of operating interest in these thrusters by Western spacecraft time to clear this short and repair the thrust stand, which had manufacturers for primary and auxiliary propulsion failed at cycle 5,818. The wear test was continued and applications. voluntarily terminated when 5,002.5 hours of operation were accumulated on cathode #1. Data from this wear test indicate Space Systems/Loral is presently flight-qualifying that the likely first failure mechanism for this thruster design SPT-100 thrusters for north/south station keeping and Earth is shorting between the ignitor and cathode emitter in the orbit raising applications and plans to provide these thrusters unused cathode. The endurance test was performed under a on their spacecraft. 13 At Design Bureau "Fakel", a steadycooperative program between Space SystemsLoral, JL, and state life test was performedl 4 , and performance, plume and EIprogram between Space Syste Lal, JP, and E /RFI evaluations were conducted at NASA Lewis the Ballistic Missile Defense Organization (BMDO). Research Centr. 1 AS-18

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