Performance characteristics of the NSTAR ion thruster during an on-going long duration ground test

A long-duration test of the Deep Space 1 (DS1) spare flight thruster (FT2) is presently being conducted. To date, the thruster has accumulated over 6700 hours of operation. Performance data-such as thrust, specific impulse and efficiency-over the full 0.5 to 2.3 kW throttling range are presented. Comparison of FT2 with the performance of the engineering model thruster 2 (EMT2) during an 8.2 khr test shows a transient, lasting for about 3000 hours, during which the discharge chamber efficiency decreases for both thrusters. After the initial transient, the performance of both thrusters at full power is comparable with the exception of the electron backstreaming limit, which is 6 V lower for FT2. Degradation of electrical isolation for neutralizer and for discharge cathode components has occurred during FT2 testing; although this has made starting the thruster slightly more difficult, it is not expected to cause thruster failure