National Aeronautics and Space Administration

A description and an analysis of the three methods used to measure the thrust of the SERT n (Space Electric Rocket Test) ion thrusters in flight are given. The first is the use of the MESA (miniature electrostatic accelerometer) to measure the 2 jug’s result-ing from the radial component of the thrust. The second is the use of telemetered beam electrical parameters to calculate thrust. The third is the measurement of orbit change resulting from the thrust. The three methods are shown to yield values of thrust which agree with each other within the error bands of the methods. It is concluded that the thrust was measured to within –1 percent by the MESA, to within –2. 2 percent by beam electrical parameters, and to within about –5 percent by orbit changing. 17. Key Words (Suggested by Author(s)) Ion thruster In-flight thrust measurement Electrostatic acceleromete