Measuring Thruster Location and Orientation for NASA’s Solar Terrestrial Relations Observatories (STEREO) Mission

Abstract

Each of NASA's two STEREO observatories needed the location and angle of every propulsion thruster measured before launch. The thrusters were located with a clip-on precision tool carrying four mirrored spherical surfaces, which gave the nozzle's exit plane as a vector and, indirectly, the centre of the nozzle throat as a point. Triangulation with a multiple-autocollimating theodolite setup measured the tool and the coordinate-system references. John Troll of the Johns Hopkins University Applied Physics Laboratory explains that the technique was chosen largely for the equipment already on hand, sets out the error estimates, and reports the lessons learned.