Space Technology 7 Disturbance Reduction System – Precision Control Flight Validation

Abstract

The NASA New Millennium Program Space Technology 7 (ST7) project validates technology for precision spacecraft control. The disturbance reduction system (DRS) is part of the European Space Agency's LISA Pathfinder project. The DRS controls the position of the spacecraft relative to a reference to an accuracy of one nanometer over time scales of several thousand seconds. To perform the control, the spacecraft use a new colloid thruster technology. The thrusters operates over the range of 5 to 30 micro-Newtons with precision of 0.1 micro-Newton. The thrust is generated by using a high electric field to extract charged droplets of a conducting colloid fluid and accelerating them with a precisely adjustable voltage. The control reference is provided by the European LISA Technology Package, which includes two nearly free-floating test masses. The test mass positions and orientations are measured using a capacitance bridge. The test mass position and attitude is adjustable using electrostatically applied forces and torques. The DRS controls the spacecraft position with respect to one test mass while minimizing disturbances on the second test mass. The dynamic control system covers eighteen degrees of freedom: six for each of the test masses and six for the spacecraft. After launch in late 2009 to a low Earth orbit, the LISA Pathfinder spacecraft is maneuvered to a halo orbit about the Earth-Sun LI Lagrange point for operations.