Interplanetary Spacecraft Controllers Using Thrusters

Design of attitude controllers for interplanetary spacecraft is addressed. The first controller is for Rhumb-line precession using an almost periodic train of thruster pulses at a constant phase with the sun. Earlier relationships are expanded and interlaced coherently and demonstrated on a Mercator plot. The second controller is for nutation damping. For spacecraft with products of inertia, a control scheme is formulated that involves four phase angles, 90 deg apart in a nutation cycle, where the positive or negative control impulses about the transverse axes are injected to damp the nutations. The third controller is for attitude control during aerobraking for planetary orbit insertion. The controller seeks and maintains a zero aerodynamic torque orientation. Because this orientation may correspond to a constant bias angle of attack measured from the instantaneons velocity vector turning at a nonuniform pitch rate, a pitch angular acceleration command profile is developed for parameterizing a thruster controller. The fourth, and last, controller is for soft landing. It comprises a longitudinal velocity controller enhanced by gravity turn and a constant velocity phase at low altitudes near ground, a lateral velocity controller producing commands to pitch spacecraft at varying rates, and a reaction jet controller for tracking the commanded pitch angle and rate until touchdown. Satisfactory performance of all controllers is amply demonstrated. (Author)