Local Vertical/Local Horizontal Attitude Control for Spartan Spacecraft

A Spartan spacecraft attitude control system was reconfigured to provide attitude pointing with respect to a Local Vertical/Local Horizontal reference frame even though the baseline system uses only an initial start attitude, sun sensors, and star tracker/gyros for defining the spacecraft attitude. No earth sensors of any kind are used. Deployed from the orbiter for two days, usually for solar and stellar inertial pointing, Spartan missions use pointing programs that must be written months prior to launch with bit-level changes possible only in the on-orbit period prior to deployment. With these limitations, Spartan missions 206 and 207, flown in 1996, had requirements to point with respect to the orbital velocity vector, the direction of which in an inertial frame, varies greatly due to launch time, launch date and deploy time uncertainties. The description concentrates on the LVLH to inertial geometry, attitude maneuvering scheme, and timing considerations