Abstract: A system for determining and controlling an orbit of a spacecraft may include a GPS receiver mounted to the spacecraft to receive GPS information from a plurality of GPS satellites visible to the GPS receiver for determining a position of the spacecraft relative to a reference coordinate system. The system may also include a filter configuration control module to sense a thruster maneuver operation to adjust the orbit of the spacecraft. The system may also include an orbit determination filter to determine at least one of a spacecraft position, velocity, and residue acceleration based on the GPS information and information from the filter configuration control module related to the thruster maneuver operation.

Abstract: A method and apparatus for determining star tracker misalignments is disclosed. The method comprises the steps of defining a defining a reference frame for the star tracker assembly according to a boresight of the primary star tracker and a boresight of a second star tracker wherein the boresight of the primary star tracker and a plane spanned by the boresight of the primary star tracker and the boresight of the second star tracker at least partially define a datum for the reference frame for the star tracker assembly; and determining the misalignment of the at least one star tracker as a rotation of the defined reference frame.

Abstract: A method, apparatus, and article of manufacture for directing a payload coupled to a spacecraft substantially at a target location is disclosed. The method comprises the steps of determining spacecraft orbital parameters and spacecraft payload attitude parameters; and directing the payload at the target location by applying a spacecraft bus steering law determined at least in part from the orbit and attitude parameters. The apparatus comprises a navigation system for determining spacecraft orbit parameters and spacecraft attitude parameters, and for applying a spacecraft bus steering law to direct the payload substantially at the target location. The spacecraft bus steering law is determined at least in part from the determined spacecraft orbital parameters, the determined spacecraft attitude, and determined payload attitude parameters. In one embodiment, the apparatus includes a payload attitude control system for directing the payload relative to the spacecraft bus.

Abstract: A system and method of estimating the attitude of a spacecraft compares a three-axis inertial-based estimate of spacecraft attitude to a stellar-based estimate of the spacecraft attitude. A Kalman filter having some states associated with low spatial frequency errors compares the stellar-based attitude estimate to the inertial-based estimate of attitude and apportions total attitude error into two time varying matrices. A first time varying matrix is associated with star tracker low spatial frequency errors, a second time varying matrix is associated with gyro bias errors and attitude errors. The time varying matrices are used to apply corrective feedbacks to the stellar-based attitude estimate and the inertial-based estimate of spacecraft attitude, and are adaptively adjusted to minimize total estimated attitude error.

Abstract: High precision spacecraft attitude determination is produced by specially positioning the spacecraft's star trackers and then filtering out measurement errors produced from star tracker electronics. In addition to the conventional azimuth and elevation controls used for star tracker pointing, the star tracker detector array is rotationally positioned about its boresight so that its pixels are traversed by the imaged star path at an angle within 20° of diagonal. This forces both vertical and horizontal spatial error components in the detector plane to a high frequency range at which they can easily be filtered out in common.

Abstract: Spacecraft attitude is efficiently controlled by utilizing spatial noise and temporal noise in the calculation of gains to a Kalman filter. Spatial noise is modeled in a dynamic fashion so as to provide optimal spatial noise attenuation.