Abstract: A glitch-free data fusion method for combining multiple attitude solutions is disclosed, wherein a star camera is set as the master star camera. After acquiring attitude solutions from the star cameras, a rotation difference is calculated between a master attitude solution acquired from the master star camera and a slave attitude solution acquired from other star cameras. Then, a steady difference is acquired from the rotation difference via a low pass filter for correcting the slave attitude solution. When combining the corrected slave attitude solutions with the master attitude solution, the attitude glitches or attitude jumps, which occur while transitioning between data fusion configurations with different number of available attitude solutions, can be eliminated.

Abstract: A method, apparatus, article of manufacture, and a memory structure for designing a robust controller. The method comprises the steps of determining a plant model G of the system dynamics; bounding system dynamics unmodeled by the plant model G of the system dynamics by a weighting function W; applying a transform to an augmented plant model T having the plant model G and the weighting function W; defining a controller {tilde over (F)} from the transformed plant model T; and applying an inverse of the transform to the controller {tilde over (F)} defined from the transformed plant model and the weighting function W to generate the robust controller F.

Abstract: An airborne radio frequency (RF) antenna terminal system includes a two-axis gimbals control system and a phased array antenna. The phased array antenna electronically steers the receive and transmit beams using phase shifters. The electronically steered beams provide a virtual third-axis for the two-axis gimbals control system. The combination of the electronically steered beams and the two-axis gimbaled system provides accurate beam steering for the keyhole region of the two-axis gimbals control system so that the RF communication link is prevented from being lost in the keyhole region.

Abstract: A method, apparatus, article of manufacture, and a memory structure for designing a robust controller. The method comprises the steps of determining a plant model G of the system dynamics; bounding system dynamics unmodeled by the plant model G of the system dynamics by a weighting function W; applying a transform to an augmented plant model T having the plant model G and the weighting function W; defining a controller {tilde over (F)} from the transformed plant model T; and applying an inverse of the transform to the controller {tilde over (F)} defined from the transformed plant model and the weighting function W to generate the robust controller F.

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: An apparatus for star catalog equalization to enhance attitude determination includes a star tracker, a star catalog and a controller. The star tracker is used to sense the positions of stars and generate signals corresponding to the positions of the stars as seen in its field of view. The star catalog contains star location data that is stored using a primary and multiple secondary arrays sorted by both declination (DEC) and right ascension (RA), respectively. The star location data stored in the star catalog is predetermined by calculating a plurality of desired star locations, associating one of a plurality of stars with each of the plurality of desired star locations based upon a neighborhood association angle to generate an associated plurality of star locations: If an artificial star gap occurs during association, then the neighborhood association angle for reassociation is increased.

Abstract: The stability of a recursive estimator process (e.g., a Kalman filter is assured for long time periods by periodically resetting an error covariance P(tn) of the system to a predetermined reset value Pr. The recursive process is thus repetitively forced to start from a selected covariance and continue for a time period that is short compared to the system's total operational time period. The time period in which the process must maintain its numerical stability is significantly reduced as is the demand on the system's numerical stability. The process stability for an extended operational time period To is verified by performing the resetting step at the end of at least one reset time period Tr whose duration is less than the operational time period To and then confirming stability of the process over the reset time period Tr.

Abstract: Methods are provided for dynamically processing successively-generated star tracker data frames and associated valid flags to generate processed star tracker signals that have reduced noise and a probability greater than a selected probability Pslctd of being valid. These methods maintain accurate spacecraft attitude control in the presence of spurious inputs (e.g., impinging protons) that corrupt collected charges in spacecraft star trackers. The methods of the invention enhance the probability of generating valid star tracker signals because they respond to a current frame probability Pfrm by dynamically selecting the largest valid frame combination whose combination probability Pcmb satisfies a selected probability Pslctd. Noise is thus reduced while the probability of finding a valid frame combination is enhanced. Spacecraft structures are also provided for practicing the methods of the invention.

Abstract: Control systems and methods are provided which enhance acquisition range, transient response and offset pointing accuracy in beacon-assisted orientation of a spacecraft to a desired spacecraft attitude Adsrd. The methods receive a beacon signal with antennas that are arranged in a fixed angular relationship to thereby form an attitude error signal Serr whose magnitude is a measure of the attitude difference between a current spacecraft attitude Acrnt and the desired spacecraft attitude Adsrd. A sum power P&Sgr; that is the sum of the signal powers from the antennas is sensed and a signal modifier Smod is generated that increases with decreases in the sum power P&Sgr;. The attitude error signal Serr is then modified with a term (1+Smod) to form an enhanced attitude error signal Serrenhd. In one embodiment, the signal modifier Smod is n|Pmax−P&Sgr;|m wherein n and m are positive numbers and Pmax is the sum power P&Sgr; when the attitude error is zero.

Abstract: A method and system for minimizing attitude errors resulting from dynamic spacecraft maneuvers or time-varying mismatched attitude sensor measurements. The method includes time-tagging a primary attitude value from a primary attitude sensor and storing the value and associated time stamp in a buffer. A secondary attitude value, generated by a secondary attitude sensor, having a different associated time-stamp is then time-matched to the primary attitude valve. The corrected spacecraft attitude is then calculated as a function of the time-matched primary and secondary attitude values. In one aspect of the invention, the primary attitude sensor generates attitude data at a faster rate than the secondary attitude sensor. This primary attitude data is stored in a buffer such that, when the secondary attitude data becomes available, several nearest-in-time primary attitude data points are retrieved from the buffer. These data points are then used to interpolate a higher time-matched resolution data point.

Abstract: An attitude sensing system utilizing simplified techniques and apparatus includes a spacecraft control processor which receives signals from an inertial measurement unit and two attitude sensors. The spacecraft control processor calculates a time-varying gain matrix for estimating attitude errors and gyroscope drifts corresponding to the axes of the inertial measurement unit. In special cases where the separation angle between the attitude sensor vectors is less than approximately 10 degrees, the time-varying gain matrix is computed as a fixed gain matrix and a corresponding desensitizing factor.

Abstract: A method and apparatus for estimating attitude sensor bias in a satellite system uses attitude sensors and a spacecraft control processor. Attitude sensors provide output signals, which may contain bias. The present invention interprets the signals, determines the bias present in the signals, and generates an output signal to offset the bias in the signals from the attitude sensors, thereby leading to more accurate positioning of the satellite employing the present invention.

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.