Abstract: Method and system for determining a point-ahead angle from a first spacecraft to a second spacecraft, each spacecraft having a laser communication (“lasercom”) terminal is provided If ephemeris data regarding the second spacecraft is unavailable to the first spacecraft while the second spacecraft is mobile, (a) obtaining attitude information regarding the first spacecraft; and (b) obtaining gimbal offload commands from a fast steering mirror and a first spacecraft telescope subsystem of the first spacecraft; wherein a point-ahead determination module receives the attitude information and the gimbal offload commands; and determining an estimate of the point-ahead angle from the first spacecraft to the second spacecraft based on the attitude information and the gimbal offload commands.

Abstract: A method of estimating the alignment of a star sensor (20) for a vehicle (12) includes generating star tracker data. A vehicle attitude and a star sensor attitude are determined in response to the star tracker data. A current alignment sample is generated in response to the vehicle attitude and the star sensor attitude. A current refined estimate alignment signal is generated in response to the current alignment sample and a previously refined estimate alignment signal via a vehicle on-board filter (38).

Abstract: In accordance with an embodiment of the present invention, a resolver system has at least one resolver and at least one amplifier in electrical communication with each resolver. A reference circuit is in electrical communication with the amplifiers. The reference circuit provides reference signals to the amplifiers. A non-linearity calibration and compensation circuit in communication with each amplifier uses the amplified reference signals to provide scale factors, so as to enhance a precision of the resolver system.

Abstract: A method and apparatus for determining the attitude of a satellite using crosslink information is disclosed. The method and apparatus integrates data from the crosslinks with data available from other sources including, for example, star sensors, inertial sensors, and earth limb sensors to derive an accurate estimate of the satellite attitude, even in harsh nuclear environments.

Abstract: Method and system for determining a point-ahead angle from a first spacecraft to a second spacecraft, each spacecraft having a laser communication (“lasercom”) terminal is provided If ephemeris data regarding the second spacecraft is unavailable to the first spacecraft while the second spacecraft is mobile, (a) obtaining attitude information regarding the first spacecraft; and (b) obtaining gimbal offload commands from a fast steering mirror and a first spacecraft telescope subsystem of the first spacecraft; wherein a point-ahead determination module receives the attitude information and the gimbal offload commands; and determining an estimate of the point-ahead angle from the first spacecraft to the second spacecraft based on the attitude information and the gimbal offload commands.

Abstract: Methods, systems and devices are disclosed for positioning an antenna having a sub-reflector assembly. A conical scan processor receives a period for a reference time pulse and a time tag. The processor calculates a rotation angle of the sub-reflector assembly using the received period for the reference time pulse and the received time tag. The processor may also receive a power measurement associated with the time tag. The processor may calculate and then output antenna boresight errors based on the calculated rotation angle of the sub-reflector assembly and the power measurements associated with the time tag.

Abstract: In accordance with an embodiment of the present invention, a resolver system has at least one resolver and at least one amplifier in electrical communication with each resolver. A reference circuit is in electrical communication with the amplifiers. The reference circuit provides reference signals to the amplifiers. A non-linearity calibration and compensation circuit in communication with each amplifier uses the amplified reference signals to provide scale factors, so as to enhance a precision of the resolver system.

Abstract: A method for controlling an actuator of a vehicle comprises providing a dynamic condition sensor generating a vehicle movement signal and a position sensor for generating a reported position. A processor is coupled to the inertial sensor and the position sensor and comprises an estimator, a position measurement predictor having a filter, a comparator and a control shaping block, said estimator generating a vehicle position based upon the dynamic condition sensor, said position measurement predictor generating an estimated position measurement in response to the reported vehicle position and a matched frequency response to the movement signal, said control shaping block generating an actuator control signal in response to a comparison of the estimated position measurement and the reported vehicle position.

Abstract: A method and apparatus for determining the attitude of a satellite using crosslink information is disclosed. The method and apparatus integrates data from the crosslinks with data available from other sources including, for example, star sensors, inertial sensors, and earth limb sensors to derive an accurate estimate of the satellite attitude, even in harsh nuclear environments.

Abstract: Methods, systems and devices are disclosed for positioning an antenna having a sub-reflector assembly. A conical scan processor receives a period for a reference time pulse and a time tag. The processor calculates a rotation angle of the sub-reflector assembly using the received period for the reference time pulse and the received time tag. The processor may also receive a power measurement associated with the time tag. The processor may calculate and then output antenna boresight errors based on the calculated rotation angle of the sub-reflector assembly and the power measurements associated with the time tag.

Abstract: In accordance with an embodiment of the present invention, a resolver system has at least one resolver and at least one amplifier in electrical communication with each resolver. A reference circuit is in electrical communication with the amplifiers. The reference circuit provides reference signals to the amplifiers. A non-linearity calibration and compensation circuit in communication with each amplifier uses the amplified reference signals to provide scale factors, so as to enhance a precision of the resolver system.

Abstract: A system (18) includes: a) A vehicle (12) includes an attitude or angular velocity control system (38), a plurality of star trackers or star sensors (22) each having a field of view (28); b) a memory (30) having a star catalog (32), a star pair catalog (58) and a reference table (56) stored therein; and c) a processor (24) coupled to the attitude or angular velocity control system (38), the star trackers or star sensors (22), and the memory (30). The processor (24) determines the vehicle inertial attitude or angular velocity or sensor alignment, based, in part, on the star pair catalog (58) and reference table (56). The design of the star pair catalog (58) and reference table (56) is suitable for rapid determination of attitude or angular velocity or sensor alignment, and an efficient use of memory.

Abstract: A method and apparatus for reducing centroiding error of a star sensor having a plurality of pixels is disclosed. The method comprises the steps of computing a star sensor angular slew rate of ? pixels per star sensor integration period ?, collecting star sensor data while slewing the star sensor according to the selected star sensor angular slew rate ?, and filtering the collected star sensor data according to a frequency determined by the selected star sensor angular slew rate.

Abstract: Time-of-day tracking with INS input is described. In one embodiment, a range rate and a range acceleration is generated from inertial navigation system data received from a moveable platform (e.g. an airborne platform). A time and frequency estimation filter receives the range rate, the range acceleration and a timing-based error signal from a time discriminator, and can then generate a time-of-day correction signal and a frequency correction signal. A time-of-day generator receives the time-of-day correction signal and generates a time-of-day correction, and a clock frequency generator receives the frequency correction signal and generates a frequency correction. The time discriminator receives a satellite synchronization signal from a satellite, the time-of-day correction from the time-of-day generator, and the frequency correction from the clock frequency generator.

Abstract: A vehicle (12) including a control system (18) is used for controlling vehicle attitude or angular velocity (38). The processor (24) is coupled to a star sensor or tracker (22) and a memory (30) that may include a star catalog (32), and an exclusion list (36). The exclusion list (36), a list of stars to be temporarily excluded from consideration when determining attitude or angular velocity or relative alignment of star sensors or trackers, is calculated on board. Such a calculation prevents the necessity for a costly, periodic, ground calculation and upload of such data. By manipulating the star catalog, or sub-catalogs derived from said catalog, based upon the exclusion list (36), measurements of such excluded stars are prevented from corrupting the attitude or angular velocity or alignment estimates formulated on board. The system uses multiple stayout zones for excluding stars from the exclusion list.

Abstract: A vehicle (12) including a control system (18) is used for controlling vehicle attitude or angular velocity (38). The processor (24) is coupled to a star sensor or tracker (22) and a memory (30) that may include a star catalog (32), and an exclusion list (36). The exclusion list (36), a list of stars to be temporarily excluded from consideration when determining attitude or angular velocity or relative alignment of star sensors or trackers, is calculated on-board. Such a calculation prevents the necessity for a costly, periodic, ground calculation and upload of such data. By manipulating the star catalog, or sub-catalogs derived from said catalog, based upon the exclusion list (36), measurements of such excluded stars are prevented from corrupting the attitude or angular velocity or alignment estimates formulated on board.

Abstract: A system (18) includes: a) A vehicle (12) includes an attitude or angular velocity control system (38), a plurality of star trackers or star sensors (22) each having a field of view (28); b) a memory (30) having a star catalog (32), an allocated area for a star pair catalog (58) and a reference table (56) stored therein; and c) a processor (24) coupled to the attitude or angular velocity control system (38), the star trackers or star sensors (22), and the memory (30). The processor (24) populates the star pair catalog (58), using the method described herein. The processor (24) then periodically determines the vehicle inertial attitude or angular velocity or sensor alignment, based, in part, on the star pair catalog (58) and reference table (56). The novel ability of the software to autonomously populate the star pair catalog (58) allows users to avoid uploading a large amount of data, and the problems associated with such an upload.

Abstract: A method and apparatus for estimating a slave payload attitude is disclosed. The method includes accepting a plurality of slave payload attitude measurements, deriving a model of the relative attitude of the slave payload and a master payload attitude at least in part from the plurality of slave attitude measurements, predicting the relative attitude between the slave payload attitude and the master payload attitude using the derived model, and estimating the relative attitude between the slave payload attitude and the master payload attitude at least in part from the predicted relative attitude between the slave payload attitude and the master payload attitude. Furthermore, the absolute attitude of the slave payload is computed using the relative attitude and the master payload attitude.

Abstract: A method and apparatus for refining a spacecraft state estimate, such as an attitude estimate or an angular velocity estimate, is disclosed. The method computes a plurality equations using residuals describing the difference between observed star positions and predicted positions based on inertial measurements, and solves those equations to generate refined estimates of the spacecraft state estimates.

Abstract: Methods and structures are provided for reducing pointing errors &zgr; of satellite antennas and for generating broad field-of-view satellite attitude acquisition patterns. In one method embodiment, satellite transmit beams have estimated pointing attitudes &bgr; and are transmitted to overlap on a ground-based receiving terminal which has a known terminal location &lgr; and which measures received signal strengths &agr;. Pointing errors &zgr; of the transmit beams are then determined from the estimated pointing attitudes &bgr;, the terminal location &lgr; and the signal strengths &agr; and the pointing errors &zgr; are subsequently reduced by revising the pointing attitudes &bgr;. Other method embodiments utilize known signal-strength functions and antenna signals with known signal parameters such as frequencies and/or modulations.