Hughes Electronics Corporation

Hughes Aircraft Company

The Boeing Company

Yeong-Wei A Wu

Garry Didinsky

Rongsheng Li

Douglas H Hein

Michael H Kieffer

Arunkumar Pursayya Nayak

David D Needelman

John Joseph Anagnost

Jeffrey A Kurland

David L Augenstein

David F Hartman

Mark Youhanaie

Shaun L Champion

Ray E Mc Vey

A system and method of estimating the attitude of a spacecraft is disclosed. A three-axis inertial-based estimate of spacecraft attitude is produced and is compared to a stellar-based estimate of spacecraft attitude. A Kalman filter having states associated with gyro scale factor and/or misalignment errors compares the stellar-based attitude estimate to the inertial-based estimate of attitude and apportions the total error into three time varying matrices. A first time varying matrix is associated with gyro scale factor and misalignment errors, a second time varying matrix is associated with gyro bias errors, and a third time varying matrix is associated with attitude errors. The time varying matrices are applied as corrective feedbacks to the inertial-based estimate of spacecraft attitude and are adaptively adjusted to minimize the error therein.

Autonomous gyro scale factor and misalignment calibration

A star tracker coupled to the spacecraft having a star catalog associated therewith. A sun sensor is coupled to the spacecraft. A control processor is coupled to the star tracker and the sun sensor. The processor obtains star data using a star tracker and an on-board star catalog. The processor generates a coarse attitude of the spacecraft as a function of the star data, and establishes a track on at least one star in the on-board star catalog. The processor calculates a sun tracking rate, and obtains a normal phase attitude as a function of the star data and the coarse attitude. The information is used to slew the spacecraft to a desired attitude.

Attitude determination system and method

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.

System and method for correcting star tracker low spatial frequency error in stellar-inertial attitude determination systems

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&deg; 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.

Method and apparatus for controlling spacecraft attitude with rotational star trackers

A method and apparatus for autonomous acquisition of attitude in a stellar inertial spacecraft attitude system is disclosed. The present invention uses star trackers, an on-board star catalog, spacecraft steering and inertial sensors to determine spacecraft attitude. The present invention utilizes pattern match and pattern rejection methods and uses multiple stellar snap-shots in conjunction with spacecraft steering and spacecraft inertial measurements to acquire spacecraft attitude. Spacecraft inertial measurements are used to connect multiple stellar snap-shots to provide adequate star information that can be used to acquire spacecraft attitude. In an attitude determination system using star trackers, the star trackers may have a narrow field-of-view or few stars may be available for viewing. The present invention uses pattern matching and pattern rejection on different sets of stars, thereby allowing attitude acquisition when the number of stars in view is small.

Autonomous attitude acquisition for a stellar inertial attitude

An adaptive feedforward vibration control system reduces vibrations at fundamental and harmonic frequencies of matched reciprocating pistons, such as back-to-back compressor pistons in Stirling cycle cryocooler, by driving the pistons with correction signals. The system is also applicable to reducing the vibrations generated by a pair of opposite expander and balancer pistons in a cryocooler. The correction signals are computed iteratively to increase their accuracy, and need only be updated relatively infrequently to adjust the pistons' motions, thereby enabling the use of a relatively slow microprocessor.

Adaptive feedforward vibration control system and method

An articulated viewing apparatus (10) has a pair of elevational actuators (56, 78), one of which is a coarse-position actuator (56) and the other of which is a fine-position actuator (78), and each of which pivots a mirror head (28) about respective parallel elevational axes (54, 66'). Pivotal movements of the mirror head (28) direct the line of sight of a viewer looking outwardly through a window (22). The window (22) may be formed in the wall of a vehicle or may be at the upper end of a periscope tube, for example, and includes a transparent material (24). This window (22) may admit light to an optical sensor or to the user's eye directly. The coarse-position elevational actuator (56) is positioned so that its axis (54) is located as close as possible to an edge of the mirror head (28) and close to the inner surface of the window glazing (24) so that the size of the window (22) is minimized with respect to the size of the optical aperture and field of view provided to the user of the apparatus (10). The fine-position actuator (78) is attached to the mirror head (28) at a respective axis (66') approximately at the geometric center of the mirror (28), so that the mirror (28) is statically balanced about the fine-position elevation axis (66') of this actuator (78).

Viewing apparatus with a counterbalanced and articulated mirror

A FLIR boresight alignment system (52) for aligning a sensor pod LOS associated with a weapons pod of a fighter aircraft to a navigation reference frame. A pod inertial navigation and global positioning system (62) provides position, velocity and attitude of a sensor (58) within the pod. An aircraft inertial navigation and/or global positioning system (68) provides position, velocity and attitude of the aircraft. The sensor position and velocity and the aircraft position and velocity are applied to a transfer alignment filter (64) that utilizes Kalman filtering. An output of the transfer alignment filter (64) is applied to a sensor inertial navigation system to correct the pod LOS relative to the navigation reference frame. Alternately, the transfer alignment filter (64) may operate directly upon the pseudo ranges and delta pseudo ranges to satellites being tracked by the GPS receiver.

FLIR boresight alignment

A temperature control apparatus and method for active control of a Stirling-cycle cryocooler cold finger tip temperature, by adjusting the cryocooler compressor piston stroke amplitude. In a control loop of the Stirling cryocooler, having a compressor in which the pistons are reciprocated by linear motors at fundamental frequency and the length of a stroke of the piston is varied as a direct function of cryocooler temperature, temperature is sensed at the cryocooler cold finger tip and the temperature signal is compared with a set temperature signal to produce a temperature error signal. This signal is input in a PID control law module which uses proportional, derivative, and integrated temperature error information to generate the required compressor piston stroke amplitude change for achieving the precision temperature control. The resulting signal is further processed in a distribution law module that distributes the desired piston stoke amplitude change to each compressor motor so that the force balance at the fundamental frequency is maintained.

Apparatus and method for temperature control of a cryocooler by

A cryogenic cooling system having a mechanism for canceling vibration at a fundamental frequency and at harmonics thereof. The inventive system includes a first apparatus (28, 32) for cooling a mass. The first apparatus (28, 32) creates a vibration at a first frequency and a second frequency. In a typical application, the first frequency is a fundamental frequency and the second frequency is a harmonic of the first frequency. Often several harmonics are present. The invention includes a second apparatus (30, 34) for substantially eliminating vibration at the first frequency and a third apparatus (48, 50) for substantially eliminating vibration at the second frequency. The second apparatus includes a mass (30) and a motor (34) for driving same. The mass (30) is disposed to counter the vibration created by the first apparatus when the motor (34) is driven by a first current. The third apparatus includes a sensor (48) for detecting the vibration at the second frequency and providing an output in response to a sensed force F resulting therefrom. The third apparatus further includes a feedback circuit (50) for providing a second current for driving the motor. The second current is the sum of the first current and a feedback current I.sub.b2. The feedback current I.sub.b2 is equal to -G.sub.f (s)F, where -G.sub.f (s) is a feedback transfer function. The feedback transfer function is a product of a first transfer function H.sub.I (s) representing dynamics of the second apparatus required to cancel the vibration at the first frequency and a second transfer function G.sub.D (s) representing the dynamics of the second means required to cancel the harmonic vibration.

Cyrogenic cooling system with active vibration control

A Stirling-cycle cryogenic cooler that employs a vibration control procedure based on adaptive feedforward principles. The vibration control procedure is particularly adapted for use as a spacecraft cryogenic cooler, and may be used to cool a detector array or other sensor located on the spacecraft. The vibration control procedure suppresses vibrational forces that occur during operation of the cooler. The cooler comprises an expander module and a compressor module. The expander and compressor modules employ separate motors that respectively drive an expander piston and a compressor piston, and a balancer piston is employed to dynamically balance the respective expander and compressor pistons. In the control procedure, current command signals are injected into a selected motor drive of either the compressor or expander module. The injected current command signals comprise higher-order harmonics with adaptively determined phases and amplitudes that provide for complete force cancellation in the cooler. The desired phases and amplitudes of the injected current command signals are estimated in real time using outputs of force sensors, such as load cells, coupled to the cooler housing that measure higher-order harmonic forces. In operation, when operational parameters of the cryogenic cooler have reached equilibrium, the harmonic content of its vibration force is very stable in time. Because of this unique characteristic, the phases and amplitudes of injected current command signal do not have to be determined quickly. Thus, the computation throughput required for the present control procedure are significantly reduced.

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Rancho Palos Verdes, CA, United States of America

Yeong-Wei A Wu