Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Aeronautical vehicle
Reexamination Certificate
2000-03-02
2001-09-11
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Aeronautical vehicle
C701S003000, C701S221000, C244S164000, C244S171000, C244S170000, C244S165000
Reexamination Certificate
active
06289268
ABSTRACT:
TECHNICAL FIELD
The invention relates to spacecraft attitude determination and, more particularly, to a method of an improved attitude determination capable of both ground or spacecraft implementation while optimizing attitude determination performance.
BACKGROUND ART
It is often desirable to determine the attitude of a spacecraft for payload pointing purposes. Attitude refers to angular orientation of the spacecraft with respect to three orthogonal axes. Satellites typically employ attitude determination apparatus for pointing a payload such as a telescope or antenna to a desired location on the Earth. Conventional attitude sensing apparatus may include a satellite receiver such as a Global Positioning System (GPS), ground tracking apparatus for determining the satellite ephemerides, and star or sun trackers for transforming reference measurements determined in spacecraft body coordinates into a stellar, or orbital frame of reference. Various methods have been used to process attitude sensor data to determine spacecraft attitude.
Several methods of determining spacecraft attitude using Extended Kalman Filter (EKF) based algorithms have been proposed. These estimate the spacecraft attitude and gyroscope rate biases using various attitude sensor data. For example, see E. J. Lefferts, et al., “Kalman Filtering for Spacecraft Attitude Determination,” A.I.A.A. Journal on Guidance, Control and Dynamics, September-October 1982, pp. 417-429; A. Wu, “Attitude Determination for GEO Satellites,” NASA Goddard 1997 Flight Mechanics Symposium, Greenbelt, MD, May 19-21, 1997.
The EKF is an established estimation method for attitude determination. In particular, the Kalman filter provides optimal noise attenuation performance for both process and measurement noise. EKF filtering is ideally suited for systems wherein disturbances are white noise processes. A steady state Kalman filter is a simple (fixed gain) estimator for state dynamics and measurement equations which are time-invanrant. If either the state dynamics or measurement equations vary with time, however, the Kalman filter gains become time-varying.
To reduce the computational complexity of such a system, a fixed gain filter approach can be used such as a TRIAD-based system. The TRIAD method of attitude determination is described in M. D. Shuster et al., “Three-Axis Attitude Determination From Vector Observations,” Journal of Guidance and Control, vol. 4, no. 1, January-February 1981. A fixed gain approach to attitude determination reduces the computational complexity of the system, however, performance significantly deviates from the optimal solution provided by an EKF design because it ignores the time-varying measurement geometry in the filter design.
One problem with known attitude determination techniques is that the rate of successful attitude acquisition is lower than desired. That is, a proper orientation may not be obtained. If this occurs, then the process may have to be run again. This may result in costly delays. Another problem with attitude acquisition is that the time for acquisition is relatively great. This also increases costs due to unavailability of the satellite.
SUMMARY OF THE INVENTION
In the present invention, the aforementioned drawbacks of prior systems are solved by providing an attitude determination system having 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 estimate of the attitude of the spacecraft and sensor alignments as a function of the star data, and establishes a track on at least one star identified as corresponding to one entry in the on-board star catalog. The processor then obtains a normal phase attitude as a function of the star data and the coarse attitude.
Accordingly, an object of the present invention is to provide an improved spacecraft attitude determination method.
Another object of the present invention is to provide attitude control for a satellite that can be executed on the ground or on board the satellite, or a combination of the two.
One advantage of the present invention is that the probability of successful acquisition is improved over prior systems. Another advantage of the invention is that when the slews are performed, they are safe for the spacecraft from the standpoint of the power supply and thermally-sensitive surfaces.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings.
REFERENCES:
patent: 4746976 (1988-05-01), Kamel et al.
patent: 5412574 (1995-05-01), Bender et al.
patent: 5508932 (1996-04-01), Achkar et al.
patent: 5546309 (1996-08-01), Johnson et al.
patent: 5745869 (1998-04-01), Van Bezooijen
patent: 6047226 (2000-04-01), Wu et al.
patent: 6108593 (2000-08-01), Didinsky et al.
patent: 6108594 (2000-08-01), Didinsky et al.
Didinsky Garry
Kurland Jeffrey A.
Li Rongsheng
Nayak Arunkumar P.
Needelman David D.
Cuchlinski Jr. William A.
Gudmestad Terje
Hughes Electronics Corp.
To Tuan C
LandOfFree
Attitude determination system and method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Attitude determination system and method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Attitude determination system and method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2446584