Aeronautics and astronautics – Spacecraft – Attitude control
Reexamination Certificate
1998-12-29
2001-07-17
Barefoot, Galen L. (Department: 3644)
Aeronautics and astronautics
Spacecraft
Attitude control
C244S165000, C244S169000
Reexamination Certificate
active
06260805
ABSTRACT:
FIELD OF THE INVENTION
The invention is generally related to spacecraft attitude control systems, and in particular is related to systems for controlling spacecraft rotation about a spacecraft yaw axis.
BACKGROUND OF THE INVENTION
Spacecraft have been developed that use low-thrust thrusters mounted to the spacecraft, such as, for example electric thrusters, that may be used for station keeping maneuvers. Such low-thrust thrusters can create significant disturbance torques when used for long duration burns, such as burns requiring thrust over a duration of three hours to seven hours.
In a typical communications satellite mission in which the satellite is required to maintain its attitude in a single orientation with respect to the earth, and is not required to perform frequent attitude reorientation maneuvers, a momentum biased spacecraft is the most economical configuration for attitude control. A significant advantage of a momentum biased spacecraft is that it requires minimal attitude control system hardware: a two-axis earth sensor, a pitch momentum wheel, and associated electronics. Specifically, it does not require an attitude sensor to measure attitude about the satellite-to-Earth nadir line, an axis herein called “yaw.” To improve transient behavior, some designs add an ability to steer the spacecraft pitch momentum vector (e.g., using a V-wheel, or a single or double gimbaled momentum wheel), although this is not absolutely essential for adequate performance.
The use of ion propulsion systems for satellites has been considered for a number of years. See, e.g., Krulle, G., Zeyfang, E., “Combined Orbit and Attitude Control of Geostationary Satellites Using Electric Propulsion,”
IFAC Automatic Control in Space, Noordwijkhout,
The Netherlands, 1982 and Marsh, Elbert L., “Attitude Control of Solar Electric Spacecraft by Thruster Gimbaling,” Paper AIAA 73-1116, 10
th
Electric Propulsion Conference
, Lake Tahoe, Nev., Oct. 31-Nov. 2, 1973. These early papers directed to the use of ion propulsion are survey papers postulating what might be feasible with ion propulsion. Early on in the implementation of the use of ion propulsion, it was recognized that gimbaled thrusters would be required in order to point the thrust vector of an ion propulsion engine through the spacecraft center of mass, or to intentionally offset the thrust vector to create desired torques for attitude control.
As ion propulsion designs moved closer to realization, attitude control system designers were forced to design control systems that were capable of sensing and correcting relatively large disturbances created by ion engines. It was generally concluded that, in addition to ion thrust vector steering, a yaw sensor would be required for the purpose of measuring yaw response to the disturbance torque created by an ion propulsion system. An article authored by T. G. Duhamel entitled “Implementation of Electric Propulsion for North-South Stationkeeping on Eurostar Spacecraft,” paper AIAA 89-2274
, AIAA/ASEM/SAE/ASEE
25
th
Joint Propulsion Conference,
1989, described a typical concept for attitude control on a momentum biased spacecraft using ion propulsion. The attitude control system design described in the Duhamel AIAA article was developed for the Eurostar spacecraft, and indicates that a yaw sensor must be added to measure yaw motion created by the ion engines. In the Eurostar design, a star sensor was added, even though the attitude control system already had a yaw gyro. The yaw gyro was not used to measure yaw motion created by the ion thrusters, because the yaw gyro was not capable of the numerous on/off cycles nor the long life operation necessary to support ion propulsion.
The following references describe several other attitude control system designs that have been modified to adapt a momentum biased spacecraft to use ion propulsion:
Nakashima, A., Fujiwara, Y., Okada, K., Yamada, K., Miyazaki, H., Matsue, T., “The Attitude Control Subsystem and Inter Orbit Pointing Subsystem for Communications and Broadcasting Engineering Test Satellite”, 13 IFAC Symposium Automatic Control in Aerospace—Aerospace Control '94, Sep. 12-16, 1994;
Potti, J., Mora, E. J., Pasetti, A., “An Autonomous Stationkeeping System for Future Geostationary Telecommunication Satellites (An ARTEMIS based ASK System),”
International Astronautical Federation,
1993;
Duhamel, T. G., Benoit, A., “New AOCS Concepts for ARTEMIS and DRS,”
Proc. Pirst International Conference on Spacecraft Guidance, Navigation and Control Systems
, ESTEV, Noordwijk, The Netherlands, Jun. 4-7, 1991;
Mazzini, L., Ritorto, A., Astin, E., Attitude Control Design Concepts in the DTRM Satellites,” i Pro., First International Conference on Spacecraft Guidance, Navigation and Control Systems, ESTEV, Noordwijk, The Netherlands, Jun. 4-7, 1991;
Duhamel, T. G., “Implementation of Electric propulsion for north-south Stationkeeping on the EUROSTAR Spacecraft,” Paper AIAA 89-2274
, AIAA/ASME/SAE/ASEE
25
th
Joint propulsion Conference,
1989; and
U.S. Pat. No. 5,349,532, “Spacecraft Attitude Control and Momentum Unloading Using Gimbaled and Throttled Thrusters,” issued to Tilley, Scott W., Liu, Tung Y., Highman, John S., Sep. 20, 1994.
In each of the six references listed above, the modifications to the attitude control systems have included the addition of a yaw sensor to measure yaw attitude during the period when ion propulsion is activated. The yaw sensor may take the form of a sun sensor, a long life gyro, or a star sensor. In addition, the modifications to the attitude control system typically include some means for steering the ion propulsion thrust vector, such as a two-axis gimbaled mechanism, a translational mechanism, or a throttling mechanism.
The foregoing references provide a sampling of the state of the art in attitude control for spacecraft using ion engines in order to account for the relatively large disturbances created by firing such ion engines. The design for the ARTEMIS satellite also employed a star sensor used solely for attitude sensing during ion propulsion operation, as set forth in the above-noted Potti et al., Duhamel et al., and Mazzini et al. references. The ARTEMIS spacecraft was eventually launched circa 1994, but the ion propulsion payload failed almost immediately. In a totally independent design, Tilley et al., U.S. Pat. No. 5,349,532 discloses a control system that also incorporates a yaw sensor in the preferred embodiment. The control system disclosed in the Tilley et al. '532 patent employs both a sun sensor and a yaw gyro, either of which may be selected by a ground commandable switch. This suggests that Tilley et al. also believed that a yaw sensor was mandatory and that the life of a yaw gyro was insufficient to permit its use as the only option for sensing yaw rate.
A paper entitled “On Orbit Robust Control Experiment of Flexible Spacecraft ETS-VI”, authored by Kida et al. and published in the
AIAA Journal of Guidance, Control and Dynamics
, Volume 20 No. 5 September-October 1997, described an attitude control systems used on ETS-VI, a Japanese satellite which flew an experimental ion propulsion payload. The basic attitude control system designed for ETS-VI is a zero-momentum, 4-reaction wheel configuration which also incorporates a yaw attitude sensor.
A paper authored by Nakashima et al. entitled “The Attitude Control Subsystem and Inter Orbit Pointing Subsystem for Communications and Broadcasting Engineering Test Satellite,” published in 13
IFAC Symposium Automatic Control in Aerospace-Aerospace Control '
94, September, 1994, describes engineering test satellite COMETS, that includes ion propulsion. The attitude control system on the COMETS satellite is a momentum biased design using a V-wheel concept to achieve three-axis torquing capability. The COMETS spacecraft also includes strapdown gyros to perform three-axis attitude determination, presumably to facilitate attitude control during ion engine firing.
Barsky et al. U.S. Pat. No. 5,765,780 entitled “Systematic Vectored Thrust Calibration for
Baker Douglas A.
Cazeau Patrick A.
Koffman Stephen J.
Yocum, Jr. John F.
Barefoot Galen L.
Gudmestad Terje
Hughes Electronics Corporation
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