Aeronautics and astronautics – Spacecraft – Spacecraft formation – orbit – or interplanetary path
Reexamination Certificate
2001-10-28
2003-07-22
Barefoot, Galen L. (Department: 3644)
Aeronautics and astronautics
Spacecraft
Spacecraft formation, orbit, or interplanetary path
C244S164000, C244S171000, C342S354000, C343S711000, C343S757000, C343SDIG002, C701S013000
Reexamination Certificate
active
06595469
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to spacecraft and, more particularly, to spacecraft attitude control systems.
2. Description of the Related Art
The diagram
20
of
FIG. 1
illustrates a conventional spacecraft
22
that orbits in an orbital plane
23
about the earth
24
. Although the spacecraft's orbital plane may be coplanar with the earth's equatorial plane
25
, it is shown, for generality, as having an inclination
26
.
Spacecraft generally carry a payload which facilitates performance of the spacecraft's intended service. An exemplary service provides communications for a service area (e.g., the area
28
on the earth
24
) and, accordingly, the spacecraft's body
30
carries a corresponding payload
32
which includes antennas
33
. The body also carries solar panels
34
which provide electrical current to operate the payload and an attitude control system which maintains a spacecraft service attitude that is necessary to carry out the service. The attitude control system generally includes an attitude determination system which generates an attitude estimate in response to attitude measurements from spacecraft attitude sensors.
As spacecraft have evolved, their service demands have generally increased which has caused their payloads to become more complex so that many spacecraft now carry multiple payloads. Despite great care in design and fabrication, small relative attitude errors generally exist between these multiple payloads. More significantly, relative attitude errors are generated by differential thermal heating as the spacecraft rotates relative to the sun and passes in and out of the earth's shadow. This differential heating induces thermal deformations and consequent relative attitude errors that often exceed the spacecraft's design budget. Conventional spacecraft systems that determine a single attitude cannot remove these significant relative errors.
SUMMARY OF THE INVENTION
The present invention is directed to attitude control methods and systems for multiple-payload spacecraft. The invention recognizes that payload attitudes must be determined to reduce relative attitude errors between payloads. The invention thus provides an integrated attitude determination architecture that combines attitude measurements from all payloads to determine a master attitude estimate for a master payload and relative slave attitude estimates for the remaining slave payloads. These estimates are then used to control the attitudes of spacecraft elements that correct the absolute and relative attitude errors.
It has been found that systems of the invention significantly enhance the accuracy of the attitude estimates when compared to systems that realize independent payload estimates, determine payload attitudes. In addition, it has been found that estimating relative slave attitudes provides significant processing advantages (e.g., simpler algorithms, reduced data throughput and slower processing rate) when compared to other methods.
The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.
REFERENCES:
patent: 5587714 (1996-12-01), Chu et al.
patent: 6000661 (1999-12-01), Price
patent: 6022005 (2000-02-01), Gran et al.
patent: 6263264 (2001-07-01), Herman
Li Rongsheng
Wang Hanching Grant
Wu Yeong-Wei A.
Barefoot Galen L.
Koppel, Jacobs Patrick & Heybl
The Boeing Company
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