Aeronautics and astronautics – Spacecraft – Attitude control
Reexamination Certificate
2000-01-10
2001-11-20
Barefoot, Galen L. (Department: 3644)
Aeronautics and astronautics
Spacecraft
Attitude control
Reexamination Certificate
active
06318676
ABSTRACT:
BACKGROUND
The present invention relates generally to spacecraft and control methods therefor, and more particularly, to an equatorial-normal body-stabilized spacecraft that operates in an inclined orbit and a method of controlling the spacecraft.
The assignee of the present invention manufactures and deploys communication satellites or spacecraft that orbit the Earth. Heretofore, certain spacecraft have been launched and positioned in geosynchronous equatorial or non-inclined orbits. In such geosynchronous equatorial or non-inclined orbits, the spacecraft is controlled to point its payload (communication antennas or instruments) at the Earth and point its solar arrays at the sun. When the spacecraft is positioned in a geosynchronous equatorial or non-inclined orbit, it is controlled to maintain sun pointing by rotating the body of the spacecraft around a single axis, which is the pitch axis. The pitch axis is normal to the orbit plane.
However, for conventional spacecraft positioned in inclined orbits, control is achieved by rotating or steering the spacecraft about two axes, the pitch and yaw axes, to maintain Earth and sun pointing. This is referred to as yaw steering.
It is an objective of the present invention to provide for an equatorial-normal body-stabilized spacecraft that operates in an inclined orbit. It is another objective of the present invention to provide for an equatorial-normal body-stabilized spacecraft that operates in an inclined orbit that is controlled to provide Earth-pointing payloads and sun-pointing solar arrays wherein the spacecraft body and solar arrays each rotate only around a single axis. It is another objective of the present invention to provide for an improved method of controlling a spacecraft to provide payload pointing with minimal spacecraft rotation, in that all large-angle spacecraft rotation occurs around the pitch axis.
SUMMARY OF THE INVENTION
To accomplish the above and other objectives, the present invention provides for an equatorial-normal body stabilized spacecraft that operates in an inclined orbit. A control method is used that controls pointing of payloads (communication antennas and instruments) and solar arrays disposed on the spacecraft. The spacecraft is controlled to provide Earth-pointing payloads and sun-pointing solar arrays in a manner such that the spacecraft body and solar arrays each rotate only around a single axis.
More particularly, the spacecraft body is controlled to rotate only around the pitch axis of the spacecraft, which is aligned nominally in a north-south direction. The solar arrays are also controlled to rotate only around the pitch axis of the spacecraft.
In using the present invention, spacecraft communications payload antennas have a footprint on the surface of the Earth that undergoes minimal rotation due to spacecraft motion. This improves upon conventional yaw steered spacecraft that have a yaw rotation of as little as 0 degrees to as much as 180 degrees daily during yaw steering operation.
Using the present invention, the spacecraft communications payload antenna footprint undergoes minimal rotation due to orbital and attitude motion, enabling spot beams to be precisely targeted to small geographical regions with high traffic. Attitude motion of the spacecraft body with respect to the sun is also minimized, thus simplifying the layout of sun sensors used for attitude control, and simplifies rotation of the solar arrays
REFERENCES:
patent: 4374579 (1983-02-01), Renner et al.
patent: 5738309 (1998-04-01), Fowell
patent: 6076774 (2000-06-01), Shah et al.
Ford David F.
Stoen Jeffrey D.
Turner Andrew E.
Barefoot Galen L.
Float Kenneth W.
Space Systems Loral, Inc.
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