Spacecraft methods and structures for enhanced service-attitude accuracy

• US 6,695,262 B2
• Filed: 12/07/2001
• Issued: 02/24/2004
• Est. Priority Date: 12/07/2001
• Status: Expired due to Fees

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Wang, Grant, Fowell, Richard
• Primary Examiner(s): Carone, Michael J.
• Assistant Examiner(s): Sukman, Gabriel S.
• Application Number:
  US10/013,137
• Publication Number:
  US 20030106966A1
• Time in Patent Office: 809 Days
• Field of Search: 244/158.R, 244/164, 342/352, 342/354, 342/355, 342/357.11, 342/357.02, 701/1, 701/13, 701/226, 701/205, 455/427, 455/430
• US Class Current: 244/164
• CPC Class Codes: B64G 1/242 Orbits and trajectories
• CPC Class Codes: B64G 1/244 Spacecraft control systems
• CPC Class Codes: B64G 1/26 using jets
• CPC Class Codes: B64G 1/285 using momentum wheels
• CPC Class Codes: B64G 1/36 using sensors, e.g. sun-sensors, horizon sensors
• CPC Class Codes: B64G 1/363 using sun sensors
• CPC Class Codes: B64G 1/66 Arrangements or adaptations of apparatus or instruments, not otherwise provided for

Abstract

Methods and structures are provided that enhance the accuracy of the service attitude of an inclined-orbit spacecraft and, thereby, facilitate reduction of service error between a communication service area and the spacecraft'"'"'s payload beam. The enhancement is realized by configuring a beacon-receiving antenna to have a beacon-receiving field-of-view that substantially matches a beacon-station window. Preferably, the beacon-receiving field-of-view is elongated and tilted to enhance its match with the beacon-station window in both size and orientation. The goals are also realized by configuring the beacon-receiving antenna to have a beacon-receiving field-of-view that is substantially smaller than the beacon-station window and successively steering a beacon-receiving boresight to successive beacon-receiving attitudes that maintain the beacon station within the beacon-receiving field-of-view over each solar day. In an embodiment of the invention, successive positions of the beacon-receiving field-of-view are arranged in a tiled arrangement. Spacecraft structures are also provided to practice the methods of the invention.

Claims

1. A method of enhancing the accuracy of the service attitude of a spacecraft that orbits the earth each solar day wherein an earth-based beacon station radiates a beacon signal and, relative to said spacecraft, moves along a path that defines a beacon-station window, the method comprising the steps of:

configuring a beacon-receiving antenna to have a beacon-receiving field-of-view that is substantially smaller than said beacon-station window wherein said beacon-receiving antenna has a beacon-receiving boresight and generates a difference signal that corresponds to a difference angle between said beacon-receiving boresight and a line-of-sight from said spacecraft to said beacon station;

successively steering said beacon-receiving boresight to beacon-receiving attitudes, relative to said service attitude, that maintain said beacon station within said beacon-receiving field-of-view over said solar day;

receiving said beacon signal with said beacon-receiving antenna; and

controlling said service attitude in response to said difference signal;

said accuracy enhanced because said beacon-receiving field-of-view is substantially smaller than said beacon-station window.

2. The method of claim 1, wherein said steering step includes the step of moving said beacon-receiving field-of-view along a generally-tilted path to thereby enhance its match with said beacon-station window.

3. The method of claim 1, wherein said configuring step includes the step of arranging said beacon-receiving field-of-view as a segment of said beacon-station window.

4. The method of claim 1, wherein said configuring step includes the step of arranging said beacon-receiving field-of-view to have an area less than ½

the area of said beacon-station window.

5. The method of claim 1, wherein said configuring step includes the step of arranging said beacon-receiving field-of-view to have an area less than {fraction (1/10)} the area of said beacon-station window.

6. The method of claim 1, wherein said configuring step includes the step of forming said beacon-receiving antenna with an array of antenna elements.

7. The method of claim 1, wherein said configuring step includes the step of forming said beacon-receiving antenna with a reflector and an associated array of antenna horns.

8. The method of claim 1, wherein said steering step includes the step of arranging successive positions of said beacon-receiving field-of-view in a tiled arrangement.

9. The method of claim 1, wherein said controlling step includes the step of supplementing said difference signal with attitude signals from a second attitude sensor.

10. The method of claim 1, wherein said controlling step includes the steps of:

determining a desired beacon station line-of-sight from ephemeris data;

determining a measured beacon station line-of-sight as the sum of said difference angle and said beacon-receiving boresight; and

pointing said beacon-receiving boresight to reduce the difference between said desired beacon station line-of-sight and said measured beacon station line-of-sight.

11. A spacecraft that enhances the accuracy of the spacecraft'"'"'s service attitude as it orbits the earth each solar day wherein an earth-based beacon station radiates a beacon signal and, relative to said spacecraft, moves along a path that defines a beacon-station window, the spacecraft comprising:

a spacecraft body;

an attitude-control system carried by said body to maintain a service attitude of said body;

at least one solar panel coupled to said body to provide electrical power to said attitude-control system;

an antenna system that forms a beacon-receiving antenna which has a beacon-receiving boresight and a beacon-receiving field-of-view that is substantially smaller than said beacon-station window wherein said beacon-receiving antenna generates a difference signal that corresponds to a difference angle between said beacon-receiving boresight and a line-of-sight from said spacecraft to said beacon station; and

a data processor in said attitude-control system that is programmed to instruct;

a) said antenna system to successively steer said beacon-receiving boresight to successive beacon-receiving attitudes, relative to said service attitude, that maintain said beacon station within said beacon-receiving field-of-view over said solar day;

b) said antenna system to receive said beacon signal with said beacon-receiving antenna; and

c) said attitude-control system to control said service attitude in response to said difference signal;

said accuracy enhanced because said beacon-receiving field-of-view is substantially smaller than said beacon-station window.

12. The spacecraft of claim 11, wherein said beacon-receiving antenna is formed by an array of antenna elements.

13. The spacecraft of claim 12, wherein said antenna elements are antenna horns and said beacon-receiving antenna further includes a reflector positioned to reflect a beacon signal to said horns.

14. The spacecraft of claim 11, wherein said antenna system also forms a payload beam and wherein said data processor is programmed to steer said payload beam to substantially match a service area on said earth over each solar day.

15. The spacecraft of claim 11, wherein said data processor is programmed to instruct said attitude-control system to:

determine a desired beacon station line-of-sight from ephemeris data;

determine a measured beacon station line-of-sight as the sum of said difference angle and said beacon-receiving boresight; and

point said beacon-receiving boresight to reduce the difference between said desired beacon station line-of-sight and said measured beacon station line-of-sight.

16. The spacecraft of claim 11, wherein said beacon-receiving field-of-view has an area less than ½

the area of said beacon-station window.