United States Patent  [ii] Patent Number: 5,248,118
Cohen et al.  Date of Patent: Sep. 28, 1993
 SPACECRAFT ATTITUDE CONTROL SYSTEM WITH REACTION WHEEL BEARING PROTECTION
 Inventors: Walter J. Cohen, Hightstown; Neil E.
Goodzeit, East Windsor; Michael A.
Paluszek, Lawrenceville, all of N.J.
 Assignee: General Electric Co., East Windsor, N.J.
 Appl. No.: 882,507
 Filed: May 13,1992
 Int. CI.' B64G 1/24
 U.S. CI 244/164; 244/165;
 Field of Search 246/164, 165, 166, 167,
 References Cited
U.S. PATENT DOCUMENTS
4,010,921 3/1977 Pistiner et al 244/166
5,020,745 6/1991 Stetson, Jr 244/165
5,058.835 10/1991 Goodzeit et al 244/165
5,123,617 6/1992 Linder 244/166
Primary Examiner—Galen Barefoot
Attorney, Agent, or Firm—W. H. Meise; C. A. Berard; S.
A spacecraft includes an attitude control system using one or more reaction wheels, the speed of which from time to time lie near and pass through zero angular velocity. When operated for extended periods of time at low speeds, the lubrication films are not distributed uniformly on the wheel bearings, leading to reduced lifetime. Reliability is maintained by a threshold comparator coupled to compare wheel speed with a lower limit value, for operating a torquer associated with the spacecraft body when the wheel speed drops below the lower limit, in a manner which tends to raise the wheel speed. In a particular embodiment of the invention, the lower limit is integrated with a wheel overspeed unloading.
13 Claims, 4 Drawing Sheets