Method for thermal stabilization of a communications satellite
A method for thermally stabilizing a communication satellite in orbit around the Earth relies on the discrete rotational symmetry of the pattern of antenna beams of the satellite. Exploiting the symmetry, the orientation of the satellite is changed from time to time by rotating the satellite through a symmetry angle of the rotational symmetry. Because of the symmetry, the beam pattern is unchanged after the rotation; but, because the rotation angle is less than 360°, a different side of the satellite is exposed to sunlight. The use of different thermal radiators and thermal shields on different sides of the satellite means that the thermal budget of the satellite is different after the rotation. By judiciously applying rotations as needed, as the orbit's orientation relative to the Sun evolves in time, it is possible to achieve effective control on the thermal budget of the satellite.
1. A method for changing the thermal budget of a communication satellite in orbit around the Earth, wherein the satellite has plural communications antennas that result in a beam pattern, the beam pattern having an axis of symmetry and possessing discrete rotational symmetry around the axis of symmetry, the method comprising rotating the satellite around the axis of symmetry of the beam pattern of the satellite, wherein the satellite is rotated by a symmetry angle of the discrete rotational symmetry.
2. The method of claim 1 wherein the satellite comprises one or more thermal radiators, and
wherein rotating the satellite causes a change in the amount of radiant heat from sunlight received by the one or more thermal radiators.
3. The method of claim 1 wherein rotating the satellite occurs when the satellite is above a sparsely populated region of the Earth.
4. The method of claim 1 wherein the satellite is in a polar orbit, and wherein rotating the satellite occurs when the satellite is above a polar region.
5. The method of claim 4 wherein rotating the satellite occurs when the beta angle of the polar orbit reaches a predetermined value.
6. The method of claim 5 wherein the predetermined value is adjusted to reduce temperature variations on the satellite.
7. The method of claim 1 wherein the beams of the beam pattern are turned off while rotating the satellite.
8. The method of claim 1 wherein the axis of symmetry is a yaw axis.
9. The method of claim 1 wherein the symmetry angle is one of 90°, 180°, or 270°.
10. A method for controlling a temperature of a communication satellite in orbit around the Earth, the method comprising:
monitoring the temperature;
in response to the temperature reaching a predetermined value, rotating the satellite around an axis of symmetry of a beam pattern of the satellite;
wherein the beam pattern has discrete rotational symmetry around the axis of symmetry, and the rotation is by a symmetry angle of the discrete rotational symmetry.
11. The method of claim 10 wherein rotating the satellite occurs after a delay has elapsed subsequent to the temperature reaching the predetermined value.
12. The method of claim 11 wherein rotating the satellite occurs when the satellite is above a sparsely populated region of the Earth.
13. The method of claim 10 wherein the beams of the beam pattern are turned off while rotating the satellite.