Satellite transmit antenna ground-based pointing

1. A system comprising:

a ground station configured to:

make a comparison of a set of beacon signals in calibration beams provided by a spacecraft by determining differences between power levels of respective calibration beams, the power levels being compared to generate a raw vector error representing the differences between the power levels;

generate a pointing error estimate for the spacecraft based on the raw vector error determined with the comparison; and

provide updated beamforming coefficients to the spacecraft based on the pointing error estimate.

2. The system of claim 1 , wherein the set of calibration beams includes a first beam positioned opposite of a second beam as a first beam pair, and a third beam positioned opposite of a fourth beam as a second beam pair, and the comparison includes determining a first difference corresponding to the first beam pair, and a second difference corresponding to the second beam pair.

3. The system of claim 2 , wherein the first difference corresponds to a difference in power levels of the first beam and the second beam, and the second difference corresponds to a difference in power levels of the third beam and the fourth beam.

4. The system of claim 3 , wherein the power levels of the calibration beams are measured from a position of the ground station.

5. The system of claim 1 , wherein the set of calibration beams includes three overlapping beams, and the comparison includes comparing powers of corresponding beacons in the three overlapping beams.

6. The system of claim 1 , wherein the set of beacon signals are compared by measuring a phase of each beacon and differences in the phases are used to determine the pointing error estimate.

7. The system of claim 1 , wherein the beamforming coefficients are compressed before being sent to the spacecraft.

8. The system of claim 1 , wherein the set of calibration beams provide corresponding spread spectrum signals beneath noise floors of communication signals provided by the spacecraft.

9. The system of claim 1 , wherein the ground station is configured to determine an updated running average of raw vector errors with the raw vector error representing the differences between the power levels.

10. The system of claim 9 , wherein the ground station is configured to use the updated running average of raw vector errors to generate the pointing error estimate.

11. A communications calibration sub-system configured to measure signal powers of calibration signals received from a spacecraft, and the sub-system configured to generate a pointing error estimate representing drift of the spacecraft based on the measured signal powers of the calibration signals, and generate beamforming coefficients for the spacecraft based on the pointing error estimate to adjust amplitudes and phases of communication signals provided by the spacecraft to account for the drift of the spacecraft.

12. The sub-system of claim 11 , further configured to update a running average of the signal powers of the calibration signals and use the running average to generate the pointing error estimate.

13. The sub-system of claim 11 , wherein the beamforming coefficients are compressed before sending to the spacecraft.

14. The sub-system of claim 11 , wherein the calibration signals are spread spectrum signals beneath noise floors of the communication signals.

15. The sub-system of claim 11 , wherein the communication signals are forward user downlinks signals.

16. The sub-system of claim 11 , wherein the calibration signals includes a first signal positioned opposite of a second signal as a first signal pair, and a third signal positioned opposite of a fourth signal as a second signal pair, and the measured signal powers correspond to determining a first difference corresponding to the first signal pair, and a second difference corresponding to the second signal pair.

17. The sub-system of claim 16 , wherein the first difference corresponds to a difference in power levels of the first signal and the second signal, and the second difference corresponds to a difference in power levels of the third signal and the fourth signal.

18. The sub-system of claim 17 , further configured to generate a raw vector error representing the first difference and the second different, and the pointing error estimate is based on the raw vector error.

19. A method comprising:

receiving, by a ground station, calibration signals transmitted by a spacecraft;

determining, by the ground station, power levels of the calibration signals;

generating, by the ground station, a raw vector error corresponding to differences in the power levels of the calibration signals;

updating, by the ground station, a running average of raw vector errors with the raw vector error;

estimating, by the ground station, a pointing error of communication signals transmitted by the spacecraft based on the running average indicating an average of the differences of the power levels of the calibration signals;

generating, by the ground station, beamforming coefficients for the communication signals based on the pointing error; and

transmitting, by the ground station, the beamforming coefficients to the spacecraft.

20. The method of claim 19 , wherein the calibration signals include a first signal positioned opposite of a second signal as a first signal pair, and a third signal positioned opposite of a fourth signal as a second signal pair, and the determining the power levels includes determining a first difference in power levels corresponding to the first signal pair, and a second difference in power levels corresponding to the second signal pair.

21. The method of claim 19 , wherein the calibration signals are spread spectrum signals beneath noise floors of the communication signals.

22. The method of claim 19 , wherein the beamforming coefficients are compressed before being transmitted to the spacecraft.