Free-space optical communication module for small satellites
Communication bottlenecks, particularly in the downlink direction, are a common problem for many CubeSat developers. As described herein, a CubeSat module for a CubeSat comprises an optical transmitter to transmit data to a remote terminal, a receiver to acquire an optical beacon from a remote terminal, and a fine-pointing module operably and directly coupleable to a coarse-pointing module of the CubeSat. The fine-pointing module is configured to point the optical transmitter toward the remote terminal with an accuracy range that overlaps with an accuracy range of the coarse-pointing module of the CubeSat so as to establish a communications link between the CubeSat and the remote terminal over a low-Earth-orbit (LEO) distance.
1. A Cubesat module for a CubeSat, the CubeSat module comprising:
an optical transmitter to transmit data to a remote terminal;
a receiver to acquire an optical beacon from the remote terminal;
a coarse-pointing module to point the CubeSat toward the remote terminal with an attitude accuracy of within about 3°; and
a fine-pointing module, operably coupled to the coarse-pointing module, to point the optical transmitter toward the remote terminal with an accuracy of about 0.03°.
2. The Cubesat module of claim 1 , wherein the coarse-pointing module is operably coupled to the receiver and configured to point the Cubesat toward the remote terminal with an attitude accuracy of within about 1° in response to the receiver acquiring the optical beacon.
3. The Cubesat module of claim 1 , wherein the optical transmitter is configured to transmit the data to the remote terminal via a first aperture and the receiver comprises a focal plane array configured to receive the optical beacon from the remote terminal via a second aperture.
4. The Cubesat module of claim 1 , wherein the optical transmitter is configured to transmit the data to the remote terminal via a first aperture and the receiver comprises a focal plane array configured to receive the optical beacon from the remote terminal via the first aperture.
5. The Cubesat module of claim 1 , wherein the coarse-pointing module comprises at least one of a thruster, a magnetorquer, a reaction wheel, or a control moment gyroscope.
6. The Cubesat module of claim 1 , wherein the fine-pointing module comprises a fine-steering mirror.
7. The Cubesat module of claim 1 , further comprising:
a processor, operably coupled to the beacon receiver, to determine a range of the CubeSat to the remote terminal and an attitude of the CubeSat with respect to the remote terminal based on the beacon acquired at the beacon receiver.
8. A method of pointing, acquisition, and tracking by a satellite, the method comprising:
pointing an entirety of the satellite at a remote terminal with an attitude accuracy of within about 3°;
acquiring, by the satellite, an optical beacon from the remote terminal, the acquiring comprising closing a control loop, with a coarse-steering module on the satellite, around the optical beacon; and
tracking, by the satellite, the optical beacon from the remote terminal, the tracking comprising rejecting residual tracking error with a fine-steering module on the satellite.
9. The method of claim 8 , wherein the closing the control loop comprises pointing the satellite at the remote terminal with an attitude accuracy of within about 1°.
10. The method of claim 8 , wherein the rejecting residual error comprises pointing the satellite at the remote terminal with an accuracy of about ±0.03°.
11. The method of claim 8 , further comprising:
transmitting a free-space optical beam modulated with data from the satellite to the remote terminal.
12. The method of claim 11 , further comprising:
mitigating atmospheric fading so as to reduce a bit-error rate of the free-space optical beam.
13. A satellite comprising:
a receiver to receive an optical beacon from a remote terminal;
a coarse-steering module, operably coupled to the beacon, to point an entirety of the satellite at the remote terminal with an attitude accuracy of within about 3° by closing a control loop around the optical beacon; and
a fine-steering module, operably coupled to the beacon and the coarse-steering module, to reject residual tracking error associated with the control loop.
14. The satellite of claim 13 , wherein the coarse-steering module is configured to point the satellite at the remote terminal with an attitude accuracy of within about 1° upon closing the control loop.
15. The satellite of claim 13 , wherein the fine-steering module is configured to point the satellite at the remote terminal with an accuracy of about ±0.03°.
16. The satellite of claim 13 , further comprising:
an optical transmitter to transmit a free-space optical beam modulated with data from the satellite to the remote terminal.
17. The satellite of claim 16 , further comprising:
an interleaver, operably coupled to the optical transmitter, to mitigate atmospheric fading so as to reduce a bit-error rate of the free-space optical beam.
18. A satellite comprising:
a beacon receiver to acquire an optical beacon from a remote terminal;
a coarse-pointing module to point an entirety of the satellite at the optical beacon with an attitude accuracy of within 3°;
an optical transmitter to transmit a free-space optical beam modulated with data to the remote terminal;
a fine-pointing module, operably coupled to the coarse-pointing module, to point the free-space optical beam toward the remote terminal with a second accuracy that overlaps with the attitude accuracy; and
an electronics module, operably coupled to the optical transmitter, to perform interleaving to mitigate atmospheric fading so as to reduce a bit-error rate of the free-space optical beam.