Link architecture and spacecraft terminal for high rate direct to earth optical communications

Patent metadata

Field	Value
Publication number	US-9998221-B2
Application number	US-201614991377-A
Country	US
Kind code	B2
Filing date	Jan 8, 2016
Priority date	Jan 9, 2015
Publication date	Jun 12, 2018
Grant date	Jun 12, 2018

Abstract

A satellite in low-Earth orbit (LEO) or medium-Earth orbit (MEO) with a modern image sensor and/or other remote sensing device can collect data at rates of 10 Mbps or higher. At these collection rates, the satellite can accumulate more data between its passes over a given ground station than it can transmit to the ground station in a single pass using radio-frequency (RF) communications. Put differently, the sensors fill the spacecraft's memory faster than the spacecraft can empty it. Fortunately, free-space optical communications signals can carry far more data than RF communications signals. In particular, a spacecraft can transmit over 1 Tb of data in a single pass using burst wavelength-division multiplexed (WDM) optical signals. Each burst may last seconds to minutes, and can include tens to hundreds of WDM channels, each of which is modulated at 10 Gbps or more.

First claim

The invention claimed is:

1. An apparatus for transmitting information from a spacecraft to an optical receiver via a free-space optical communications channel, the apparatus comprising:
a buffer to store data acquired by the spacecraft, the buffer receiving the data at a first rate;
a plurality of optical transceivers, operably coupled to the buffer, to generate a plurality of optical signals from the data stored in the buffer;
a wavelength-division multiplexer, in optical communication with the plurality of optical transceivers, to form a wavelength-division multiplexed (WDM) optical signal modulated at a second rate greater than the first rate from the plurality of optical signals;
a telescope, in optical communication with the wavelength-division multiplexer, to transmit the WDM optical signal from the spacecraft to the optical receiver via the free-space optical communications channel;
a sensor to detect a signal from the optical receiver; and
a processor, operably coupled to the sensor, the buffer, and the plurality of optical transceivers, to cause the plurality of optical transceivers to generate the plurality of optical signals in response to the signal from the optical receiver.

2. The apparatus of claim 1 , wherein at least one optical transceiver in the plurality of optical transceivers is configured to generate an optical signal modulated at a data rate of at least 100 Gigabits per second.

3. The apparatus of claim 1 , wherein at least one optical transceiver in the plurality of optical transceivers is configured to generate a coherently modulated optical signal.

4. The apparatus of claim 1 , wherein the telescope is configured to emit a beam with a divergence angle from 15 microradians (μrad) to 1,500 μrad.

5. The apparatus of claim 1 , wherein the telescope has an aperture with a diameter from 0.1 centimeters (cm) to 10 cm.

6. The apparatus of claim 1 , wherein:
the sensor is configured to acquire a beacon from the optical receiver; and
the processor is configured to determine a change in a pointing angle of the telescope based on the beacon acquired by the sensor.

7. The apparatus of claim 1 , wherein the signal from the optical receiver comprises a repeat.

8. The apparatus of claim 1 , further comprising:
an encoder, operably coupled to the buffer, to encode data stored in the buffer with a forward error correction code.

9. The apparatus of claim 1 , further comprising:
an optical amplifier, in optical communication with the wavelength-division multiplexer, to amplify the WDM optical signal to a power level of at least 100 milliwatts.

10. The apparatus of claim 1 , wherein the buffer has an output speed matched to an input speed of the plurality of optical transceivers.

11. The apparatus of claim 1 , wherein the data stored in the buffer is prioritized for transmission according to a data delivery protocol.

12. The apparatus of claim 1 , wherein the second rate is greater than 40 Gigabits per second.

13. A method of transmitting information from a spacecraft to an optical receiver via a free-space optical communications channel, the method comprising:
receiving a signal from the optical receiver;
reading, at the spacecraft, data encoded with a forward error correction code from a buffer at a first rate;
generating, at the spacecraft, a plurality of optical signals from the data read from the buffer in response to the signal;
forming, at the spacecraft, a wavelength-division multiplexed (WDM) optical signal modulated at a modulation rate greater than the first rate from the plurality of optical signals; and
transmitting the WDM optical signal from the spacecraft to the optical receiver via the free-space optical communications channel.

14. The method of claim 13 , wherein generating the plurality of optical signals comprises generating at least one optical signal at a data rate of at least 40 Gbps.

15. The method of claim 13 , wherein generating the plurality of optical signals comprises coherently modulating at least one optical carrier.

16. The method of claim 3 , wherein the signal from the optical receiver comprises a repeat request.

17. The method of claim 13 , wherein transmitting the WDM optical signal comprises amplifying the WDM optical signal to a power level of at least 100 milliwatts.

18. The method of claim 13 , wherein transmitting the WDM optical signal comprises forming a beam with a divergence angle from 15 microradians (μrad) to 1,500 μrad.

19. The method of claim 13 , wherein transmitting the WDM optical signal comprises emitting a beam via a telescope having an aperture with a diameter from 0.1 centimeters (cm) to 10 cm.

20. The method of claim 13 , further comprising:
acquiring a beacon from the optical receiver.

21. The method of claim 13 , further comprising:
storing the data in the buffer at rate less than a product of the modulation rate and a duration between transmissions from the spacecraft.

22. An apparatus for transmitting information from a spacecraft to an optical receiver via a free-space optical communications channel, the apparatus comprising:
a sensor to detect a signal from the optical receiver;
a buffer to store data encoded with a forward error correction code;
a processor, operably coupled to the buffer, to read the data stored in the buffer at a rate of at least 40 Gigabits per second (Gbps);
a plurality of optical transceivers, operably coupled to the processor, to coherently modulate a plurality of optical signals with the data in response to the signal from the optical receiver;
a wavelength-division multiplexer, in optical communication with the plurality of optical transceivers, to form a wavelength-division multiplexed (WDM) optical signal from the plurality of optical signals; and
a telescope, in optical communication with the wavelength-division multiplexer, to transmit the WDM optical signal from the spacecraft to the optical receiver via the free-space optical communications channel.

Assignees

• Boroson Don M
• Robinson Bryan S
• Reid Bryan M
• Burnside Jamie W
• Khatri Farzana I
• Constantine Steven
• Massachusetts Inst Technology

Inventors

• Boroson Don M
• Robinson Bryan S
• Reid Bryan M
• Burnside Jamie W
• Khatri Farzana I
• Constantine Steven

Classifications

• H04B10/1121

  One-way transmission · CPC title

• H04B10/118 Primary

  specially adapted for satellite communication · CPC title

• H04B10/40

  Transceivers · CPC title

• H04B10/61

  Coherent receivers · CPC title

• H04B7/18513 Primary

  Transmission in a satellite or space-based system · CPC title