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The Field of Optical Communications (view source)
Revision as of 03:06, 3 May 2016
, 03:06, 3 May 2016→OCSD-2 (A/B): Removed reference to sat to sat communications
What follows is a high level overview of notable milestones in the development of space-based optical communications.
== MIT Lincoln Labs LLCD/LADEE ==
Nasa's Lunar Laser Communication Demonstration (LLCD) was a rousing success that demonstrated duplex laser communications at previously unheard-of speeds between lunar orbit and ground stations on Earth (These download speeds were at times faster than the ground lines on Earth when distributing downloaded scientific data). The LLCD's space component was attached as an optical payload to the larger scientific satellite LADEE.
The LLCD project operated on the 1.5-micron band with maximum downlink speeds of 622Mbs. The project featured a 1kHz squarewave acquisition signal and could measure its round-trip Time of Flight (TOF) to within 200 psec.
==MIT Lincoln Labs LLCD/LADEE==
All systems operated at or above expected levels, and it was demonstrated that an optical link could be established without human-in-the-loop interaction. Several demonstrations of the system were executed, and are described below.
[[File:LADEE w flare - cropped.jpg |475px|right]]
==== High Speed Telemetry ====
The typical 50kbps telecommunications via RF were replaced during a lock-on window by a 2.7Mbps optical telemetry transmission. This information was then plotted graphically in real time against the slower RF data.
==== High Volume Download ====
During one experiment, test data from another LADEE experiment was transmitted via the optical link. The 1GB of data was transmitted in under five minutes (error-free). The same amount of data would have consumed every RF window for three days to transmit.
The information was then relayed to scientist on the ground using existing infrastructure that was often slower than the optical link itself. This process was executed several times at the request of LADEE scientists and gave them an unprecedented amount of data to process.
==== Webcam Livestream ====
An HD webcam was setup in the operations center and broadcast its information up and around the moon before coming back. Viewers would see their movements about seven seconds delayed on the big screen. "Needless to say, this was a very popular feature of the demonstration" [http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=1841892].
==== Ground Station Handover ====
During testing with the LLGT, cloud cover became stronger than anticipated. With very little time delay, the link was turned off, locked onto the LLOT (one of the back-up stations), and then reactivated perfectly. This was the first demonstration of a control "Handover" and showed the systems robustness.
==== Open-Loop Optical Lock On ====
After lock on had become routine, LADEE was loaded with predefined instructions to turn on the LLST system. Then when LADEE next came into view, without any RF communication, the LLST system was activated and locked on to the ground.The entire transmission window was then operated entirely upon optical commands, and RF was never used.
=== The Ground and Space terminals (LLGT and LLST) ===
The Lunar Lasercom Space Terminal (LLST) optics consisted of a 10cm reflective telescope capable of ~15uRad beam width. It was connected via fiber to the modem where transmissions up to .5W were processed. This module was used for uplinks as well. LADEE was the host satellite to this experiment, and LLST's optics were gimballed on a side-mount of the satellite.
The ground stations for the LLCD project consisted of the primary Lunar Lasercom Ground Terminal (LLGT), and the two backup terminals, the Lunar Lasercom OCTL Terminal (LLOT) and the Lunar Lasercom Optical Ground System (LLOGS).
==== LLGT ====
The LLGT contained four 15cm 10W transmit telescopes and four 40cm Downlink telescopes. Its downlink telescopes were linked by fiber to an array of superconducting nanowire single photon detectors. All eight of these telescopes were then contained within an environmentally controlled enclosure. The entire LLGT device was transportable, and was thoroughly tested near MIT Lincoln Labs before being transported to White Sands where it stayed for the tests.
==== LLOT ====
The LLOT is a 60W transmitter with six uplink apertures. The downlink receiver utilizes a super conducting nanowire photon counting array and exhibits 78Mbits downlink with tracking and uplink acquisition abilities.
==== LLOGS ====
Based upon the earlier OGS, the LLOGS was LLCD's third backup solution. Created with a 1 meter downlink telescope, with 3 outrigger telescopes for uplinking and acquisition, this 60W transmitter and receiver is most similar to SSI's optical communications modules. It uses hardware post processing to downlink at 39Mbs, and a photo-multiplier tube array as its primary sensor.
==JPL 1U Optical Comms Terminal==
==JPL 1U Optical Comms Terminal==
{{:JPL 1U Optical Communications Terminal}}
==NASA Small Satellites Technology Project==
==NASA Small Satellites Technology Project==
====OCSD-2 (A/B)====
====OCSD-2 (A/B)====
OCSD-2 is scheduled for launch during 2016 aboard a currently unidentified Falcon 9 launch from Vandenberg AFB. The first such launch is currently scheduled for July. OCSD-2 contains the remaining two of the three planned satellites, which will launch as a single 3U unit and separate into 2 independent satellites. The OCSD-2 A and B payloads will attempt satellite-earth and satellite-satellite communications at speeds in excess of 500 Mbit/s, with the primary purpose of demonstrating technologies for satellites operating in proximity to each other. It is unclear what systems will differ between the OCSD-1 and OCSD-2 payloads.
OCSD-2 is scheduled for launch during 2016 aboard a currently unidentified Falcon 9 launch from Vandenberg AFB. The first such launch is currently scheduled for July. OCSD-2 contains the remaining two of the three planned satellites, which will launch as a single 3U unit and separate into 2 independent satellites. The OCSD-2 A and B payloads will attempt satellite-earth communications at speeds in excess of 500 Mbit/s, with the primary purpose of demonstrating technologies for satellites operating in proximity to each other. It is unclear what systems will differ between the OCSD-1 and OCSD-2 payloads.
===Space Optical Communications Using Laser Beam Amplification (SOCLBA)===
===Space Optical Communications Using Laser Beam Amplification (SOCLBA)===