Session
Advanced Technologies 2
Location
Salt Palace Convention Center, Salt Lake City, UT
Abstract
The CubeSat radio frequency (RF) spectrum licensing step has always been long and therefore stressful to developers. With more satellites entering orbit, spectral congestion in the available RF frequency bands has become a problem. An optical-only solution eliminates this problem and provides a path for a lower power and higher throughput data link. The risk of a weather outage drives a solution that requires enough geographically diverse optical ground locations that a clear line-of-sight is always available. The Aerospace Corporation, with funding from NASA, has developed a CubeSat light emitting diode (LED) transmitter and an inexpensive commercial portable optical telescope to demonstrate an efficient, low-cost solution for low-data rate optical space-to-ground links. An LED was chosen over a laser because it is simpler, has a lower cost, has fewer safety considerations, and is more robust. It has a significantly wider beamwidth than a laser, which makes the link extremely tolerant of satellite pointing errors, but it will still deliver data rates equivalent to S-band radios.
In the smallest configuration, the LED transmitter developed weighs 86 grams, has a 70 cm diameter footprint, and a height of 2.3 cm. It has two independent LED channels, both at 617 nm. The first channel is a beacon with a modulation rate of 100 bps to 10 Kbps and a beamwidth of 120 degrees. The second channel is a communication beam with a data rate of 0.1 Mbps to 1 Mbps and a beamwidth of 2.5 degrees. The data rate is varied with a satellite command and is selected by the link budget for a communication event. The optical ground terminal (OGT) is assembled from commercial amateur telescope components that include a 28 cm diameter F/2.2 telescope, a motorized mount, and a portable tripod. The portable OGT used a two-line element (TLE) to open-loop track the ISS to demonstrate its stability and commercial software for this purpose. Two configurations of the LED transmitter were environmentally tested to TRL 6 and delivered to NASA’s R5 CubeSat program.
Document Type
Event
CubeSat LED Transmitter for Optical Communication Downlink
Salt Palace Convention Center, Salt Lake City, UT
The CubeSat radio frequency (RF) spectrum licensing step has always been long and therefore stressful to developers. With more satellites entering orbit, spectral congestion in the available RF frequency bands has become a problem. An optical-only solution eliminates this problem and provides a path for a lower power and higher throughput data link. The risk of a weather outage drives a solution that requires enough geographically diverse optical ground locations that a clear line-of-sight is always available. The Aerospace Corporation, with funding from NASA, has developed a CubeSat light emitting diode (LED) transmitter and an inexpensive commercial portable optical telescope to demonstrate an efficient, low-cost solution for low-data rate optical space-to-ground links. An LED was chosen over a laser because it is simpler, has a lower cost, has fewer safety considerations, and is more robust. It has a significantly wider beamwidth than a laser, which makes the link extremely tolerant of satellite pointing errors, but it will still deliver data rates equivalent to S-band radios.
In the smallest configuration, the LED transmitter developed weighs 86 grams, has a 70 cm diameter footprint, and a height of 2.3 cm. It has two independent LED channels, both at 617 nm. The first channel is a beacon with a modulation rate of 100 bps to 10 Kbps and a beamwidth of 120 degrees. The second channel is a communication beam with a data rate of 0.1 Mbps to 1 Mbps and a beamwidth of 2.5 degrees. The data rate is varied with a satellite command and is selected by the link budget for a communication event. The optical ground terminal (OGT) is assembled from commercial amateur telescope components that include a 28 cm diameter F/2.2 telescope, a motorized mount, and a portable tripod. The portable OGT used a two-line element (TLE) to open-loop track the ISS to demonstrate its stability and commercial software for this purpose. Two configurations of the LED transmitter were environmentally tested to TRL 6 and delivered to NASA’s R5 CubeSat program.
