Optical communications downlink from a 1.5U cubesat: OCSD program (Conference Presentation)

In this presentation, we discuss the first demonstration of a lasercom downlink from a LEO 1.5U CubeSat to our optical ground station at The Aerospace Corporation in El Segundo, CA. Two vehicles, AC7-B&C, were built under NASA’s Optical Communications and Sensors Demonstration (OCSD) which is a flight validation mission to test commercial-off-the-shelf components and subsystems that will enable new communications and proximity operations capabilities for CubeSats and other small spacecraft. As designed, the 1.5 U CubeSats weigh 2.3 kg and consume ~2 W during most of the mission life. During lasercom engagements, ~3 minutes, the spacecraft consumes an additional 10-20 W power depending on the set point of the laser transmitter, which yields 2-4 W at 1.06 m. The transmitter consists of a directly modulated laser diode followed by a Yb fiber amplifier and exhibits an overall wall-plug efficiency ~20%. The AC-7B&C vehicles were launched in November 2017 and placed in a 450-km circular orbit. Following on-orbit checkouts and preliminary pointing calibration utilizing on-board star trackers, we have demonstrated (at the time of this submission) first time communications downlinks up to 100 Mbps from the 7B vehicle using open loop pointing (beaconless) to our ground terminal, which is near sea level. The preliminary link experiments at 50 and 100 Mbps (OOK/PRBS23) using the AC-7B CubeSat were recorded at 100 ms intervals. At 50 Mbps, error rates near 1E-6 were observed with numerous error free intervals. At 100 Mbps we observed BERs approaching 1E-6. At the time of these collects, however, the B vehicle was still exercising a scan pattern since the final alignment had not been completed. Thus, the optical link was not continuous over the entire pass. Link budget estimates indicate that lower BERs should be achievable and we will continue to assess the link performance as the system is optimized.