Terabyte Infrared Delivery 200Gb/sec Laser Communications System for LEO Direct-to-Earth Missions (TBIRD)

Satellites in low-Earth orbit (LEO) have on-board sensors that can generate large amounts of data to be delivered to a ground user. Direct-to-Earth delivery from LEO is challenging because of the sparse contact with a ground terminal, but the short link distances involved can enable very high data rates by exploiting the abundance of spectrum available at optical frequencies. NASA's Terabyte Infrared Delivery (TBIRD) program will demonstrate a direct-to-Earth laser communication link from a small satellite platform to a small ground terminal at burst rates up to 200 Gbps. Such a link is capable of transferring several terabytes per day to a single ground terminal. The high burst rates are achieved by leveraging off-the-shelf fiber-telecommunications transceivers for use in space applications. A 2U TBIRD payload is currently being developed for flight on a 6U NASA CubeSat.  The relatively short distance (~ 1000 km) and corresponding reduced range loss of a direct-to-Earth (DTE) LEO laser link offers an opportunity to provide extremely high bandwidth downlinks at very low cost, size, weight, and power (SWaP). Under NASA SCaN support, MIT Lincoln Laboratory is developing the TeraByte InfraRed Delivery (TBIRD) terminal [6,7] to demonstrate a 200 Gbps downlink using only 1.8U x 1U x 1U volume (1U=10 cm) and less than 2.25 kg. The two baseline 100 Gbps modems are variants of a highly-integrated COTS design that was modified to be space-qualified; current efforts are now focused on the on-board 2.0 terabyte (TB) memory and controller which must be read at similar data rates. A demonstration flight is planned on the NASA Space Technology Mission Directorate (STMD) Pathfinder 3 CubeSat in late 2020 and it is expected to demonstrate downloads of the entire 2.0 TB data buffer on a single pass. While the initial demonstration will use existing NASA optical ground stations with adaptive optics (AO), there are plans to develop low-cost optical ground stations to support such rates to be specifically co-located at mission data storage facilities or even commercial data centres to reduce the cost of ground-based fiber backhaul at such data rates.