Design of a High-Speed Space Modem for the Lunar Laser Communications Demonstration

The space terminal modem for the Lunar Laser Communications Demonstration (LLCD) provides duplex lasercom capabilities between the Earth and a satellite in lunar orbit with a 0.5-W optical transmitter delivering downlink data rates of 39-620 Mbps and an optically-preamplified direct detection receiver supporting uplink data rates of 10-19 Mbps. The modem consists of four subsystem modules: digital electronics, analog electronics, power conditioning, and electro-optics. This modular approach permits subsystems to be built and tested in parallel and provides design flexibility to address evolving requirements. Other important design considerations for the modem include the utilization of commercial-off-the-shelf (COTS) components to reduce delivery time, cost, minimization of size, weight, and power, and the ability to survive launch conditions and operate over a broad temperature range in lunar orbit.