For all of their advanced technologies, modern satellites still rely on low-bandwidth radio transmitters to communicate with ground control. But they could soon be upgraded to beyond broadband speeds once NASA's new laser-based communication system prototype gets off the ground.
The comm system, dubbed the Lunar Lasercom Space Terminal (LLST), is the result of the Lunar Laser Communication Demonstration (LLCD) program, a joint venture by NASA's Goddard Space Flight Centre and MIT Lincoln Labs. It's composed of three parts: the Optical Module, a 10-cm telescope mounted on a two-axis gimbal that helps aim the laser beam towards one of three ground terminals in New Mexico, California, and Spain; the Modem Module, which forms the laser, encodes and transmits data; and the Controller Electronics, which handles telemetry processing and overall system command. In all, the system weighs in at about 30 kg. To survive the rigours of space, the LLST has been integrated into another NASA project, the Lunar Atmosphere and Dust Environment Explorer (LADEE) — an orbiter being launched later this year aboard a Minotaur V rocket from the Wallops Flight Facility in Wallops Island in the US to gather information on the lunar atmosphere.
The LLST, if successful, will extend the range of space-based laser communication to a staggering 400,000 kilometres (238,900 miles) — ten times the distance of any previous system. And with transfer rates approaching 622 Mbps downstream and 20 Mbps up, it will provide six times the bandwidth of even the most powerful radio-based comm systems. Perhaps most impressive, as the LLST is continuously firing syncopated laser beams over that huge distance while speeding along its orbital trajectory, it will still be able to make targeting adjustments with sub-centimetre accuracy. [NASA 1, 2, 3 - IEEE - Image: NASA]