Satellites and space probes currently communicate the Earth and with each other via radio waves. Despite the innovative solutions for higher data transfer rates and compression techniques though, NASA's capabilities will not keep pace with the needs of future instruments and human spaceflight. The solution is to augment the current radio-based systems with optical technology. Laser-based communications will increase the data rates by anywhere between 10 to 100 times. New technologies must be tested though, before trusting critical operations on them.

Experiments have already been carried out involving satellite-to-satellite communications in Earth orbit. Now however, scientists at NASA's Goddard Space Flight Center are working on a new payload called Lunar Laser Communications Demonstration (LLCD) that will extend the range of laser communications all the way up to the Moon. The unit will be hosted on the small LADEE (Lunar Atmosphere and Dust Environment Explorer) spacecraft that will be launched in 2013 to characterize the dust and gas environment of the Moon. The LLCD experiment will prove fundamental concepts of deep-space laser communications with transfer rates up to 622 Mb/s, about five times faster than the best radio-frequency based solutions.

Subsystems of the Lunar Laser Communications Demonstrator: the optical module (a), the modem (b) and the control electronics (c).

Full-scale tests have wait however for the Laser Communications Relay Demonstration (LCRD) project that was selected recently as a Technology Demonstration Mission by NASA. LCRD, to be hosted on a commercial satellite, will include two different modems: one similar to LLCD, ideal for deep-space missions with low power levels, and another with much higher data rates, up to tens of gigabit per second, for Earth-orbiting satellites including the International Space Station.

Forget the radio dishes: meet the Lunar Lasercom Ground Terminal. Four 40cm (16") telescopes receive the transmissions and four 15cm (6") telescopes send laser signals back to LADEE.

So if lasers are so superior, why haven't we transferred our comm techniques already? Well, though laser can transmit data more efficiently, it has drawbacks too: bad weather and clouds – transparent to radio waves – can distort and block optical light. Successful operations will require multiple ground stations and the ability to change satellite/transmitter attitudes frequently. Lasers also require sophisticated technology: optical telescopes instead of antennae and much more accurate pointing and tracking. Radio waves will come in handy in the future too.

The Laser Communications Relay Demonstration payload in action aboard a telecom satellite.

László Molnár

Source: NASA Lunar Science Institute

Image sources:

1.) 4.): NASA

2.) 3.): NASA / MIT