Laser communication in space

Laser communication in space refers to the use of laser communications and visible light communication in outer space.

In outer space, the communication range of free-space optical communication is currently of the order of several thousand kilometers, but has the potential to bridge interplanetary distances of millions of kilometers, using optical telescopes as beam expanders.

In November 2001 the worlds first laser data connection was achieved in space between the European Space Agency Artemis satellite providing an optical data transmission link with the CNES Earth observation satellite SPOT 4.

In November 2014 the first ever gigabit laser-based communication was achieved by ESA and called the European Data Relay System (EDRS). Now demonstrated the fully completed geostationary EDRS system supporting permanent and high data transfers for low earth orbit weather satellites and many other systems is expected to be in place in the 2016-2017 time frame.

NASA's OPALS announced a breakthrough in space-to-ground laser communication December 9, 2014, uploading 175 megabytes in 3.5 seconds (a speed of 400 megabits a second). The system is also able to re-acquire tracking after the signal is lost due to cloud cover.

In January 2013, NASA used lasers to beam an image of the Mona Lisa to the Lunar Reconnaissance Orbiter roughly 390,000 km (240,000 mi) away. To compensate for atmospheric interference, an error correction code algorithm similar to that used in CDs was implemented.

The distance records for optical communications involved detection and emission of laser light by space probes. A two-way distance record for communication was set by the Mercury laser altimeter instrument aboard the MESSENGER spacecraft. This diode-pumped infrared neodymium laser, designed as a laser altimeter for a Mercury orbit mission, was able to communicate across a distance of 24 million km (15 million miles), as the craft neared Earth on a fly-by in May, 2005. The previous record had been set with a one-way detection of laser light from Earth, by the Galileo probe, as two ground-based lasers were seen from 6 million km by the out-bound probe, in 1992.

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