Interplanetary laser links?
January 5th, 2006

“A laser communication link has been made across a record 24 million kilometres (15 million miles),between the Messenger spacecraft and instruments on Earth,”New Scientist reports.”The craft and the ground station transmitted pulses back and forth to each other,and although no actual information was transmitted,the experiment shows the potential for interplanetary laser links,says David Smith of NASA’s Goddard Space Flight Center in Maryland,US.Interplanetary space probes currently communicate via microwaves,but those transmitters are not as tightly focused as laser beams.This spreading reduces microwave power received,and thus the maximum data rate.For example, NASA’s Mars Odyssey probe can send only 128,000 bits per second to Earth.Because laser beams spread much more slowly,they can deliver more power to ground-based optical receivers,allowing higher data rates.This advantage was clear as far back as 1960 when Theodore Maiman,who had just made the first laser,listed space communications as an important potential application.However,laser beams proved so narrow that space communications only worked if moving spacecraft were precisely tracked.This difficulty meant the development of practical laser links has taken decades.It was only in late 2005 that the first laser link was demonstrated between two satellites in different Earth orbits:the low-orbit Japanese Kirari satellite and the European Artemis satellite in geosynchronous orbit.”

Longest laser link bridges the gulf of space

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