Longest laser communications link

In May 2005, NASA's Messenger spacecraft successfully communicated with Earth using a laser beam, from a distance of around 24 million km (15 million miles). This experimental form of long-distance space communication is designed to allow a higher rate of data return from interplanetary space than current methods of microwave communication. The Messenger spacecraft entered orbit around Mercury in March 2011 and performed science operations until it crashed into the surface on 30 April 2015.

The laser communication between Earth and Messenger was experimental, and no actual data was exchanged. Messenger used its onboard laser altimeter, along with its detector, to look for the pulse of laser light from Earth and then reply.