Laser Ranging at Interplanetary Distances

In May 2005, timed observations of short laser pulses of light between the Mercury Laser Altimeter (MLA) instrument aboard the MESSENGER spacecraft, and the Goddard Geophysical Astronomical Observatory (GGAO) measured the two-way range time-of-flight with sub-nanosecond precision. A one-way optical experiment was conducted a few months later from GGAO to the Mars Orbiter Laser Altimeter (MOLA) aboard the Mars Global Surveyor (MGS) spacecraft at a distance of 81 Gm (0.54 AU). These experiments demonstrated the possibility of interplanetary communication and precise ranging using modest power