NASA engineers have successfully transmitted a narrow laser beam from the ground to an Earth-orbiting satellite, and back to the ground again, to prove the viability of using lasers for communications with spacecraft both in Earth orbit and deep space.
The test was a joint effort of the Jet Propulsion Laboratory with the Japanese Ministry of Posts and Telecommunications' Communications Research Laboratory.
The demonstration, conducted during the early morning hours of November 8, consisted of transmitting a laser beam one thousandth of a degree wide through a 0.6-meter-diameter (24inch) telescope at JPL's Table Mountain Facility near Wrightwood, CA, to the Japanese Engineering Test Satellite VI (ETS VI).
The uplink laser beam was detected and tracked by the satellite, and used as a pointing reference to return a second two-thousandths degree wide laser beam back to a 1.2-meterdiameter (48-inch) telescope, also located at Table Mountain.
"This was the first space-to-ground communication by laser," said Dr. Chad Edwards, one of the JPL scientists involved in the test. "We are looking at laser for communications for both orbiting satellites and spacecraft in deep space," he said, "and the commercial market is also interested in lasers for communications between satellites in orbit."
After traveling 40,000 km (25,000 miles) from the ground station to the satellite, the laser beam at the spacecraft was only 800 meters (2,525 ft) in diameter. That is equivalent to transmitting a laser signal from Los Angeles and hitting a target in Washington, D.C., whose diameter is half the height of the Washington Monument.
The ETS VI spacecraft was launched by the National Space Development Agency of Japan (NASDA) on August 28, 1994 and contains an onboard experimental laser communications system.
Although the satellite failed to reach its intended geostationary orbit due to an engine problem, it was transferred into a three-day orbit suitable for communication experiments. Operation of the satellite, including special attitude control adjustments needed to point the laser communications experiment at Table Mountain, is performed by NASDA, while acquisition and tracking control are performed by Japan's Communications Research Laboratory.
JPL's Table Mountain facility has been the location for a number of important laser beam transmission experiments over the years, including the original transmissions to the Surveyor 7 spacecraft on the Moon in 1968 and an historic uplink laser beam transmission to the Galileo spacecraft at a distance of 6 million kilometers (3.7 million miles) in December 1992.
The November 8 achievement is part of a series of laser communications demonstrations using the ETS VI spacecraft being conducted cooperatively by the Japanese laboratory and JPL. These demonstrations are expected to last into 1996.
The demonstrations will validate the performance of the technology and assist future mission planners in evaluating the applicability of laser communications for meeting their space-to-space and space-to-ground communications needs.
Activities at the Communications Research Laboratory are sponsored by the Japanese Ministry of Posts and Telecommunications. Work at JPL is sponsored by NASA's Office of Space Communications, Washington, D.C.
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