Global Positioning System Celebrates 20th Anniversary

EL SEGUNDO, Calif. (2/16/98) -- Ancient mariners such as Magellan and Columbus relied on landmarks and celestial observations as their primary navigational methods, which could result in serious miscalculations.

But serious errors are impossible today with the use of the Navstar Global Positioning System (GPS), perhaps the greatest navigation improvement in history, now marking the 20th anniversary of its origin. It was on February 22, 1978, that the first 1,100-pound GPS satellite was launched from Vandenberg Air Force Base, Calif.

GPS currently is operated by the Air Force Space Command and originally was created for national defense use. Today, however, it provides navigational information to commercial aircraft, ships at sea, hikers, rental car customers and anyone with a GPS receiver, as well as military users. It is accurate to within a few meters of the military user's latitude and longitude, slightly more for civilian users.

In all, four GPS satellites were launched in 1978 from Atlas-F booster rockets. Additional satellites were added in the 1980s and 1990s, launched from Cape Canaveral, Fla., by Delta II rockets to form the constellation of 24 that currently blankets the planet with precise, three-dimensional, all-weather, real-time navigation information any time of day or night, anywhere on Earth.

GPS was created by a special team of the United States Air Force, United States Naval Research Laboratory, The Aerospace Corporation, Rockwell International Corporation (now Boeing) and IBM Federal Systems Company (now Lockheed Martin).

The Aerospace Corporation was an integral part of the team, assisting in creating and refining system specifications, performing and evaluating early tests to refine the system design and reviewing contractor progress.

GPS satellites travel in 12-hour, circular orbits 11,000 nautical miles above Earth. They occupy six orbital planes, inclined 55 degrees, with four operational satellites in each plane.

The spacecraft are positioned so that an average of six are observable nearly 100 percent of the time from any point on Earth, and each is equipped with an atomic clock, accurate to within ten-billionths of a second (or 10 nanoseconds). Additional GPS satellites are being readied for use when aging satellites require replacement.

By the year 2000, 17,000 U.S. military aircraft are expected to be equipped with GPS receivers, and more than 100,000 portable receivers will be in use by U.S. ground forces and on military vehicles. Rapid growth also is occurring in the civilian market.