Satellite positioning.

Geodetic positioning programs with the U.S. Navy Transit and GPS satellite systems and satellite laser ranging programs are described. As of 1982 the number of Doppler receivers had increased to over 16,000 units, 1000 with two-frequency geodetic apparatus. The Nova 1 satellite, launched in 1981, was a drag-free satellite, incorporating a single-axis disturbance compensation system (DISCOS) to continuously correct track aberrations due to perturbing forces acting on the satellite. One of the Transit system units, Nova 1 lowered the broadcast ephemeris prediction errors to 5-15 m rms, compared to the 5-70 m rms error for the Oscar satellite. The Navstar GPS system is in full engineering development and will lead to an 18 satellite configuration, with four in view from any point on earth. Global positioning accuracies of 10 m have been found in tests. The Lageos, Starlette, beacon Explorer-C, and Geos-3 satellites have been used in laser ranging experiments to measure polar motions by reflecting laser light from the ground off reflectors on the satellite surfaces. NASA is currently moving a transportable laser station to Easter Island to obtain an accuracy of 10 cm.