LAGEOS II

Description

LAGEOS II (LAser GEOdetic Satellite) was a very dense (high mass-to-area ratio) laser retroreflector satellite that provided a permanent reference point in a very stable orbit for precision Earth dynamics measurements such as crustal motions, regional strains, fault motions, and polar motion. The satellite also provided a reference point for measurement of Earth rotation variations, solid earth tides, and other kinematic and dynamic parameters associated with earthquake assessment and alleviation. LAGEOS II, launched from the Shuttle STS 52, was a joint project between NASA and the Italian Space Agency (ASI). LAGEOS II was a passive satellite consisting of 426 reflectors designed to return a laser beam to the originating station. Of the 426 reflectors (called ``cube corner retroreflectors''), 422 were made of fused silica and four of germanium. Each reflector was 3.8 cm in diameter, and had a flat, circular front face with three faces in the back that formed a solid right angle. The satellite was only 60 cm in diameter and weighed only 405 Kg. Its compact and dense design was to insure the orbit was as stable as possible. In conjunction with appropriate laser-tracking systems (about 16 mobile and 10 fixed laser-ranging facilities), LAGEOS II permitted extreme precision ranging measurements for both geometric mode (multilateration) and orbital dynamic mode determinations of positions of points on the Earth. The high-accuracy range measurements from LAGEOS II's reference point were used to accomplish many extreme precision earth-dynamics measurements required by the earthquake hazard assessment and alleviation objectives of the Crustal Dynamics Project (CDP). The performance of LAGEOS II in orbit was limited only by degradation of the retroreflectors, so many decades of useful life can be expected. LAGEOS II was carried into its parking orbit by the Italian Research Interim Stage (IRIS) solid-fueled booster from the Shuttle payload bay. The apogee kick motor (AKM), aboard LAGEOS II, placed the satellite in a circular orbit. The IRIS system consisted of the IRIS Spinning Stage (ISS) and the Airborne Support Equipment (ASE). The ISS was a spin-stabilizing expendable stage that lifted LAGEOS II to its parking orbit. The ASE contained reusable structures and electrical equipment that controlled the payload until deployment and returned with the Shuttle. The IRIS provided power while in the Shuttle payload bay while six batteries from the AKM provided power during orbit insertion. The power supply was carried in the LAGEOS Apogee Stage (LAS), which contained all of the satellite's subsystems. LAGEOS II was identical to LAGEOS I.