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Gravitational Relativistic Physics (GRP)

Gravitational and Relativistic Physics (GRP)

PRESENT: Ongoing Research
    FUTURE: Gravity Probe B Seperator Dot AMS Seperator Dot STEP Seperator Dot LISA Seperator Dot SUMO
    PAST: Gravity Probe A Seperator Dot Viking Seperator Dot Lunar Laser Ranging Seperator Dot LAGEOS I & II

Launch and Duration:
LAGEOS-1: 1968 - 1977
LAGEOS-2: 1988 - Present
LAGEOS-3: Proposed


LAGEOS missions place into Earth orbit large, dense satellites, shaped like giant golf balls and covered by reflectors. These serve as targets for laser ranging and thereby provide an orbiting benchmark for geodynamical studies of the Earth. The high density of these satellites makes them resistant to outside forces, so their orbits are stable enough to constitute the most precise position references ever created.

Measurements are made by transmitting pulsed laser beams from Earth ground stations to the satellites. The laser beams then return to Earth after hitting the reflective surfaces. The travel times are precisely measured, permitting ground stations in different parts of the Earth to measure separations between the satellites to better than one inch in several thousand miles.

The LAGEOS mission has following key scientific goals:

  • Determine our planet's shape
  • Determine tectonic plate movements associated with continental drift
  • Further prove Einstein's General Theory of Relativity

It is the last goal that is the fundamental physics goal. With two or more LAGEOS satelllites in orbit, the prediction of Einstein's General Theory of Relativity that the spin of the Earth will drag space around with it may be tested by looking for common motion of satellites in different orbits. This is referred to as the gravitational magnetic effect.

LAGEOS 1 was launched in 1976. It was the first spacecraft dedicated exclusively to high-precision laser ranging and provided the first opportunity to acquire laser-ranging data that were affected by errors originating in the satellite orbit or satellite array.

LAGEOS-2, based on the LAGEOS-1 design, was built by the Italian Space Agency and launched in 1992. Although the orbit of LAGEOS-2 was not ideal for the purpose of testing General Relativity, the predicted dragging of space has now been observed.

LAGEOS-3 is a proposed multinational program to place a LAGEOS satellite in the ideal orbit for testing General Relativity, allowing refinement in the measurement of the gravitational magnetic dipole moment of the Earth.

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