Laser Astrometric Test Of Relativity
Slava Turyshev
NASA Jet Propulsion Laboratory
turyshev@jpl.nasa.gov
Additional authors: Michael Shao, Kenneth L. Nordtvedt, Jr. Thomas W. Murphy, Jr.
The Laser Astrometric Test of Relativity (LATOR) mission is a 21st century Michelson-Morley experiment designed to search for the presence of a cosmologically evolved scalar field in the solar system. This new fundamental physics experiment is designed to test relativistic gravity at an accuracy never achieved before – probing for the first time second-order effects in the gravitational field strength. As such, LATOR will improve the current accuracy in the tests of general relativity by a factor of 3,000 reaching an accuracy of one part in 10^8 in measuring space-time curvature (as parameterized by the Eddington parameter gamma). The LATOR mission uses laser interferometry between two laser sources placed on separate small spacecraft, whose lines of sight pass close by the Sun, to measure accurately the deflection of light in the solar gravity field. The key element of the experimental design is a redundant geometry optical truss provided by a long-baseline (~100m) Michelson stellar optical interferometer. The interferometer is used for measuring the angles between the two spacecraft and for orbit determination purposes. The interferometer will be placed on the International Space Station (ISS). The three arms of the spacecraft-ISS-spacecraft triangle are monitored with laser metrology. From the three length measurements one can calculate the Euclidean value for any of the angles in this triangle. The direct interferometric angular measurement and resulting geometric redundancy enables LATOR to measure the departure from Euclidean geometry caused by the solar gravity field to a very high accuracy. The 0.1 picoradian precision will allow us to test the relativistic departure from Euclidean geometry to one part in 10^8. The two LATOR spacecraft will be placed in a 3:2 Earth resonant orbit that provides three observing sessions during the initial 21 months after the launch with the first session starting in 15 months. The spacecraft will use the standard Spectrum Astro SA200S bus and will be launched on a Delta II launch vehicle. The nominal mission life time is 22 months with a minimal life of 16 months. The work described here was carried out at the Jet Propulsion Laboratory, California Institute of Technology under a contract with the National Aeronautics and Space Administration
