The NASA Origins program has as one of its main goals the search for planets around nearby stars. This field came of age with the discovery first of a planet around 51 Peg by M. Mayor and almost immediately afterward the discovery of many more planets by G. Marcy. The principle instrument used to date is a high resolution spectrometer that measures the radial velocity of the star. The motion of the star is modulated by any planet orbiting that star.
A complementary technique is astrometry, where the transverse motion of the star is measured with respect to nearby "reference" stars. Several years ago, theoretical calculations of the limits of ground based astrometry due to atmospheric turbulence showed that very narrow angle astrometry with long baseline interferometers could achieve an astrometric precision that was perhaps 100 times better than what was generally accepted in the 1980's. PTI was designed to test this hypothesis.
In addition PTI is designed to test several key technologies for the Keck interferometer as well as future space based interferometers, SIM.
PTI is now maintained and operated by the Michelson Science Center. Please see the MSC PTI site for more information, including access to PTI data.