PARCS will be used to test gravitational theory, study laser-cooled atoms in microgravity and explore ways to improve the accuracy of timekeeping on Earth.
Atoms in microgravity can be slowed to speeds significantly below those used in atomic clocks on Earth, providing a predicted 10-fold improvement in clock accuracy. (The current U.S. standard, the NIST-F1 clock, is accurate to within one second in 30 million years.) The PARCS space clock will be compared continuously to the hydrogen maser, a fundmentally different clock, to provide a test of an Einstein theory that predicts that two different kinds of clocks in the same environment will keep the same time.
To measure gravitational frequency shift, comparisons will be made between the space clock and a clock on Earth. Signals conveyed to the ground from such space clocks someday might serve as an international time standard available to anyone around the world.
PARCS is a cooperative effort involving NASA's Jet Propulsion Laboratory (JPL), NIST, Harvard-Smithsonian Center for Astrophysics, the University of Colorado at Boulder, and the University of Torino in Italy. JPL is leading the actual development of the space package.