The goal of RACE is to place a rubidium atomic clock in orbit. This clock will be used to perform a series of experiments to test Einstein's Theory of Relativity, and as well will advance the state of clock science into a new frontier. The RACE clock will keep time so well that if it ran for three billion years it would lose less than 1 second! Future clocks based on the technology developed for RACE might be used to coordinate all of the world's clocks, as well as for and telecommunications, and navigation-both on Earth and in space.

What We Already Know:

RACE will build on the technology of the PARCS clock experiment that will fly two years previously, using advanced shutters similar to those developed for PARCS, and laser cooling techniques to produce ultra-cold atoms with a temperature of just one-millionth of degree above absolute zero. However, RACE will introduce several new features that will allow it to achieve its unprecedented accuracy. First it will employ rubidium atoms rather than cesium, because this largely eliminates a major source of error in laser-cooled clocks, namely a frequency shift that arises due to collisions between atoms within the clock. It will also use a novel "two clocks in one" configuration featuring two back-to-back sets of clock cavities, with a source of ultra-cold atoms between them. The RACE design allows for the reduction of several other sources of error, including those induced by vibrations of the satellite.

What We Hope to Find Out:

One of the many relativity experiments that we would like to do involves a comparison of the RACE clock with another clock, perhaps one like SUMO. The SUMO clock keeps time by measuring how long it takes for microwaves to bounce back and forth within the extremely reflective surfaces of a superconducting cavity (for more information, see SUMO experiment). If we can compare the clocks at different parts of the satellites' orbit, we can test whether the speed of microwaves (which is the same as the speed of light, since both are forms of electromagnetic waves) is the same for all parts of the orbit, regardless of their orientation or velocity. This experimental test of a relativity prediction can be performed a million times better than ever before.

How We'll Conduct Our Experiment:

Laser pulses sent by a ground station will be used to compare the time kept by a ground clock with that of the clock in orbit.

Closely related experiments:

• Additional Information: See the SUMO experiment information.
• The Principle Investigator for RACE is at Yale University.