Twenty-four hours after a previous launch attempt was stopped with just three minutes to go, NASA successfully sent its Gravity Probe B mission into space. The satellite was deployed from California¿s Vandenberg Air Force Base at 12:57 p.m. (EDT) on Tuesday and will orbit Earth every 97.5 minutes at a height of 640 kilometers directly over the poles. "Gravity Probe B has the potential to uncover fundamental properties of the invisible universe, a universe which seems very bizarre and alien to our everyday perceptions yet one that Einstein tried to show us almost a century ago," says Anne Kinney, director of the Astronomy and Physics Division in NASA¿s Office of Space Science.

The $700-million spacecraft is designed to test two predictions of Einstein¿s general theory of relativity, which he proposed in 1916. GP-B contains ultraprecise gyroscopes made up of nearly perfect spheres of fused quartz. The four ping-pong-size balls sit in a housing chamber chilled to near absolute zero to minimize interference from both their molecular structure and outside sound waves. After about 60 days of calibration, the spacecraft will collect data for more than a year, sending information back to ground-based controllers twice a day.

GP-B will be attempting to measure the angle at which Earth is curving its surrounding spacetime, a phenomenon known as the geodetic effect. The second prediction of general relativity that GP-B is testing is known as frame dragging, which is caused by a spinning celestial body dragging spacetime with it ever so slightly as it turns. Measuring this so-called gravitomagnetic force would be a first for scientists. Both disturbances are incredibly small: investigators anticipate that the gyroscopes will drift just 6.6 arcseconds in relation to a guide star because of the geodetic effect. (An arcsecond is 1/3,600 of a degree and is equivalent to the width of a dime as seen from a distance of two kilometers.)