Press Release

NASA Successfully Launches Gravity Probe B Mission

By SpaceRef Editor
April 20, 2004
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NASA Successfully Launches Gravity Probe B Mission

The NASA space vehicle designed to test two important predictions of Albert
Einstein’s Theory of General Relativity launched today from Vandenberg Air
Force Base, Calif., aboard a Boeing Delta II expendable launch vehicle.

The spacecraft is being inserted into an almost perfect circular polar orbit
around the Earth at an altitude of 400 statute miles. “The solar arrays are
deployed, and we have received initial data that indicates all systems are
operating smoothly. We are very pleased,” said Gravity Probe B (GP-B)
program manager Rex Geveden of NASA’s Marshall Space Flight Center (MSFC),
Huntsville, Ala. “The Gravity Probe B space vehicle houses one of the most
challenging science instruments ever devised and seeks to answer some of the
most important questions about the structure of our universe,” he said.

The GP-B mission will use four ultra-precise gyroscopes to test Einstein’s
theory that space and time are distorted by the presence of massive objects.
To accomplish this, the mission will measure two factors, how space and time
are very slightly warped by the presence of the Earth, and how the Earth’s
rotation very slightly drags space-time around with it.

“This is a great moment and a great responsibility, the outcome of a unique
collaboration of physicists and engineers to develop this near-perfect
instrument to test Einstein’s theory of gravity,” said the experiment’s
principal investigator Dr. Francis Everitt of Stanford University in
Stanford, Calif. “We are very grateful for all the support we have received
at NASA and elsewhere for this exacting effort, truly a new venture in
fundamental physics.”

In-orbit checkout and calibration is scheduled to last 60 days, followed by
a 12-month science-data acquisition period and a two-month post-science
period for calibrations.

During the mission, data from GP-B will be received a minimum of twice
daily. Either Earth-based ground stations or NASA’s data relay satellites
can receive the information. Controllers will be able to communicate with
the orbiting space vehicle from the Mission Operations Center at Stanford

Data will include space vehicle and instrument performance, as well as the
very precise measurements of the gyroscopes’ spin-axis pointing. By 2005 the
GP-B mission will be complete. A one-year period is planned for scientific
analysis of the data.

MSFC manages the GP-B program. NASA’s prime contractor for the mission,
Stanford University, conceived the experiment and is responsible for the
design and integration of the science instrument, as well as for mission
operations and data analysis. Lockheed Martin, a major subcontractor,
designed, integrated and tested the space vehicle and some of its major
payload components. NASA’s Kennedy Space Center and Boeing Expendable Launch
Systems were responsible for the pre-launch preparations, countdown and
launch of the Delta II.

For information about NASA and agency missions on the Internet, visit:

For information about the GP-B mission on the Internet, visit:


SpaceRef staff editor.