World's Most Precise Gyroscopes Ready To Test Einstein Theory
The completed space vehicle during solar array installation.
(Image credit to Russ Underwood, Lockheed Martin Corporation)
Gravity Probe-B, NASA's spacecraft designed to test two important
predictions of Albert Einstein's general theory of relativity,
was successfully launched from Vandenberg Air Force Base, Calif., at
12:57 p.m. EDT, April 20, 2004.
NASA's Gravity Probe B mission, also known as GP-B, will use
four ultra-precise gyroscopes, orbiting the Earth in a unique
satellite, to experimentally test two extraordinary
predictions of Einstein's 1916 theory that space and time are
distorted by the presence of massive objects. The two effects
being tested are: The geodetic effect, the amount by which
the Earth warps local spacetime in which it resides, and the
frame-dragging effect, the amount by which the Earth drags
local spacetime around with it as it rotates.
"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," said
Dr. Anne Kinney, director of the Astronomy and Physics
Division in NASA's Office of Space Science, Washington.
"Testing the key aspects of Einstein's theory, such as GP-B
will do, will provide crucial information to science just as
it has already helped America by pushing technological
progress in developing the tools needed for these ultra-
precise measurements," she added
Artist concept depicting Gravity Probe B's
measurement of the geodetic effect (in the x-z plane) and of
the frame dragging effect (in the y-z plane).
(Credit: York University/Dr. Norbert Bartel)
Once placed in its polar orbit of 640 kilometers (400 miles)
above Earth, GP-B will circle the globe every 97.5 minutes,
crossing over both poles. In-orbit checkout and calibration
is scheduled to last 40-60 days, followed by a 13-month
science-data acquisition period and a two-month post-science
period for calibrations.
To test the general theory of relativity, GP-B will monitor
any drift in the gyroscopes' spin axis alignment in relation
to its guide star, IM Pegasi (HR 8703). Over the course of a
year, the anticipated spin axis drift for the geodetic effect
is a angle of 6.6144 arcseconds, and the
anticipated spin axis drift for the frame-dragging effect is
even smaller, only 40.9 milliarcseconds. To illustrate the
size of the angles, if you climbed a slope of 40.9
milliarcseconds for 100 miles, you would rise only one inch
During the mission, data from GP-B will be received a minimum
of two times each day. Earth-based ground stations or NASA's
data relay satellites can receive the information.
Controllers will be able to communicate with GP-B from the
Mission Operations Center at Stanford University.
Data will include space vehicle and instrument performance,
as well as the very precise measurements of the gyroscopes'
spin-axis orientation. By 2005 the GP-B mission will be
complete, and a one-year period is planned for scientific
analysis of the data.
"Developing GP-B has been a supreme challenge requiring the
skillful integration of an extraordinary range of new
technologies," said Professor Francis Everitt of Stanford
University, and the GP-B principal investigator. "It is hard
to see how it could have been done without the kind of unique
long-term collaboration that we have had between Stanford,
Lockheed Martin, and NASA," he said. In 1962, Dr. Everitt
joined the team at Stanford that conceived the idea for GP-B.
He has been working on it ever since.