Stanford's and NASA's Gravity Probe B
satellite, launched April 20, 2004, used four ultra-precise gyroscopes to measure two key aspects of gravity in Einstein's general relativity theory.
The geodetic effect, or the warping of space-time around a gravitational body is the first. Frame-dragging, or the amount a spinning object pulls space and time along for the rotation, is the second.
Both effects were determined by pointing the Gravity Probe B's instruments at the single star IM Pegasi
while the the satellite maintained a polar orbit 400 miles above Earth. Gravity Probe B's gyroscopes would keep pointing in the same direction as long as the satellite remained in orbit if Einstein had been wrong and gravity had no effects on space and time.
But, in spite of unexpected data-muddying wobbles the researchers had to clear up, the satellite's gyroscopes measured definite minute changes in spin direction while in orbit, successfully demonstrating the pull of Earth's gravity, according to the team.
In prepared remarks
, Stanford physicist and principal researcher Francis Everitt described the experiment's findings metaphorically:
"Imagine the Earth as if it were immersed in honey. As the planet rotated its axis and orbited the Sun, the honey around it would warp and swirl, and it's the same with space and time."
The confirmation of the geodetic effect and frame-dragging have far-reaching implications for all further astrophysics investigations, while the technological innovations behind the mission itself have produced many groundbreaking applications on Earth, Everitt maintains.
For example, NASA applied Gravity Probe B technologies during the Cosmic Background Explorer mission to measure the universe's background radiation, a central phenomenon of the "big bang" theory.
Perhaps of greater interest to the general public, especially to frequent travelers, the development of Gravity B Probe's precision star tracker and gyroscopes spun off major advances in Global Positioning System (GPS) and aircraft control technologies.
NASA funded Standford as its main contractor since the project's early stages in 1963, as the multidisciplinary team tested and tweaked its systems for decades, working towards integrating design, instrumentation and science, while technologies advanced enough to test Enstein's predictions about gravity were invented, piece by piece.
The mission's findings and conclusions have been published in the online journal Physical Review Letters