Gravity Probe B - A Sphere of Near Perfection

Now orbiting Earth, Gravity Probe B is a technological tour de force. It is on a mission to test an unproven aspect of Einstein's theory of relativity.

Engineers don't often indulge in poetic flourish when discussing the things they build. So when words like "beautiful" and "elegant" and "artful" frequently cross the lips of scientists and engineers as they talk about the design of Gravity Probe B (GP-B), one might suspect that this spacecraft is truly something special.

The probe, which launched April 20th on a mission to test an unproven aspect of Einstein's theory of relativity, is by all accounts a marvel of human ingenuity and know-how. Only recently has it even become technologically possible to build Gravity Probe B, despite the fact that the idea for the experiment has been around since the 1950s.

"If experimental science is an art, then I would look at GP-B as a Renaissance masterpiece," says Jeff Kolodziejczak, NASA's Project Scientist for GP-B at the Marshall Space Flight Center.

The beauty of GP-B's design lies in part in its ability to create, in the messy real world, a pocket of near-perfection. The goal of the experiment demands it. Researchers hope to detect a bending of spacetime around Earth so subtle that even a minute interference from some outside force or a tiny internal imperfection in the spacecraft itself would mask the effect they're hunting for.

Einstein's theory of General Relativity predicts that Earth, by rotating, twists space and time around with it, forming a mild vortex in the fabric of spacetime around our planet. Researchers call this "frame dragging." Most physicists believe the spacetime vortex is real, but no experiment to date has been sensitive enough to detect it unequivocally.

more Using the most perfect spheres humans have ever created, Gravity Probe B just might turn Einstein's theories upside-down.

Enter Gravity Probe B.

It sounds like a straightforward experiment; the trick is in actually building it. The gyroscope's axis won't drift much, only 0.042 arc seconds over a year, according to calculations. (An arc second is only 1/3600th of a degree.) To measure this angle reasonably well, GP-B must have a precision of 0.0005 arc seconds.

"Every aspect of the experiment has to be nearly perfect," Kolodziejczak says. Meeting this challenge has taken almost 40 years of effort from many bright scientists and engineers, primarily at Stanford University, NASA's Marshall Space Flight Center, and Lockheed-Martin.