One of Albert Einstein's grandest theories is about to be put to the test. NASA has launched a new satellite designed to probe his general theory of relativity.

Almost 100 years after Einstein began writing about relativity, NASA launched a satellite it calls Gravity Probe B from the Vandenberg Air Force Base in California on Tuesday afternoon.

One of the most precise scientific instruments ever made, the $700 million US device is headed for orbit some 640 kilometres above the Earth.

Once there, it will turn its attention to measuring a subtle effect predicted by Einstein: that massive stellar objects such as planets and stars have a warping effect on time and space. That distortion, or geodetic effect, he argued, is gravity.

The probe is also designed to test Einstein's theory that the space-time continuum is twisted and dragged by the spinning of massive objects, an effect known as "frame dragging."

According to the principal investigator on the NASA project, the effect is so miniscule that it takes unprecedented technology to measure it.

"This test of relativity is very simple in concept, but when you get down to the technology of how to do it, it's a testimony to perseverance, to say the least," Stanford professor Brad Parkinson told Reuters.

First proposed in 1959, the idea for the mission has been subject to constant cancellation and delays as a result of budget reviews.

But the time lag has also given scientists time to devise a tool that meets the experiment's stringent standards.

Ping-pong ball-sized spheres used to measure the gravitational effect are the most perfect ever made, NASA says. In turn, the spheres are housed in the quietest container ever produced, and thus protected from the effects of sound waves.

They must also be kept at a constant temperature of absolute zero, so that the minute stirrings of their component molecules don't skew the readings.

Once in orbit, and oriented on their gyroscopic axes to point to the "guide star" IM Pegasi, the spheres will be monitored over the course of 18 months.

Scientists hope that by the end of the experiment any change in their spin axes relative to the guide star will prove Einstein's theory.

They'll have to look carefully, though, as NASA expects the spheres to be deflected by an angle essentially equivalent to the width of a hair viewed from a distance 15 kilometres.

According to NASA, should it all work as planned, the elaborate experiment will go a long way to seeing if the tenets of Einstein's general theory add up.

If not, the U.S. space agency said in a paper, "we may be faced with the challenge of constructing a whole new theory of the universe's structure and the motion of matter."