Almost 90 years after Albert Einstein published his theory that space and time are "curved", it is about to be put to a $US850 million ($A1.1 billion) test.

Next Sunday week, if all goes well, a NASA satellite fitted with four tiny gyroscopes will be fired from Vandenberg Air Force Base, California, into a 640-kilometre- high orbit.

The size of ping-pong balls, the gyroscopes will be set rotating, aligned to a star tracked by the satellite's on-board telescope.

If Einstein's theory of relativity is right, the angle at which they spin should gradually drift over the next two years as the satellite orbits.

According to the theory, gravity does not only distort space up and down, left and right, forward and backward but can also make time run slower, so that the tick of a second on a clock may not always take exactly one second.

But Einstein's theory has only been partially verified.

"Until a theory is thoroughly tested," said Stanford University scientists, who helped develop the mission, "we cannot accept it as fact."

NASA said the satellite "will measure how space and time are warped by the presence of the Earth, and, more profoundly, how the Earth's rotation drags space-time around with it".

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$US850 million ($A1.1 billion)

I hope it works, but I think that kind of money would be better spent else where, like feeding the hungry, housing the homeless, saving endangered animals and the environment

the homeless aren't going to advance humanities understanding of existance now will they?