Scientists at the American National Aeronautics and Space Administration (Nasa) have found that gyroscopes on the telescope, which normally provide its highly sensitive sense of balance, are faulty.
Only three of the Hubble's six gyros are working correctly and, if one more should fail, the instrument's flight computer would shut down the telescope, leading to the first important fault since the discovery of a defective mirror soon after it was launched in 1990.
Nasa is trying to reorganise the launch schedule of its space shuttles to repair the Hubble. Losing one of its star performers would be a public relations disaster.
Dan Goldin, Nasa's administrator, has told the United States Congress that a "rapid-response" mission to repair the Hubble in October is being considered.
"What we're concerned about is losing the scientific data stream for a year or so," Dr Goldin said. A scheduled repair mission due to be launched next year could be brought forward to replace the defective gyros, he said.
John Campbell, associate director for Hubble at Nasa's Goddard Space Flight Center in Greenbelt, Maryland, said: "It wasn't very smart to wait for more than a year and we began working then with the shuttle folks to see if there wasn't a way to get there earlier."
Since the Hubble was launched it has provided breathtaking images of distant cosmological phenomena, such as the birth and death of stars, exploding nebulae, and pictures of the oldest galaxies created soon after the Big Bang.
Because the telescope orbits above the Earth's atmosphere, it can take clearer images of objects that can barely be seen even with highest- powered terrestrial telescopes.
However, the clarity depends on the telescope being able to keep its position with incredible accuracy, equivalent to holding a beam of light on a coin on Earth. Repairing the six gyros will ensure the Hubble continues to be able to focus on the faintest of distant objects.