The expectation was that this enormous satellite, the size of a double- decker bus, would reach out to see the edge of the universe and even find planets, capable of supporting life, circling other stars. Costing $1.5bn, and orbiting 600 kilometres above the Earth, it was clear of the distorting murky atmosphere through which ground-based telescopes peer.
But these expectations were dashed when it was realised that it was out of focus. It could barely take decent pictures of the planets in our own solar system.
Subsequently, it emerged that military secrecy had restricted Nasa's ability to oversee the critical work of constructing the primary light- gathering mirror. The manufacturer, Perkin-Elmer, had been given the contract because it had experience in making components for military spy satellites. But because of its military connections, the plant was off-limits to all but a few Nasa staff. In the end, the curvature of the mirror, 94.5in across, was wrong by about one-fiftieth of the diameter of a human hair.
On 2 December 1993, Nasa launched a rescue mission, in effect to fit the instrument with a pair of spectacles. It was completely successful. Hubble was able to "see" with the precision its designers had originally intended and the scientific results started to flow.
Among the discoveries is the detection of primordial helium, the second lightest of all the chemical elements, created at least 13 billion years ago, close to the birth of the universe.
But some of the results have puzzled rather than clarified astronomers' understanding of the early days of the universe. Some suggest it could be half the age that had been thought - eight billion years rather than the conventional value of 15 to 16 billion.Reuse content