It is not everyday that you launch telescopes into space, so how would you feel if someone just said “Oh dear! the space telescope you launched the other day, after years of research and billions of dollars spent, is having problems with its lens”? It was really a sad moment but the scientists did not give up but sent a repair mission into space to fix the lens problem in January 1994.
The mirror in the telescope had a defect in how smoothly the surface was polished. This error was of the order of 1/50 times the width of a human hair, yet big enough to blur the vision of the telescope. This meant that the images taken by the telescope were not properly focused so it needed repair. But repairing a telescope racing in the Low Earth Orbit at nearly 17,000 mph is not the same as getting your glasses repaired from an ophthalmologist. It required 7 highly-trained astronauts to be sent in space to carry out the repair, which could be compared to putting contact lenses in your eyes to correct your imperfect vision. The repair mission was a huge success and boosted NASA's confidence in conducting complicated repairs in space. This confidence was tested to the extreme, as the shuttle, Altantis, launched in October 2008 to execute the most complicated repair mission to date. This mission was described by the astronauts as more "surgery" than repair!
Several other repair missions have been carried out since the telescope was placed in orbit to replace faulty parts. The latest one in October 2008 will most likely be the last.
