When and how did space and time begin? The birth of the Universe is one of the biggest mysteries in astronomy. It has perplexed the best scientific minds for centuries. Decades before space travel was possible, astronomers dreamed of putting a telescope into orbit to try and answer these fundamental questions. It wasn't until the 1970s, when space flight had become a reality, that NASA resolved to build just such a space telescope. They named it Hubble. This was one of the most ambitious missions ever conceived. The technical challenges were enormous and it took 12 years to design and build. Travelling at seventeen thousand miles an hour, the Hubble Telescope would take pictures of the furthest reaches of space, transmitting them 400 miles back to Earth. In April 1990 the Hubble Space Telescope was launched. But just weeks later, disaster struck - the $2 billion telescope had a fatal flaw in its main mirror. This was not just a disaster for NASA; it was a national scandal. Hubble had to be saved; scientists and engineers began to search desperately for a solution to the problem. Plans for an adventurous repair mission began to take shape but it was two years before work could be carried out. It took astronauts five gruelling space-walks to carefully replace the instruments and patch up the telescope. But nobody knew if Hubble would be able to deliver on any of its original promises. Finally, the miracle happened. An unexpected avalanche of data from Hubble confirmed that the telescope was fixed. At last it began to solve the most fundamental puzzles of the Universe. Hubble has given us breathtaking images of the birth of stars; it has found black holes swallowing matter at the centre of galaxies; and last year the Hubble Telescope resolved the most fundamental question in astronomy - the age of the Universe. At last, half a century of scientific endeavour was rewarded. Horizon marks the 10th anniversary of the launch of the Hubble Space Telescope by tracing the extraordinary tale of triumph, disaster and eventual success of this unique window into the Universe.