Earth's atmosphere is like looking through a foggy window. It blurs light from distant stars. On April 24, 1990, the Space Shuttle Discovery carried the Hubble Space Telescope into orbit 340 miles above Earth. Up there, Hubble has a perfectly clear view of the universe. But Hubble had a rocky start. Its main mirror had a tiny flaw, about one-fiftieth the width of a human hair. Every image came back blurry. Scientists were embarrassed. The telescope that cost $1.5 billion was not working right. In 1993, astronauts flew up and installed a set of corrective lenses, like giving Hubble a pair of glasses. The fix worked perfectly. Since then, Hubble has captured some of the most stunning images in science history. It photographed galaxies billions of light-years away. It helped scientists calculate the age of the universe at about 13.8 billion years. Hubble also discovered that the universe is expanding faster than anyone expected.