__1990: __The Hubble Space Telescope sends its first image back to Earth.

The new telescope's imaging prowess clearly exceeded that of the best ground-based telescopes, as shown in theimage above of stars in the Carina cluster. But after a few weeks, scientists began to realize something was amiss.

Hubble's images weren't as sharp as they should be. A NASA investigation discovered that the telescope's 8-foot primary mirror had been ground just a little bit too flat around the edges due to a miscalibrated measuring instrument.

Though the slightly blurry images were still good enough for scientists to see space as never before and do ground-breaking research, the mirror's aberration meant Hubble would not be able to complete some of its mission, and its images wouldn't be as spectacular as they could be.

This would have been hugely disappointing for the many scientists and engineers who had been dreaming of – and working toward – launching a telescope into space since the National Academy of Science formed a committee to study the possibility in 1966.

A heroic effort to devise a fix for the problem before the space shuttle was due to visit Hubble in 1993 was able to correct the flaw and rescue the mission. Astronauts replaced the telescope's Wide Field/Planetary Camera with the Wide Field/Planetary Camera 2, which compensated for the mirror aberration.

If the repair had not succeeded, the Hubble Space Telescope almost certainly would not have come to occupy its current place in the hearts of people across the world. It's the astonishing detail of Hubble's images that has turned people on to space for the last 17 years, as one of the telescope's most recent shots of the Carina Nebula (below) demonstrates.

The mirror issue was not the only setback the Hubble mission has faced over the years. The telescope was originally scheduled to launch in 1983, but though the mirror was finished in time, the entire optical apparatus didn't come together until 1984.

The entire spacecraft was ready to go by 1985, and slotted for launch in October 1986, but the Challenger disaster in January of that year halted shuttle flights for two years. Hubble finally made its way into space aboard Discovery on April 24, 1990.

Once the mirror mistake had been found and corrected, the space telescope performed beautifully, receiving upgrades and repairs from shuttle servicing missions in 1997, 1999 and 2002. Hubble has enthralled scientists and the public alike with stunning images and unparalleled data about the universe.

In more recent years, Hubble's future was again thrown into question by a shuttle disaster when Columbia disintegrated upon re-entry in 2003, and questions arose whether repairing the telescope was worth the risk. Ultimately, the National Academy of Sciences recommended that a shuttle service mission be scheduled.

Hubble narrowly escaped having its life span drastically shortened once again in 2008. The final service mission was scheduled for October, but in September a central data controller on the craft failed, effectively shutting Hubble down. If this had happened just weeks later – after the shuttle visit – it would have left the telescope with just the backup system, and the next failure would have spelled the end.

Instead, engineers scrambled to get a second backup system ready on the ground, and after several more shuttle delays and some fears that space junk from a satellite collision could make the mission too risky, astronauts were able to repair, service and upgrade Hubble one last time in May 2009. The famous telescope got right back to sending us amazing images just a few months later.

Source, Images: NASA

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