In Pictures: Hubble telescope clocks up 25 years

Iconic space observatory has proved a spectacular success after bad start

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NEW YORK - The world's most famous telescope, which Nasa has called "the most significant advance in astronomy since Galileo's telescope", is celebrating its 25th year in space.

The powerful Hubble telescope has provided more than one million observations to date, allowing scientists to make groundbreaking observations about distant galaxies, black holes and supernovas, fundamentally altering man's understanding of the universe.

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But the telescope, named after late astronomer Edwin Hubble, was the butt of jokes when it was launched 25 years ago.

Just weeks after it was put into orbit, the makers of the US$1.5 billion "time machine" realised that they got one of their measurements wrong - the Hubble's mirror was a tiny bit flatter than it should have been.

The measurement was off by about one-fiftieth the thickness of a piece of paper, but it meant that the telescope sent back nothing but blurry images of deep space, rendering it virtually useless - a huge embarrassment for the National Aeronautics and Space Administration (Nasa).

To mark the anniversary of the telescope, National Geographic made the documentary Hubble's Comic Journey and spoke to the engineers and scientists about the telescope's rocky start.

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Mr Charlie Pellerin, Nasa's head of astrophysics between 1983 and 1993, was candid about his feelings, saying "I looked back on this and wondered how could I have been so stupid. It was leadership failure and I was leader of the team".

"I was 38 years old when I got that job and I had never managed a multi-hundred-million-dollar project before, and so I assumed the people before me knew how to do it and they didn't," he told the documentary makers.

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He also recalled a confrontation with senior senator Barbara Mikulski, who had fought hard for government funding to build the Hubble.

"She's mad and she's screaming with invectives and puts her finger in my chest, 'Charlie, you need to understand that this is a mess that's just gotta go away. We're gonna forget this nightmare ever happened'," he said.

But Nasa did not give up. After three years of brainstorming, it sent seven astronauts in a space shuttle to repair the telescope.

It was an extremely difficult task, as the astronauts had to wear full space suits and leave the shuttle to do the repairs.

Astronauts likened the work to fixing a car while hanging upside down, wearing ski mittens and travelling at 27,000kmh.

Fortunately, the space agency's hard work paid off, fixing the mistake by correcting the optics with lenses and mirrors designed to be just as perfectly at fault - but in the opposite way.

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Nasa calls the Hubble telescope "one of the most productive instruments ever built" as its data has been used in more than 12,700 scientific papers.

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Its groundbreaking revelations include discovering the oldest galaxy ever seen, dating back 13 billion years, as well as confirming that the Jupiter-orbiting moon has an ocean beneath its surface, raising the prospects for life.

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So far, the Hubble has exceeded expectations of how long it can last. Its components were expected to degrade by 2013, but it is still going strong.

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Nasa officials say they want the iconic space observatory to go on working for as long as possible and expect it to last until 2018, reported Space.com.

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Nasa had hoped to use a shuttle to bring the Hubble back to Earth to be a museum exhibit, but the telescope outlived the shuttle programme, CNN reported.

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To replace the Hubble, Nasa will reportedly launch the James Webb telescope in 2018.