NASA's prolific Hubble Space Telescope recently celebrated the 20th anniversary of its launch, but time is ticking down on this beloved and iconic symbol of space-based astronomy.
To date, Hubble has observed more than 30,000 celestial targets and amassed more than half a million pictures in its archive. Images like the classic "Pillars of Creation" photo from 1995, and the recent photo of the Carina Nebula that was released the weekend of its anniversary milestone, have revolutionized our understanding of the cosmos.
Launched into orbit on April 24, 1990, Hubble very nearly became a national embarrassment. A defective mirror and fuzzy pictures beamed back to Earth made its debut less than stellar. But a 1993 repair mission corrected the flaw, and soon after, stunning images were being relayed home.
In its 20 years in space, Hubble has undergone many repairs and additions to its mechanical parts. The most recent astronaut servicing mission to Hubble in May 2009 made the telescope 100 times more powerful than it was two decades ago when it was first launched.
But it is unlikely that Hubble, which orbits about 300 miles (480 kilometers) above the Earth, will be serviced again in the future.
"The last servicing mission gave it a five to 10-year lifetime for science," John Grunsfeld, an astronaut and physicist who has performed several repairs on Hubble, said at a 2010 World Science Festival event in New York City. "But, at some point, a tiny bit of drag will cause Hubble to get lower and lower."
If left untouched, the telescope would eventually start to tumble toward Earth.
"We would need to go back to Hubble one more time to either boost it up or send it into the atmosphere," Grunsfeld said.
At the moment, no definite plans have been made for Hubble's future, but NASA is already paving the way for a successor to the aging space observatory.
Pegged as the next great space telescope, construction on the $5 billion James Webb Space Telescope is underway.
The massive, state-of-the-art space observatory, which is slated to launch in 2014, will use infrared technology to peer deep into the distant reaches of the universe. And, it will orbit at about 1 million miles (1.5 million kilometers) from Earth, much farther up than Hubble's orbit.
With its ability to travel farther into the universe and use its infrared eyes to cut through the clutter and see things beyond the range of visible light, there are high expectations for the discoveries that the Webb telescope could yield. After all, it's got some big shoes to fill.
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