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Friday, 25 January 2008

A Whole New View: Hubble Overhaul to Boost Telescope's Reach

When astronauts overhaul the Hubble Space Telescope this summer, they will leave behind a vastly more powerful orbital observatory to scan the universe.

Set to launch aboard NASA's shuttle Atlantis on Aug. 7, the Hubble servicing mission will be the fifth — and final — sortie to upgrade the aging space telescope.

"We're not only going up to Hubble to refurbish it, but also to expand its grasp tremendously," said Alan Stern, associate administrator for NASA's science mission directorate, in a recent briefing. "We expect to make the very best discoveries of the entire two-decade plus Hubble program with the new instruments to be installed."

NASA's Hubble Space Telescope maintains its orbit around Earth. The space agency hopes to upgrade the aging observatory some time in August 2008.

Astronauts Steven Smith, and John Grunsfeld, appear as small figures in this wide scene photographed during an STS-103 extravehicular activity (EVA) to service the Hubble Space Telescope in December 1999.

The Hubble Space Telescope's Wide Field Camera-3 undergoes integration and testing at NASA's Goddard Space Flight Center in Greenbelt, Maryland.

The Hubble Space Telescope's Cosmic Origins Spectrograph is subjected to integration and testing at NASA's Goddard Space Flight Center in Greenbelt, Maryland.

A deeper look

In addition to performing vital repairs, astronauts will add two new instruments to Hubble's observation platform — Wide Field Camera-3 and the Cosmic Origins Spectrograph — that will drastically boost its vision range.

"This refurbished Hubble [will be] a new telescope," said astronomer Sandra Faber of the University of California, Santa Cruz. "We estimate that at the end of this repair Hubble will be 90 times more powerful than when it was first launched."

That means that Hubble will be able to see at least 90 times more objects in deep space than it could when it was deployed in April 1990, she added.

With its ability to scan the universe at wavelengths ranging from the near-infrared, visible spectrum to the near-ultraviolet, the new Wide Field Camera-3 should allow Hubble to see objects that formed fewer than 800 million years after the beginning of the universe.

"To follow galaxy formation to times that are even earlier than this, we need a camera that can take sharp pictures efficiently at longer wavelengths," Faber said. "And that's exactly what Wide Field Camera-3 is going to do."

The new camera has better resolution than its Wide Field Planetary Camera-2 predecessor and a wider field of view than Hubble's current NICMOS spectrometer, and could reveal objects that formed when the universe was just 400 or 500 million years old, she added.

"A difference like this makes a huge difference in the structure and formation of the galaxies that we'll see," Faber said. Astronomers currently estimate that the universe is about 13.7 billion years old.

Hubble's new Cosmic Origins Spectrograph, meanwhile, will scan the universe in the ultraviolet range with about 10 times more sensitivity than the observatory's current tools.

"I believe it's the most sensitive UV spectroscopic capability ever to fly in space for astronomical purposes," said Hubble senior project scientist David Leckrone of NASA's Goddard Space Flight Center in Maryland. "It's designed, because it's so sensitive, to go as deep as possible out across the universe as fast as possible."

Researchers hope the new spectrograph will map the so-called cosmic web, the universe's large-scale structure made up of strands of galaxies that branch out in three dimensions like an astronomical spider's web.

"It is amazing to me how we've been able to reinvent the Hubble Space Telescope with each of these missions," said astronaut John Grunsfeld, who will serve as the lead spacewalker for the telescope's last overhaul.

Full power ahead

Hubble service astronauts will also replace failed gyroscopes, fine guidance sensor and aged batteries, and make unprecedented repairs to the space telescope's main camera and a vital spectrograph.

"When the astronauts leave Hubble for the last time, it will be at the apex of its capabilities," said Leckrone. "It will be the first time since 1993 that there will be five working instruments aboard."

Spacewalkers will replace Hubble's cracked thermal insulation and replace each of its 16-year-old batteries among other hardware.

They will also repair the observatory's Space Telescope Imaging Spectroscope and the Advanced Camera for Surveys (ACS), both of which were never designed to be fixed in orbit. Spacewalkers will remove more than 111 tiny screws to repair the two units.

"The good news is we're going to try and repair ACS. The bad news is we've never done it before," said Grunsfeld. "It's very tricky."

Grunsfeld and his six crewmates plan to stage five spacewalks to service Hubble during their STS-125 mission. NASA initially canceled the spaceflight following the 2003 Columbia tragedy, but later reinstated the mission after a detailed risk analysis.

The result, researchers said, is about five extra years of science for Hubble before its controlled deorbit sometime after 2020. To prepare for the space telescope's eventual demise, spacewalkers will also attach a connecting port that will allow a robotic tug to dock with Hubble.

"None of us could have imagined what this fourth-generation suite of instruments can do," said Stern, adding the 90-fold jump in observation power for Hubble will be unprecedented. "We will have the capability, literally, of approximately 100 Hubbles [circa] 1990 when this mission is done."

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