The Hubble Space Telescope, one of the greatest scientific instruments of all time, is about to get an extreme makeover — an overhaul so delicate and risky that NASA astronaut John Grunsfeld likens it to "brain surgery."
At 19 years old, the famous telescope is showing its age. Three of its scientific instruments are broken. Half of its six gyroscopes, which keep the Hubble pointed in the right direction, aren't working. And its batteries are slowly dying.
The seven-member crew of space shuttle Atlantis is scheduled to blast off Monday in an attempt to fix it.
It will be the fifth, final and most difficult mission to service the Hubble — a mission that was judged so risky to astronauts it was canceled in 2004 before safety precautions were added to ease the concerns.
If the work succeeds, it will mean a glorious rebirth of the Hubble. The telescope would be 90 times more powerful than when it was launched in 1990. If the mission fails, astronomy's crown jewel could become a $6.9 billion "piece of space junk" with no chance to save it, astronaut and mission commander Scott Altman says.
No other flights to Hubble are planned. That's because the shuttle — the only vehicle that can reach the telescope — is 17 months from retirement.
There had always been the possibility of "another shot" at Hubble, says Mike Weiss, the telescope's deputy program manager.
That's no longer the case.
"This is the last opportunity," Weiss says. "There's no margin for error."
Even if Hubble were to blink off tomorrow, it would leave a legacy richer and more vast than that of any other astronomy tool. It has more discoveries to its credit than any other observatory, NASA's Jon Morse says.
It "has already earned its place in history as a triumph of science in our modern era," says Heidi Hammel, an astronomer at the Space Science Institute, a research institute. "Hubble brings the heavens down to us."
• Helped narrow the age of the universe to 12 billion to 14 billion years, rather than the 10 billion to 20 billion years known previously.
• Captured the farthest pictures of deep space ever taken, showing early galaxies born in the era when the first stars were forming.
• Detected exploding stars in a pattern that suggested a mysterious "dark energy" is propelling galaxies apart.
•Provided the first analysis of the atmosphere of planets in other solar systems and taken the first picture of such a planet.
For all those accomplishments, the Hubble's potential is perhaps even more tantalizing. The period after the mission will be "the grand finale of the Hubble symphony," says David Leckrone, Hubble project scientist at NASA.
"Everything we've done up to this point," he says, "has been in preparation for these final five years, where Hubble is at its peak of capability."
Viewing deep into space
Hubble's namesake is the late U.S. astronomer Edwin Hubble, who discovered that our galaxy is only one of countless others.
The observatory owes its scientific achievements mostly to one simple fact: It's out in space. Images snapped by telescopes on the ground are distorted by the Earth's atmosphere, as if they had been taken though a grimy windshield. Hubble sits comfortably above the atmosphere, offering a stunningly clear view of the universe.
That vantage point makes it possible for Hubble to produce pictures such as the famous Ultra Deep Field: a snapshot showing 10,000 galaxies, some not long after they emerged from the Big Bang.
Its lofty perch also means that Hubble doesn't contend with light pollution — the haze of city light and moonlight that can blind ground-based telescopes. That allows Hubble to see very faint objects, including those that are very far away.
All these advantages add up to make Hubble "the most powerful astronomical observatory in history," wrote a National Research Council committee that assessed options for fixing the telescope.
The committee said the shuttle mission should proceed, noting that no telescope with Hubble's powers will be built for decades. A potential of a retooled Hubble, the committee said, "would be comparable to the telescope's promise when first launched."
Restoring Hubble to full health will be such a daunting task that NASA officials such as Hubble program manager Preston Burch play down the likelihood of a complete success.
None of the previous missions to fix the telescope has been so packed with chores. And never before have astronauts tried to repair Hubble's scientific instruments.
Astronauts have made four house calls on Hubble.
The first was to fix a humiliating goof discovered after Hubble's launch: Its main mirror turned out to be defective because of a manufacturing error, and the telescope produced only blurry pictures. During a 1993 mission, astronauts installed a $74 million series of mirrors that acted like eyeglasses to correct Hubble's squint.
Previous visits were "heart surgery on Hubble," says Grunsfeld, who will make his third mission as a Hubble-repair spacewalker. This one is "comparable to doing brain surgery."
Consider what Grunsfeld faces to fix the Advanced Camera for Surveys, which snapped some of Hubble's best-known images.
Its builders thought no one would work on the camera, so they closed it with 36 tiny screws — impossible to handle wearing a spacewalker's clunky gloves.
To fix the camera, Grunsfeld will have to pull out four circuit boards with razor-sharp edges, which could puncture his spacesuit. He'll do all this without a good direct view of what he's touching, because the work site is around a corner and deep in the bowels of the telescope.
To make the camera repair possible, engineers at NASA's Goddard Space Flight Center in Greenbelt, Md., custom-built several tools to aid Grunsfeld. One, a forceps-like instrument, will be used to grip the circuit boards and yank them out.
Another grasps the miniature screws so they don't float away.
A loose screw inside Hubble might seem trivial, but even a minute foreign object could be disastrous for the telescope.
It would take only "an immeasurable amount of debris in the right place to cause problems with the telescope's ability to image," says astronaut Andrew Feustel, who will perform three spacewalks during the mission.
The frailty of the Hubble and the complexity of the mission were brought into focus last fall, when a critical system on the telescope failed just 2½ weeks before the scheduled launch. NASA delayed the mission while engineers devised a fix.
Now the hour is at hand — again — and the anxiety and anticipation are running high. "I can hardly wait," Leckrone says. "Let's get this thing off."
Making it safer
Just as Hubble faces risks from the astronauts' visit, the astronauts themselves face dangers from trying to fix it.
If Atlantis is badly damaged by launch debris or space junk, the telescope-repair team can't take refuge on the International Space Station, the way all other shuttle crews can. The station will be just too far away.
That led Sean O'Keefe, then the head of NASA, to cancel the mission in 2004. A public outcry ensued. Schoolchildren pooled their lunch money to fund a rescue of Hubble, and ordinary citizens flooded NASA's website with protests.
O'Keefe's successor, Michael Griffin, reinstated the servicing mission in 2006 after satisfying himself that the mission's risks could be minimized.
To make sure the crew can be rescued, NASA added an unprecedented safety measure: A second shuttle will be waiting on the launch pad, ready to go to space, when Atlantis lifts off. That means that a second shuttle crew could rescue the Hubble astronauts before they run out of air or food.
None of this comes cheaply.
A shuttle flight costs roughly $500 million, and the new scientific instruments and other hardware add up to $887 million.
Even so, there's little opposition among scientists to the mission to fix Hubble, says astronomer Warren Moos of Johns Hopkins University. "The community is very excited," he says.
During the upcoming mission, Hubble will be fitted with two new sophisticated scientific instruments in addition to the two now in orbit that will be fixed.
"We will be getting a whole new telescope," says Mario Livio of the Space Telescope Science Institute, the non-profit group that manages the observatory.
The scientific possibilities after Hubble's makeover "are just endless and exciting and hard to fathom," Leckrone says.
Among the questions a refurbished Hubble will tackle:
• How common are planets outside our solar system, and how big are they?
• How and when do galaxies form stars?
• What's the composition of the cosmic "web," the filaments of stuff that fill the universe and make up most of its matter?
When a new observatory opens, astronomers generally foresee only half of its major discoveries. The same can be expected with Hubble, said the National Research Council committee, meaning that the greatest science that lies ahead cannot be predicted.
Eventually Hubble, which was originally envisioned to last 10 to 15 years, will have to take a bow. NASA expects to get five to seven more years of life out of it, assuming the repairs succeed, before it makes a controlled plunge into the ocean.
In a few years, NASA will launch a Hubble follow-up, the James Webb Space Telescope, named for a former NASA chief who is not related to Sen. Jim Webb, D-Va.
The Webb telescope won't be able to see objects that emit ultraviolet light, as Hubble can, nor will it have Hubble's talent for taking pictures in ordinary light.
In some areas, though, it will "clean our clocks," Leckrone says.
The Webb, for instance, should be able to find galaxies that are even closer to emerging from the Big Bang, because it specializes in detecting light from the earliest stars.
Crewmembers want to give the Hubble's successor a high bar to cross. They know a lot is riding on this mission.
Altman, who was also commander of the last Hubble repair mission in 2002, recalls thinking at that time: "Well, there's going to be another servicing mission coming around."
"This time, this is it," he says, "So we're going to be giving it our best."