Alone once again in the sky, the space telescope Hubble is flying today 350 miles above the Earth preparing to send home fresh images of the stars and galaxies studding the fabric of our early Universe. Exploding stars, black holes, the puzzling cosmic "bulge" of stars inside our own Milky Way, and a clear look at the universe itself as it was 500 million years after its violent birth in the Big Bang - these are now targets for Hubble's cameras and instruments renewed and repaired by the seven astronauts of the shuttle Atlantis during a historic and risky mission last week. For 19 years, Hubble's work has amazed millions of admirers with images sent back to Earth of brilliantly colored cosmic clouds, whirling galaxies and blazing stars at the moment of their explosive deaths. At the same time, Hubble has had a profound impact on basic astrophysics, shedding much new light on the nature of the universe, its dark matter and dark energy. The newly repaired Hubble promises to have more to offer.
"It will now be the most powerful telescope that ever existed, and it's 10 times better than it was," said Mario Livio, an astrophysicist at Hubble's scientific home, the Space Telescope Science Institute in Baltimore, in a phone interview Wednesday after the fifth and final servicing mission ended.
"In our wildest dreams we never thought that the astronauts could actually repair instruments that were broken, besides replacing the old ones with new ones," he said. "It's fantastic."
Making delicate repairs
Throughout their mission, the spacewalkers from Atlantis - weightless and floating in their bulky space suits - skillfully accomplished extraordinary repairs on Hubble's worn-out innards.
Working two at a time, spacewalkers Michael J. Massimino, Michael T. Good, John Grunsfeld and Andrew Feustel labored tirelessly through five ventures into the large and weightless cargo bay of Atlantis. Their colleagues, comfortable in the artificial gravity of the shuttle's main cabin, guided, encouraged and applauded them as they worked.
The spacewalking repairmen replaced Hubble's 16-year-old Wide Field Camera with a brand-new one; swapped out the six worn-down gyroscopes that keep the telescope pointed in the right direction; installed three new vital batteries; and repaired the telescope's Advanced Camera for Surveys - a job never designed to be accomplished in space.
High-precision tools designed for the most delicate work helped them, but occasionally brute force had to be employed. Massimino, for instance, had to work especially hard to loosen a single stripped bolt whose removal was crucial to repair the power supply of Hubble's Imaging Spectrograph. After struggling with his high-tech tools, he finally gave the bolt one sharp yank with the touch of a tough old mechanic. The bolt loosened, and Massimino was home free - to the applause of his crewmates.
That was typical of the way things went for all the spacewalks: The astronauts followed the procedures they had rehearsed for three years on the ground, but when all else failed, they resorted to their innate smarts.
When all was finished Tuesday, with Hubble and Atlantis joined in space 350 miles high over northwestern Africa, Atlantis commander Scott Altman phoned home to Mission Control in Houston
"An incredible journey," he said.
Hubble then was turned loose - alone once more, newly refurbished and ready to explore the distant skies for at least the next five years.
Since the amazing telescope was sent into space in 1990, data have been received by more than 4,000 astronomers around the world - some of them young scientists yet to make their mark, and many veteran astrophysicists who have reported major new insights into the cosmos based on Hubble's images and data.
Astronomers pick targets
Around the world, 900 astronomers have already been approved as "observers" with authority to order specific targets for the versatile telescope, according to astronomer Neill Reid of the Space Telescope Institute. Nearly 9,000 other scientists worldwide are signed up as users of Hubble's data archive, and they will be waiting to use the new data as soon as it is released, Reid said.
So Hubble's future will be busy, for the cosmos is wide and filled with mysteries.
With the Wide Field Camera, astronomers will now be able to see galaxies and exploding stars billions of years older than ever seen before and speeding faster in the expanding universe than any galaxies ever observed, Livio said.
The refurbished Hubble, he said, will also examine a mysterious region within the Milky Way that bulges with millions of stars whose composition is yet to be understood.
"Hubble will tell us how the bulge was formed," Livio said, "and we will understand the metallicity of the stars there."
(Metallicity is a term astronomers use to define the composition of all the varied chemical elements within a star other than the hydrogen and helium of which they're primarily made. The term has nothing to do with metal as we know it.)
More distant supernovae
Certain types of exploding stars called supernovae are used by astronomers as "standard candles" to measure the distance of the galaxies in which they lie. Until now Hubble could observe them as far off as 9 billion light-years away, but now the space telescope will be able to measure their distance up to 11 billion light-years off.
"This was the early universe before acceleration and gravity had the upper hand," said Livio. "So we will begin to understand more about that great mystery, the properties of dark matter."
Then there is Hubble's renewed Cosmic Origins Spectrograph.
"It will let us examine the great cosmic webs we cannot see," Livio said.
Those webs are great regions of intergalactic space that are so thin and tenuous they can never be seen from Earth. Where they are backlit by the brilliance of hugely energetic quasars, however, Hubble will be able to change that.
It will "reveal the structure of the immense filaments inside the webs we cannot see," Livio said.
Another target, he said, will be the centers of "starburst galaxies." Those are poorly understood galaxies where new stars are "born at a furious rate," as he put it, and are believed to be created when two distant galaxies collide.
"We need to understand the complex processes that create the starbursts," he said.
Studying more atmospheres
"Exoplanets" are planets orbiting distant stars far beyond our solar system. Hubble has already analyzed one exoplanet's atmosphere and found oxygen, methane, carbon dioxide, sodium and even water vapor there.
Now the repaired Space Telescope Imaging Spectrograph that Massimino repaired with a yank will soon be peering at more exoplanetary atmospheres, and will also look at those massive objects called black holes whose immense gravity sucks up everything around them with enormous bursts of energy.
Hubble's final servicing mission has been an outstanding success; its future tasks will give the world's scientists and ordinary citizens a new understanding of our Milky Way galaxy, and the universe around it.
Its successor, the far larger and more powerful James Webb Space Telescope, with its 21-foot mirror and its sunshield the size of a tennis court, is being built right now. It is scheduled for launch in 2014. The stars and galaxies, black holes and supernovae will still be there, waiting.