By Andrew Luck-Baker

BBC Radio Science Unit

Please turn on JavaScript. Media requires JavaScript to play. Expect "shock and awe in science" from a repaired and upgraded Hubble Space Telescope. This is the prediction from a Nasa astronomer who has worked on the mission since its inception. If all goes completely to plan on Hubble Servicing Mission 4, the orbiting observatory will be reborn as the most productive telescope in history, with even greater powers to probe the Universe's deep history and help cosmologists make sense of one of their biggest problems - "dark energy". Over five long days of well rehearsed but exhausting work on Hubble, the astronauts on the shuttle Atlantis have the task of installing a new panoramic camera and a latest-generation spectrograph. A spectrograph is an instrument for measuring the chemistry, temperatures and motions of celestial objects. The servicing spacewalkers also have the goal of bringing back to life what was Hubble's most important camera (the Advanced Camera for Surveys) and another defunct spectrograph. Both of them were knocked out by electronics failures. According to David Leckrone, project scientist at Nasa Goddard Spaceflight Centre: "For the first time since 1993, Hubble will have a full set of first class hi-tech scientific instruments onboard. It's not just one camera and one spectrograph. It's a variety of instruments covering a lot of capabilities and are used for different purposes." Any astronomer around the world can apply for time to observe with the orbiting telescope. Dr Leckrone has high hopes for the combination of massed human brain power and the telescope's new and repaired hardware. Between these vast films and fingers of galaxies are even more immense voids of very nearly empty darkness

"You couple that global intellect with that set of tools and you produce shock and awe in science with Hubble," he told the BBC. It is not as though Hubble has failed to shock with its data and inspire awe with its images already. The tally of the telescope's historic achievements is unmatched by any other observatory, since the first shuttle servicing mission in 1993 corrected the blurring problem with Hubble's main mirror. • Hubble was the first instrument to fix the Universe's age at about 13.7 billion years. • Hubble was the first to analyse the chemical make-up of the atmosphere of planets beyond the solar system. • It was one of two telescopes to make the first direct images of planets orbiting another star - historic images made public last November. Hubble was also at the forefront of unveiling the existence of dark energy: the name coined for a mysterious and pervasive force which appears to be inflating the Universe at an ever increasing speed. Cosmologists had assumed that for most of the 14-odd billion years since the Big Bang, the Universe's expansion had been slowing down. In the mid-1990s Hubble - along with the ground-based Keck telescope in Hawaii - made the key measurements on distant exploding stars, supernovae, which showed otherwise. A direct image of a planet orbiting another star

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It was the most shocking cosmological revelation since the 1920s when astronomer Edwin Hubble discovered that the Universe was expanding. The mystery of dark energy may be a little clearer, if not solved, with the new camera the astronauts are going to install. This is the Wide Field Camera 3 - an instrument with the dimensions of a street telephone box. Like Hubble's existing, but currently dead, Advanced Camera for Surveys, the WFC-3 has a sensitive detector which can form images of very distant galaxies in the same wavelengths of light our eyes perceive. These objects are so faraway, their starlight started its journey across the cosmos just under 13 billion years ago. The camera catches them as they were at that early time - though only just. They are very faint. But the new Wide Field Camera will make its great advance by virtue of a second detector chip, sensitive to wavelengths of light in the infrared part of the spectrum. This will let astronomers use Hubble to see deeper with more detail. This is because visible light from stars that has travelled from very far away in the cosmos has been "stretched" en route as the Universe itself has expanded. Its wavelengths are widened - or "red-shifted" - in proportion to the distance it has crossed. So if a galaxy or supernova is well beyond 13 billion years away, all of its light reaches us as infra-red radiation. The WFC-3 will seek out even earlier galaxies According to Steven Beckwith - professor of astronomy at University of California, Berkeley, and former director of the Space Telescope Science Institute - the new Wide Field Camera should help to characterise the nature of dark energy. Thanks to its infrared vision, it will be able to pick up large numbers of supernovae too distant and red-shifted for other instruments. Studies of the light from each exploding star will allow astronomers to get a better idea of how fast or slowly the Universe was expanding at different times in its early history. Plotting this is vital in the challenge of figuring out what dark energy is. Theorists have come up with many possibilities but none fit with our current understanding of physics. Steven Beckwith said: "I think the new instrument will let us zero on those few ideas that could be right and get rid a lot of bad ideas. But I don't think it will tell us the answer." The problem of dark energy aside, the new Wide Field Camera will give us a deeper view into the early Universe in general: the epoch when the first galaxies and stars came into being. To date Hubble has seen back to 900 million years after the Big Bang. Steven Beckwith says that with WFC-3, the telescope's view will extend to 400 million years after creation. Hubble has stunned and surprised us It is almost anyone's guess what astronomers will see, although theory would suggest the earliest mini-galaxies of stars should have formed by then. They would be untidy ill-formed blobs lacking the size and regular shapes of "modern day" galaxies like our own Milky Way. They would be populated by stars much more massive and burning more fiercely than our Sun. This is how astronomers picture the first galaxies and stars that formed out of dark gaseous debris created in the Big Bang. Exactly when that happened and starlight began to flood across the Universe is unknown. Steven Beckwith speculates that Hubble's new camera might pin-point the "Cosmic Dawn", if it broke more than half a billion years after the Big Bang. The refurbished Hubble will be able to look even deeper

The other new instrument for Hubble is the Cosmic Origins Spectrograph (COS). COS is also the size of a phone booth. It does not make spectacular images but its kind of work is just as important for astronomers. Spectrographs make measurements of the motions, temperatures and chemical make-up of galaxies, stars and planets. What distinguishes COS is its great sensitivity to very faint objects and that it works at the ultraviolet end of the spectrum - a "flavour" of light radiation largely screened out by the Earth's atmosphere. COS team member Mike Shull at the University of Colorado, Boulder, describes the instrument as "a very fancy prism which takes the light from Hubble's mirror and spreads it out into its component colours." "Every element whether it is helium, oxygen or carbon has a unique set of fingerprints that get imprinted on the light." The imprinting of particular wavelengths at tell-tale intensities reveals which chemical elements are present in distant planets, stars, galaxies or even the great expanses of space between galaxies. In the past 20 years, astronomers have found that galaxies are not uniformly distributed across the sky. Galaxies are concentrated along a filamentary network called the Cosmic Web. Between these vast films and fingers of galaxies are even more immense voids of very nearly empty darkness. But there is something in them - a vanishingly tenuous amount of gas. 'Gas accounting' Mike Shull wants to use COS to discover which particular elements are there and to measure how much is there. He says it is possible there is as much as 20% of the original hydrogen and helium created out of the Big Bang lingering in these great interconnected voids. It is gas that never made it into stars and galaxies but it may do in due course. The plan is to use the light from brilliant and distant objects called quasars, which will have sampled the composition of the voids during its passage across billions of light years of space. The imprinted information in the spectrum of this light will reveal the quantity and make-up of the inter-galactic gas at different times. Because this gas may be destined eventually for stars and galaxies, there should be important insights into the big picture of how galaxies grow from their small sizes at the Cosmic Dawn to form the modern day spiral behemoths such as our own Milky Way. According to Mike Shull, astrophysicists have begun this inter-galactic accounting but progress has been very slow for the lack of an efficient instrument to do the job. "Right now, there's only 20 or 30 places we've looked to sample this gas. With COS we'll be 20 to 30 times more sensitive but moreover we'll be more efficient. So something that used to take 20 or 30 orbits of Hubble time, we can do in one orbit." Listen to Science in Action this week on BBC World Service for more coverage of the Hubble servicing - including an interview with mission astronaut John Grunsfeld on the challenge of installing and repairing the telescope's instruments. This edition will be broadcast on Friday 15 May, and available on-line from 0930 GMT



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