One astronomer compared it to the fate of the faithful dog in the movie Old Yeller. On Thursday, astronomers will crowd into a hotel ballroom in Washington to discuss when and how NASA should put down one of its and astronomy's most spectacular successes, the Hubble Space Telescope.
Since it was launched in 1989 with a flawed mirror and then repaired by spacewalking astronauts, the Hubble, floating above the murky atmosphere, has been a matchless time machine, providing astronomers with views of unprecedented clarity deep into space and time. "The Hubble is the single most important instrument ever made in astronomy," said Sandra Faber, an astronomer at the University of California in Santa Cruz.
PHOTO: NY TIMES
But its days, and nights, have always been numbered. NASA has long planned to end Hubble's spectacular run and bring it down in 2010 to make way in the budget for the James Webb Space Telescope, scheduled to be launched in 2011.
PHOTO: NY TIMES
Still, some astronomers are urging that Hubble's life be extended. They argue that the telescope has grown even more productive in its years in orbit, thanks to periodic service calls by astronauts.
These astronomers say that killing Hubble in its prime makes little sense, either scientifically or from the standpoint of public relations. "Hubble is by far the best news NASA has now," said a senior astronomer, speaking on the condition of anonymity.
An extension of Hubble's life, they say, will ensure that there is no gap in coverage before the Webb telescope goes into operation, but it would require an extra shuttle visit to Hubble late in the decade. That would cost at least US$600 million, said Anne L. Kinney, director of astronomy and physics in NASA's Office of Space Science, and the money would have to come at the expense of the Webb telescope or some other project.
As a result, whatever NASA does is bound to make someone unhappy. "It's terribly important," Kinney said. "There is a lot of anxiety in the astronomical community about it. You have to listen to them."
Kinney has appointed a panel of scientists led by John Bahcall, an astrophysicist at the Institute of Advanced Study in Princeton, New Jersey, to evaluate NASA's plans for Hubble and to see if there is justification for a change. "Our charge is to advise about how to maximize the science. We are going to focus on just that task," Bahcall said.
He called the topic of Hubble's demise "a hot potato," adding, "But someone has to do it."
The other members of the panel are Barry Barish of the California Institute of Technology; Jacqueline Hewitt of the Massachusetts Institute of Technology; Christopher McKee and Charles Townes, both of the University of California at Berkeley; and Martin Rees of Cambridge University in England.
"They are my dream team," Bahcall said. "We may catch hell for what we do, but we will learn a lot while we do it."
The group has set up a Web site (hst-jwst-transition.hq.nasa.gov/hst-jwst/home.cfm) on which astronomers can post their opinions and read a growing assortment of policy and fact sheets. It is holding a public meeting at the Loew's L'Enfant Plaza Hotel in Washington on Thursday. "It's going to be high opera," Kinney said.
In an interview, Edward J. Weiler, NASA's associate administrator in charge of the Office of Space Science, pointed out that the Hubble's mission had been extended once. The telescope was originally designed to last 15 years and come down in 2005.
The next and final astronaut visit to the telescope is scheduled for next year, but might not happen until 2005 or even 2006, depending on when the shuttles start flying again in the wake of the loss of the Columbia in February. On that occasion the telescope will be fitted with two new instruments, and astronomers say it should work well until the end of the decade.
The decision about what happens then has been complicated by the breakup of the Columbia. The telescope is too big to leave to fall out of orbit and crash uncontrollably to Earth on its own. NASA had originally planned to fetch it with the space shuttle and put it in the Smithsonian's Air and Space Museum, but that now seems "exceedingly unlikely," in Kinney's words. Such a mission would take the shuttle into an orbit in which it could not rendezvous with the space station if anything went wrong.
Instead NASA is studying the possibility that a robotic rocket could be sent to attach itself to the telescope and ease it out of orbit safely into the ocean. That would require developing new technology. If it seems feasible, Kinney explained, astronauts could add attachments for the rocket to hook onto during the upcoming service mission.
The telescope is in no imminent danger even if the next service mission is put off indefinitely. It is now in an orbit about 563km high. How long it could stay there depends on sunspot activity, which bloats the atmosphere, causing drag on the telescope. Even under the worst circumstances, Hubble would not fall until 2013, according to a NASA study. But with a series of small altitude boosts supplied by the shuttle in 2005 and 2009, it could stay up until 2020 or beyond.
Leading the charge for another extension are the astronomers of the Space Telescope Science Institute on the Johns Hopkins campus in Baltimore. In a policy statement full of statistics testifying to Hubble's dominance of contemporary astronomy, Steven V.W. Beckwith, the director of the institute, argued that as a result of the astronauts' service calls, Hubble had essentially been reborn every few years, allowing it to stay on top of its game.
"A servicing mission to Hubble is comparable in science value to the launch of a new satellite and should be judged as such," Beckwith wrote.
As a result, the number of scientific papers based on Hubble observations still grows every year.
Beckwith argued that sending astronauts to fit the telescope with a propulsion module would be less risky than trying to develop a robot. If such a trip was necessary, he said, the marginal cost of fixing it up for a few more years of science would be a bargain.
Kinney of NASA said the agency was merely following the wishes of the astronomical community itself, as expressed in a recent report prepared under the auspices of the National Academy of Sciences. That report listed what would become the Webb telescope, designed to probe early cosmic history when galaxies and stars were first forming, as the highest priority.
"We have to ask, what is the best research for the taxpayer's dollar?" she said.
Robert Kirshner of the Harvard-Smithsonian Center for Astrophysics said in an e-mail message that he thought Hubble was working better than it ever had, "so the equation has changed." He said it would not be easy to decide how best to serve science.
Wendy Freedman, director of the Carnegie Observatories in Pasadena, California, said NASA was asking the right questions with the Bahcall committee. "At some point, it makes sense to go on and do new things -- the risks, budget and promise of greater potential make this easy to determine," she said. "The question is, is HST at this point? Or not?"
Faber of the University of California said she thought there was a lot of support to keep Hubble going.
"Hubble is unique. Nothing else can do what it can do," she said. "Once it's gone, we're going to be paralyzed. We've gotten hooked. We're addicted."
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