WASHINGTON -- Despite pleas from a parade of astronomers that NASA consider extending the life and capabilities of the Hubble Space Telescope (HST), the U.S. space agency appears unlikely to change its plans to deorbit the space borne astronomy platform in 2010.

Now that NASA is firmly committed to the James Webb Space Telescope, a deep-space observatory due for launch in 2011 on a European Ariane 5 rocket, there is no compelling reason to invest further in the aging Hubble telescope, said Anne Kinney, division director of astronomy and physics at NASA headquarters. While Hubble can at best be souped up with new instruments, its planned successor offers vastly superior capabilities, Kinney said in an interview during a NASA-sponsored conference organized to debate Hubble's future.

At issue during Thursday's public hearing organized by the HST-JWST Transition Plan Review Panel was whether it is feasible for NASA to mount an extra space shuttle mission to the Hubble telescope late in the decade to add instruments and ensure the observatory remains in service beyond the deployment of the JWST.

A Blue Ribbon panel of scientists appointed by NASA plans to issue recommendations to NASA about whether such a mission is worthwhile by Oct. 1, based in part on presentations from Hubble users at the conference, held here at the Loews L'Enfant Plaza Hotel.

John Bahcall, chairman of the panel, declined in an interview to speculate on what the advisory board might suggest to NASA. "I think the committee will take a bottom-up approach and look at all the possibilities together."

While astronomers at the event argued vehemently that it would be wasteful to remove Hubble from service before it is absolutely necessary, Kinney told SPACE.com she is worried about more immediate concerns, such as an already-planned servicing mission intended to add two new instruments to the telescope, repair the Hubble's troubled gyroscopes, and prepare the spacecraft for a guided descent into the Earth's atmosphere.

With the space shuttle fleet still grounded following the Columbia accident, even that mission is uncertain, Kinney said. Moreover, NASA has not budgeted for the extra missions Hubble advocates are pushing for, she added. "They think we have a big pile of money, but our funds are already committed to approved projects."

NASA had intended to use a shuttle mission to retrieve Hubble and return it to the ground so it could be displayed by the Smithsonian Institution, but that plan had to be scrapped after the loss of Columbia due to concerns that such a mission would be too risky. NASA instead is looking into ways to push Hubble into the atmosphere, possibly with rockets sent up on an unmanned rocket. Kinney said NASA is considering attaching boosters to Hubble during the servicing mission, but the devices may not be ready in time for that shuttle flight.

Steven Beckwith, director of the Space Telescope Science Institute in Baltimore, said it would be shortsighted for NASA to forego an effort to further expand Hubble's capabilities. "The added cost...is very small compared with the amount of value" that would be obtained, he said.

Others argued that Hubble is providing so much material to astronomers that abandoning it is unthinkable. "Hubble is a national asset. It's not a question of putting it out of its misery," said Riccardo Giacconi, professor of astrophysics at Johns Hopkins University, also in Baltimore.

Bruce McCandless, a two-time shuttle astronaut who flew on the 1990 mission that carried Hubble, urged NASA to set a clear benchmark for determining when to abandon the telescope. NASA should operate Hubble until professional interest in the telescope clearly drops, he said.

McCandless added that it should be up to astronauts to decide whether it is worth risking human lives on space missions to Hubble. John Grunsfeld, a shuttle astronaut who has flown five of 18 space walks to repair Hubble, said one thing NASA should not do is consider bringing Hubble back to Earth. But Grunsfeld said the already-planned servicing mission is a different story. "We have not yet seen what will be Hubble's last hour," he said.

Astronomers said they have plenty of ideas for instruments that could be added to Hubble should NASA decide - or be directed by Congress or other government officials - to invest further in the telescope. Jon A. Morse, of Arizona State University, proposed an instrument that would help scientists learn more about how stars are born, for example.

John P. Huchea, chairman of the board of directors at the Association of Universities for Research in Astronomy, said losing Hubble would eliminate an invaluable ultra-violet and optical observatory that enjoys heavy support astronomers. He added that the gap between the termination of Hubble in 2010 and the launch of JWST in 2011 or beyond would deprive the world of irreplaceable opportunities. "Wouldn't it be a real pity if the next supernova went off three days after the Hubble Space Telescope was deorbited?"

But when asked by the panel whether his organization had considered what NASA should give up in order to pay for the additional Hubble investments it supports, Huchea said the group had not had such a discussion.