NASA is in a cosmic quandary as to the fate of the Hubble Space Telescope (HST). The end of the grand old telescope's mission is scheduled for 2010, but the agency has yet to decide whether it should be deorbited, abandoned or plucked from its orbit and returned to Earth in the cargo bay of a space shuttle.

However, an astronaut that has serviced the observatory now says that bringing Hubble back to Earth is far too risky.

A special panel of noted scientists has started wrestling with how best to end HST operations and transition to a next generation orbiting eye on the universe - the James Webb Space Telescope (JWST). That observatory is still years in the making, headed for a sendoff into space in August 2011, but barring technical or budgetary snags.

John Grunsfeld, a NASA astronaut and astronomer, is on tap to detail his views before the panel. A four-flight shuttle veteran, two of his space travels -- in 1999 and 2002 -- were HST servicing missions.

In a prepared text obtained by SPACE.com via the panel's web site, he backs a future servicing mission to Hubble, now scheduled for 2005. But the astronaut nixes the idea of returning the telescope to Earth.

"If there were to be a mission after the SM4 [Servicing Mission 4] for the purpose of returning Hubble to Earth in the shuttle payload bay, the Astronaut Office would have reservations supporting the mission," Grunsfeld's prepared statement explains.

"Initial analysis shows that perhaps four spacewalks are required, significant hardware would have to be jettisoned, and a heavyweight return through the atmosphere would have to be performed. In a sense this mission would be risking human lives, and a unique national resource [the space shuttle], for the purpose of disabling great science, albeit due to necessity at end-of-life," Grunsfeld explains.

Favored by the Astronaut Office, Grunsfeld states, are alternate approaches to handling Hubble, including the installation of a propulsion module to the telescope, via robotic or human servicing.

Also on Thursday's public docket to discuss his thoughts is former astronaut, Bruce McCandless II. He was onboard space shuttle Discovery in 1990, the HST deployment mission.

In his written statement, McCandless cautions against premature deterioration of the Hubble Space Telescope. The former astronaut supports the SM4 mission to HST, as well as a "novel concept" for an SM5 trek to the telescope.

McCandless proposes trying out robotic tele-servicing of the observatory, backed up by on-the-scene spacewalking astronauts. This trial run of dexterous devices could be done from onboard the shuttle, or by ground-based operators, he contends.

Gaining experience with tele-robotic servicing, McCandless reports, is key to advancing in-space servicing. The technology of space compatible telemanipulators has progressed substantially over the last two decades, "but the devices themselves have had no real use," he explains.

The prospect that Hubble may never be brought down via a shuttle has prompted other ideas.

Documents on the HST-JWST Transition Plan Review Panel website show support in some quarters for attaching a propulsion module to Hubble. This hardware could boost the telescope to a somewhat higher altitude, delaying a fatal fall to Earth.

According to a HST Project report from NASA's Goddard Space Flight Center, a small shuttle reboost of the telescope during the next servicing mission could forestall HST's reentry by some two years. That would allow more time to pull together a robotic retrieval mission and a controlled re-entry of Hubble to Earth, destroying the multi-billion dollar asset in the process.

On the other hand, Hubble could be overhauled and outfitted with advanced instruments for a new round of stargazing. The observatory might then be propelled into an orbit adding a decade or more to its lifetime. This scenario also brings with it the need for hefty amounts of money.

Without intervention, the HST orbit is doomed to decay. The telescope would reenter and breakup in an uncontrolled manner, now predicted in one study to occur late 2013 or early 2014

The five member HST-JWST panel is chaired by John Bahcall of the Institute for Advanced Studies, The other panel members are: Barry Barish, California Institute of Technology; Christopher McKee, University of California, Berkeley; Martin Rees, Cambridge University; and Charles Townes of the University of California, Berkeley.

Chartered by NASA's Office of Space Science, the Bahcall study group is to complete and submit their final report to the space agency on October 1.