NASA's upcoming verdict about the Hubble Space Telescope's (HST) future is an unprecedented decision -- one that entails money, politics, orbital mechanics, and risk-avoidance ripple effects stemming from the Columbia space shuttle catastrophe.

At present, 2010 is the desired retirement date for Hubble operations. But what to do with the school bus-sized mega-star of the heavens is up for grabs. The answer may foretell when, and if, NASA can pull itself out of low Earth orbit and think bigger thoughts.

At NASA, the hope is to park a "beyond Hubble" observatory -- the super-powerful James Webb Space Telescope (JWST) -- in space by late 2011.

One on-going discussion inside NASA in the wake of the Columbia disaster is always flying space shuttle missions on "safe haven" inclinations -- trajectories whereby a space plane and its crew can link up with the International Space Station (ISS) if problems crop up.

That would leave Hubble out in the cold -- it resides in a different orbit than the station. Hubble is at an altitude of 380 miles (612 kilometers), inclined 28.5 degrees to the equator while the ISS orbits at altitude ranging roughly between 225 miles (362 kilometers) and 264 miles (425 kilometers), inclined at 51.6 degrees to the equator. According to industry and government sources close to the Hubble project, there is some chatter about no more servicing missions to the orbiting observatory, period.

If that's the case, Hubble is doomed to spiral in on its own accord. It would reenter and breakup in an uncontrolled manner as it careens through Earth's atmosphere. According to experts at the NASA Goddard Space Flight Center, "a significant debris field" would hit the surface of the Earth.

"In particular the massive primary mirror and its surrounding titanium main ring -- the structural backbone of HST -- will almost certainly impact the Earth," a Goddard report obtained by SPACE.com notes. Moreover, a special reentry computer calculation done by NASA's Johnson Space Center predicts a 1/700 probability of human casualty resulting from an uncontrolled Hubble reentry. The current NASA requirement is a probability of less than 1/10,000.

But there is good news. At present, the official policy of NASA's Office of Space Science is that the HST will not be allowed to reenter in an uncontrolled manner.

NASA's Office of Space Science presently has provisions, with money attached, for one more Hubble servicing mission. That would be followed by a final mission to "decommission" the telescope safely. In other words, protect the surface population from reentry harm. This budget includes a shuttle flight.

There are advocates for yet another Hubble servicing mission. That desire rests largely with astronomers with optical observing programs, aerospace vendors, and some parts of NASA itself. Also, toss in some general public boosters and you've got what former NASA chief, Daniel Goldin, criticized as a bunch of "Hubble huggers."

Charles Beichman, Chief Scientist at the Jet Propulsion Laboratory's Astronomy and Physics Directorate recently captured the issues at hand. He submitted his own opinion recently to the blue ribbon panel charted by NASA to figure out a pathway from Hubble to the James Webb Space Telescope.

"We should call on the bravery of NASA's astronauts for one last flight to Hubble to add its final suite of instruments, to service its aging systems, and to prepare Hubble for its eventual safe de-orbit into the Pacific Ocean sometime after 2010," Beichman said. "But we should not let our attachment to a cherished telescope hold back a new and more capable generation of observatories that will produce the breakthroughs of the future," he added.

How best to bring down Hubble…or for that matter, shove it high above Earth?

NASA engineers are studying use of some form of rocket stage. Yet that hardware would have to be hauled up to the telescope and attached. The job would call for either a shuttle mission or some sort of automated robotic gear, built to rendezvous and dock with Hubble.

There's a slight hitch, however. Notions of robotic hookups to Hubble are currently hypothetical and conjectural. No such capability exists presently. This hardware could be made available in future years, given proper funding.

In fact, once installed, such a propulsion module offers flexibility in deciding Hubble's ultimate fate. Re-boost could permit continued telescope operations. Using the module for de-orbiting Hubble means no need for a shuttle.

NASA Goddard engineers have flagged one possible problem with this idea.

"Its principal drawback is that if it [the propulsion module] does not work properly when commanded, another shuttle mission would be required to repair or replace it. Otherwise uncontrolled reentry is inevitable. Of course the shuttle mission to install the propulsion module could also do other maintenance and upgrades of HST, thus extending its scientific lifetime," a Goddard report points out.

A complicated matrix of issues now face the HST-JWST Transition Plan Review Panel, chaired by John Bahcall of the Institute for Advanced Study in Princeton, New Jersey.

Key tasks before the panel: Identify the best science path to be taken; what overlap is needed between the orbiting instruments; and how best to serve science given a constrained budget. Should it be continued support of HST at the expense of JWST schedule and/or content? Or close down HST in favor of an earlier JWST?

In NASA circles, discussion has begun of peppering space with "gap-scopes". Several NASA Mid-Class Explorer (MIDEX) missions that are not now on the books could be flown. They would take up some science duties between a gone-from-the-scene Hubble and a still-to-fly James Webb Space Telescope.

Some view Bahcall's panel as addressing the road ahead in terms of science versus science. But there are other issues too. The group cannot resolve, for instance, science versus budget. Ultimately, that is a NASA Office of Space Science responsibility.

Furthermore, there's the science versus risk. That determination falls into NASA's human spaceflight enterprise, with consensus all the way up to the higher levels of the Congress and White House. Still to weigh in is the Columbia Accident Investigation Board and its menu of shuttle return-to-flight rules.

How long NASA takes to regain confidence and credibility in its human spaceflight endeavors remains to be seen.

An even broader question also looms large: Will NASA consider low Earth orbit a safe haven for crews for years to come…putting on hold any taking of steps to return humans to the nearby Moon or sending out an expedition to distant Mars?