Last week anonymous documents began to circulate on Capitol Hill, among the astronomy community, and through out the media. These documents describe the risks of a shuttle repair mission in a somewhat different light than NASA has stated.

One of these two documents states "The final planned HST Servicing Mission, SM4, will be at least as safe as shuttle flights to the International Space Station (ISS)."

The other document says "one can also conclude that no additional work needs to be performed over and above what must already be performed for ISS missions launched in the same timeframe."

In announcing the decision last month not to send a Shuttle mission to the Hubble in 2006, NASA Administrator Sean O'Keefe said that the prime reason was safety - not budget. O'Keefe cited recommendations from the Columbia Accident Investigation Board (CAIB) and internal assessments by NASA as the basis for making this decision. O'Keefe was very clear that this decision was made by him.

The SM4 Hubble Servicing mission (the fifth one to visit the telescope) was originally scheduled for 2006 and would have replaced gyroscopes and batteries and installed several new scientific instruments. In the post-Columbia way of doing business NASA had decided that in order to assure the safety of a crew flying to service Hubble that another shuttle would need to be fueled and ready to go in case the first shuttle was damaged and unable to return to Earth.

This would be required since the Hubble and the space station are in different orbits. This would prevent a crippled orbiter from reaching the space station as a "safe haven" if problems arose. Of course this would add considerable complexity to the standard way of doing things. "This means two countdowns, two control centers, two of everything" NASA's Associate Administrator for Spaceflight William Readdy said in a teleconference with reporters on Monday.

Were that rescue mission to fly to assist the crew of a Hubble servicing mission it would require the rescue crew to practice the very risky, and never before staged transfer of crew from one space shuttle to another. This would compound the risk even further.

Given the risks that went with all of these contingencies, O'Keefe decided that the risks were too great in flying a shuttle mission to service the Hubble. Instead, NASA would allow the telescope to work as long as it could without direct human intervention and then use a robotic spacecraft to send it safely back to Earth once it had reached the end of its useful life.

Now, the Hubble will be left to operate in its slowly deteriorating fashion. NASA has come up with some clever ways to allow science to continue if another gyroscope fails and is looking at ways to start conserving electrical power to extend the life of the telescope.

Weiler believes that the Hubble could be doing useful science through 2006 and into 2007. Some of these advanced measures under development might extend its life further - perhaps another 18 months beyond 2007.

Once the telescope has failed it will still orbit Earth safely until around 2013 allowing NASA plenty of time to develop a robotic spacecraft that would dock with the Hubble and then steer its 25,000 pounds of mass into a safe disposal in the Pacific Ocean

When the Hubble does fail and become inoperable, Weiler said that it will still be straightforward to dock with the spacecraft and sent it back to earth. However, trying to launch a shuttle mission to fix Hubble on short notice would be quite another matter altogether.

It is possible that the time when the shuttle flights would be needed might not provide a lot of warning. In addition to the possibility of gyroscope failure, there is a possibility that the batteries might start to fail.

According to Weiler "once the batteries go the heaters fail and all critical components get very cold - some could never be revived." As such the need to mount a repair mission might come on short notice.

According to Readdy this unpredictability could cause a lot of what he termed "schedule pressure." "You'd have to drop in not only the Hubble Servicing mission but also the standby rescue mission." That would take two orbiters out of station work and pretty much put station assembly on hold.

NASA's official views not withstanding, the two anonymous documents see things in a different light.

One document said that NASA would need to develop the ability to repair a space shuttle on its own without flying to the Space Station anyway. The document goes on to argue that if NASA was comfortable with not having a rescue shuttle on standby for space station missions, and that this repair hardware needed to be developed, then the agency should not raise objections to flying a mission to service Hubble since, the documents argue, the risk is the same.

When asked to comment on the documents and whether the Space Telescope Science Institute backs their findings, Readdy said "I really can't offer opinion on the Institute or their views. I would assume that they'd like to see it continue to be as healthy as long as possible." He went on to observe that some people still held out hope that things might change - but then sought to limit that hope by stating emphatically that "Hubble's future does not include another Shuttle servicing mission."

Readdy went on to say that the documents "did not capture the totality of the process" and said that a point by point response had been prepared for briefing to House Science Committee staffers tomorrow. Readdy declined to say whether this detailed response would be made public.

The decision not to visit the Hubble one last time is a slow motion death sentence of sorts. But all spacecraft eventually come to the end of their useful lives.

According to NASA Chief Scientist and astronomer John Grunsfeld, who is also an astronaut and has participated in two Hubble Servicing missions, "I am the last person to ever hug Hubble. This is something very personal."

In describing the fondness people have for Hubble Grunsfeld said "we have allowed the American public to fall in love with Hubble. It is arguably one of the most important science tools ever made. Now, we have decided that we are not going back -and it is based on good rationale ."

Referring to Hubble as being like a member of the family Grunsfeld said "there is now a time table for when this family member departs. We want the remaining time to be quality time."

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