UPI obtained copies of the documents, which also have made the rounds in the astronomy community since last week. They describe the risks of a repair mission in a somewhat different light than the National Aeronautics and Space Administration has characterized.
One of these two documents states: "The final planned (Hubble) Servicing Mission, SM4, will be at least as safe as shuttle flights to the International Space Station."
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."
Last month Sean O'Keefe, NASA's administrator, said safety -- not budget -- was the prime factor in his decision not to send a shuttle mission to the Hubble in 2006. It was a reference to President George W. Bush's announcement on Jan. 14 that he wanted to retire the shuttle fleet in preparation for a new effort to return to the moon and explore the solar system.
In making his decision regarding Hubble, O'Keefe cited recommendations from the Columbia Accident Investigation Board, as well as internal NASA assessments. He also made it clear it was his decision -- not the president's.
SM4 -- which would have been the fifth to visit the orbiting telescope -- would have replaced gyroscopes and batteries and installed several new scientific instruments. In the aftermath of the Feb. 1, 2003, Columbia tragedy, however, NASA decided that to assure the safety of a crew flying to service Hubble, another shuttle would have to be fueled and ready to go in case the first orbiter was damaged and unable to return to Earth.
This strategy would be necessary because the Hubble and the space station follow different orbits. A crippled shuttle could not reach the station and use it as a safe haven if problems arose during a telescope repair mission. This technicality would add considerable risk and complexity to NASA's standard procedures.
"This means two countdowns, two control centers -- two of everything," William Readdy, NASA's associate administrator for spaceflight, said Monday afternoon in a teleconference with reporters.
If a rescue mission became necessary to assist the crew of a Hubble servicing mission, the rescue crew would have to attempt the very risky and never-before-staged transfer of crew members from one space shuttle to another.
Given the risks that would accompany such an operation, and in the wake of Columbia, O'Keefe canceled the 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 endeavor to create a controlled disintegration upon re-entry into Earth's atmosphere.
Hubble will be left to operate in its slowly deteriorating fashion, although NASA has concocted some clever ways to allow science to continue aboard the telescope even if another of its gyroscopes fail. The agency also is considering ways to begin conserving electrical power to extend Hubble's operational life.
If all goes well, Weiler thinks Hubble could continue doing useful science through 2006 and perhaps into 2007. Some of the advanced control measures under development might extend its life further -- perhaps another 18 months.
Once the telescope fails, it will continue orbiting Earth until around 2013, allowing NASA plenty of time to develop a robotic docking spacecraft that could steer its 25,000 pounds of mass into a safe Pacific Ocean disposal.
Weiler said the task of docking with the telescope and sending it back to Earth would be relatively straightforward. That would not be the case, however, if NASA engineers tried to launch a shuttle mission to fix Hubble -- especially on short notice.
Such a contingency would arise if Hubble malfunctions suddenly and unexpectedly -- for example, the onboard 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."
Readdy said such a development 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," he explained. That would take two orbiters out of station work and pretty much put station assembly on hold.
NASA's official views notwithstanding, the two anonymous documents see things in a different light.
One document said NASA needs to develop the ability to mount a shuttle rescue mission whether or not the space station is available. If the agency is comfortable with not having a rescue shuttle on standby for space station missions, and repair hardware needs to be developed, then NASA should not raise objections to flying a mission to service Hubble -- because the risk is the same.
When asked to comment on the documents, Readdy said: "I really can't offer opinion on ... their views. I would assume that they'd like to see (Hubble) continue to be as healthy as long as possible."
Readdy went on to observe that some people still hold out hope things might change. He also sought to limit that hope by stating emphatically: "Hubble's future does not include another shuttle servicing mission."
Readdy said the so-called anonymous documents "did not capture the totality of the process," and added a point-by-point response had been prepared for briefing the House Science Committee staff Tuesday. He declined to say whether this detailed response would be made public.
Although the decision not to visit the Hubble one last time is a slow-motion death sentence of sorts, all spacecraft eventually come to the end of their useful lives.
NASA Chief Scientist and astronomer John Grunsfeld, who also is an astronaut and has participated in two Hubble Servicing missions said: "I am the last person to ever hug Hubble. This is something very personal."
"We have allowed the American public to fall in love with Hubble," he said. "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."
Grunsfeld likened the Hubble to family and added: "There is now a timetable for when this family member departs. We want the remaining time to be quality time."
Keith Cowing is editor of NASAWatch.com. E-mail email@example.com