NASA Administrator Sean O'Keefe said last month that due to safety considerations there would be no more servicing missions by shuttle astronauts to the famed Earth orbiting telescope.
Believed to be written by engineers associated with the Hubble program, the papers describe a rationale for flight that concludes that NASA's plans to deal with the risk of damage to an orbiter's heat shield after it departs the ISS would apply during a Hubble servicing mission.
Moreover, the papers suggest the risk of damaging the shuttle's heat protection tiles and reinforced carbon-carbon leading edge wing panels from orbital debris is less during a Hubble mission than an ISS mission.
While it all sounds logical, the analysis doesn't hold water, officials said.
"Although well intentioned, (the documents) over simplifies these complicated interrelated issues," William Readdy, NASA's top spaceflight official, told reporters in a telecon on Monday.
In order to accept flying a shuttle mission back to Hubble, the space agency would have to fully prepare a rescue mission capable of being launched almost immediately, Readdy said.
That would put undue schedule pressure on NASA and put managers into a position of having to launch no matter what weather or technical-related issues got in the way, he said.
"You'd be intentionally walking into a very high pressure, very schedule critical situation up front," Readdy said.
Other concerns about a rescue mission also played a role in the decision not to return to Hubble.
"Although there was no singular factor that tipped the balance, the added extreme schedule pressure associated with mounting a Hubble servicing mission rescue flight, due to the lack of International Space Station safe haven capability, as well as the notion of an untried, free space transfer of crew from one orbiter to another were clearly factors," Readdy said.
Meanwhile, those operating the Hubble still have job security for several more years, said Ed Weiler, NASA's space science chief.
Hubble engineers are working on ways to extend the telescope's science lifetime once systems begin failing, but after the batteries fail the observatory will quickly become too cold to function, Weiler said.
Moving Hubble from its present orbit to the same inclination as the ISS orbits was studied this past weekend, but more from an academic point of view as Weiler said it would take some 20,000 kilograms of propellant to do the trick and the telescope is not equipped with rocket engines.
"The amount of energy required to change the orbit is substantial," Weiler said.
Still, if a way can be found to keep Hubble going -- with or without using the shuttle -- scientists would applaud the effort, said John Grunsfeld, NASA's chief scientist, a former astronaut who has visited Hubble twice.
"There's no question that Hubble science is important. We would support going back to Hubble if we could," Grunsfeld said, agreeing with his colleagues that it's just not safe to do so using the shuttle no matter how popular the science from Hubble has been.
"It's not really a science priority question. If we could do it, we would do it," Grunsfeld said.
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