NASA's final shuttle flight to overhaul the Hubble Space Telescope will fly only when it is safe to do so, the agency's science chief said Tuesday.
Alan Stern, associate administrator for NASA's science mission directorate, said the agency's planned August launch to Hubble by seven astronauts aboard the Atlantis orbiter is dependent on the success of three other shuttle flights to lift off in upcoming months.
The shuttle must first haul a new European laboratory to the International Space Station (ISS). But that flight — slated to launch no earlier Jan. 24 — has been waylaid by fuel sensor system glitches since December and faces a likely slip to early February, NASA officials have said.
"Our watch word in all this is safety," Stern said during a meeting at the American Astronomical Society in Austin, Texas. "Hubble is perfectly capable of taking care of itself, and if the servicing mission needs to be in September, October, later in the year - whenever - we're going to do it the safest way we can as an agency. Safety is going to be first."
Hubble's final visitors
Targeted for an Aug. 7 launch, Atlantis and its STS-125 astronaut crew will fly the fifth servicing mission — dubbed SM-4 — to Hubble since the observatory's launch in 1990.
But the mission is not without risk.
Unlike shuttle astronauts on ISS construction flights, Hubble-bound spaceflyers will not be able to return to the space station should their spacecraft suffer major damage. Instead, another NASA shuttle is expected to be ready to launch a rescue mission within about 25 days of any serious problem aboard Atlantis, NASA officials have said.
In fact, the agency canceled the Hubble servicing mission outright after the loss of seven astronauts and the space shuttle Columbia during atmospheric reentry in 2003. An errant piece of fuel tank foam damaged the Columbia's left wing-mounted heat shield during liftoff, leading to the accident.
"The decision not to fly the Hubble servicing mission following the tragic loss of Columbia was based on an assessment of risk, given the circumstances at the time," said astronaut John Grunsfeld, lead spacewalker for the upcoming Hubble servicing mission.
Since the agency resumed shuttle flights in 2005, NASA engineers and astronauts have repeatedly proven their ability to use new inspection techniques to ensure orbiter heat shield health on seven successful missions. It was based on the success of those techniques that NASA revisited, and ultimately approved, Hubble's final servicing flight in October 2006.
"We felt that the risk of this Hubble mission is comparable to the risk of, say, an STS-115 [mission], which we flew post-Columbia," said Grunsfeld, who will make his third trip to Hubble and fifth spaceflight during the servicing flight.
Without one last servicing mission, Hubble could physically last until 2011, but this summer's flight is designed to extend its science-producing lifetime through 2013.
Planned upgrades for the orbital observatory include fresh batteries and gyroscopes; unprecedented repairs to its main camera and a spectrometer; as well as the installation of the new Wide Field Camera 2 and Cosmic Origins Spectrograph. If all goes well, the STS-125 mission would leave Hubble 90 times more powerful than the original telescope that launched in 1990.
Hubble has proven itself to be a watershed astronomical tool for researchers and the public-at-large, said Grunsfeld, a physicist. But the agency has not shirked safety to support that science, he said, as proven by the repeated delays for NASA's upcoming shuttle flight so engineers can fix a redundant, but vital, system.
"We need to fly safe, that's our number one job," said Grunsfeld. "I still believe that Hubble, and Hubble science and Hubble program ? is still something that's worth risking my life for, and I know I have a crew of six other crewmembers who believe that as well.
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