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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