The
decision of two top NASA managers to vote
against the upcoming July 1 launch of the space shuttle Discovery pivoted
on the risk of losing the orbiter, but not its astronaut crew, the officials said
Wednesday.
NASA chief
engineer Christopher Scolese and the agency's top safety officer Bryan O'Connor
said that, despite their objections, neither official believed the planned
launch of Discovery's STS-121
mission carried unacceptable risk for the seven astronauts making the space
shot.
"We felt
that the risk was to the vehicle and not the crew," Scolese told reporters
during a teleconference, adding that NASA's plan
to keep shuttle astronauts aboard the International Space Station (ISS) if
their orbiter is damaged and can't return home is vital to crew safety. "While
it's an undesirable situation to be in, it is certainly something that's viable
and provides us with the additional security for this mission."
Scolese and
O'Connor each cast a negative vote for Discovery's scheduled July 1 liftoff
during a standard Flight
Readiness Review meeting that concluded June 17. Their concerns revolved around
the hazard posed by foam insulation that could fall from a series of ice
frost ramps coating brackets on shuttle's external tank and strike the
orbiter. [Click here for NASA chief Michael Griffin's rationale for the STS-121 launch decision.]
External
tank launch debris has been a serious concern since the 2003 Columbia accident, when
damage from a foam strike breached that orbiter's heat shield during liftoff
and led to its destruction, and the loss of seven astronauts, during reentry. Despite
more than two years of work and modifications, large
foam pieces were seen falling from Discovery's fuel tank during its STS-114
launch last summer.
Discovery
is now poised to launch its STS-121 crew, commanded by shuttle veteran Steven
Lindsey, on a 12-day trip to the ISS. The flight will test new fuel tank changes,
methods for shuttle inspection and repair, and deliver fresh supplies to the
ISS.
"The crew
is okay with this, as I'm sure you've heard them say,"
O'Connor said of the launch decision.
Future
fix and safe haven
NASA shuttle
officials have said the primary reason for not delaying Discovery's STS-121 flight
until a proper ice
frost foam ramp fix is ready is two-fold.
First,
Discovery's current fuel tank has already been stripped of a 38-foot (11-meter)
foam-covered ramp to reduce the amount of debris that could shake loose during
launch. The change constitutes the biggest aerodynamic modification to the
shuttle launch system in 25 years, and should be tested alone without
additional changes, NASA officials have said.
Adding to
that is the absence of a viable ice frost ramp modification.
"Right now
we really don't have an ice frost ramp fix," William Gerstenmaier, NASA's
associate administrator of space operations, said in the teleconference.
A fix could
be ready by the end of the year, he added.
Meanwhile,
the space station is primed to support a nine astronauts - the two members of
Expedition 13 is already onboard - for more than 80 days should it be required
to provide safe haven for the STS-121 crew, NASA officials said. But it is also
not a situation shuttle managers want to put Discovery's crew into
unnecessarily.
"Putting
nine people on that space station is a real stress," O'Connor said. "It's not
like you've brought them home yet."
But with the
risk posed by the ice frost ramps understood and accepted by NASA administrator Michael
Griffin and other top agency officials, O'Connor said he felt his concerns had been
heard.
"I felt
that I was not going to lie down in the flame trench or throw down my badge," O'Connor
said. "We now go forward and see if we can get this vehicle off the launch pad
next week."
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