Schematic details of ice frost ramps on the external tanks for NASA's space shuttle.
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."
- The Great Space Quiz: Space Shuttle Countdown
- NASA Safety Chief Speaks Out on Foam Concerns
- STS-121 Crew to Fly on July 1
- Return to Flight: NASA's Road to STS-121