This
story was updated at 5:41 p.m. EST.
Engineers investigating
a debris shedding problem with NASA's shuttle fuel tanks have found a series of
hairline cracks in the same area where foam popped free during the July launch
of the Discovery orbiter, agency officials said Tuesday.
A total of
nine cracks - only two of them visible on the surface - were detected along a
protective foam ramp on NASA's External Tank
120 (ET-120), one of several under scrutiny at the agency's Michoud Assembly
Facility in New Orleans, tank officials said during a briefing at the agency's
Johnson Space Center in Houston.
"We're
still trying to figure out what this means," said NASA's John Chapman, external
tank project manager at Marshall Space Flight Center in Huntsville, Alabama. "I
wouldn't consider that a Eureka [moment] or smoking gun at all."
Originally tapped
to fuel Discovery's STS-114 liftoff
but later replaced,
ET-120 was one of three tanks sent back to Michoud from NASA's Kennedy Space
Center in Florida and the only one of them to hold the supercooled liquid fuel
used during shuttle launches.
Shuttle
program manager Wayne Hale added that, while the engineering assessment of the
cracks is still pending, it appears that the thermal and pressurization changes
involved in fueling the tank during two tests
may be one potential cause.
"It does
appear that that's a factor," he told reporters.
Hale said
that if everything proceeds as expected, NASA could be ready to launch
Discovery on STS-121, the agency's second return to flight mission, in May
2006, but stressed that the external tank work - not a schedule - comes first.
Safeguarding
shuttles
Preventing
the loss of potentially harmful chunks of external tank foam during a shuttle
launch has been a major focus of NASA since the loss of the Columbia orbiter and its seven-astronaut
crew during reentry Feb. 1, 2003.
A
1.37-pound chunk of foam critically damaged Columbia's heat shield at launch
leaving it vulnerable to the searing hot atmospheric gases during its descent,
investigators later found.
NASA spent
two and a half years and some $200 million to reduce the amount of large foam
debris during shuttle launches, but was surprised when an onboard camera caught
a one-pound chunk fall from a protective ramp thought to be safe.
The cracks
on ET-120 were found on the same ramp - known as a Protuberance Air Load (PAL)
ramp - designed to protect fuel length cabling from the aerodynamic pressures
of launch.
Hale said
that while initial shuttle fuel tanks designed in the late 1970s required PAL
ramps, newer containers have been improved and strengthened over time. Plans
are underway to streamline foam applications on the PAL ramp - which consists of
22 pounds of insulation foam - as well as strip it from future tanks altogether,
he added.
"It is
possible that we may get there for the first flight," Hale said, referring to
STS-121. "It is more likely that it may take us until the fall to complete that
work."
Orbiter
work
While
engineers continue their work on shuttle fuel tanks, other workers are
preparing the orbiters themselves for flight.
Steve Poulos,
head of NASA's orbiter project office, said that engineers have determined that
faulty stitching caused a nose-mounted thermal blanket
to balloon outward during Discovery's STS-114 flight.
"We've
inspected 486 blankets on both Discovery and Atlantis," Poulos said, adding
that 40 blankets will be replaced aboard Discovery and 60 on Atlantis."
Shuttle
workers have also pored over Discovery's heat-resistant reinforced carbon
carbon (RCC) panels that its nose and wing leading edges to determine which
need replacement or repair.
Poulos
added that new adhesion processes are also in hand to glue ceramic cloth gap fillers
between the heat tiles that line a shuttle's underside.
During
Discovery's STS-114 flight, orbital
photographs showed two gap fillers jutting out of the orbiter's tile-lined
belly, raising concern that they may lead to hotter reentry temperatures along
the shuttle's aft. STS-114 astronaut Stephen Robinson plucked the offending gap
fillers from Discovery's hull during the flight's
third spacewalk.
"At the end
of the day, we will have checked every gap filler on the vehicle," Poulos said.
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