An unknown
object pierced a radiator mounted to one of two cargo bay doors aboard NASA's
shuttle Atlantis during its September
spaceflight, but did not endanger the vehicle or its six-astronaut crew at
any time, the space agency said Thursday.
"Although
it's small, by comparison it may be the second largest impact we've been able
to detect on a payload bay door," NASA spokesperson Kyle Herring told SPACE.com.
"It did not do any other damage to the vehicle other than penetrate the
radiator."
The impact occurred
at some time during Atlantis' STS-115
mission to install new trusses
and solar
arrays at the International
Space Station. The 13-day spaceflight ended with a predawn
landing on Sept. 21. Images
of the damage site - dubbed
"Ding 18" were first published by the website collectSPACE.com, and later
released by NASA.
According
to a schematic
of the damage, the unknown object - either a micrometeoroid or other piece
of orbital debris - caused a small, one-tenth of an inch (2.5-millimeter) puncture
in Atlantis' aft starboard radiator and appeared to leave a 0.031-inch (0.7-millimeter) exit
hole and a nearby crack.
"The nature
of the object that hit the shuttle radiator isn't known," a NASA update said,
adding that shuttle processing crews discovered the hole while working on the
spacecraft.
The impact
also damaged a one-inch (2.5-centimeter) area in the radiator's honeycomb-like
aluminum mesh, but did not sever any of the panel's 26 vital coolant tubes as
it passed through the half-inch wide panel.
Atlantis's aft
radiator panels each measure about 15.1 feet (4.6 meters) by 10.5 feet (3.2
meters) and house 26 tubes for Freon-21 coolant.
Even if the
breach had severed one of the coolant tubes, Atlantis carries two redundant cooling
lines, Herring said, adding that a Freon loop breach in one loop would have led
the shuttle's onboard software to shut down the damaged system.
About 70
percent of the orbiter's cooling needs could be met by one cooling loop, though
the situation would prompt discussions of whether to power down non-vital
electronics or returning to Earth early depending on the mission's timeline, he
added.
"It becomes
a discussion and not an emergency situation," Herring said.
Atlantis'
mystery objects
Atlantis'
STS-115 astronauts - commanded by veteran
shuttle flyer Brent Jett - conducted three
in-depth scans of their spacecraft, though most of them were aimed at
evaluating the health of the orbiter's heat shield and not its payload bay.
"This is
exactly why we instituted the late inspection in this program," Herring said. "We've
known for the life of this program that [micrometeorite and orbital debris] was
a top risk to the space shuttle. Definitely in the top five, and maybe in the
top three."
Just before
landing, flight controllers and the astronauts themselves noted several items -
later dubbed "mystery
objects" - that appeared to have floated out of Atlantis' payload bay after
a series of thruster tests. The debris prompted
a third and final round of heat shield inspection.
That scan also
included a camera survey of Atlantis' payload bay to search for any missing
objects, and mission managers later gave the shuttle a clean
bill of health and cleared
its crew for landing.
Mission managers
did not report any signs of the radiator impact after the payload bay survey. The
region is not subjected to the severe heating stresses of atmospheric reentry,
and would not have posed a threat to the orbiter during its Earth return, NASA officials
have said.
Watching
debris
NASA has
kept a close watch on launch and orbital debris since the loss of seven
astronauts and their space
shuttle Columbia during reentry on Feb. 1,
2003.
The vital
heat shield on Columbia's left wing leading edge - an area that sees some of
the highest temperatures during reentry - was breached by a suitcase-sized
chunk of foam insulation from orbiter's external fuel tank 16 days earlier during
launch, and led to its destruction. NASA has since taken great strides to
prevent foam insulation debris during launch, an effort that led to two,
near-flawless launches this summer.
The damage
seen on Atlantis' radiator - while not a threat to the spacecraft or its crew -
is indicative of the potential impacts from micrometeoroids and orbital debris
(MMOD) to spacecraft in flight. It is that hazard that prompted shuttle managers
to add
the second heat shield inspection to July's STS-121
mission and subsequent spaceflights.
"In simple
terms, there is a risk that you could be struck my MMOD," Atlantis' lead shuttle
flight director Paul Dye said last month during the STS-115 mission, adding
that the risk is small but always present for any piloted spacecraft. "So we
think it's a prudent thing to take a look."
Meanwhile,
NASA shuttle engineers continue to prepare Atlantis' sister ship Discovery for
its STS-116
mission to continue ISS construction. Commanded by experienced NASA
astronaut Mark
Polansky, the STS-116 will deliver a new piece of framework to the ISS,
stage several spacewalks to rewire the station's power grid and ferry
a new crewmember - first-time
flyer Sunita Williams - to join the outpost's Expedition
14 crew.
The
spaceflight is slated to launch no earlier than Dec. 7 at 9:38 p.m. EST (0138
Dec. 8 GMT) and mission managers discussed the mission's planned night launch,
which would be the first since the Columbia accident, in a Thursday meeting.
"The
consensus was that restoring night launch capability for the shuttle does not
impose any additional risk to the safety of the vehicle or the crew," Herring
said. "Clearly launching in daylight is desirable, but everyone agreed it's not
required."
advertisement
advertisement
