NASA: Shuttle Discovery’s Heat Shield Fit for Earth Return

NASA: Shuttle Discovery’s Heat Shield Fit for Earth Return
This view of the nose and part of the crew cabin of Space Shuttle Discovery was provided by an Expedition 14 crewmember during a back-flip performed by the approaching STS-116 crew to the International Space Station on Dec. 11, 2006.
(Image: © NASA.)

HOUSTON--The heat shield designed to safeguardNASA's space shuttleDiscovery and its astronaut crew against the searing temperatures ofatmospheric reentry is in good health, mission managers said late Tuesday.

JohnShannon, NASA's deputy shuttle program manager, told reporters that analysts havesettled concerns over tworemaining areas of interest on Discovery's heat shield.

"The vehicleis extremely clean, and we got all of our areas cleared off," Shannon saidduring a night briefing here at NASA's Johnson Space Center. "The thermalprotection system is ready to come home."

ClearingDiscovery's heat shield removes the need to add additional inspections to the busyWednesday work roster for the spacecraft's STS-116 crew. The astronauts andtheir International SpaceStation (ISS) counterparts already have a packed day ahead of them thatspotlights the first-ever solar array retraction in the orbital laboratory'ssix years of human habitation.

"We reallywanted to clear the decks of any orbiter issues," Shannon said, adding thatDiscovery's crew will perform a final heat shield inspection after undockingfrom the ISS next week.

Shannonthat he was surprised that pre-docking photography of Discovery's belly foundno signs of protruding bits of ceramic cloth--known as gap-fillers--or plastic shims,which have popped up on in one form or another during the last three shuttleflights.

Discovery'sSTS-116mission is a planned 12-day spaceflight to delivera new segment of the ISS, rewire the station's power grid and perform a one-personcrew change for the outpost's Expedition14 astronauts.

NASA has paid close attention to shuttleheat shield health since the 2003Columbia accident, in which wing damage caused by external tank debris atlaunch led to the loss of the orbiter and its seven-astronaut crew duringreentry at the mission's end.

Minorissues

Shannon said analysts first focused on theport external tank door on Discovery's belly, where high-resolutionphotographs showed minor damage to the orbiter's protective heat-resistant tilesand orange bits of cellophane-like material jutting from the door seal [image].

"The teamworked very hard overnight on both of those problems," Shannon said.

Thecellophane appears to be barrier material used inside shuttle external tankumbilical areas, Shannon added. The material has been seen to jut out in the past,is not obstructing the external tank door's seal from its proper closedposition, and will likely burn off quickly during reentry, Shannon said.

Likewise, somescuffed tiles that appear as white splotches on the uniformly black surface ofDiscovery's underbelly near the orbiter's portside external tank door appear tobe the result of recirculated ice or even the cellophane barrier material rubbingthe coating from heat tiles during launch.

Similardamage has been in many shuttle flights in the same region, NASA officialssaid.

Not satisfiedsimply with past flight history that the damage-prone region has not impactedshuttle flight safety, engineers ran a series of analytical assessments of thedamage as well.

"It cameback that we had no concerns at all for that damaged tile area," Shannon said. "So the team was able to very quickly last night able to conclude that noneof the problems around the port external tank door were going to be an issuefor the safe return of Discovery."

Analystsalso cleared a sensor reading indicating a potential it by a micrometeoriteor orbital debris (MMOD) to one of Discovery's wing leading edges. Imagesof the region taken by cameras at the tip of the International Space Station'srobotic arm found no signs of damage late Monday, and a subsequent round ofphotography using Discovery's own robotic appendage was on tap for Tuesdaynight.

"It's notclear whether we were struck by MMOD or not," Shannon said, adding that impactsto other nearby areas could have caused the same reading and that no damage hasbeen found. "We're interested in getting the vehicle back on the ground and takinga look at it, but it was very clear that we had sufficient imagery to clear thevehicle of this concern and not worry about it anymore."

In a debrisrelated note, STS-116 lead spacewalk officer Tricia Mack said that NASA had confirmedin spacesuit camera video that European Space Agency astronaut ChristerFuglesang did lose a 7.8-inch extension for a pistol grip tool during a Tuesdayspacewalk to install the new Port 5(P5) spacer truss at the ISS [image].The metal extension weighs just under a pound and was last seen drifting in a "portish"direction, Mack said, adding that debris experts are working to track it.

Discovery'screw was alerted of the spacecraft's healthy status earlier Tuesday.

"Soundslike you guys have obviously done your usual thorough analysis," STS-116commander Mark Polansky said Tuesday. "We're happy to hear that we'll be ableto go ahead with the nominal timeline tomorrow."

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  • Mission Discovery: The ISS Rewiring Job of NASA's STS-116
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