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. CREDIT: NASA.

HOUSTON--The heat shield designed to safeguard NASA's space shuttle Discovery and its astronaut crew against the searing temperatures of atmospheric reentry is in good health, mission managers said late Tuesday.

John Shannon, NASA's deputy shuttle program manager, told reporters that analysts have settled concerns over two remaining areas of interest on Discovery's heat shield.

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

Clearing Discovery's heat shield removes the need to add additional inspections to the busy Wednesday work roster for the spacecraft's STS-116 crew. The astronauts and their International Space Station (ISS) counterparts already have a packed day ahead of them that spotlights the first-ever solar array retraction in the orbital laboratory's six years of human habitation.

"We really wanted to clear the decks of any orbiter issues," Shannon said, adding that Discovery's crew will perform a final heat shield inspection after undocking from the ISS next week.

Shannon that he was surprised that pre-docking photography of Discovery's belly found no 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 shuttle flights.

Discovery's STS-116 mission is a planned 12-day spaceflight to deliver a new segment of the ISS, rewire the station's power grid and perform a one-person crew change for the outpost's Expedition 14 astronauts.

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

Minor issues

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

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

The cellophane appears to be barrier material used inside shuttle external tank umbilical 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 closed position, and will likely burn off quickly during reentry, Shannon said.

Likewise, some scuffed tiles that appear as white splotches on the uniformly black surface of Discovery's underbelly near the orbiter's portside external tank door appear to be the result of recirculated ice or even the cellophane barrier material rubbing the coating from heat tiles during launch.

Similar damage has been in many shuttle flights in the same region, NASA officials said.

Not satisfied simply with past flight history that the damage-prone region has not impacted shuttle flight safety, engineers ran a series of analytical assessments of the damage as well.

"It came back 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 none of the problems around the port external tank door were going to be an issue for the safe return of Discovery."

Analysts also cleared a sensor reading indicating a potential it by a micrometeorite or orbital debris (MMOD) to one of Discovery's wing leading edges. Images of the region taken by cameras at the tip of the International Space Station's robotic arm found no signs of damage late Monday, and a subsequent round of photography using Discovery's own robotic appendage was on tap for Tuesday night.

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

In a debris related note, STS-116 lead spacewalk officer Tricia Mack said that NASA had confirmed in spacesuit camera video that European Space Agency astronaut Christer Fuglesang did lose a 7.8-inch extension for a pistol grip tool during a Tuesday spacewalk 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's crew was alerted of the spacecraft's healthy status earlier Tuesday.

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

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