NASA resolves worries about wing panels, nose cap
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: July 8, 2006
With the Discovery astronauts chalking up a surprisingly successful spacewalk, NASA's Mission Management Team today cleared the shuttle's critical nose cap and wing leading edge panels for re-entry and expressed optimism two final question marks about the ship's heat shield will be resolved Sunday.
MMT Chairman John Shannon also unveiled a spectacular eight-second video clip from a camera mounted in one of DIscovery's twin solid-fuel boosters showing the shuttle and its external tank rocketing out of the atmosphere, a view of the shuttle never before seen.
The cameras were on board the boosters to look for signs of foam insulation falling from Discovery's external tank and footage from both rockets is expected to be released Sunday.
As it is, Shannon said analysis of radar data, wing leading edge sensors, high-resolution photographs, laser scans and focused inspections by the astronauts show Discovery suffered less ascent damage than any shuttle ever launched and its tank lost less foam than any in NASA's 115-flight history.
"I would say by far. By far," Shannon said. "Seeing no tile damage that exceeded any of the inspection requirements was a great, pleasant surprise. The tank performance was as expected. We saw a little bit of loss that was consistent with our flight history, the areas we redesigned performed really well."
Said Steve Poulos, manager of the orbiter projects office at the Johnson Space Center: "This was the best, cleanest orbiter I've seen."
Even the tank's ice-frost ramps, which remain officially classified as a "probable/catastrophic" risk, performed well, with no major loss of foam. A thin sheet of insulation just in front of an ice-frost ramp peeled away about two minutes and 50 seconds after launch, but it posed no threat to the shuttle.
While NASA still plans to redesign the ramps to eliminate thick foam around 34 brackets, "this flight was really, really good. It will add to our understanding of it," Shannon said.
"When we do a redesign, we need to make sure that it's the right redesign," he said. "Now, do I have more confidence flying STS-115 (the shuttle Atlantis) in August with these ice-frost ramps? I would tell you yeah, I do."
Late last week, engineers identified six "regions of interest," that is, areas where potential damage was seen on Discovery's heat shield. By today, all but two had been officially eliminated, including lingering concerns about potential punctures or cracks in the shuttle's reinforced carbon carbon nose cap and RCC wing leading edge panels. The nose cap and RCC panels experience the most extreme heating during re-entry and it was a breach in an RCC panel that brought down Columbia in 2003.
A white, circular marking on Discovery's nose cap, which engineers initially worried might be a hyper-velocity impact site, is now believed to be bird droppings. Discoloration on two leading edge panels is thought to be harmless discoloration, perhaps caused by launch pad spills of hydraulic fluid or some other material.
Protruding gap filler material near Discovery's nose was deemed no threat after high-resolution photographs showed it extended just two-tenths of an inch above the surrounding tile.
But engineers are continuing to assess the potential impact of a protruding gap filler near a propellant feedline access door in Discovery's belly and the potential impact of a slightly damaged thermal protection blanket in front of the ship's cockpit windows.
Poulos showed extremely sharp pictures taken with a new digital camera on Discovery's inspection boom that clearly show the gap filler in question tore apart at some point during ascent. The part that's remaining likely will bend over or break off during entry and pose little threat of increased heating. But engineers have not yet finished their evaluation and the gap filler remains an open issue.
Likewise, tests are being conducted to make sure the slightly damaged blanet in front of the cockpit windows on Discovery's forward reaction control system rocket pod poses no impact threat if a piece rips away during the descent. Poulos said it looks like the blanket will hold up, but additional tests are needed to make sure.
Even so, he said he was confident the Mission Management Team would be able to give Discovery a clean bill of health Sunday.
"These last two development flights have been phenomenal," he said. "We have learned so much about what the capability of the boom sensor system is. We now understand what different defects or areas of interest look like and we're just going to be much smarter as we go into our future flights."
Late today, mission control shared the news with the Discovery astronauts.
"As of now, we've been able to clear all the RCC," mission control radioed. "We continue to march forward and by tomorrow's MMT (meeting), we will have resolution on the ET door gap filler as well as the forward RCS blanket. We're very happy with our current situation."
"Well, that's great news," commander Steve Lindsey replied. "We'll look forward to hearing that word."
In the meantime, the MMT formally cleared Discovery and its crew for emergency descent if some major malfunction forced the astronauts to make a swift return to Earth.
Good performance from the shuttle and its external tank are only part of the big picture for NASA. The space agency also is trying to develop techniques for fixing heat shield damage in orbit if something goes wrong on the way up hill.
The Discovery astronauts took a big step in that direction today by successfully testing a novel approach to gaining access to damage sites that could play into an eventual decision to launch a Hubble Space Telescope servicing mission.
The idea was to find out if the shuttle's 50-foot-long robot arm and the 50-foot-long boom used to inspect the shuttle's heat shield could be used as a work platform to repair impact damage.
During a seven-hour 31-minute spacewalk, astronauts Piers Sellers and Mike Fossum tested the stability of the spindly space crane and found it performed better than engineers had predicted.
"We had some fantastic results,:" said Tomas Gonzales-Torres, the lead spacewalk officer in mission control. "The crew went through the various positions and I think the most impressive thing we saw was that the boom did dampen (oscillations) faster than we had expected. Many of the activities, we had expected around one minute of damping and it actually took around 15 or 20 seconds. In addition, some of the deflections were smaller as well."
Shannon said the results show the crew of a Hubble servicing mission would have access to damage sites even though the space station, in a different orbit, would not be available for safe haven.
"I think today was a significant step forward in that decision process because previously, we had said we would like to have the space station as our work platform to repair any tile or RCC," Shannon said. "If the results from the test of the boom hold (up), then we'll show we have an ability to put a crew member, without a station there, anywhere on the shuttle to do any kind of repairs."
Lead flight director Tony Ceccacci summed up his part of a status briefing by saying, "it was a really super, super day today."