NASA Leaders Express Confidence In Shuttle Atlantis Tank Repairs

By | June 4, 2007 | Uncategorized

Launch Set For 7:38 ET Friday Evening

NASA leaders expressed confidence that repairs to the storm-damaged Space Shuttle Atlantis external fuel tank are sound, and the spaceship likely will have a safe flight when it lifts off from Kennedy Space Center (KSC), with a daylight launch slated for 7:38 p.m. ET Friday.

The countdown to launch begins at 9 p.m. ET tomorrow.

If weather or other problems occur, the launch window initially would be open until June 12, then close until reopening June 17.

Weather problems wiped out earlier NASA plans to launch Atlantis in March. A violent storm slashed hail onto the Atlantis external fuel tank, forcing NASA to repair thousands of dings in foam insulation covering the tank.

Mike Leinbach, NASA launch director, termed the hail storm “a freak event,” one that he wouldn’t expect to see repeated in the remaining three-year life of the shuttle program.

The key question now is whether the dings, even after repairs, will lead to chunks of foam insulation breaking free from the tank when Atlantis lifts off from Launch Pad 39A for a mission of about 11 days.

In 2003, a large chunk of foam insulation ripped loose from the external fuel tank on Space Shuttle Columbia, punching a hole in the leading edge of the Columbia orbiter vehicle, damage that went undetected. Later, on returning to Earth, super-hot gases of reentry rushed into the wing and heated it to the point of structural failure. Both the ship and crew were lost.

The space agency leaders also said they believe that NASA will be able to fly its full roster of shuttle missions before the shuttle fleet retires Sept. 30, 2010. The shuttles are the only ships large enough to hoist immense structural elements into orbit to complete construction of the International Space Station (ISS).

Some three months were lost because of the hail damage to the Atlantis fuel tank, but that can be made up in the coming year. There is adequate time remaining to execute the schedule of flights, leaders indicated.

But the space agency leaders stressed as well that they won’t permit the tight schedule of 16 planned shuttle flights (mostly to the ISS, and one to service the Hubble Space Telescope) to rush them, saying that NASA will ensure that each flight is conducted safely. After the Atlantis launch, NASA contemplates shuttle launches in early August, in late October and early December.

Unanimous ‘Go’ Vote

Their comments came after a flight readiness review Thursday concluded with NASA officials giving a unanimous “go” for the Atlantis STS-117 mission to the ISS.

“The poll was unanimous,” said Wayne Hale, space shuttle program manager.

Referring to fixes on dings in the tank insulation, Hale said, “These are good repairs.”

One reason for his confidence, he said, is that similar repairs have been performed on other external fuel tanks and there has been no major foam insulation loss from the repairs in liftoffs. “We’ve never had any of these repairs break loose,” he said.

“We haven’t seen any of them liberate,” said William Gerstenmaier, associate NASA administrator for space operations.

Many of the repairs are small, or low-mass, and thus unlikely to inflict damage even if they did strike the orbiter vehicle, he noted.

Gerstenmaier also rated the Atlantis tank with its repairs as almost the equal of a regular tank in routine usage, though perhaps “not quite as good a performer as a regular tank.”

Clearly, he said, the tank now attached to the Atlantis orbiter vehicle is ready to fly.

Further, NASA has performed many computational fluid dynamics runs, studying where foam insulation breaking free from the tank would be likely to hit the orbiter vehicle in its ascent phase, Hale said. Wind tunnel, vacuum and other tests were run as well.

In one literal sense, frequency of release of foam-repair chunks of insulation is zero, because they haven’t broken free. But Hale explained that statisticians don’t like being told that it’s zero, so they assume a probability of release.

NASA ran studies of a worst-case scenario, where a “Monte Carlo simulation” showed that there is just a one in 650 chance of having a critical debris strike from a repair that failed, and even then, “I wouldn’t go off and tell you the [probability] of losing the orbiter is one in 650,” Hale said. Other estimates might go to a one in 1,000 or one in 2,000 range, and even that would be open to question.

“I wouldn’t take any of those numbers to the bank,” he said.

The launch will be in daylight, all the way past the point where the external tank separates. That means that any large chunk of foam insulation breaking off from the external fuel tank and hitting the orbiter vehicle likely would be spotted by cameras during launch.

As well, since Columbia, NASA has instituted exhaustive post-launch inspection procedures, both visuals from the space station while the orbiter vehicle does a flip-over, and with a probe on an arm that examines the leading-edge heat shields on the orbiter vehicle for any damage. As well, there is another check of the vehicle after it undocks from the ISS, prior to the vehicle beginning reentry.

Briefers added that there were some items still open at the end of the review, and that there were dissenting opinions voiced during the review.

For example, one participant wished to change out bolts on oxygen pump equipment on the main engines, because two different metals were used in an assembly (steel and aluminum), raising a threat of galvanic corrosion.

But an inspection showed no major problem here, Hale said, though there could be “a potential redesign” of the assembly in future. It involves bolts being screwed into a steel insert, instead of being screwed directly into a flange on a part that has 3,500 pounds per square inch of liquid oxygen passing through it. “We’ve had very few of these inserts pull out,” Hale said. “I am highly confident that we will be safe.” NASA also will do a potential redesign and may go back and replace inserts in the fleet, he said.

Rescue Mission?

What if, the NASA officials were asked, something does happen to damage the Atlantis orbiter vehicle and a spacecraft had to be launched from Earth to rescue Atlantis astronauts? The answer is that there would be more than enough oxygen, 68 days worth, to sustain crew members until another craft could be sent aloft in a rescue mission, in 50 days. Space Shuttle Endeavour could be in flight status fairly quickly.

Hale said NASA doesn’t expect a major increase in the amount of small bits of foam insulation to break free from the Atlantis external fuel tank. “We do not expect increased popcorning,” he said. “We don’t expect more than usual, but we will watch it” with a suite of cameras providing video of the tank and orbiter during launch.

After the years-long freeze in shuttle flights caused by the Columbia disaster, shuttle missions last year resumed construction of the space station.

In the Atlantis STS-17 mission, Rick Sturckow will command the mission and Lee Archambault will serve as pilot. Mission Specialists James Reilly, Steven Swanson, John Olivas and Flight Engineer Clayton Anderson round out the crew. They will arrive at KSC this evening at 6:30 p.m. ET.

After blasting off on Atlantis, they will deliver the S3/S4 starboard truss segments, batteries and another pair of solar arrays to the space station.

Briefers said that this will be a major step forward, with the solar arrays ensuring that the ISS has sufficient power to run the various modules being added to the artificial moon.

As well, spacewalkers will have to retract another solar array. Balky arrays can pose a challenge to crew members, but this time there will be a new type of “hockey stick” tool to help.

Anderson will replace Expedition 15 Flight Engineer Sunita Williams on station and Williams will return to Earth aboard Atlantis. While aboard the space station, she recently took a picture of Atlantis and KSC from a few hundred miles up, directly above the launch pad, in a shot that included her space shuttle ride home. STS-117 is the 21st space shuttle mission to the ISS.

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