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Atlantis rolls back
Battered by an intense hail storm six days earlier, space shuttle Atlantis retreated off launch pad 39A and returned to the cavernous Vehicle Assembly Building on March 4 to undergo thorough inspections and repairs.

 Video | Time-lapse

STS-117: Astronauts meet the press
The STS-117 astronauts meet the press during the traditional pre-flight news conference held at the Johnson Space Center a month prior to launch. The six-person crew will deliver and activate a solar-power module for the International Space Station.

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Atlantis rolls to pad
After a six-hour trip along the three-and-a-half-mile crawlerway from the Vehicle Assembly Building, space shuttle Atlantis arrives at launch pad 39A for the STS-117 mission.

 Roll starts | Pad arrival

Atlantis rollover
Space shuttle Atlantis emerges from its processing hangar at dawn February 7 for the short trip to the Vehicle Assembly Building at Kennedy Space Center's Complex 39.

 Leaving hangar | To VAB

Time-lapse movies:
 Pulling in | Sling

Technical look at
Project Mercury

This documentary takes a look at the technical aspects of Project Mercury, including development of the capsule and the pioneering first manned flights of America's space program.

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Apollo 15: In the Mountains of the Moon
The voyage of Apollo 15 took man to the Hadley Rille area of the moon. Astronauts Dave Scott and Jim Irwin explored the region using a lunar rover, while Al Worden remained in orbit conducting observations. "Apollo 15: In the Mountains of the Moon" is a NASA film looking back at the 1971 flight.

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NASA holds off on making shuttle tank decision
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: March 21, 2007

NASA is pressing ahead with work to repair the shuttle Atlantis's hail-damaged external fuel tank in hopes of getting the orbiter off on a space station assembly mission before the current launch window closes in late May, officials said today.

 
Atlantis is surrounded by access platforms in the VAB. Credit: NASA-KSC
 
At the same time, shuttle Program Manager Wayne Hale said he is holding open the option of moving Atlantis to a new external tank, scheduled for delivery to the Kennedy Space Center on April 10, if it turns out the current tank needs more extensive work or if there are unresolved safety questions. Under that scenario, launch would be delayed to mid June.

"The repair study is still in work and we need to see how quickly we can make repairs and what the final number and types of repairs come out of the engineering assessment," Hale said. "So I'm hesitant to tell you what the earliest launch date would be based on repairing this tank.

"It is possible we could still squeak into the May part of the launch window. If we go to the other tank, we're probably looking at the middle of June. So we're talking about a difference of maybe three weeks."

While NASA managers are hopeful the current tank can be repaired in time to make the May 21 end of the current launch window, it will be difficult to meet that goal. To have more than a few attempts, Atlantis would have to be back out on the pad by the last week in April, giving engineers a little more than one month to complete repairs and other routine preparations.

But Hale said NASA has until April 10 to make a decision. That's when the next tank will arrive from Lockheed Martin's Michoud Assembly Facility in New Orleans and that's when program managers will have to decide whether to press ahead with repairs or switch Atlantis to the new tank.

Hale said the delay in launching Atlantis will push a flight that had been planned for late this year into 2008, leaving four flights on the agency's 2007 manifest. But however the tank repair issue plays out, Hale said he believes the shuttle program can make up the long-range impact of the delay by the end of 2008.

"There is always speculation about what this means to the long-range manifest," he said. "We expect we will be able to get back on the previously described manifest within about 12 months. So it does not affect us out much more than a year in terms of getting back to the manifest and it certainly does not affect our capability of completing the international space station by 2010."

NASA managers had hoped to launch Atlantis on the first of five planned 2007 shuttle missions March 15. But during a freak storm that thundered over pad 39A on Feb. 26, the shuttle's external tank was blasted by hail, suffering thousands of pits and gouges in its foam insulation. Wind gusts reached 62 knots and hail up to 1.5 inches in diameter was found at the pad.

Atlantis, shielded by moveable weather protection panels, was unscathed. But NASA managers ultimately decided to move the shuttle back to the Vehicle Assembly Building for detailed inspections and, if possible, repairs.

As it turned out, most of the damage was restricted to the upper liquid oxygen section of Atlantis's tank. Only a handful of dings were found lower down on the hydrogen section and while two dozen heat shield tiles on the orbiter were scraped by hail that worked its way behind the weather protection panels, detailed inspections show the ship's critical carbon composite wing leading edge panels and nose cap were undamaged.

Much of the damage to the external tank - some 2,400 sites - can be resolved by either flying as is, sanding and blending areas with relatively shallow crush damage or by pouring in fresh insulation that can be sanded and shaped after it cures. The latter two are considered "standard" repair techniques that are known to hold up well based on past experience.

But up near the very top of the tank, the hail damage was so extensive - some 1,600 sites were catalogued, many of them overlapping - that engineers concluded the best way to make repairs would be to simply remove a large section of damaged robotically sprayed NCFI foam and replace it with hand-sprayed BX insulation.

The two types of foam have different characteristics and manual large-area sprays are considered "non-standard" work that will require considerable analysis to demonstrate the repaired areas can withstand the thermal and aerodynamic rigors of launch.

The tip of the tank experiences the most extreme heating and buffeting during ascent and any foam insulation that might break free could impact the shuttle's heat shield. As the shuttle climbs out of the thick, lower atmosphere, that becomes less of a threat. But for the first 135 seconds or so of flight, foam debris is considered a serious issue because the shuttle is still in air thick enough to quickly decelerate lightweight debris, resulting in high relative impact velocities.

"The issue we're working is from an aerodynamic heating standpoint," said John Honeycutt, deputy manager of the external tank project at NASA's Marshall Space Flight Center. "We've always flown the robotically sprayed foam in that area of the tank. ... So the issue, or the thing the technical folks have got to get comfortable with is how does this (BX) foam we're going to spray on (manually) interact with the aerodynamic heating?

"It's a function of how the foam comes off. When we're going up hill, the foam ablates, which means as it heats up, small particles of it just erode away. And what we want to look at is the ablation, or the erosion characteristics of the BX, which is our hand-sprayed foam, in that area."

Hale said engineers "have got to do some work to prove first of all that it doesn't come off in big hunks, we don't think it will, and secondly that it will stand up to the heating and not expand or degrade thermally. And that impact is a major part of the testing that's ahead of us."

Engineers will use a mockup of the tip of the external tank to practice manually spraying on BX foam. The mockup then will be put in a test chamber to assess aerodynamic and thermal effects. That data, plus an assessment of the work to repair the other 2,400 damage sites, will play into the eventual decision on which tank to use.

"We have to go to this engineering evaluation process where we build a mock up, practice spraying foam onto that mockup and trimming it and then putting that into a test facility where we can see how it reacts to ascent heating and other things," Hale said. "So there is that group of work going on, which we think will come to a point where we can evaluate whether we've got a good technique or not about the end of the first week in April. That is one thing. The other thing are these 2,400 damage sites and how quickly we can repair them and with which technique."

The current shuttle launch window closes around May 21 because of thermal issues related to the space station's orbit. The next launch window opens June 8 and extends through July 17. During a management briefing today, engineers laid out two general launch options, one based on use of the current tank and one that assumed a tank swap. The former led to a launch right around the end of the May window while the latter showed a launch around June 17.

But Hale downplayed those timelines, saying that until the analysis is complete, the dates were little more than discussion points. All he would say when pressed was that if engineers are able to complete the 2,400 less demanding repairs faster than currently projected NASa will have a shot at getting Atlantis off before the end of the May window.

Regardless of whether Atlantis flies in May or June, Hale said, "my confidence level we'll be able to repair and fly this tank is high."



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