NASA managers today formally - and unanimously - cleared the shuttle Atlantis for blastoff Aug. 27 on a mission to restart space station assembly, pending resolution of two down-to-the-wire technical issues.

A crew of six will fly aboard Atlantis. Credit: NASA-KSC

Bill Gerstenmaier, NASA's associate administrator for space flight, said engineers remain concerned about the status of so-called ice-frost ramps on the shuttle's external tank that prevent ice from forming around fittings that hold pressurization lines in place.

The ice-frost ramps remain classified "probable/catastrophic" in NASA's risk matrix, meaning there's a 50-50 chance a piece of foam insulation could break away from one over the 100-flight design life of an orbiter and cause catastrophic damage.

Before Discovery's flight last month on the second post-Columbia mission, NASA's top safety manager and chief engineer dissented with the decision to proceed before a redesign was in place. NASA is working on a new ice-frost ramp design, but it won't be available until next year.

This time around, chief enginer Chris Scolese signed the Certificate of Flight Readiness without comment. Safety chief Bryan O'Connor appended an "exception" saying he concurred with the decision to launch Atlantis because Administrator Mike Griffin accepted the known risk for the agency; because the programmatic need, cited earlier by Griffin, to get on with station assembly remained unchanged; and because the shuttle's risk posture was "no worse" now than it was for Discovery's flight last month.

Gerstenmaier said representatives of the Johnson Space Center and the Marshall Spaceflight Center weighed in with observations that NASA must continue its efforts to redesign the ice-frost ramps, but they too signed the CoFR, making the launch decision unanimous.

"There were no no-go votes," said Gerstenmaier. "The board's position is we are go for STS-115. We now give them the luxury of adding any other words they want beyond go, which we did last time, and both Marshall and JSC emphasized to us they would like to have the ice-frost ramps redesigned. And that's all they said. So it was essentially a unanimous decision by the board that we are go."

Engineers are still trying to figure out what caused problems with a critical thermostat in a hydraulic power unit aboard the shuttle Discovery during its flight last month. And managers are still debating what, if anything, to do about two of four bolts holding Atlantis' KU-band antenna in place at the front of the shuttle's cargo bay.

Shuttle program manager Wayne Hale said the thermostat issue is currently classified as an "unexplained anomaly," one that he would like to resolve before Aug. 27. But if not, he said he would be comfortable pressing ahead anyway because of redundancy in the hydraulic system.

The KU antenna bolts are another matter. The two forward bolts are known to be properly threaded and sufficiently engaged in capture nuts. The two aft bolts, however, may be only partially engaged because the bolts in question are too short.

The concern is that an insufficiently secured antenna box could break free during launch and fall the six-story length of the shuttle's payload bay with catastrophic results.

"We're not going to fly if we think there's a possibility the antenna could come off," said Griffin.

The mistake was made in the 1980s when Atlantis was built and the shuttle has flown 26 times in the current configuration. Both bolts are firmly torqued, albeit without the desired six to eight threads engaged, and they have not backed out any detectable amount. As such, some engineers believe NASA should simply launch Atlantis as is and replace the bolts after the upcoming flight.

Hale said today the fly-as-is option is still on the table. Engineers are carrying out a detailed analysis of launch vibrations in that area of the cargo bay to determine their effect on the antenna box and to find out if it can safely fly with just two fully engaged bolts.

"Having that small number of threads engaged is just not good practice and there are circumstances where those threaded fasteners can come out," Hale said. "So that is a poor design, or a poor application, and we need to rectify it. It's something that you really don't want to have."

But he did not rule out flying as is, if engineers can prove the box will remain securely in place with just two bolts. It seems more likely, however, that engineers will be asked to replace the bolts in question.

Kennedy Space Center engineers are refining a plan to do just that, but the repair job would be difficult, requiring technicians to build scaffolding on an extended access platform six stories above the shuttle's aft payload bay bulkhead.

Because of ongoing hazardous operations at pad 39B, engineers cannot open Atlantis' cargo bay doors until Friday. Hale said he hopes to make a decision on how to proceed by Friday or Saturday.

Launch director Mike Leinbach said he believes the repairs, if required, can be completed in time to support the Aug. 27 launch date, but safety will be the watchword. Even with safety nets and tethers, working in a cramped space on scaffolding six stories up surrounded by fragile flight hardware raises the possibility of inadvertent damage to other equipment.

"It all looks good on paper, in the CAD modeling," Leinbach said. "Once we get into the job, if we get scared by something and we shouldn't proceed on we're going to stand down. ... It's not a long job, it's probably two days total to do this and out of those two days, probably 44 hours of the 48 is the access installation and removal. The bolt change out itself is probably going to be very straight forward assuming we don't get any 'gotchas' when we get out there."

Leinbach said engineers currently have two full days of contingency time left in the processing schedule to handle unexpected problems. On paper, at least, the bolt change out can be accomplished without delaying launch.

Additional coverage for subscribers:
VIDEO: LAUNCH PAD PRESS CHAT DIAL-UP | BROADBAND
VIDEO: ATLANTIS ARRIVES AT LAUNCH PAD 39B PLAY
VIDEO: ROLLOUT FROM VEHICLE ASSEMBLY BUILDING BEGINS PLAY

VIDEO: TRUSS IN PAD'S PAYLOAD ROOM PLAY
VIDEO: PAYLOAD HOISTED INTO THE PAD PLAY
VIDEO: STATION TRUSS PAYLOAD DELIVERED TO PAD PLAY
MORE: STS-115 VIDEO COVERAGE
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