NASA’s shuttle Atlantis and its six-astronaut crew will launch toward the International Space Station (ISS) on Aug. 27 provided engineers conquer some final issues, among them a possible antenna bolt swap, agency officials said Wednesday.

Top spaceflight officials voted unanimously to press ahead with Atlantis STS-115 mission today after an extended two-day meeting at NASA’s Kennedy Space Center (KSC) in Florida, William Gerstenmaier, NASA’s associate administrator for space operations, said in a press briefing Wednesday following a Flight Readiness Review. 

Two senior NASA directors – in charge of the agency’s Johnson Space Center and Marshall Space Flight Center – gave their approval with the caveat that some shuttle fuel tank modifications be made as soon as possible, Gerstenmaier added.

“This was a great review and I’m looking forward to moving toward a great launch,” NASA chief Michael Griffin said of the meeting, adding that the agency is already committed to making the next fuel tank fix – the removal of several ice frost ramps to reduce the amount of foam insulation debris at launch – in two shuttle flight’s time.

Atlantis and its STS-115 astronaut crew are now set to launch at 4:30 p.m. EDT (1030 GMT) on Aug. 27 to deliver a new pair of solar arrays and truss segments to the ISS. The mission, commanded by veteran shuttle flyer Brent Jett, will mark the first major ISS construction flight since late 2002.

The spaceflight will also be NASA’s third shuttle mission since the 2003 Columbia accident.

Antenna bolt bustle

Shuttle officials spent less time debating the ice frost ramp fix and safety of Atlantis’ foam-covered external tank, as they did the potential need to replace two bolts on a vital antenna attached to the forward right wall of the orbiter’s payload bay, NASA officials said.

Engineers found that two of four bolts holding Atlantis’ Ku-band antenna – which provides video, voice and data communications – to the payload bay wall are too short despite performing as expected for 26 spaceflights. There is some concern that the bolts could give way during launch, sending the antenna plunging down the length of Atlantis’ cargo bay and causing serious – possibly catastrophic – damage to the orbiter.

“For the last 25 years we’ve been flying with these thread fasteners, bolts, that just barely have a thread or two engaged into the nut that holds them on,” said NASA’s space shuttle program manager Wayne Hale. “That is not good engineering practice.”

Similar antenna bolts aboard NASA’s Discovery and Endeavour orbiters have already been replaced with longer units, but the swap will be harder for Atlantis since the shuttle sits in launch position atop Pad 39B at KSC instead of its maintenance hangar.

“We’ve flown 26 times and everything has been okay, and there is a school of thought that suggests it will be okay one more time,” Hale said. “But I would rather have the engineering data to back that up.”

To replace the antenna bolts, pad workers would have to extend a slim platform out between the top of Atlantis’ solar array-truss payload and ISS docking port at the upper end of the orbiter’s 60-foot (18-meter) cargo bay.

“Imagine operating on a surfboard that’s tied down at one end, sticking out over a six-story balcony,” Hale said. “If we have to do it, it will be done safely and will be done properly, but if we don’t have to do it than that would just be great too.”

A decision on whether that work is required could be made this weekend. With two extra days built into Atlantis’ launch schedule, the extra work- if needed – should not affect the Aug. 27 target, NASA launch director Michael Leinbach said.

Hale also said that engineers are working through a heater thermostat issue on one of Discovery’s three auxiliary power units (APUs) feeding its hydraulic system to determine if a similar problem could be present aboard Atlantis.

“Right now we think Atlantis has tested out just fine, so whatever problem there is on Discovery it’s likely not there on Atlantis,” Hale said.

Unanimous decision

Unlike NASA’s last shuttle Flight Readiness Review, in which NASA’s top safety official – former shuttle commander Bryan O’Conner – and chief engineer Christopher Scolese voted against moving ahead with Discovery’s STS-121 launch, today’s final discussion proved less of a contest.

O’Conner and Scolese did not object to the STS-115 launch plan, and added that the flight rationale given for Discovery’s STS-121 mission – in which the risk was to the orbiter itself but not its astronaut crew – was still valid. [Click here for Griffin’s STS-121 launch rationale].

“I would say that this review was less contentious, maybe not a lot less but I don’t want them to be,” Griffin said, adding that airing concerns is a vital part of the engineering process. “The point is we don’t feel that we’re risking crew, and no one in the room felt like we were risking crew.”

Even if Atlantis suffers damage serious enough to force the STS-115 crew to take refuge aboard the ISS and await a rescue mission, the station could support the shuttle astronauts for between 86 and 110 days, NASA station officials said last week.

“In the end, everybody said let’s go,” Griffin said.

Izvor:http://www.space.com/missionlaunches/060816_sts115_launchdate.html