CAPE CANAVERAL, Fla. - NASA's space shuttle Atlantis and its six-astronaut crew are cleared to launch toward the International Space Station (ISS) Sunday as long as the weather holds, shuttle managers said today.
Atlantis is poised to rocket toward the ISS at 4:29:57 p.m. EDT (2029:57 GMT) Sunday from its Pad 39B launch site here at NASA's Kennedy Space Center (KSC) to haul new solar wings and a bus-sized pair set of trusses to the ISS and jump start construction of the orbital laboratory.
"We feel like we're going into the weekend here in pretty good shape," said LeRoy Cain, NASA's shuttle integration manager, in a press briefing. "We are go to continue here into the launch countdown."
About the only issue plaguing NASA's shuttle launch team and the STS-115 crew is the weather. Current forecasts predict a 60 percent chance of favorable flight conditions on launch day, though remnant clouds from afternoon thunderstorms are still a concern. Atlantis' heat resistant tiles can be damaged in rain, and persistent electrically-charged anvil clouds are a lightning hazard during shuttle flights.
Lightning struck Atlantis' launch pad at about 2:00 p.m. EDT (1800 GMT) today, though all initial reports indicate that the orbiter itself is functioning perfectly and that safety measures performed as designed, said NASA launch director Michael Leinbach, adding that heavy rain and afternoon thunderstorms prevented pad workers from loading all of the cryogenic propellant used to power Atlantis' fuel cells aboard the orbiter today. That activity is expected to resume by 9:00 p.m. EDT (0100 Aug. 26 GMT), he added.
The shuttle is protected from weather at the launch pad by the shell-like Rotating Service Structure, which swings into place when an orbiter is present. Metal cables run from the ground up to the top of a mast on the pad's structure, serving as a lightning rod that prevents lightning from striking NASA orbiters, Leinbach said.
Shuttle and ISS mission managers are also watching Tropical Storm Ernesto - formerly Tropical Depression 5 - which is building strength as it approaches the Gulf of Mexico. While the storm could reach hurricane strength next week, it is not expected to impact Sunday's planned STS-115 launch, Lt. Kaleb Nordgren, of the 45th Weather Squadron at Cape Canaveral Air Force Station, told reporters.
There is a slight chance that Ernesto, should it develop into much stronger storm and maintain its present course into the Gulf, could impact Atlantis' shuttle Mission Control Center, particularly if it hit reaches the Houston area and forces an evacuation - which could effectively end the spaceflight early - but it is still too early to tell, Cain said.
"The storms that we're looking at right now are just too, too far away," Cain said.
A milestone mission
Commanded by veteran NASA astronaut Brent Jett, Atlantis' STS-115 mission marks a return to ISS construction for the first time in more than three years.
The 2003 loss of Columbia and NASA's subsequent return to flight effort have delayed shuttle missions to finish the half-built space station, which saw its last major construction work during 2002's STS-113 spaceflight.
Jett and his STS-115 crewmates arrived here at KSC Thursday and expect a busy 11-day mission. They will stage three spacewalks in four days to connect their cargo - the integrated Port 3/Port 4 truss segments - to the space station's port side, deploy two expansive solar arrays and wire up their power and cooling lines. Other tasks include two heat shield inspections, the first to check Atlantis' for launch debris impacts on Flight Day 2 and the final scan to detect any signs of damage from orbital debris or micrometeorites.
The upcoming spaceflight marks the first ISS construction mission since NASA's Endeavour orbiter delivered the Port 1 (P1) truss to the station during 2002's STS-113 flight. Atlantis' P3/P4 truss segments are destined to be attached to the end of that P1 truss, and are just the first of a series of elements that must be launched and attached in order to complete the ISS by the 2010 retirement date of NASA's shuttle fleet.
"This flight has to work for the next flight to occur," said NASA ISS program manager Michael Sufferdini. "The next few have to kind of happen in the right order."
NASA's STS-115 mission is also a milestone for the agency's ISS partners such as the Canadian Space Agency (CSA), which built the robotic arm - Canadarm2 - used aboard the station for assembly and other tasks. STS-115 astronaut Steven MacLean will be the first from his country to actually use the Canadian-built arm.
"In short, we're proud, we're ready to go," said Beno?t Marcotte, station program director for the CSA, adding that his space agency - like NASA's other ISS partners - is eager to resume station construction. "We're pleased to be where we are right now and we're pleased to see the [assembly] sequence starting again."
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