CAPECANAVERAL, Fla. - NASA's spaceshuttle Atlantis and its six-astronautcrew are cleared to launch toward the International SpaceStation (ISS) Sunday as long as the weather holds, shuttle managers saidtoday.
Atlantis ispoised to rocket toward the ISS at 4:29:57 p.m. EDT (2029:57 GMT) Sunday fromits Pad 39B launch site here at NASA's Kennedy Space Center (KSC) to haul new solarwings and a bus-sized pair set of trusses to the ISS and jump startconstruction of the orbital laboratory.
"We feellike 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 continuehere into the launch countdown."
About theonly issue plaguing NASA's shuttle launch team and the STS-115 crew is theweather. Currentforecasts predict a 60 percent chance of favorable flight conditions onlaunch day, though remnant clouds from afternoon thunderstorms are still aconcern. Atlantis' heat resistant tiles can be damaged in rain, and persistentelectrically-charged anvil clouds are a lightning hazard during shuttleflights.
Lightningstruck Atlantis' launch pad at about 2:00 p.m. EDT (1800 GMT) today, though allinitial reports indicate that the orbiter itself is functioning perfectly andthat safety measures performed as designed, said NASA launch director MichaelLeinbach, adding that heavy rain and afternoon thunderstorms prevented padworkers from loading all of the cryogenic propellant used to power Atlantis'fuel cells aboard the orbiter today. That activity is expected to resume by9:00 p.m. EDT (0100 Aug. 26 GMT), he added.
The shuttleis protected from weather at the launch pad by the shell-like Rotating ServiceStructure, which swings into place when an orbiter is present. Metal cables runfrom the ground up to the top of a mast on the pad's structure, serving as alightning rod that prevents lightning from striking NASA orbiters, Leinbachsaid.
Shuttle andISS mission managers are also watching Tropical Storm Ernesto - formerlyTropical Depression 5 - which is building strength as it approaches the Gulf of Mexico. While the storm could reach hurricane strength next week, it is notexpected to impact Sunday's planned STS-115 launch, Lt. Kaleb Nordgren, of the45th Weather Squadron at Cape Canaveral Air Force Station, toldreporters.
There is aslight chance that Ernesto, should it develop into much stronger storm andmaintain its present course into the Gulf, could impact Atlantis' shuttleMission Control Center, particularly if it hit reaches the Houston area andforces an evacuation - which could effectively end the spaceflight early - butit is still too early to tell, Cain said.
"The stormsthat we're looking at right now are just too, too far away," Cain said.
Commandedby veteranNASA astronaut Brent Jett, Atlantis' STS-115mission marks a return to ISS construction for the first time in more thanthree years.
The 2003 loss of Columbia andNASA's subsequent return toflight effort have delayed shuttle missions to finish the half-builtspace station, which saw its last major construction work during 2002'sSTS-113 spaceflight.
Jett andhis STS-115 crewmates arrived here at KSC Thursday and expect a busy 11-daymission. They will stage threespacewalks in four days to connect their cargo - the integrated Port3/Port 4 truss segments - to the space station's port side, deploy twoexpansive solar arrays and wire up their power and cooling lines. Other tasksinclude two heat shield inspections, the first to check Atlantis' for launchdebris impacts on Flight Day 2 and the final scan to detect any signs of damagefrom orbital debris or micrometeorites.
The upcomingspaceflight marks the first ISS construction mission since NASA's Endeavourorbiter delivered the Port 1 (P1) truss to the station during 2002's STS-113flight. Atlantis' P3/P4 truss segments are destined to be attached to the endof that P1 truss, and are just the first of a series of elements that must belaunched and attached in order to complete the ISS by the 2010 retirement dateof NASA's shuttle fleet.
"This flighthas to work for the next flight to occur," said NASA ISS program managerMichael Sufferdini. "The next few have to kind of happen in the right order."
NASA'sSTS-115 mission is also a milestone for the agency's ISS partners such as theCanadian Space Agency (CSA), which built the robotic arm - Canadarm2- used aboard the station for assembly and other tasks. STS-115 astronaut StevenMacLean will be the first from his country to actually use the Canadian-builtarm.
"In short,we're proud, we're ready to go," said Beno?t Marcotte, station program directorfor the CSA, adding that his space agency - like NASA's other ISS partners - iseager to resume station construction. "We're pleased to be where we are rightnow and we're pleased to see the [assembly] sequence starting again."
- VIDEO: First Tasks of NASA's STS-115 Mission
- Gallery: Prepping Atlantis
- Complete Space Shuttle Mission Coverage
- NASA's STS-115: Shuttle Atlantis to Jump Start ISS Construction
- The Great Space Quiz: Space Shuttle Countdown