By Laurent Thomet - NASA has analysed the impact of a powerful lightning strike on the Atlantis shuttle's launch pad that forced a 24-hour delay of the liftoff to the International Space Station.
Officials said analysts would pore over a mountain of documents today to determine if the lightning caused any damage to the ground and flight systems.
The six Atlantis astronauts will have to wait until at least 4:04 pm Monday (0600 Tuesday AEST) to lift off on the first ISS construction mission in nearly four years. The launch window closes September 13.
Atlantis will carry a new 16-tonne segment with two huge solar panels to the ISS on the first of 16 flights planned to complete assembly of the half-finished space station by 2010, when the shuttle fleet is set to retire.
The Columbia shuttle disaster in February 2003 forced a halt in the orbiting laboratory's construction.
Although lightning strikes are common on the launch pad, launch integration manager LeRoy Cain said Friday's was believed to be the strongest to hit the structure.
"At this point, we don't have data yet to really know whether or not we have any problems," Mr Cain said. "We need to make sure we have a good ground and flight system."
The storm discharge struck a lightning protection rod atop the launch pad and did not directly hit the orbiter.
"The lightning arresting system did its job, but you can get an induced voltage field around a lighting strike," launch director Mike Leinbach said.
NASA managers were to meet today after the conclusion of the analysis to decide the next steps.
Thunderstorms had also threatened the launch, with forecasts saying there was a 60 per cent chance they would force a delay. The weather is expected to improve dramatically on Monday.
Officials were also monitoring Tropical Storm Ernesto in the Caribbean, which was moving toward the Gulf of Mexico, as forecasters warned that it could become a hurricane.
Once it launches, the Atlantis mission will be the third shuttle flight since the Columbia disaster, which was caused by debris that struck its heat shield during liftoff, dooming its return home with seven astronauts aboard.
After two Discovery shuttle flights in the past two years aimed at improving safety, NASA declared it was ready to resume construction of the station, which is key to US ambitions of sending humans to Mars.
Safety remains a priority, however, and NASA will employ the same thorough shuttle inspection techniques used in the Discovery missions.
The Atlantis mission is a critical first step in the ISS's assembly.
"This flight has to work for the next flight to occur, and the next flight to occur, and the next flight to occur," ISS program manager Mike Suffredini emphasised.
The installation of the solar panels, which will eventually provide a quarter of the station's power, is one of the most complex parts of the ISS assembly sequence.
Three spacewalks are planned during the 11-day mission, which will be followed by another shuttle flight planned for December for another assembly sequence that officials said would be even trickier.
The ISS currently weighs 197 tonnes and will mushroom to a massive, 454-tonne structure once it is completed.
The station, launched in November 1998, allows scientists to study the effects of living in zero gravity.
The United States, Russia, Japan, Canada, Brazil and 11 countries from the European Space Agency are involved in the orbiting space lab.
The Atlantis crew will be commanded by Brent Jett; Chris Ferguson will be the co-pilot, and the four mission specialists will be Steve MacLean of the Canadian Space Agency, Dan Burbank, Heidemarie Stefanyshyn-Piper and Joe Tanner.
Source: news.com