Already a month behind schedule, launch of the shuttle Endeavour on a 16-day space station assembly mission was delayed at least 24 hours, from Saturday to Sunday, to give engineers time to evaluate the effects of multiple lightning strikes at the launch pad during a severe thunderstorm Friday.
Eleven lightning strikes were recorded within 1,800 feet of the launch pad 39A, and while the shuttle is protected from lightning-induced electrical surges, NASA managers decided more time was needed to make sure no critical systems were affected.
"We've seen nothing so far that indicates anything was actually affected by the lightning strikes," said Mike Moses, director of shuttle launch integration at the Kennedy Space Center. "So I fully expect this to be a positive story, but we have a lot of equipment that has to be checked and that's what takes time."
Assuming no problems are found -- and assuming predicted afternoon thunderstorms cause no additional trouble -- NASA will reset Endeavour's countdown for a launch Sunday at 7:13:55 p.m. EDT. Forecasters are predicting a 70 percent chance of acceptable weather.
Friday afternoon, however, severe storms rumbled across the space center bringing torrential rain and electrical activity. "It was snap, crackle, and pop out there," one official said.
"If you were here in town yesterday, you saw a pretty spectacular electrical storm here at the Cape yesterday afternoon," Moses said. "We have several different systems out there monitoring lightning and we have a bunch of different rules and regulations and guidelines. But the bottom line is, we took 11 strikes within the point-three nautical miles (1,800 feet) of the pad."
The fixed gantry at the pad features a huge lightning mast that is connected to the ground by a catenary wire system anchored on the north and south sides of the complex. Seven of the 11 strikes hit the wires and two of those were above the threshold that requires additional analyses.
"We don't have any attached strikes to the orbiter itself, to the external tank, to the SRBs (boosters)," Moses said. "But we do know from our camera system that we took strikes on the lightning mast, the water tower, the wires themselves. So there were seven different events.
"With a lightning event, you have the initial spike of electricity that you are worried about, but then you also have a very fast-moving electrical field, which causes a magnetic field that can induce voltage on circuits that aren't even connected to it."
Two of the lightning strikes Friday resulted in 110-volt surges in the shuttle's electrical systems, just enough to qualify the strikes as official "lightning events."
"Strikes that close to the pad kick off extensive data analysis to make sure there are no problems," Moses said. "We have a panel, called the E3 panel, the electromagnetic effects panel, they take a look and decide if that strength of strike was big enough to then cause concern for the integrated stack, the orbiter, the ET, the SRBs. And if it was, then our engineering review panel will then go off, gather more data, and determine if a re-test is required."
By early today, engineers had determined Endeavour's external tank was in good shape, as were the shuttle's main engines and associated ground systems. The shuttle's payload also appears unharmed, although additional checks are planned.
The additional day was required primarily to make sure the shuttle's sensitive electronics were undamaged, along with the critical pyrotechnic systems needed to safely operate the ship's twin solid-fuel boosters.
"Those two areas decided they did need a little more retest to make sure that their systems are good," Moses said. "Part of the problem is, that retest can take different forms. If you think about it, on the SRBs, one of the things we're worried about are the pyro systems to separate the SRBs away from the external tank. Well, you can't really go check that system and turn it on because you don't want to go fire off those pyros.
"So we have various levels of tests we can do on some circuitry, but you've really got to make sure you're really checking what you need to check. So the teams were pretty confident we have enough data on other buses (circuits) to know that that (pyro) circuitry was OK, but we weren't quite there this morning."
Updated at 7:15 p.m. EDT: Weather forecast improves to 70 percent "go" Sunday.