Cape Canaveral, Fla. ? NASA postponed today’s scheduled launch of the space shuttle Atlantis for at least 24 hours while engineers look into possible damage to the orbiter from a massive lightning strike.

During Friday’s big thunderstorm, a bolt of lightning measured at 100,000 amps, believed to be the largest ever to hit the launch site, struck the lightning mast above the shuttle on Launch Pad 39B.

Although the mast did its job in preventing the lightning from hitting the orbiter directly, National Aeronautics and Space Administration officials said Saturday they were concerned that electricity in the atmosphere around the pad just off the Atlantic seaboard could have damaged critical control systems.

“We did see a couple of indications that make us want to look at the ground and flight systems and make sure we’re able to fly,” said Leroy Cain, chairman of NASA’s Mission Management Team, which has final authority over launch decisions.

At least two instrument readings went out of line after the lightning strike, worrying safety engineers. One was in an electrical buss that supplies power to certain systems on the orbiter, which carries the crew.

Rain clouds obscure the top of the Vehicle Assembly Building on Saturday at the Kennedy Space Center in Cape Canaveral, Fla. NASA officials decided Saturday to delay the launch of space shuttle Atlantis by at least 24 hours to give engineers time to determine if lightning caused any problems.

The other was in the hydrogen vent arm, an umbilical that allows excess hydrogen to boil off just before launch. The arm is designed to swing free of the shuttle less than a minute before liftoff. Both systems must operate correctly for a successful launch, which is why NASA took the unusual step of scrubbing the launch a full day ahead of time.

NASA officials said they could not predict the chances of launching on Monday.

“We know just enough to know we don’t know enough” about the possible damage, Cain said. “We need to let the (engineering) folks go off and look at the data.”

The weather outlook for Monday was improving. Even without the lightning strike, today’s launch looked uncertain because of continuing thunderstorms. The storm front is expected to move off by Monday.

The upcoming shuttle mission, known as STS-115, will be one of the most challenging in the shuttle’s recent history. Atlantis will carry aloft a 17-ton truss to serve as the backbone for a new wing of the space station. Along with the truss, new solar arrays will be attached to supply more power to the station.