Why Lightning Struck the Shuttle Launch Pad

CAPE CANAVERAL, Fla. ? The lightning that thwarted today's planned launch of the space shuttle Endeavour is a familiar problem for NASA's shuttle fleet.

NASA called a 24-hour delay to Endeavour's scheduled STS-127 lift off to investigate possible damage after a powerful electrical storm hit yesterday and 11 lightning bolts impacted Launch Pad 39A here at the seaside Kennedy Space Center.

The Florida coast is often the victim of lightning, as frequent thunderstorms and even hurricanes come in from the ocean on the East. If lightning does occur nearby, the giant metal space shuttle standing tall atop its launch pad tends to attract the brunt of it.

Lightning ? a discharge of electricity from the atmosphere ? usually targets the tallest thing around. The space shuttle stands a towering 184 feet (56 meters) high, on top of a mounded pad. In addition to its height, the shuttle and its accompanying structures are mostly made of metal, which is a good conduit for electricity, so collects more of it.

"The launch pad gets hit all the time," said NASA spokesman Allard Beutel. "We've never had a direct hit [to the shuttle itself], though."

He estimated the pad had been struck dozens of times, though luckily no catastrophic damage has been done to a shuttle from lightning.

The space shuttles ? composed of main orbiter, orange external fuel tank and twin solid rocket boosters ? have never sustained a direct lightning hit because of NASA's Lightning Protection System. A tall metal lightning rod is installed on top of the Launch Pad to attract nearby lightning and route the electricity away from the shuttle through a series of attached metal wires.

"The Lightning Protection System takes the charge and channels it away," Beutel told SPACE.com.

In 2006 the space shuttle Atlantis postponed its STS-115 flight after a powerful lightning bolt impacted with a current of 100,000 amps ? the strongest lightning strike yet.

And lightning isn't just a risk while the vehicles sit at the pad; If lightning struck a shuttle during flight the results could be disastrous, as the shuttle contains sensitive vital electronics and flammable propellant. The rocket's pyrotechnic system ? the fuel materials that undergo chemical reactions to ignite and thrust the shuttle space-ward ? could easily ignite if hit with a powerful electric shock.

That's why NASA takes careful precautions not to launch if there is a chance of an electrical storm in the area. The metal shuttle could even cause a lightning bolt while flying through the sky.

"Rockets can trigger lightning by channeling electrical charge in clouds," Beutel said.

Airplanes have also been known to be struck by lightning.

So why does NASA launch space shuttles from this lightning-prone spot?

"We're closest to the equator," Beutel said. "The Earth's rotation gives an extra push, so you use less fuel to get up."

When rockets lift off from Cape Canaveral, the planet's spin this far south helps loft the vehicle into orbit easier than from a location toward the north of the United States.

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SPACE.com is providing continuous coverage of STS-127 with reporter Clara Moskowitz at Cape Canaveral and senior editor Tariq Malik in New York. Click here for mission updates and SPACE.com's live NASA TV video feed. Live launch coverage begins at 2:30 p.m. EDT (1830 GMT).