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But no one worried much about the problem until Nov. 19, 1969, when Apollo 12 was struck twice by lightning in the 36.5 seconds after liftoff, when it was just 1.8 km (6,000 ft) high. "That opened our eyes to the hazards that lightning could pose to a spacecraft traveling through an electrified cloud," said John Willett, a retired research scientist with the U.S. Air Force Research Laboratory outside Boston. The subject was reemphasized in 1987 when an Atlas Centaur was struck by lightning that damaged its electronics and caused an engine to steer the rocket off course. Willett was an invited speaker Monday afternoon at the International Conference on Atmospheric Electricity being held this week in Guntersville. |
For now, the conditions are not fully known, so Willett and scientists at other institutions have developed a rocket program to find out. They use a small sounding rocket that uses surplus 2.75-inch-diameter Mighty Mouse motors designed for launch from attack aircraft. With a diagnostic payload designed for the rocket, the complete package is 6 feet tall. Above: Lightning strikes the launch pad 36 seconds after Apollo 12 takes off for the moon. (NASA) Willett said the rocket is launched into electrified clouds to measure conditions, principally how the electric potential or voltage changes with altitude. Then a small rocket, trailing a copper wire, is launched to trigger a lightning flash. "When we do it we take great care to protect ourselves," Willett said. The launch team and their equipment are inside a trailer that is modified to serve as a Faraday cage, a sort of electrical isolation chamber that conducts any stray lightning around them. |
The same cannot be done for rockets. "I don't anticipate any way of preventing the lightning from striking the spacecraft," Willett said. "We'll have to take measurements in advance and say it is safe to launch, or it is not safe." For the time being, launch sites like Cape Canaveral and Kennedy Space Center operate with lightning safety constraints that cost them a few launch opportunities, but minimize the chance of getting struck. |
Aircraft pose a different challenge. Most aircraft are well shielded against lightning because of the design of their metal airframes. Lightning is conducted around the skin and continues on its way in most cases. But as designers move to lightweight composites that don't conduct electricity, they face an increased risk of damage to the aircraft. Willett noted that some strikes have splintered the plastic or rubberized radar domes on the nose of some aircraft. "You don't want that happening to wings or other major structures," he said. Further, the electronics that really control the aircraft will have to be shielded so they don't blank out for several seconds, as happened when Apollo 12 was struck. |
More Space Science Headlines - NASA research on the web NASA's Earth Science Enterprise Information on Earth Science missions, etc. 45th Weather Squadron at Patrick AFB,
lightning reference page. |
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