Learning how to diagnose bad flying weather
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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.
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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.
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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.
|Human Voltage (June 18, 1999) Scientists discuss biology, safety, and statistics of lightning strikes.
News shorts from Atmospheric Electricity Conference (June 16, 1999) Poster papers on hurricanes and tornadoes summarized.
Soaking in atmospheric electricity (June 15, 1999) 'Fair weather' measurements important to understanding thunderstorms.
Lightning position in storm may circle strongest updrafts (June 11, 1999) New finding could help in predicting hail, tornadoes
Lightning follows the Sun (June 10, 1999) Space imaging team discovers unexpected preferences
Spirits of another sort (June 10, 1999) Thunderstorms generate elusive and mysterious sprites.
Getting a solid view of lightning (June 9, 1999): New Mexico team develops system to depict lightning in three dimensions.
Learning how to diagnose bad flying weather (June 8, 1999): Scientists discuss what they know about lightning's effects on spacecraft and aircraft.
Three bolts from the blue (June 8, 1999): Fundamental questions about atmospheric electricity posed at conference this week.
Lightning Leaders Converge in Alabama (May 24, 1999): Preview of the 11th International Conference on Atmospheric Electricity.
What Comes Out of the Top of a Thunderstorm? (May 26, 1999): Gamma-rays (sometimes).
Lightning research at NASA/Marshall and the Global Hydrology and Climate Center.
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.
National Severe Storms Laboratory, Norman, OK
Numerical Modeling at NSSL
The New Mexico Tech 3D Lightning Mapping System
Lightning Detection and Ranging project at Kennedy Space Center.
National Severe Storms Laboratory Photo Library, where we got a lot of the neat pictures in these stories.
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|Author: Dave Dooling
Curator: Bryan Walls
NASA Official: John M. Horack