From: Marshall Space Flight Center
Posted: Tuesday, November 13, 2001
From Mongolia to Maui, researchers from NASA's Marshall Space Flight Center in Huntsville, Ala., will use special cameras to scan the skies and report meteor activity around the clock during the Nov. 17-18 Leonids shower.
From six key points on the globe, they will record and transmit their observations to the Marshall Center's Leonid Environment Operations Center - a data clearinghouse that will provide meteor updates in near real-time intervals through the NASA Web site:
SpaceWeather.com, a website sponsored by email@example.com.
Led by the Engineering Directorate at the Marshall Center, the effort is part of a long-term goal to protect spacecraft such as NASA's Chandra X-ray Observatory from dazzling - but potentially damaging - meteoroids.
"We're collecting this data to analyze and refine our meteor forecasting techniques," said Dr. Rob Suggs, the Leonid Environment Operations Center team leader. "If we can better determine where, when and how the meteors will strike, we can take protective measures to prevent or minimize damage to our spacecraft."
Those protective measures can range from turning a satellite so its most sensitive surface faces the direction of minimal exposure, to shutting down a spacecraft's electronic operations until the storm has passed.
"Good planning is essential, because in many cases, your only opportunity to protect the spacecraft is before the first meteor strikes," Suggs said. "For example, Chandra's orbit takes it one third of the way to the Moon, and its flight plans are uploaded days ahead of time. Once a meteor storm has begun, it's often too late to do anything about it."
Even though today's satellites are engineered to withstand daily meteoroid strikes, the risk of damage is a bit different for high-speed meteoroid streams, according to Dr. Jeff Anderson of Marshall's Engineering Directorate.
"The 'plasma effect' is more important," he said. "When a meteoroid hits a satellite, it can heat the impact site to thousands of degrees Kelvin - rivaling the surface temperature of the Sun. The entire meteoroid is vaporized along with a tiny bit of the spacecraft."
Considering that meteors are only about the size of a grain of sand, their potential for damage can be surprising. Their speed must also be considered. "They're small, but they move very fast - about 45 miles per second (71 kilometers per second)," said Dr. Bill Cooke of the Marshall Center, who -- along with researchers at the University of Western Ontario in London, Ontario -- generated one of the primary meteor forecast models NASA is evaluating.
According to Cooke's forecast, sky-gazers could see up to 1,400 meteors per hour if they are away from city lights, where the sky is dark enough to see the faint, as well as more brilliant, meteors. In the Eastern United States, the shower is predicted to peak near dawn, while in the Western United States, it is expected to peak around 2 a.m. PST.
A Leonid shower happens every year when Earth passes close to the orbit of the Comet Tempel-Tuttle and the debris left in the comet's path. This year it is expected to be exceptionally strong because of the timing and position of the comet tails.
The material crossing Earth's path this year was ejected from the comet at least 100 years ago. Meteor viewers in the United States, for example, will see material ejected from the comet in 1766 - a decade before the country was founded.
The NASA researchers, along with colleagues from the University of Western Ontario and the U.S. Air Force, will monitor the storm from six locations, each selected based on meteor forecasts and the area's climate. Sites include Huntsville, Ala.; Eglin Air Force Base, Fla.; Maui, Hawaii; Sunspot, N.M.; the U.S. Territory of Guam, and the Gobi Dessert in Mongolia.
Thanks to special equipment, the monitoring team has the capability to detect meteors the visual observer may miss. Using special image-intensified cameras that can detect faint objects even in low-light conditions, the researchers will monitor the shower, using the video screens as windows to the skies. Every hour, the teams will relay their observations to the Marshall control center, helping to paint a comprehensive picture of the meteor storm.
Another tool at Marshall's disposal is "forward-scatter radar" - a system built by Suggs, Cooke and Anderson to monitor near-Earth meteoroid activity around the clock.
"Our system is pretty simple," said Suggs. "We use an antenna and computer-controlled shortwave receiver to listen for 67 MHz signals from distant TV stations."
The transmitters are over the horizon and normally out of range. But when a meteor streaks overhead the system records a brief ping - the echo of a TV signal bouncing off the meteor's trail. Like the cameras, this system is capable of detecting meteors too dim to see with the unaided eye.
The Marshall Center has provided Leonid forecast information to dozens of spacecraft operators to help prepare for this year's meteor shower. "More importantly, by comparing the meteor shower predictions to the actual meteor counts, we are laying the groundwork to improve forecasts in the future," said Suggs.
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