NASA Meteor Balloon Rises Again
	Fonte : NASA
	Scientists and radio amateurs team up for a live webcast of the 1999 Leonids from the stratosphere. Nov. 1, 1999: Last year when Science@NASA flew a weather balloon to the stratosphere for a high altitude view of the Leonids, over one million people watched the live webcast or saw the replay the next day at LeonidsLive.com. While the video camera on the balloon captured images of blazing fireballs, an aerogel collecting device may have captured bits of comet Tempel-Tuttle -- the parent of the Leonid meteoroid stream. Researchers are still poring over the data. This year, with experts predicting an even bigger Leonid display, the meteor balloonists are planning another flight. Liftoff is scheduled for 0630 UT (0130 EST) on Thursday, November 18 from the Marshall Space Flight Center. The balloon will carry a sensitive low-light CCD video camera to monitor the shower from an altitude of about 32 km (105,000 ft), far above any obscuring clouds or bad weather. Web surfers can watch and listen to live transmissions from the balloon at LeonidsLive.com between 0130 and 0430 EST, on November 18th. Replays will be available after the flight. "We're going to be carrying a more sensitive camera than we did in 1998," said Ed Myszka, an engineer and radio amateur who built the balloon payload, "so the images could be even better than before. The payload this time around will be similar to what we flew during the August Perseid shower. One of the problems we encountered during that flight was the balloon spinning. The camera was sweeping across the sky pretty quickly, which made it hard to see faint meteors. This time I've added ball bearing swivels to the lines between the balloon and the payload package. That'll reduce spin and make it easier to pick up meteors and fireballs during the webcast." An important addition to this year's payload is an INSPIRE VLF radio receiver, which is sensitive to radio emissions below 10 kHz. The very low frequency (VLF) radio band is filled with exotic-sounding signals called spherics, tweeks and whistlers. All three are impulsive bursts caused by distant lighting. "Spherics," which are caused by lightning strokes within a couple of thousand kilometers of the receiver, sound like twigs snapping or bacon sizzling on a grill. Tweeks and whistlers are caused by more distant lightning, and sound like brief descending musical tones. Dennis Gallagher, a plasma physicist at the Marshall Space Flight Center, thinks that the VLF receiver might also pick up natural radio emissions from the Leonid meteors. "Meteoroids produce an ionized trail as they plummet through the atmosphere," explained Gallagher. "There's a low density wake right behind the meteoroid. Because electrons are more mobile than protons, they move in to fill the void faster. That could set up plasma oscillations and trigger radio emissions." Whistlers are sounds that can be heard in the audio region. They are caused by VLF radio emissions from lightning strokes that travel long distances along magnetic field lines. Other types of VLF radio emissions include tweeks, chorus, and spherics. The VLF receiver was donated to the Marshall Space Flight Center for this and possible future flights by the Goddard INSPIRE program. It's been christened the "Marina receiver" after the newborn daughter of Flavio Gori, an Italian scientist who first suggested flying the receiver. Gallagher and his colleagues also plan to operate a Marina VLF receiver at the launch site to provide a ground reference for comparison with data collected from the stratosphere. During the flight signals from the receiver will be converted to audio sounds and transmitted along with images from the CCD video camera. Web viewers at LeonidsLive.com will be treated to an unusual combination of meteoritic sights and sounds. The question of radio emissions from meteors is an intriquing one, says Gallagher, and you don't need to send your receiver to the stratosphere to listen in. Anyone with a VLF receiver can monitor the Leonids on November 18 and Gallagher hopes that INSPIRE participants across the USA will join in the effort. The best way to collect data is to record the output of the receiver on a two-track audio recorder. Record the VLF signal on one track and a WWV time signal on the other. This way VLF pulses can be correlated with the times of bright meteors seen from your observing site. It's also a good idea to conduct at least one observing session a few days before or a few days after the Leonids for comparison. Details about the upcoming meteor shower may be found at http://www.LeonidsLive.com. Catch a falling star.... he video images and VLF sounds will be exciting, but the most important part of the payload may be something else entirely. The balloon will also carry aloft a special device designed to capture actual Leonid meteoroids and return them to Earth. Meteoroids are typically smaller than a grain of sand and much less dense. Although they are insubstantial, they can create very bright "shooting stars" because they travel at high speeds -- over 160,000 mph (72km/sec) for the Leonids. How do you catch a fluffy, microscopic, 160,000 mph fast ball? Very carefully! The meteoroid capture device on the upcoming flight uses xerogel (a close relative of aerogel) and a variety of low density acrylic materials to capture flying particles. "It works like flypaper," explains NASA astronomer Dr. John Horack. "We expose these materials to the air up in the stratosphere while the meteor shower is underway. When tiny particles strike the exposed xerogel, they stick. Then they return to Earth along with the rest of the payload." Aerogel is the lightest known solid, and is considered the best substance available for capturing fragile particles like comet dust without damaging them. When a high-velocity dust particle hits the aerogel, it buries itself in the material, creating a carrot-shaped track up to 200 times its own length. Since aerogel is translucent scientists can use these tracks to find the tiny particles. The track is largest at the point of entry, and the particle can be collected intact at the point of the cone. Experimenters agree that the chances of catching a Leonid meteoroid are slim, but that it's worth a try. Costing less than $4,000, the balloon mission could snag a tiny piece of comet Tempel-Tuttle (the parent of the Leonid meteoroid stream) and enable scientists to study material formed in the outer solar system. The balloon is scheduled to lift off from the The Atmospheric Research Facility (ARF) on the Marshall Space Flight Center (MSFC) Campus in Huntsville, AL at 0130 EST on Thursday, November 18. It will climb to a maximum altitude of approx. 105,000 ft in 200 minutes, followed by a 20-minute descent. Video and audio from the payload will be downlinked as an amateur TV signal at 426.25 MHz transmit frequency (Cable Ready TV Channel 58). The transmission should be detectable for several hundred miles around the launch site for readers who would like to directly monitor the flight. For more information, please contact: Dr. John M. Horack , Director of Science Communications Author: Dr. Tony Phillips Curator: Linda Porter NASA Official: M. Frank Rose LoScrittoio.it want send many thanks to Ron Koczor, Dennis Gallagher (both at Marshall Space Flight Center), William Taylor and William Pine (both at Goddard Space Flight Center) for their kind permission to reproduce this article, first published at: http://science.nasa.gov/newhome/headlines/ast01nov99_1.htm LoScrittoio.it ringrazia sentitamente Ron Koczor, Dennis Gallagher (entrambi al Marshall Space Flight Center), William Taylor and William Pine (entrambi al Goddard Space Flight Center) per la gentile concessione a pubblicare l'articolo originariamente apparso su: http://science.nasa.gov/newhome/headlines/ast01nov99_1.htm Allo suddetto indirizzo web é tuttora visibile l'originale dell'articolo con le immagini a corredo. Flavio Gori