To Catch a Shooting Star
Researchers investigate the destructive potential of meteoroids.
By Chris Palmer
Aboard NASA's famed "vomit comet"—a modified 727 airplane with all the seats ripped out—graduate student Nicolas Lee folds a one-meter-square sheet of Mylar plastic. An origami whiz, Lee, MS '07, PhD '13, twists and wraps the sheet like a giant ribbon around a spool. He then gently crams the whole thing into the bay of a nanosatellite slightly larger than a Rubik's Cube. As the plane peaks at 32,000 feet and begins its descent, Lee gives the CubeSat a slight rotation and tosses it into the weightless environment. When the cube's hinges swing open a second later, the Mylar canopy pops out and floats elegantly in place. Three dozen successful attempts later, the prototype is one step closer to being ready for its mission: orbiting Earth as a target for incoming meteoroids.
Once dismissed as relatively harmless, these high-speed, microscopic chunks of ice and rock shed by passing comets and asteroids have recently become suspects in multimillion-dollar hit-and-run collisions with satellites. Stanford aerospace engineer Sigrid Close theorizes that when they crash into a satellite at 60 kilometers per second, meteoroids can vaporize into balls of electrically charged gas. That plasma has the potential to fry the delicate circuits at the core of any of the 1,000 or so satellites currently orbiting Earth. "It would essentially behave like a small lightning bolt in space," she says.
Close's CubeSat should set off many such bolts in orbit. By studying those emissions, Close and her team hope to collaborate with NASA and commercial satellite operators to ascertain the destructive capacity of the diminutive saboteurs—which may be on par with that of space junk, pieces of manmade debris trapped in orbit around the planet. Nearly a billion pea-sized meteoroids pass through the Earth's atmosphere every day without incident. But because they move so fast, even microscopic ones can pack a wallop. "It's impossible
to tell the difference between a satellite's collision with a large piece of relatively slow-moving space debris and a collision with a small, but speedy, meteoroid," Close says.
She should know. Close has spent her career—including a two-year stint manning a space surveillance telescope on an island in the middle of the Pacific Ocean—studying dangers to satellites. Her interest in meteoroids first arose when she realized the radar systems she used to track space debris were disrupted by the ionosphere's constant bombardment by the tiny rocks.
The National Academy of Sciences commissioned a report in 2011 to assess the collision risk of both meteoroids and space debris with spacecraft. Close, along with University of Western Ontario astronomer Peter Brown, wrote the chapter about meteoroids. Brown concludes, "There is strong evidence for some satellites having been operationally affected and some missions being terminated as a result of meteoroid impacts."
In 1993 the experimental European Space Agency telecommunications satellite Olympus 1 suffered electrical problems and spun out of control during the peak of a particularly strong Perseid meteor shower. Close speculates that a meteoroid was responsible. However, she believes the electronics aboard Olympus may have been knocked out by an electrostatic spark in combination with a more nefarious danger. When a high-velocity collision occurs, electrons radiate outward; if enough do so at the same time, they can create an electromagnetic pulse, or EMP.
Recently, Close's EMP theory was put to the test at a venue that mimics space nicely: a hot-tub-sized vacuum chamber in the Van de Graaff accelerator at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. She and her students used the accelerator to blast small iron particles into palm-sized mock-ups of solar panels. Sensors in the vacuum chamber detected puffs of plasma followed by sharp radio frequency (RF) pulses lasting a few microseconds. The results, published in the journal Physics of Plasmas in September, showed that plasma could in theory create a rogue electromagnetic wave in space.
Close calculates that such an EMP may be 10 to 100 times stronger than current satellite shielding can withstand. Her research suggests several ways to protect satellites against anomalies caused by meteoroids, such as installing heavy-duty insulation and separating vital components so that plasma bridges are less likely to fry anything critical. Satellites could also be repositioned during meteor storms so that charged surfaces face away from the incoming stream. But every pound launched into space costs approximately $10,000, so the case for beefing up satellite defenses against meteoroids will have to be ironclad.
The next step is to send the experiment to space. Close has funding from NASA to build miniature plasma detectors that would ride aboard the CubeSat. The final device should be built and ready to launch by 2015, she says. Once in orbit, the Mylar canopy would unfold and telescope out along four booms, providing a target the size of a card table for incoming meteoroids. The plasma detectors, trained on the sheet like patrons watching a movie theater screen, could record minuscule plasma eruptions that occur as meteoroids skid across its surface. (Another design under consideration would place the plasma detectors on the back of the CubeSat's solar panels.) Close expects about one strike per day, enough to determine how often electrostatic discharges and EMPs occur, and how powerful they really are.
Chris Palmer is a science writer based in Maryland.
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