Washington: A Stanford scientist has come close to solving a mystery that has long bedevilled space exploration: Why do satellites fail?
It is popularly believed that satellites are imperiled by impacts from "space junk"-particles of man-made debris the size of a pea (or greater) that litter the Earth`s upper atmosphere-or by large meteoroids like the one that recently exploded spectacularly over Chelyabinsk, Russia.
Although such impacts are a serious concern, most satellites that have died in space haven`t been knocked out by them. Something else has killed them.
And Sigrid Close, an assistant professor of aeronautics and astronautics at Stanford, is proving that the effects of "space dust" are a more likely cause.
These natural micro-meteoroids are not directly causing satellites harm. When they hit an object in space, however, they are traveling so fast that they turn into a quasi-neutral gas of ions and electrons known as plasma. That plasma, Close theorizes, has the potential to create a radio signal that can damage, and even completely shut down, the satellites they hit.
The signal is an electromagnetic pulse, or EMP-similar in concept but not in size to what is generated by nuclear detonations. (Tellingly, a massive EMP knocked out cell phones when the Chelyabinsk meteoroid hit.)
"Spacecraft transmit a radio signal, so they can receive one that might potentially disable them. So our question was: Do these plasmas emit radio signals, and if so, at what frequencies and with what power?" Close said.
Now, through experiments she`s led at the Max Planck Institute for Nuclear Physics in Germany, Close has proof that particles that mimic space dust can indeed cause trouble.
The researchers fired tiny dust particles at targets resembling satellites at speeds of 60 kilometers per second.
"We found that when these particles hit, they create a plasma or quasi-neutral gas of ions and electrons, and that plasma can then emit in the radio frequency range," Close said.
These plasma-induced bursts of energy could explain mysteries like the European Space Agency`s loss of its Olympus communication satellite in 1993, Close believes.
Many other satellites have also failed electronically rather than mechanically.
If Close is right, her experiments point to design modifications that might lessen the damage that space dust inflicts. How the satellite is oriented in space, whether it is being heated or cooled at the time and whether it is positively or negatively charged, all appear to make a difference to whether a plasma-induced radio signal actually causes damage.
"Spacecraft are being hit all the time by these particles. So we feel like we found a smoking gun here in the sense of explaining why this doesn`t always happen. And once we know what`s going on, there are solutions we could implement to save billions and billions of dollars," said Close.
Her next step will be to show that these effects occur in space as well as in the laboratory. To that end, Close is working with James Smith and Henry Garrett of NASA`s Jet Propulsion Laboratory to design an experiment that could be anchored to the International Space Station.