Radio signal-emitting space dust a danger to satellites

Research by Stanford aeronautics and astronautics assistant Prof Sigrid Close suggests she’s on track to solve a mystery that has long bedevilled space exploration: why do satellites fail?

The popular thought is that satellites are imperilled by impacts from ‘space junk’ - particles of man-made debris that litter the earth’s upper atmosphere - or by large meteoroids like the one that recently exploded 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. The likely culprit, it turns out, is material so tiny its nickname is ‘space dust’.

These natural micrometeoroids are not directly causing satellites harm. When they hit an object in space, however, they are travelling so fast that they turn into a quasineutral gas of ions and electrons known as plasma. That plasma, Close theorises, has the potential to create a radio signal that can damage, and even completely shut down, the satellites it hits.

The signal is an electromagnetic pulse (EMP) - similar in concept but not in size to what is generated by nuclear detonations.

“Spacecraft transmit a radio signal, so they can receive one that might potentially disable them,” Close said. “So our question was: do these plasmas emit radio signals and, if so, at what frequencies and with what power?”

Through experiments she 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 km 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.

“Olympus failed during the peak of a meteor shower, but they never detected a momentum transfer, which means whatever hit it wasn’t big enough to be detected mechanically,” she said. “And yet, this multimillion-dollar spacecraft was effectively taken out.”

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,” said Close. “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.”

Her next step will be to show that these effects occur in space as well as in the laboratory. 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.

“The idea is to try and get hit as much as possible!” Close joked.