When spacecraft and satellites travel through space, they encounter tiny, fast-moving particles of dust and space debris. If the particle is moving fast enough, its impact appears to create electromagnetic radiation (in the form of radio waves) that can damage or even disable the craft’s electronic systems.
A new study published this week in the journal Plasma physics, from AIP Publishing, uses computer simulations to show that the plasma cloud generated by the impact of the particle is responsible for creating the damaging electromagnetic pulse. They show that as the plasma expands into the surrounding vacuum, the ions and electrons move at different speeds and separate in a way that creates radio frequency emissions.
“For the past few decades, researchers have been studying these hypervelocity impacts, and we’ve noticed that there’s radiation from the impacts when the particles are going fast enough,” said lead author Alex Fletcher, now a postdoctoral fellow at the Boston University Center for Space Physics. . “No one has really been able to explain why it’s there, where it came from, or the physical mechanism behind it.”
The study is a step towards verifying the theory of lead author Sigrid Close, an associate professor of aeronautics and astronautics at Stanford University. In 2010, Close and colleagues published the initial hypothesis that hypervelocity impact plasmas are responsible for some satellite failures.
To simulate the results of a hypervelocity impact plasma, the researchers used a method called particle-in-cell simulation that allows them to model plasma and electromagnetic fields simultaneously. They fed the simulation details from a previously developed hydrocode – a computational tool they used to model the fluid and solid dynamics of the impact. The researchers let the simulation evolve and calculated the radiation produced by the plasma.
When a particle hits a hard surface at high speed, it vaporizes and ionizes the target, releasing a cloud of dust, gas and plasma. As the plasma expands into the surrounding vacuum (of space), its density decreases and it enters a collisionless state where its particles no longer interact directly with each other.
In the current study, the researchers hypothesize that the electrons in this collisionless plasma then move faster than the larger ions. Their simulation predicts that this large-scale charge separation generates the radiation. The model results are consistent with Close’s original theory, but predict a higher emission frequency than that detected experimentally by the researchers.
The authors point out that the hypothesis that electrons move en masse when separating from ions deserves more attention. The group is building new simulations to test whether moving to a collision-free state is enough to create separation.
Fletcher also notes that they neglected to account for dust.
“The impact creates dust particles that interact with the plasma,” Fletcher said. The dynamics of these “dusty plasmas” is an area for future research.
The next stage of work is to use the simulation to quantify the radiation generated so they can assess the threat to satellites and design ways to protect satellites and spacecraft from meteoroids and orbital debris.
“More than half of electrical failures are unexplained because it’s very difficult to make diagnoses on a satellite that fails in orbit,” Fletcher said. “We think we can attribute some of these failures to this mechanism.”
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