Nanosats—satellites weighing a few pounds or less—are poised to colonize space. Already, hundreds of these cubes (their usual shape) are launched a year, for research, communication and education. But while their electronics can last years, they usually fall out of orbit in a matter of months, thanks to atmospheric drag.
Space propulsion works on the principle that every action has an equal and opposite reaction: If you sit on a wheeled chair and throw something one way, you go the other. Most rockets burn fuel and throw the exhaust out the back, making the rocket go forward. Another option is electric propulsion, which uses electromagnetic fields to accelerate charged particles out the back. But conventional electric thrusters are bulky, and when made very small, they produce a lot of extra heat, rendering them inefficient and likely to corrode. So existing options are not ideal for those hundreds of cubesats we send up into space every year.
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