New Kind of Mini-thruster Could One Day Power Micro Rockets

Researchers at Michigan Technological University have developed a prototype of a microscopic thruster that could one day be used to power miniature rockets.

Nanosatellites, also known as nanosats, are spacecraft roughly the size of smartphone used by a variety of agencies and private companies to gather a wide range of data. And while many of their features are borrowed from everyday gadgets, such as wireless radios and GPS receivers, there is one feature that remains totally unique to space.

"Even the best smartphones don't have miniaturized rocket engines, so we need to develop them from scratch," study lead L. Brad King said in a statement detailing the research.

And while miniature rockets aren't necessary in order to launch nanosats into space given their ability to hitchhike on a regular rocket, propulsion is required to position the device into orbit.

Over the last several years, research on mini rockets has largely focused on using microscopic needles that spray thin jets of fluid. However, with a single thruster needler finer than a human hair, these designs are vulnerable to anything from "a careless bump or an electrical arc when they're running," King explained.

For this reason, he and his colleagues have taken up a new approach that circumvents these small needles altogether.

"We're working with a unique type of liquid called a ferrofluid that naturally forms a stationary pattern of sharp tips in the liquid surface," he said. "Each tip in this self-assembling structure can spray a jet of fluid just like a micro-needle, so we don't actually have to make any needles."

Ferrofluids are made of tiny magnetic particles that become suspended in a solvent when a magnetic force is applied. King and his team were trying to make an ionic liquid that behaved like a ferrofluid when news reached them of a team at the University of Sydney that was already one step ahead of them, using magnetic nanoparticles to treat liver cancer.

"They sent us a sample, and we've used it to develop a thruster," King said. "Now we have a nice collaboration going. It's amazing that the same technology used to treat cancer can also function as a micro rocket for spacecraft."

The team's first thruster is comprised of a one-inch block of aluminum and a small ring of the fluid. When a magnet is placed beneath it, a small crown is formed from the liquid that produces liquid jets when an electric force is applied, resulting in thrust. 

"It's fascinating to watch," King said. "The peaks get taller and skinnier, and taller and skinnier, and at some point the rounded tips instantly pop into nano-sharp points and start emitting ions."

Moreover, the thruster is self-healing and thus apparently immune to any kind of permanent damage -- a fact the team found out in a surprise experiment.

"We accidentally turned the voltage up too high, and the tips exploded in a small arc," King said. "A completely new crown immediately formed from the remaining ferrofluid and once again resumed thrusting."

Before the thruster is orbit-ready, the researchers still have to determine what exactly is occurring on a microscopic level and then develop a larger prototype based on their findings.

"We're not quite there yet; we can't build a person out of liquid, like the notorious villain from the Terminator movies," King said. "But we're pretty sure we can build a rocket engine."