Propellant is one of the most important things that any spacecraft needs to carry – without it, a spacecraft will be unable to move or change course. This is why spacecraft tend to carry a lot of it on board.

Carrying propellant, however, brings its own set of problems. Not only is the chemical highly flammable, but it also takes up a lot of space, which is problematic when designing a small spacecraft.

In a bid to address some of these problems, researchers at the University of Illinois (U of I) and the Missouri University of Science and Technology (Missouri S&T) developed a new method of propulsion for small spacecraft that uses nanoparticles as its propellant.

Nanoparticles instead of rocket fuel

The concept of using nanoparticles as a form of propellant isn’t a novel one. A previous study published in 2003 by the French-German Research Institute of Saint Louis in the journal Nano Letters demonstrated the use of ammonium perchlorate nanoparticles as a form of solid rocket fuel.

What makes the joint U of I and Missouri S&T study different is the fact that the nanoparticle propellant isn’t burned like a traditional solid-fueled rocket. Instead, electromagnetic energy is used to push the nanoparticles in a specific direction.

The propellant that the team used is made of neutral nanoparticles derived from glass or other materials that insulate rather than conduct electric charges.

These particles are fed through a system that uses light to generate an electromagnetic field. When the nanoparticles are fed through the system, they become polarized. All the positive charges are displaced in one direction of the field, while all the negative charges are displaced in the opposite direction.

This polarization and subsequent displacement create an internal electric field that, in the researchers’ simulation, produces a force that moves the particles from their reservoir through an “engine” consisting of an injector and accelerator that shoots them out to produce thrust.

Electromagnetic fields from light

One of the key features of the researcher’s design is its use of light to produce a magnetic field. This helps simplify the design of the system as it doesn’t need to consume as much power to run.

The technology is based on a field of physics called plasmonics that studies how optical light or optical electromagnetic waves, interact with nanoscale structures.

As explained by Joshua Rovey, associate professor in the Department of Aerospace Engineering in U of I’s Grainger College of Engineering, when the light hits a nanoscale structure a resonant interaction occurs creating strong electromagnetic fields right next to that structure.

Those electromagnetic fields can manipulate particles by applying forces to nanoscale particles that are near those structures.

“One of the main motivating factors for the concept was the absence of or lack of a power supply in space,” said Rovey. “If we can just harness the sun directly, have the sun shine directly on the nanostructures themselves, there’s no need for an electrical power supply or solar panel to provide power.”

The fact that the system doesn’t need much power makes it a good fit as an alternative form of propulsion for small spacecraft that require very small levels of thrust.

So far the study has only tested the concept in numerical simulations. The next step would be to actually create the nanoscale structures in the lab and load them into the system and observe how the nanoparticles move.

“The challenge is in selecting the right permittivity of the medium, the right amount of charge, in which all of this happens,” explained Rovey. “You have to choose the right materials for the nanoparticles themselves as well as the material surrounding the nanoparticles as they move through the structure.”