Rubik's-cube-sized CubeSats are a nifty, cheap way for scientists to put a research vessel into space, but they're limited to orbiting where they're launched – until now. Los Alamos researchers have created and tested a safe and innovative rocket motor concept that could soon see CubeSats zooming around space and even steering themselves back to Earth when they're finished their mission.
Consisting of modules measuring 10 x 10 x 11.35 cm (3.9 x 3.9 x 4.5 in), these mini-satellites first launched in 2003, but are currently lacking in propulsion because they're designed to hitch a ride into space with larger, more expensive space missions. They're usually deployed along with routine pressurized cargo launches, usually into low orbits that limit the kinds of studies that CubeSats can perform.
This limitation is, of course, frustrating for space researchers. In fact, the National Academy of Science recently identified propulsion as one of the main areas of technology that needs to be developed for CubeSats.
Bryce Tappan, lead researcher on the Los Alamos National Laboratory Cube Sat Propulsion Concept team says propulsion would greatly expand the mission-space that these small, low-cost satellites can cover. "It would allow CubeSats to enter higher orbits or achieve multiple orbital planes in a single mission, and extend mission lifetimes," he says.
The roadblock to building a self-propelling CubeSat is the inherent risk in the way conventional spacecraft propel themselves through space. Usually, spacecraft use mixed liquid fuel and oxidizer systems to achieve propulsion – methods that are somewhat unstable. This poses a level of risk that would make self-propelling CubeSats unacceptable aboard another organization's space mission.
"Obviously, someone who's paying half a billion dollars to do a satellite launch is not going to accept the risk," says Tappan. "So, anything that is taken on that rideshare would have to be inherently safe; no hazardous liquids."
The rocket propulsion concept that the researchers have developed is a solid-based chemical fuel technology that is completely non-detonable. They're calling the new concept a "segregated fuel oxidizer system," with solid fuel and a solid oxidizer kept completely separate inside the rocket assembly.
The researchers recently tested a six-motor CubeSat-compatible propulsion array with great success.
"I think we're very close to being able to put this propulsion system onto a satellite for a simple demonstration propulsion capability in space," says Tappan.
The system works in many of the same ways as a conventional chemical rocket motor works, with a pyrotechnic igniter initiating burn in a high nitrogen, high hydrogen fuel section, releasing hydrogen rich gases that flow into the oxidizer section. The chemical reaction there creates tremendous heat and expanding gases that flow through a nozzle to provide thrust.
"Because the fuel and oxidizer are separate," said Tappan, "it enables you to use higher-energy ingredients than you could use in a classic propellant architecture. This chemical propulsion mechanism produces very fast, high-velocity thrust, something not available with most electrical or compressed gas concepts."
As well as expanding research capabilities, Tappan says that another desirable application for a self-propelling CubeSat would be a de-orbit capability.
With more than half a million individual pieces of "space junk" now in various orbits around the Earth, small satellites may eventually have to demonstrate a compelling mission before they can be launched, or have a de-orbit capability so they can burn up in the atmosphere without adding to the space junk problem.
If CubeSats were self-propelling, they could send themselves back towards Earth after their mission is complete and burn up in the atmosphere, so they don't add to the space junk issue.
Tappan would eventually like to see their new rocket motor concept used in more ambitious space missions. "Not only simple things like de-orbiting, but in groundbreaking missions like taking a small spacecraft to the moon, or even to somewhere as far away as Mars," he says.
To learn more about the new propulsion system, watch the video below:
Source: Los Alamos National Laboratory
