A mini-satellite, no bigger than a loaf of bread, could push itself out of Earth’s orbit as soon as next year if a crowdfunding campaign to support development of a diminutive propulsion system succeeds. If such small spacecraft can be made to operate far from Earth, they could one day make inexpensive expeditions to asteroids, Mars, and beyond.
Interplanetary spacecraft are typically bigger than a car, cost hundreds of millions to billions of dollars, and take many years to develop and launch. In recent years researchers have been pondering how to send small satellites, called CubeSats, which have been launched into Earth orbit over the past decade, mainly by university teams, farther afield.
Researchers at the University of Michigan have a design for a propulsion system they believe is ready to send a CubeSat on an expedition into deep space. Their campaign on the fundraising site Kickstarter asks for $200,000 to pay for development needed to make a test launch next year.
Since July 4, more than 800 people have pledged over $32,000 to the CubeSat Ambipolar Thruster project. That’s well short of the final goal, but the campaign seems likely to succeed thanks to interest from some deep-pocketed donors. “We’ve already had a couple of people contact us and tell us they just want to fund the whole thing,” says team leader Benjamin Longmier. The Michigan researchers have also applied for grants from U.S. government agencies.
The satellite could launch in a year, says Longmier, and embark on an interplanetary trip after being tested in low-Earth orbit. It is not clear how long it would survive, but on the Kickstarter page, the team jokes that 100 million years from now, the little probe could be found and displayed in a museum in the Alpha Centauri system.
No CubeSat has left Earth orbit before, but the Michigan team believes its propulsion system solves a key barrier to cheaper interplanetary exploration. CubeSats are made from one or more 10-centimeter-wide instrument boxes, and hitch rides to orbit with larger, more expensive spacecraft. That limits the kinds of propulsion systems that can be installed onto a CubeSat. Common systems that use explosive chemicals or highly pressurized gases to produce thrust would pose too much risk to a CubeSat’s pricier launch mates. Nearly all of the 100 or so CubeSats launched to date have had no propulsion system at all.
The Michigan system would pose no danger to the launch it was hitchhiking with because it would use a non-explosive propellant such as iodine or water stored in an unpressurized container.
To propel the satellite, a heater would vaporize the propellant, sending neutral atoms of gas into a small chamber. A radio antenna around that chamber would energize the gas, causing collisions that would knock electrons off the gas atoms to create a plasma. A ring-shaped permanent magnet would then accelerate these charged particles out a nozzle to thrust the CubeSat in the opposite direction.
The Michigan team says its system could fit inside one 10-centimeter-wide module of a three-unit CubeSat, and propel it at speeds of up to 10 kilometers per second. That would be enough to push the satellite at least a million kilometers from Earth, out of the planet’s gravitational grip.
Paulo Lozano, director of the space propulsion lab at MIT, says he has some doubts about the project. The plasma will need to be extremely dense to provide ions for thrust, he says, and high-density plasmas tend to damage anything they contact. “If they are able to do it, that’s great,” says Lozano, who is developing another electric propulsion system that uses ions in salty liquids, rather than plasmas, to generate thrust.
Longmier responds that the magnet that directs the spew of ions out of the thruster will also prevent most plasma from contacting the walls of its chamber, buying enough time for a CubeSat to escape Earth’s orbit. “It looks like we can process up to about 10 to 20 kilograms of propellant with our little thruster,” says Longmier, and simulations suggest less than three kilograms are needed to send a CubeSat beyond Earth. Erosion, he says, seems to be a “nonissue.”
Other spacecraft components—such as power and communication systems—still need to be developed for CubeSats to do much when they’re far from Earth. But in a few more years, they could be sent to study asteroids or to look for signs of life on distant icy moons, the team writes on its Kickstarter page. Because of their size, the petite probes may be able to take only a single type of measurement at each location rather than carry multiple instruments like a traditional craft, but Lozano says they have one big advantage over larger missions: “They are very inexpensive.”