Small satellites are becoming increasingly popular tools for Earth-imaging, communications, and other applications. But they have major control issues: once in space, they can’t accurately point cameras or change orbit, and they usually crash and burn within a few months.
What these satellites lack is a viable propulsion system, says MIT aeronautics and astronautics alumna Natalya Brikner, co-founder and CEO of Accion Systems. “You can make a satellite the size of a softball with a surprising amount of capabilities, but it can’t manoeuvre properly and falls from orbit quickly,” she says. “People are waiting for a solution.”
Now Accion has developed a commercial electrospray propulsion system — their first is about the size of a pack of gum — made of tiny chips that provide thrust for small satellites. Among other advantages, Accion’s module can be manufactured for significantly less than today’s alternatives.
This technology could enable low-cost satellites, such as 'CubeSats', to become more viable for various commercial and research applications, including advanced imaging and communications, where numerous satellites could provide global coverage. “That requires propulsion, but something so small that it won’t interfere with the small volume and resources a small satellite already has,” says Accion technical advisor Paulo Lozano, an associate professor of aeronautics and astronautics who invented the underlying technology.
Accion’s first commercial system is MAX-1, a module comprising eight chips — each about 1 square centimetre, and 2 millimetres thick — that can be applied anywhere on a satellite. On Earth, it provides enough thrust to move around a sheet of paper, but in space, it can push around a CubeSat, or a slightly larger satellite.
The module has a plastic tank that stores a non-toxic, non-volatile, liquid-salt propellant. Above the reservoir are the chips, which each have a porous substrate with about 500 pointed tips and, above that, an extractor grid with small holes. Capillary forces cause the propellant to flow from the reservoir to the substrate tips.
When a high voltage is applied between the tips and grid, charged ions burst through the holes. “When you extract and accelerate these ions, that momentum exchange propels the spacecraft in the opposite direction.
Accion is on target to launch MAX-1 in July, and plans to start shipping the system to customers by the end of the year.
Because the module doesn’t have pressurized tanks, bulky valves, or neutralizing cathodes, it has a higher thrust-to-mass ratio than low-power, plasma-based ion engines. In January, Accion tested a miniature version of MAX-1, called MIN-0, inside a vacuum chamber at MIT. The team measured the emitted current of the released ions after applying certain levels of voltage. From that experiment, and others, they conclude the MAX-1 can provide about 100 microNewtons of force per square metre.
This is enough thrust, for example, to stabilize a CubeSat launched from the International Space Station, and to compensate for atmospheric drag, which is the force that pulls small satellites into the atmosphere prematurely, where they burn up.
Moreover, the system could also help control how long they stay in space, so they don’t become floating space junk.