“A thruster chip contains hundreds of microscopic emitters that emit beams of ions.”
Dime-Size Thrusters Could Propel Satellites, Spacecraft
by Tracy Staedter / March 23, 2017
“A new propulsion engine with dime-size thrusters could be used to propel a host of spacecraft, from small satellites to crewed ships designed for interplanetary exploration. The new propulsion engine, called Tile, could serve as an efficient and lightweight way to keep constellations of small satellites in orbit. Spaceflight companies — including OneWeb, Boeing and SpaceX — want to launch hundreds of thousands of these small satellites to provide broadband internet to everyone around the globe. And because several Tiles can be connected to produce more power, the engine has the potential to propel astronauts to Mars, according to Accion Systems, the company that designed Tile.
“Our technology starts on a nanometer scale, and then we can array that and scale that up to serve satellites,” said Natalya Bailey, CEO of Accion Systems. Bailey described the propulsion engine to an audience here at the New Space Age Conference at the Massachusetts Institute of Technology’s (MIT) Sloan School of Management on March 11. Bailey developed the underlying propulsion system with Accion co-founder Louis Perna while they were Ph.D. students at MIT. The Tile engine uses a method called ionic liquid electrospray propulsion. The system draws from a decades-old technology for thrusting satellites, called electric propulsion, which uses electromagnetic fields to shoot charged atoms, or ions, out the back of a satellite to push it forward.
But these engines, known as Hall-effect thrusters, have some major downsides. First, they use compressed-gas propellants that have to be stored in large, pressurized containers. Hall thrusters also require electric power in a couple of different places, first to charge the particles to create an ionized gas, and then to accelerate that plasma to propel the satellite. All of these things add bulk and weight to the engines, which make them way too big to serve as propulsion systems for small satellites, Bailey said. And thanks to the laws of plasma physics, the engines are just plain impossible to shrink down. “Essentially, you end up running into some problems with really hot electrons and melting the device,” she said.
Schematic of an Accion Systems TILE thruster engine
In contrast, the Tile’s ionic liquid electrospray propulsion system has more in common with a computer chip than a huge, bespoke engine, Bailey said. In fact, Accion calls the dime-size propulsion device a “thruster chip.” It’s made of hundreds of emitters that produce beams of ions generated from a nontoxic and nonexplosive propellant that’s a salt-based solution. An array of 36 thruster chips make up the outward-facing surface of a Tile module, which measures about 4 inches by 4 inches by 5 inches (10 by 10 by 12.5 cm) — about the size of a grapefruit. Beneath the top layer of the module are other components stacked in a particular order, including the salt-based propellant, which is stored in tiny tanks, and the system’s power electronics, which run off of the satellites’ solar panels and batteries. When the power is on, the battery creates an electric field that draws ions up from the salty propellant and pulls them through the tanks to the thruster chips, which funnel them into a beam and eject them for propulsion.
Illustration of the microscopic thrusters in an Accion Systems thruster chip
One to four Tiles could propel a small satellite weighing anywhere from 100 to 440 lbs. (50 to 200 kilograms), Bailey said. Arranging more modules together in a larger array could steer larger satellites, without the added bulk, she added. Bailey and Perna founded Accion Systems in 2014 to commercialize the Tile technology. In 2015, the company received a $3 million contract from the U.S. Department of Defense (DOD) to develop their technology. This summer, the company will test the Tile to see how well it can withstand temperature extremes, the vacuum of space, and the shock and vibration of a launch.
After it passes those tests, Accion plans to integrate a Tile with a customer satellite, Bailey said. “We’re definitely going to space,” she added. In another 10 to 15 years, Accion Systems hopes to have the technology refined to make the long journey to Mars. According to the company’s estimates, if a crewed spacecraft were to rely on conventional engines, the journey would require so much fuel that the ship would have to support 4,000 Hall thrusters. The fuel tanks alone would equal the size of the International Space Station. But if the trip were made using Accion’s Tile propulsion, the engine and fuel system would take up the space of shoebox, Bailey said.”
PLASTIC FUEL TANKS
Electric propulsion system improves maneuverability of small satellites
by Rob Matheson / March 11, 2015
“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 PhD ’15, 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 maneuver 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 those known 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. Ultimately, he adds, the technology could give small startups—and even countries without well-funded space programs—the opportunity to use low-cost satellites for space exploration. “It’s what other people have called the ‘democratization of space,'” Lozano says. “I think this will contribute to making that a reality.”
Accion’s first commercial system is MAX-1, a module comprising eight chips—each about 1 square centimeter, and 2 millimeters thick—that can be applied anywhere on a satellite. On Earth, it provides enough thrust to “move around a sheet of paper,” Brikner says. But in space, it can push around a CubeSat, or a slightly larger satellite.
Accion’s first product, MAX-1 (shown here), is a module comprising eight chips — each about 1 square centimeter, and 2 millimeters thick
The module has a plastic tank that stores a nontoxic, nonvolatile, 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,” Brikner explains.
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—meaning it packs a punch. 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 meter.
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,” Brikner says. However, with dozens of small satellites being launched annually, Lozano adds, the system could also help control how long they stay in space, so they don’t become floating space junk. “You can climb to an orbit where drag is less, and stay there for longer, and use the same propulsion system to re-enter [the atmosphere],” he says.
While it is possible to create low-cost chemical-propulsion systems, it’s not practical, Brikner says. Chemical systems are made with explosive pressurized tanks, which are not allowed to piggyback on the larger rockets that carry small satellites into space. Electric-propulsion systems are, therefore, safer and more popular alternatives. But these are expensive to make, as they use the rare gas xenon as a propellant, which also needs pressurization for storage.
Accion’s propellant is a liquid salt material, similar in structure to common table salt, which can be made in large quantities. With that novel propellant, and a simple design, Accion can batch-manufacture modules—much like computer chips—in quantities of around 200 at once. According to Brikner, this costs about one-tenth as much as other electric-propulsion systems.”