Tiny satellites, not much bigger than a Rubik’s Cube, are routinely sent into space to perform a range of research and maintenance tasks. This unique propulsion system is set to send them further than ever before.
[Image source: Wikimedia]
CubeSats: Tiny Modular Research Vessels
NASA’s CubeSat Launch Initiative (CSLI) allows researchers and educational institutions to conduct space research. These tiny satellites, 100 millimetres to a side, weigh less than 1.5 kilograms and can do everything from structural repair in orbit to disaster monitoring.
Due to their small dimensions, the propulsion system required to drive CubeSats around must be correspondingly small and lightweight. Traditional chemical fuels are heavy, bulky, and highly explosive. Research out of MIT has produced the Scalable ion Electrospray Propulsion System (S-iEPS), a compact and efficient thruster system for these nanosatellites.
Scalable ion Electrospray Propulsion System (S-iEPS)
S-iEPS comprises tiny thruster modules, incorporating an array of hundreds of emitters used to accelerate ions from microscopic openings at forces measured in nanonewtons. While this is an incredibly tiny force, a group of modules’ combined output can yield impressive results. Using a scant 150 grams of fuel, a CubeSat could be driven from a low Earth orbit of less than 2,000 kilometres, way out to a geosynchronous orbit of 36,000 kilometres and beyond. This volume of fuel still leaves plenty of room inside the CubeSat for vital research equipment.
Ion engines have no moving parts, drawing up an ionic liquid via capillary action to the emitters. Here, ions are accelerated through an electrical field, requiring only 5 Watts of electricity from batteries recharged by solar panels. The degree of thrust depends upon the concentration of emitters on the module; over 400 emitters per square centimeter.
Paulo Lozano, Associate Professor of Aeronautics and Astronautics at MIT, leads the research team developing S-iEPS. In an interview with ASME, he said ‘They produce little force, but because they can fire for a long time, you accelerate the spacecraft to a velocity that would be impossible to get with a chemical engine. That is a big value’.
S-iEPS compares favorably with plasma ion engines, which, though delivering greater thrust, are too complex to miniaturize for CubeSat applications. ‘You have thrust that is about an order of magnitude higher than what we have now. If you wanted to substitute that thruster for ours, you would need an area about 10 times larger,’ Lozano reported to ASME.
S-iEPS in Space
The size and longevity of ion electrospray engines allows for a greater range of potential applications. Proposed missions include maintenance, inspection, and repair of structures in orbit, adjustment of larger satellite trajectories, and space junk removal.
Commercialisation of S-iEPS is currently underway via Accion Systems, implementing batch manufacturing to make space research cheaper and more accessible.