Since their introduction in 1999, CubeSats have made a dramatic mark in space, widely used for technology demonstrations, earth sensing, telecom and other missions. But their full potential has been held back by the lack of a good propulsion solution.
That’s about to change, thanks to a breakthrough engine design which Howe Industries has submitted to the National Science Foundation (NSF) in fulfillment of their SBIR grant.
It is estimated that of the 2700 CubeSats (and other nanosatellites) which have been created, less than 10% have included a means of propulsion. This leaves them at the mercy of gravity and atmospheric drag until soon falling to earth (even when still fully functional).
“The problem with existing propulsion options is twofold,” according to Dr. Troy Howe (PhD), Howe Industries CEO. “On the one hand, these systems require substantial power to operate, siphoning energy from the primary payload.
“And then there are the more ‘energetic’ propulsion systems (typically scaled down from use on much larger satellites). These rely upon toxic, highly pressurized or even explosive liquids, such as hydrazine. This is problematic as most CubeSats share a ride to orbit and launch providers are leery of endangering their other, often more valuable cargo. While deployment from the International Space Station (which is common for CubeSats) precludes any satellite propulsion which likewise might pose a risk to the station and personnel.
“The ThermaSat steam engine overcomes these obstacles while fulfilling other must-have requirements for a successful CubeSat propulsion system”, concludes Dr. Howe.
Quite simply, the ThermaSat propellant is plain water. But unlike in a traditional steam engine, there’s no boiler. Rather, the water is flashed into superheated steam in the instant before expanding out of the nozzle. Even better, the self-sufficient, plug-n-play ThermaSat requires no power from the satellite; nor are there bulky, protruding reflectors to obstruct the mission objectives. (In the image, shown above, the extended solar panels are there solely for powering the satellite payload).
While simple and reliable (with only two moving parts) and smaller than a loaf of Wonder Bread®, the ThermaSat delivers enough total impulse (1,800 Ns with 1kg/2.2 lbs. of water) to maintain a CubeSat in a Low Earth Orbit altitude of 375 km (233 miles) for more than five years. This represents a huge potential savings in satellite replacement.
Alternatively, the ThermaSat can enable months-long missions as low in the ionosphere as 250 km (155 miles). At this altitude – without propulsion – a CubeSat would otherwise come crashing down after just a few weeks. Sustaining such missions at the edge of space enables much higher resolution for remote sensing while dramatically decreasing communications latency (with an increase in total communications throughput). This could be particularly important in an emergency (whether meteorological or geopolitical). A monitoring satellite could even park in a higher orbit, firing up the ThermaSat to descend for a closer look on short notice.
“The heart of the system is the unique thermal capacitor, made from phase-changing materials, which concentrates and stores the solar heat collected from just 20 square inches of exposed surface area”, according to Jack Miller, R&D engineer for the ThermaSat program. “Using a combination of photonic crystals and gold-tinted mirrors the completely inert capacitor reaches a blistering operating temperature of 1,052K (1,433 Fahrenheit). This results in a specific energy comparable to a lithium-ion battery, but without the potential for explosion.”
In addition to station keeping, the ThermaSat can be used to raise orbits, for geolocation missions (which require formation flying) as well as for scheduled deorbiting and collision avoidance (likely to become a requirement). The system can also enable rapid constellation deployment (without relying upon variable drag). And because it requires no power from the satellite, the ThermaSat might be deployed as a strap-on propulsion unit when servicing/upgrading even much larger satellites. But perhaps most exciting, is the potential to enable a new class of smart, autonomous satellites able to relay data and even to ‘swarm’ together for specific tasks.
Whatever the mission, with the ThermaSat steam engine, a satellite will unerringly maintain course as it rides invisible tracks through space.