In 1999, technicians from the California Polytechnic State University (Cal Poly) and Stanford University developed the specifications for CubeSat technology. In no time at all, academic institutions were launching CubeSats to conduct all manner of scientific research and validate new satellite technologies. Since 2013, the majority of launches have been conducted by commercial and private entities rather than academia.
Unfortunately, CubeSats have been held back until now because of a lack of good propulsion technology. In addition, there are concerns that with the proliferation of small satellites, Low Earth Orbit (LEO) will become overcrowded. Thanks to Howe Industries and a breakthrough engine design (known as the ThermaSat) that utilizes steam to generate propulsion, all of that could change very soon.
Of all the estimated 2700 CubeSats and other “nanosatellites” that have been created to date, less than 10% have had their own means of propulsion. This leaves them at the mercy of gravity and atmospheric drag, which can cause them to deorbit while they are still functional. In addition, they are unable to maneuver and adjust their orbit and get out of the way of other satellites and space debris.
Dr. Troy Howe (Ph.D.), Howe Industries CEO, explained in a company press statement, the problem with existing propulsion options is twofold:
“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 thanks to its proprietary plug-n-play technology. While the propellant is plain water, ThermaSat differs from conventional steam engines by relying on solar power. This is provided by an exposed optical surface on the unit’s capacitor (rather than bulky, protruding reflectors) that turn the water into superheated steam an instant before it is shot out the rear nozzle.
The engine also has the benefit of being compact and lightweight and consists of only two moving parts. Nevertheless, it can deliver 1,800 Newton-seconds of total impulse (or 203 lbs/s of specific impulse) using just 1 kg (2.2 lbs) of propellant (about the size of a 4 cup teapot). This is enough to maintain a CubeSat at an altitude of 375 km (233 mi) for more than five years and at altitudes as low as 250 km (155 mi) for several months.
Without propulsion, the orbit of a CubeSat at this altitude would decay in a matter of weeks. By being able to sustain such orbits over longer periods of time, small satellites could provide higher-resolution remote sensing and decreased communications latency, which could come in handy in the event of a natural disaster or crisis. A satellite equipped with the ThermaSat could even alter its orbit to get a better look at a situation in progress.
The engineering teams at Howe are currently looking into improving their engine’s capability so that it could enable extended stays at even lower orbits – like a week’s duration at 150 km (90 mi) in altitude. According to Jack Miller, the R&D engineer for the ThermaSat program:
“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. 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.”
According to Howe Industries White Paper, the system has a dry weight of 1,445 g (3.2 lbs) and 2,445 g (5.4 lbs) when fully-fueled. It is capable of supporting standard configuration (2U) CubeSats but can also be paired with 1U, 4U, and 16U payloads. It can generate as much as 200 m/s (656 ft/s) of acceleration (delta-V) and requires 2.3 – 4.6 Watts of electrical power (provided by solar panels).
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).
Since it requires no power from the satellite, the ThermaSat can be used to upgrade larger satellites with an additional propulsion unit. But according to Howe Industries, the greatest asset of their “steampunk” engine is the way it can enable a “new class of smart, autonomous satellites able to relay data and even to ‘swarm’ together for specific tasks.”
Howe Industries developed the ThermaSat with support provided by the National Science Foundation (NSF) as part of a Phase I Small Business Innovation Research (SBIR) grant. With the design now delivered to the NSF, Howe intends to pursue a Phase II SBIR grant, which will entail creating a prototype and getting it ready for a test flight in space.
Howe Industries has also designed a number of applications for NASA, including the High Irradiance Peltier Operated Tungsten Exo-Reflector (HI-POWER) and the Swarm-Probe Enabling ATEG Reactor (SPEAR) probe. The HI-POWER concept is a lightweight solid-state radiator concept for rovers that can ensure thermal management without the added bulk or mass that usually comes with such systems.
Meanwhile, the SPEAR probe concept calls for a nuclear propulsion spacecraft that would rely on advanced thermoelectric generators (ATEGs) and a lightweight reactor moderator to reduce mass. The end result of this is a lightweight spacecraft that could allow for long-duration and cost-effective missions to deep-space – i.e. Mars, the Asteroid Belt, Jupiter, and beyond.
Earlier this year, the HI-POWER concept was selected for Phase I funding as part of the NASA Innovative Advanced Concepts (NIAC) program’s 2020 solicitation. Similarly, the SPEAR probe was selected for Phase I funding by the 2019 NIAC and was selected for Phase II development by the 2020 NIAC.