In 1999, engineers from California Polytechnic State University (Cal Poly) and Stanford University developed the specifications for CubeSat technology. In no time, academic institutions launched CubeSats to conduct all kinds of scientific research and validate new satellite technologies. Since 2013, most of the launches have been carried out by commercial and private institutions rather than universities.
Unfortunately, CubeSats have so far been held back due to a lack of good drive technology. Additionally, there are concerns that the Low Earth Orbit (LEO) will be crowded with the proliferation of small satellites. This could change very soon, thanks to Howe Industries and a groundbreaking motor design (known as ThermaSat) that uses steam to generate propulsion.
Of all the estimated 2,700 CubeSats and other “nanosatellites” that have been manufactured so far, less than 10% had their own propulsion systems. As a result, they are exposed to gravity and drag, which can cause them to desorb while they are still functional. In addition, they are unable to maneuver and adjust their orbit and avoid other satellites and space debris.
Trackable objects in low earth orbit. Image credit: ESA
Dr. Troy Howe (Ph.D.), CEO of Howe Industries, stated in a company press release that the problem with existing drive options is twofold:
“On the one hand, these systems require considerable power to operate, which derives energy from the primary payload. And then there are the more “energetic” propulsion systems (which are usually scaled down from being used on much larger satellites). These are based on toxic, high pressure or even explosive liquids such as hydrazine.
“This is problematic as most CubeSats go into orbit together and the launch providers are suspicious of endangering their other, often more valuable, cargo. While the use of the International Space Station (which is common for CubeSats) excludes any satellite propulsion that could also pose a risk to the station and its personnel. “
The ThermaSat steam engine overcomes these obstacles thanks to its proprietary plug-n-play technology. While the propellant is clear water, ThermaSat differs from conventional steam engines in that it uses solar energy. This is ensured by an exposed optical surface on the device’s condenser (instead of bulky, protruding reflectors) that converts the water to superheated steam a moment before it shoots out of the rear nozzle.
Artist’s impression of the orbital debris problem. Image credit: UC3M
The motor also has the advantage that it is compact and light and consists of only two moving parts. Nevertheless, with just 1 kg of propellant (about the size of a 4-cup teapot) it can deliver 1,800 Newtons total impulse (or 203 lbs / s specific impulse). This is enough to keep a CubeSat at an altitude of 375 km for more than five years and at an altitude of only 250 km for several months.
Without a drive, the orbit of a CubeSat would decrease at this altitude in a few weeks. With the ability to maintain such orbits for extended periods of time, small satellites could provide high resolution remote sensing and reduced communication latency, which could be useful in the event of a natural disaster or crisis. A satellite equipped with the ThermaSat could even change its orbit to better see a current situation.
Howe engineering teams are currently trying to improve the performance of their engine so that longer stays in even lower orbits are possible – for example a week at 150 km. According to Jack Miller, the research and development engineer for the ThermaSat program:
“At the heart of the system is the unique heat condenser made from phase-change materials that concentrates and stores the sun’s heat, which is collected on an exposed surface of just 20 square inches. With a combination of photonic crystals and gold-colored mirrors, the completely inert capacitor reaches a bubble temperature of 1,052 K (1,433 Fahrenheit). This leads to a specific energy that is comparable to a lithium-ion battery, but does not present a risk of explosion. “
Concept of the HI-POWER rover. Photo credit: Troy Howe / Howe Industries
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 supports CubeSats with standard configuration (2U), but can also be coupled with payloads of 1U, 4U and 16U. It can generate an acceleration of up to 200 m / s (656 ft / s) (Delta-V) and requires 2.3 to 4.6 watts of electrical power (provided by solar panels).
In addition to being deployed, the ThermaSat can be used for orbit raising, geolocation missions (which require formation flights), and planned deorbitation and collision avoidance (likely required). The system can also enable fast constellation deployment (without relying on variable resistance).
Since the satellite does not require electricity, the ThermaSat can be used to upgrade larger satellites with an additional drive unit. According to Howe Industries, however, the greatest asset of their “steampunk” machine is the ability to enable a “new class of intelligent, autonomous satellites that can relay data and even swarm it for specific tasks”.
Howe Industries developed the ThermaSat with support from the National Science Foundation (NSF) as part of a SBIR (Phase I Small Business Innovation Research) grant. With the design now delivered to NSF, Howe intends to apply for a Phase II SBIR grant that will create a prototype and prepare it for a test flight in space.
Howe Industries has also developed a number of applications for NASA including the Peltier-powered tungsten exo-reflector (HI-POWER) with high irradiance and the SPEG (Swarm-Probe Enabling ATEG Reactor) probe. The HI-POWER concept is a lightweight, solid-state radiator concept for rovers that can provide thermal management without the additional bulk or bulk normally associated with such systems.
The SPEAR probe concept envisions a core-propelled spacecraft based on advanced thermoelectric generators (ATEGs) and a lightweight reactor moderator to reduce mass. The end result of this is a lightweight spaceship that could enable long-lasting and inexpensive missions into space – i.e. Mars, asteroid belt, Jupiter and beyond.
Earlier this year, the HI-POWER concept was selected for Phase I funding as part of NASA’s 2020 application for Innovative Advanced Concepts (NIAC). Similarly, the SPEAR probe was selected by NIAC 2019 for Phase I funding and selected by NIAC 2020 for Phase II development.
For more information, see the Howe Industries white paper and ThermaSat datasheet.
Further reading: Space Daily, Howe Industries
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