Jet Propulsion Part 2: the Market of Low-Thrust Engine Technologies for Satellites
Explore the growth and importance of the low-thrust engine market for humanity, why VCs invest in it, and examine various engine types and emerging technologies.
Issue No 35. Subscribers 5662. Featuring a quote from the CTO of Earth and Beyond Ventures.
After releasing our jet propulsion market overview last month, numerous venture capitalists reached out, expressing interest in delving deeper into the low-thrust engine market and requesting assistance with due diligence and pipeline development. To cater to their needs and benefit a broader audience, we chose to produce a comprehensive analysis of key players and evaluation metrics within the low-thrust engine industry.
We had the opportunity to discuss this research and the market with Assaf Wise, CTO of Earth and Beyond Ventures, an Israeli deep-tech VC fund specializing in New Space. He shared his insights on the market's growth prospects:
"The low-thrust engine market is poised for expansion, driven by several emerging trends. As a result, we are actively looking into investing in various companies in this sector. Key growth drivers include:
Upcoming regulations will require end-of-life satellites to be deorbited and burned up in the atmosphere. Low-thrust engines will play a crucial role in this process.
As satellite lifespans increase, the need for onboard low-thrust engines to maintain proper orbit becomes more pressing.
Advancements in technology are leading to smaller satellites, resulting in a growing demand for the development of even smaller and more efficient low-thrust engines.
The growing number of objects in space will soon require optimized trajectories and collision avoidance, which can be achieved using low-thrust engines on board.
We appreciate the high-quality research provided by the Space Ambition team and look forward to collaborating with them. We hope this analysis will spark increased interest from investors in the low-thrust engine market."
High vs. Low Thrust Engines
Engines can generally be classified as high or low thrust.
High-thrust engines operate for short periods, providing substantial thrust almost instantaneously, allowing for rapid and significant changes in speed. However, these maneuvers consume considerable amounts of fuel.
On the other hand, low-thrust engines can run for hours or even days, gradually increasing speed while using minimal fuel. This approach trades time for fuel efficiency, with some nuances involved.
We classify satellites based on their maneuvering capabilities into several categories:
Non-maneuvering satellites (typically amateur CubeSats or devices for technology testing purposes)
Slightly maneuverable satellites (able to make occasional adjustments to maintain orbit or avoid debris)
Moderately maneuverable satellites (able to reach the required altitude or adjust altitude during flight after being launched by a carrier rocket)
Highly maneuverable satellites (in addition to the above capabilities, they can also change orbit parameters to significant values
Another factor to consider is the timing of maneuvers, as the satellite must reach its target orbit in order for the constellation to function properly. Any delays in maneuvering result in financial losses.
In summary, the need for faster and more frequent maneuvers requires a more powerful engine.
Key Factors and Parameters in Satellite Engine Selection
In general, selecting an appropriate engine for a satellite is a complex, multi-parameter task that depends on numerous factors. Some of the primary considerations include:
Project budget.
Functional requirements, such as deployment, collision avoidance, orbit change, and end-of-life removal.
The approximate number of required maneuvers during the satellite's lifetime and mission duration.
The satellite's orbit.
Size and design of the satellite, including its capacity to accommodate fuel tanks.
Toxicity concerns, as working with toxic fuel on Earth can be hazardous.
When selecting engines for satellites, the following critical parameters are taken into account:
Thrust: This denotes the force generated by the engine. A higher value signifies a more powerful engine.
Specific impulse: This indicates the engine's efficiency in using fuel and is proportional to the jet speed. Interestingly, it is measured in seconds, though it is unrelated to the conventional understanding of a second. The higher the specific impulse, the longer the engine can maintain that thrust, meaning it's using the propellant more efficiently.
Power-to-thrust ratio: This parameter represents the amount of electric power consumed (if applicable) while the engine is operating. A lower ratio is preferable.
Engine weight: The engine's weight, along with peripheral add-ons such as fuel tanks and electronics, is a crucial factor considered during the selection process. Lighter engines are generally more desirable due to their efficiency advantages.
Energy efficiency: A composite measure of the propulsor's quality, accounting for both specific impulse and power-to-thrust ratio. It is calculated as the ratio of jet kinetic energy to the electric energy used and can be determined as (standard gravity) x (specific impulse) / (2 x power-to-thrust ratio).
In general, all low-thrust engines can be divided into the following types:
Chemical
Electric (Hall effect, electric spray, gridded ion, etc.)
Propellant-less propulsion (systems generate thrust via interaction with the surrounding environment (e.g., solar pressure, planetary magnetic fields, and planetary atmosphere)).
Cubesat development and manufacturing. Source: coldstartech
Family of Low Thrust Engines: Chemical Engines
Chemical engines are among the most commonly utilized propulsion systems in astronautics due to their proven reliability. Even low-thrust chemical engines operate on the same principle as high-thrust engines, with fuel burning and being expelled from a nozzle at high velocity to generate thrust.
Engine fuel can be either monopropellant or bipropellant. Monopropellant engines use a single propellant that decomposes (or ‘burns‘) to produce thrust, while bipropellant engines utilize two separate propellants—a fuel and an oxidizer—that react with each other to generate thrust.
Hydrazine engines, among the popular monopropellant chemical engines, can generate a thrust of up to 200 N (Newtons) and have a specific impulse of up to 300 seconds. To help put this in perspective, imagine that 200 N is roughly equivalent to the force required to lift a heavy suitcase or a weight that weighs about 20 kilograms off the ground. While this may not seem like much, it is substantial in the context of space, where satellites are not subject to air resistance or friction.
Regarding the specific impulse of 300 seconds - a higher specific impulse means the engine can generate more thrust per unit of fuel, making it more efficient. To give you a better understanding, some low-thrust engines have a specific impulse of 2,500 seconds, which means they are much more fuel-efficient but generate significantly less thrust (only 0.00001 N) compared to hydrazine engines.
On the other hand, SpaceX Merlin engines produce about 1,000,000 N of thrust with the same specific impulse of 300 seconds. This means that although they have the same fuel efficiency as hydrazine engines, they generate much more thrust due to their larger size and more powerful design. This is why engines like hydrazine engines are often used for smaller satellites or for specific maneuvering purposes, while larger engines like the Merlin are used for launching heavy payloads into space.
However, the relatively low specific impulse of chemical engines, such as hydrazine, suggests that they are not as fuel-efficient as electric propulsion systems. As a result, chemical engines necessitate a substantial amount of fuel, which contributes to the propulsion weight and subsequently increases the spacecraft's overall weight. Moreover, many of these fuels are toxic, and the development of environmentally friendly fuel components is still ongoing. This factor is crucial to consider when handling engines on Earth, as the process of fueling with toxic substances can pose significant risks.
As a result, such engines are typically used in larger satellites that require frequent maneuvers, or as thrusters for satellite orientation. For example, Astroscale has built and launched a highly maneuverable ‘chaser’ SmallSat called ELSA-d using chemical low-thrust engines. This vehicle will be used for the deorbiting of customers’ satellites.
Aerojet Rocketdyne has utilized established designs that have previously been used on large spacecraft and could be adapted for small satellites, such as the MR-103 (Thrust: 1.12 N, Unfuelled mass: 0.33 kg, Specific impulse: 227 sec) thruster which was employed for attitude control on New Horizons - a NASA spacecraft that performed a historic flyby of Pluto in 2015 and has since been exploring the Kuiper Belt.
Along with the MR-103, other Aerojet Rocketdyne thrusters, including the MR-111 (Thrust: 4 N, Specific impulse: 220 sec) and MR-106 (Thrust: 27 N, Unfuelled mass: 0.48 kg, Specific impulse: 232 sec), have been successfully utilized on various missions and could potentially be suitable for small spacecraft.
Planet Labs launched a constellation of Earth-observing satellites known as SkySat. Each satellite weighs approximately 120 kg and features the Bradford-ECAPS propulsion system (Thrust: 5.5 to 22 N, Unfuelled mass: 1.1 Kg, Specific impulse: 243 to 255 sec). As of August 2020, 13 SkySat satellites with the Bradford ECAPS propulsion system have been launched and are fully operational.
Rafael Advanced Defense Systems has developed a series of low-thrust engines suitable for various satellite applications. One notable example is their MicroSat low-thrust engine (Thrust: 0.5 N, Unfuelled mass: 0.25 kg, Specific impulse: 215 sec), which is designed for small satellites requiring precise maneuverability and orientation control.
Rafael's MicroSat engine has been successfully integrated into a number of satellite missions, including the launch of the Earth-observation microsatellite OPTSAT-3000. This satellite, weighing approximately 400 kg, relies on the MicroSat engine for efficient and accurate orbit maintenance and attitude control.
In addition to the MicroSat engine, Rafael offers other low-thrust propulsion solutions, such as the MiniSat series (Thrust: 1.5 N, Unfuelled mass: 0.35 kg, Specific impulse: 225 sec), which have been employed in various satellite missions. These engines provide versatility and adaptability for a range of satellite sizes and mission requirements.
Family of Low Thrust Engines: Electric Engines
Electric engines are generally more expensive than chemical engines; however, they provide superior fuel efficiency because of their high specific impulse. This allows them to generate more thrust with less fuel, ultimately leading to reduced satellite size and mass.
These engines operate on electricity, making them more economical than their fuel-burning counterparts when savings due to lower satellite mass are accounted for. Their low mass makes them particularly desirable for space missions, where size and weight are important considerations.
However, electric engines do have several drawbacks. They typically offer low thrust, which restricts their use for power-intensive maneuvers. Additionally, they require complex and expensive electronic systems.
Electric Engines: Hall-effect Thrusters
A widespread type of electric engine is the Hall-effect thrusters. Hall thrusters generate thrust by creating and accelerating ionized gas in a combination of electric and magnetic fields.
Notable manufacturers:
Exotrail (funding $80M) has developed a series of Hall-effect engines with thrust ranging from 2.5 mN to 80 mN and power consumption between 60 and 1500 W. In 2020, the company's engines were launched on the SpacePharma spacecraft, a vehicle designed for conducting medical and biotechnology experiments in zero gravity, as well as on other missions.
Busek has developed a series of Hall-effect engines with thrust levels ranging from 7 to 1000 mN, specific impulses between 1000 and 2700 seconds, and power consumption from 100 to 20,000 W. Their engines have been successfully employed in space on multiple occasions, including the ESA’s Swarm (focuses on monitoring Earth's magnetic field and its variations) and NASA’s Dart (Double Asteroid Redirection Test) constellations. Furthermore, Busek's engines are currently in use as part of NASA's Artemis mission.
Aerojet Rocketdyne, a publicly traded company, has created a series of Hall-effect engines with thrust levels ranging from 1 N to 100 N. These engines have already undergone successful testing in space, notably on NASA's Dawn spacecraft, which explored the asteroids Vesta and Ceres between 2011 and 2018.
Safran, a publicly traded company, is one of the pioneers in Hall-effect propulsion. Their PPS®1350 engines, which offer a thrust range of 50 mN to 1.5 N and a specific impulse between 1,600 and 2,100 seconds, are widely utilized in small and medium-sized satellites.
And many more, like SITAEL, Mitsubishi Electric Corporation, etc.
Electric Engines: Electrospray Thrusters
Electrospray thrusters are a type of electric propulsion system that uses electric fields to ionize and accelerate a liquid propellant to generate thrust. There are two main types of this thrusters: ionic liquid thrusters and Field Emission Electric Propulsion (FEEP) thrusters,
One of the advantages of electrospray thrusters is their high efficiency. The ionization and acceleration of the propellant allows for precise control over the thrust generated, as well as a high specific impulse. Another advantage of electrospray thrusters is their ability to operate at very low thrust levels. This makes them well-suited for a variety of applications, including attitude control and orbit maintenance for small satellites and other spacecraft. But the low thrust levels generated by electrospray thrusters mean that they may not be suitable for all types of missions.
Notable manufacturers of liquid ionic electrospray:
Accion Systems (funding $68.5M) TILE thrusters - one of the leaders in the production of these types of engines. The company has successfully tested its technology on various satellite launches, including the Kleos Scouting Mission, Loft Orbital, and Astro Digital.
Busek also specializes in the development of electrospray propulsion systems. Their electrospray engines deliver thrust ranging from 55 to 150 μN and boast a specific impulse of 2300 seconds.
IENAI (funding $400K), a recent market entrant, has signed a contract to supply their high-efficiency engines—boasting a specific impulse of up to 2000 seconds—to the Atlantic constellation. In addition to its engines, the company is also involved in the development of software for engine implementation.
Notable manufacturers of FEEP electrospray:
Enpulsion (funding $3.4M) has developed propulsion systems offering thrust levels ranging from 10 μN to 1 mN and a specific impulse of up to 6000 seconds. Currently, there are over 100 Enpulsion thrusters operating in space.
Morpheus Space (funding $29.6M) not only develops FEEP engines that have undergone space testing but also offers the Sphere ecosystem - an all-in-one software package that the company asserts sets it apart from competitors.
Electric Engines: Gridded-ion Propulsion
Gridded-ion propulsion systems ionize gaseous propellant via a plasma discharge, and the resultant ions are subsequently accelerated via electrostatic grids. Similar to Hall-effect engines, but without a magnetic field. This is an earlier type of engine that has been largely surpassed by Hall-effect thrusters in recent years.
Notable manufacturers:
Busek (Thrust: Up to 1.25 mN, Specific Impulse: Up to 2300s)
ThrustMe (Funding: €6.1M, Thrust: 0.3 – 1.1 mN, Specific impulse: Up to 2400s)
New principles
It is worth highlighting that propulsion systems based on entirely new principles are emerging in the market, like RF plasma iodine, Fiber-fed Pulsed Plasma, Water ion, or Resistojet thrusters. Along with established leading companies, new ideas based on novel physical principles are being explored. The trend towards miniaturization is also gaining traction, with propulsion systems becoming smaller, more cost-effective, and more energy-efficient.
Low-thrust engines play a crucial role in the maneuvering and positioning of satellites in space. While high-thrust engines are ideal for short, rapid changes in speed, low-thrust engines provide a more fuel-efficient and gradual approach to orbital maneuvering. Although the market for low-thrust engines is already quite competitive, this healthy competition drives technological advancements. As the number of satellites in space continues to increase - more and more maneuvers need to be done in space, including collision avoidance. We anticipate further growth in the propulsion market and the emergence of new players.
Apart from conventional methods, our research center has also explored non-traditional methods of space travel, such as solar sails, water engines, as well as nuclear and photon engines, which we will discuss in a future article.
Additionally, we have compiled a comprehensive list of companies in the thruster market. If you are considering an investment in the low-thrust engine sector or simply wish to learn more about the industry, please feel free to contact us at hello@spaceambition.org. Our experts would be delighted to engage in a conversation with you.
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This is a really good summation of the options that are out there!