What is Multimode Propulsion and How Does it Aim to Revolutionize the Way to Space?
Propulsion is one of the most critical elements of a satellite and its ability to perform a mission. It ensures a satellite gets where it needs to go and stays there. Propulsion systems on satellites enable orbit transfer, reaction control, station keeping, precision pointing, on-orbit servicing, and orbital maneuvering. Traditionally, these functions have been fulfilled by different energy sources, either chemical or electric, and have not worked together to perform such tasks. By working together in a single multi-mode propulsion system, we could unlock the key to longer, more adaptable missions.
On-orbit life and maneuverability of a satellite is largely determined by the efficiency of the propulsion system.
Spacecraft have two types of thrusters they can use to move around. One kind, chemical thrusters, use a chemical reaction to create hot gas which gets used as propulsion. This can generate a lot of thrust to move a satellite quickly, but it does not have good fuel efficiency. The other kind, electric thrusters, use electromagnetic force to ionize a material to push a satellite around. The fuel efficiency is about ten times better than chemical propulsion but generates very little thrust. You use electric propulsion when you want to save on fuel, and you use chemical propulsion when you need to do something quickly, like evade debris or put yourself in position to take pictures of a particular place on Earth quickly.
What is Multimode Propulsion?
Right now, satellites that need an efficient way to move between different orbits with the ability to move quickly, must have two completely different propulsion systems, sets of valves, and fuel tanks. It is as though you had a car with one tank of fuel for city driving, and a separate tank of fuel for highway driving, and if you ran out of one on the interstate, all the fuel in the world in the 'wrong' tank would not help.
“Multimode propulsion is finding a propellant and a way to use a single propellant and a single fuel tank for both chemical and electric propulsion, giving the satellite the flexibility to do whatever type of maneuvering the situation calls for, while spending less mass, volume, and cost on independent propulsion systems,” said Dr. Shae Williams, Moog Staff Engineer.
An Enabling Technology
A breakthrough toward a viable multimode system is enabled by certain types of green propellants, which are less toxic chemical propellants that are safer and easier to work with and do not have the same safety and environmental concerns as traditional chemical propellants like hydrazine. For example, personnel can fill a spacecraft with a green propellant without the need for self-contained atmospheric protective ensemble or SCAPE suits. The reason green propellants can be a revolutionizing technology for multimode propulsion is that some can have properties that allow them to be the fuel for both electric and chemical propulsion systems.
Moog has been a leader in chemical propulsion since the inception of spaceflight, with components and systems traveling to every planet in our solar system and beyond. Engineers at Moog have conducted research and development on green propulsion both on their own and in cooperation with government partners, leveraging expertise in thermal management and high-performance thrusters to develop and supply components such as valves and tanks for use with green propellant. These components are both conventionally and additively manufactured. Moog teams are building thrusters in multiple thrust classes and even full propulsion systems for customers using green thrusters from manufacturers in the U.S. and Europe.
Moog Hot Fire Test Cell
Moog Green Thruster
Unlocking the Benefits of Multimode Propulsion
Once multimode propulsion systems are a proven and operational technology, there will be significant mission benefits to warfighters as well as commercial satellite operators.
First, multimode propulsion will allow satellites to outmaneuver any satellite without a multimode propulsion system. Anything a satellite without one can do, a satellite with this type of system can do and then use the other type of propulsion to gain an advantage.
Second, multimode propulsion systems are enabling for satellites that have different mission priorities at different times of life; for example, a rapid transit through Earth's radiation belts, followed by a long period of station-keeping in geostationary orbit, or a slow plane change of a reconnaissance satellite followed by a precision deorbit at end of life.
“The biggest advantage is to decouple mission planning from propulsion system design. As it stands now, because of how specific propulsion systems are, bus providers almost need to design an entirely bespoke propulsion system for each mission,” said Williams. “With a flexible multimode system, you can mass produce propulsion systems without needing to know what the mission is within generous limits, because the same tank and feed system can give you high thrust or high efficiency whenever you want it.”
The implementation of multimode propulsion systems enables satellites to adapt to different mission priorities throughout their lifespan, providing the flexibility to perform rapid transits, station-keeping, or precise deorbiting.
Conclusion
Multimode propulsion offers unprecedented mission flexibility and adaptability for spacecraft by using a single propellant, tank, and feed system to meet all propulsion and maneuverability requirements and enable dynamic space operations. The efficient design ensures reduced lead times, operational costs, and size, weight, and power, which enhances mission readiness by allowing more of the spacecraft to be dedicated to payloads rather than propulsion systems.
As this technology matures, it keeps the promise of transforming space exploration and enabling new possibilities. The future of spacecraft propulsion is here, and Moog is excited to be at the forefront of this revolution.
Contact Moog Space media at space@moog.com