MIT has developed a new micro-propulsion device that can provide "dual-mode" propulsion for micro-satellites. The goal is to enable small satellites such as CubeSat to maneuver quickly and fly long distances and efficiently. This technology integrates chemical propulsion and electric propulsion into the same fuel system and is considered to be expected to significantly expand the mission capabilities of small spacecraft.
An MIT engineering team recently tested a hybrid propulsion system for small satellites, which combines the high thrust of chemical rockets with the high efficiency of electric thrusters, and the two propulsion methods share the same fuel. Researchers said that this design is expected to allow cheap, portable spacecraft that can only perform low-Earth orbit missions to undertake further deep space exploration missions, and even fly to Mars.
Although microsatellites have long been cheaper to launch and easier to deploy, they have been limited in size and fuel space in terms of propulsion systems. If rapid orbit changes and fine attitude adjustments are to be met at the same time, traditional solutions often require two independent propulsion systems and two types of fuel, which is difficult to achieve for small platforms.
According to the article, chemical thrusters can output powerful thrust in a short period of time and are suitable for rapid orbit changes; while electric thrusters, especially EFI thrusters, have small thrust but extremely high fuel utilization, and are suitable for long-term, slow acceleration, especially for interstellar or interplanetary navigation. The two originally have their own advantages, but they have been difficult to be compatible on small satellites.
The key to this breakthrough lies in a propellant called ASCENT previously developed by the U.S. Air Force. The green propellant, called "Advanced SpaceCraft Energetic Non-Toxic propellant," was originally developed as a chemical propulsion fuel to replace highly toxic hydrazine fuel, but the research team later discovered that it is also essentially an ionic liquid. Ionic liquids can remain liquid in a vacuum environment, making them ideal for use in electronic jet thrusters.
The team at MIT AeroAstro Laboratory, led by Professor Paulo Lozano, is advancing research around this feature and conducting experiments by loading ASCENT into a small tank connected to a CubeSat. The researchers placed the microsatellite on a magnetic levitation platform to simulate the weightless environment of space, and then remotely ignited the thrusters under different voltages to observe their operation performance.
Test results show that ASCENT is stable in propulsion performance, with a thrust-to-weight ratio of 40 to 65 micronewtons per watt, a specific impulse of 600 seconds, and an overall efficiency of approximately 15%. The thrusters are also capable of operating continuously for up to 167 hours without measurable performance degradation.
Amelia Bruno, the first author of the paper, said that compared with the electro-injection propellant commonly used by the team, the thrust performance of ASCENT is similar; now that it has been confirmed that the thruster is compatible with this fuel, the design can be further optimized in the future. The research team believes that the greatest significance of this solution is that it makes it possible for small satellites to truly "share a propellant tank and support different propulsion behaviors" for the first time.
Next, MIT will work with NASA to advance the Green Propulsion Dual Mode mission. It’s a CubeSat that will carry one chemical thruster and four EFI thrusters, all sharing a single ASCENT tank, and is scheduled to launch later this year. This will be the first attempt to use shared propellant tanks on a satellite, Lozano said.
If the mission verification is successful, the application scenarios of this technology will be very wide, ranging from more efficient deployment of satellite constellations, real-time tracking of hurricanes, to performing longer-distance deep space exploration, are all being envisioned. Lozano also mentioned that in the future, CubeSats can even be sent to Mars or the asteroid belt, allowing them to first sail at a slow speed using electronic thrusters, and then use chemical thrusters to quickly adjust their position and observe the details of the target area.