Russian scientists developed an electric rocket engine of a much higher thrust than that of foreign and domestic counterparts. The machine is designed for CubeSats—the smallest satellites. It will make it possible for the spacecrafts to stay in orbit longer as well as change course. Experts point out that such engine will reduce the amount of orbital debris, since objects that no longer serve a useful purpose will be able to descend by themselves and burn up in denser layers of the atmosphere. Scientists are planning to test a prototype of the machine as early as 2023.
Striving for minimalism
Engineers at Moscow Aviation Institute (MAI) developed an engine for CubeSat spacecrafts. This is the name of artificial Earth satellites made up of one or several 10 cm cubes, with each unit weighing no more than 1.33 kg.
In terms of its features, the engine is unmatched by any other domestic or foreign product. Its total thrust impulse (that is, the amount of fuel required to reach a certain velocity) is dozens of times greater than that of other engines of this type. The greater the value, the more efficient the engine.
Today most CubeSats are not equipped with engines, since the machines are too small and rather limited in their power generation capability. That is why they are simply placed in orbit via launch vehicles to float freely. However, the engine will allow to significantly expand the scope of satellites’ applications and increase the time that they stay in orbit.
“Due to the residual atmosphere in low Earth orbit, spacecrafts gradually lose altitude. That can be offset by the engine,” informed Svyatoslav Gordeev, engineer at the Research Institute of Applied Mechanics and Electrodynamics (RIAME) of MAI. “It will extend the useful life of small spacecrafts from several months to several years. It will also make it possible to change the orbital altitude within small limits and control the satellite’s position in a group.”
A new configuration
Ablative pulsed plasma thrusters (APPTs), which developers used as a basis for their work, have a relatively simple design that is suitable for small spacecrafts; however, thrust levels are too low. MAI engineers solved the problem. APPTs are usually made up of two ‘tubes,’ one placed into the other. These are the cathode and anode, the solid working mass—a material called fluoroplastic—placed between them. The applied voltage produces a spark discharge between the cathode and anode, which turns a thin surface layer of the solid working mass into plasma; the plasma is then being accelerated out of the engine at high velocity, generating thrust.
The problem of such design is that the plasma flow velocity, which the engine’s total thrust impulse depends on, is very limited, just like the solid working mass reserves. MAI scientists designed their engine in another way, placing plate-shaped electrodes in front of each other and ensuring a lateral feed of the solid mass, that is, fluoroplastic. Such design allowed to create a feeding system for the solid working mass, thus increasing the total thrust impulse more than tenfold.
“The total thrust impulse of our engine is 300 newton-seconds (N⋅s) versus 3.4 N⋅s for one of the well-known foreign counterparts,” Mr. Gordeev stated. “Our engine is a little larger in volume but also more powerful. Even if the mass of the engine that we developed were the same as that of the foreign counterpart, our engine’s total thrust impulse would still turn out to be significantly higher.”
Experts duly appreciated the product that the engineers had designed and wished them success in the implementation of the project.
“In my opinion, it is a very promising engine that will first and foremost extend the CubeSats’ useful life,” believes Maria Barkova, a lead research engineer at the Russian Space Systems corporation. “The main weaknesses of these satellites are the small fuel reserve and low thrust, a problem that has been rightly identified by the very creators. CubeSats can be equipped with different types of engines, from ion engines to cold gas thrusters.”
Last year, an engine of a 139 N⋅s thrust impulse was tested in the USA, which means that the engine presented by MAI engineers is more than two times more powerful than its foreign counterpart, Ms. Barkova added.
General Director of the Sputnix company and expert of the NTI Aeronet working group Vladislav Ivanenko pointed out that a nanosatellite equipped with the engine will be able to maintain its positions in orbit by itself, which means that the engine will allow the spacecraft to take up and effectively maintain the required position for a long period of time.
“Another serious problem that the new plasma engine will help to solve is the space debris problem,” Mr. Ivanenko added. “Nanosatellites that have already ceased to operate usually stay in orbit for over ten years before they slow down, affected by the upper atmosphere, and fall out of the orbital space around Earth. At the end of its life, a nanosatellite equipped with the engine will be able to descend by itself, thus reducing the time spent before burning up in the upper atmosphere by a factor of two or three.
Specialists have already manufactured and successfully tested a laboratory model of engine components. Now they are working on the entire propulsion system’s design, size and weight restrictions considered. The propulsion system testing is scheduled for 2023.
