Electric Space Propulsion and the RIT technology

Satellites and the telecommunications industry

In telecommunications, geostationary orbit (GEO) is commonly selected for missions such as television broadcasting and communications. Missions in this orbit are becoming smaller and more efficient, reducing launch costs but putting pressure on Spacecraft prices and time to market. At the end, customer asks for an increased Payload capacity, a faster delivery and a limited orbit raising duration. High Isp, provided by RIT2X technology, contributes to reduce propellant mass and volume and save significant total ownership cost for the space segment.

Focus on interplanetary exploration

Interplanetary missions in space exploration are known for their ambitious goals and unique challenges. They require a significant request in velocity (∆V) with limited allowable and mass managed by launcher capacity and heavy payload(s). These missions aim to explore planets within our solar system or distant meteoroids, requiring spacecraft mass optimization to match powerful launch vehicles such as Ariane 6, Falcon Heavy and Starship. A significant cost factor is the use of xenon in ionization grid thrusters, which costs around €20,000 per kilogram and consumes up to two tons. Reducing the mass of the spacecraft by 30% can save up to €6 million per mission and allows to embark heavier payloads and instruments. Successful missions such as GOCE, Bepi Colombo and Mars Sample Return are choosing grid ionization engines for their remarkable efficiency, with a specific impulse of over 3000 seconds and an efficiency of over 50%. These propulsion innovations are transforming interplanetary missions, making it possible and cost-effective to explore the planets of the solar system and distant meteoroids. With spacecraft mass optimization and advanced technology utilization, the future of interplanetary missions is even more promising. Mars or Lunar missions may take advantage of such technologies in the coming years.

The idea of RIT technology

The use of technology based on the Radio Frequency Ion Thruster (RIT2X SERIES) would provide perfect thrust control in terms of resolution, response, and linearity, together with very low thrust noise. This type of thruster is the largest Radio Frequency Ion Thruster in the Ariane Group’s electric propulsion range. It provides an excellent specific impulse over a wide range of thrust levels and a great efficient use of electrical energy. It enables in-situ atmospheric or solar drag compensation and high-precision formation flying. RIT uses high-frequency electromagnetic fields to ionize xenon gas atoms, forming a plasma of both light electrons and heavy positive Xenon ions. These positively charged ions are then accelerated and ejected to generate the thrust, while electrons are introduced to neutralize the plasma and prevent the satellite from building up an electrical charge.

How the RIT really works in detail

High-frequency ion thrusters belong to the class of grid ion thrusters. Grid ion thrusters generate thrust in two stages.

1. In the first stage, the fuel is ionized.
2. In the second stage, the ionized fraction of the propellant is accelerated in an electrostatic field of an optical ion system (“grid system”). Ion acceleration in a grid system is the common feature of all grid ion engines. However, different types of ionization are used.

High-frequency engines ionize the propellant in an oscillating electromagnetic field.

1. Propellant enters the ionizer through an integral insulator and gas manifold.
2. The ionizer vessel is made of an insulating material (quartz or alumina oxide) and is surrounded by the induction coil. The axial magnetic field of the RF coil induces a circular induced electric field which accelerates the discharge electrons and allows them to ionize the xenon atoms by inelastic collisions.
3. The result is an electrodeless high-frequency gas discharge (plasma). Due to thermal motion, ions from the bulk plasma find their way into the grid system.

Today xenon is the main choice for electrostatic thrusters, but cathodeless ionization enables the use of various propellants. Customizing the ionizer and grid system is key for peak performance with different propellants.

Which main components does RIT consist of?

A comprehensive RIT-based electric propulsion (EP) system consists of several key elements:

• Neutraliser: Gridded ion thrusters only eject positively charged ions, so the ion current must be compensated by an equivalent electron current. Typically, hollow cathode neutralisers are used for this purpose. However, for smaller thrusters such as RIT-μX, gasless, low perveance e-gun type neutralisers are preferred due to lower fuel consumption.
• Propellant flow management it involves two main steps: pressure regulation and flow control.

– The pressure regulator reduces the high pressure stored in the xenon storage tank, which may consist of several tanks, to provide an outltet pressure around 4 bar.

– The constant pressure is then fed to the flow control units (FCUs) for each individual thruster. The FCUs are responsible for controlling the mass flow to each thruster.