Electric propulsion (EP) has become the standard for commercial geostationary satellites due to its high specific thrust, resulting in significant savings in propellant mass. As more electrical power becomes available on telecommunications platforms and heritage is increasing, electric orbital transfer will soon become the norm. EP also offers efficiency, precise orbit control and extended mission life, providing benefits beyond mass savings. The GIESEPP MP project is designed to handle power in excess of 5 kilowatts. This platform is suitable for a wide range of applications, including medium earth orbit (MEO) navigation with payloads up to 2 tonnes, geosynchronous orbit (GEO) communications with small GEO satellites (2-3 tonnes) and medium and large GEO satellites (4-6 tonnes).
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.
- In the first stage, the fuel is ionized.
- 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.
- Propellant enters the ionizer through an integral insulator and gas manifold.
- 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.
- 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.
- The Power Processing Unit (PPU) is providing all power sources requested for a state-of-the-art spacecraft propulsion system. As well as providing variable high voltages up to +1500V for stable operation, it also generates AC power for the ionisation coil using a radio frequency generator (RFG), all under the control of the PPU. The PPU is also the high voltage wizard, supplying power to the main thruster and precisely controlling the flow control units (FCUs). In essence, it acts as a central power distributor for the entire propulsion system. But that’s not all; the PPU also acts as an interpreter for the spacecraft. It interfaces with the spacecraft’s power and data bus, translating high-level commands into operational sequences. It also incorporates autonomous exception data handling mechanisms to ensure flawless performance in the harsh environment of space.
The final architecture must be compact, economical, and highly flexible, covering a power range of 2.7 to 7 kW. High quality COTS-qualified components will be selected to ensure competitiveness and reliability during ascent orbit and 15-year GEO missions.
High frequency ion thruster family
The RIT Thruster family started with the RIT-10 engine, initially designed for mercury but later adapted for xenon due to changing preferences among satellite operators. Continuous improvements have greatly enhanced its performance. The range of ion thrusters covers a wide spectrum of space missions, with thrusts ranging from 50 µN to 219 mN. This family of thrusters includes three different models:
- RIT Micro-X: this is the smallest in our line-up and is designed to excel in precision orbital maneuvers, especially for science missions. It provides thrust levels in the range of 50 to 500 µN.
- RIT 10 Evolution: it is ideally suited for north-south station-keeping operations on GEO, LEO and MEO platforms. It provides thrust capabilities from 5mN to 25mN.
- RIT 2X Series : it is the largest and most robust option in our line-up, offering unparalleled mass savings for all-electric spacecraft. Thrust levels range from 80mN to 219mN, making it a versatile choice for a wide range of mission profiles.
The RIT2X system offers a large operational versatility for space missions. It is possible to achieve high thrust for orbital insertion and high specific thrust for on-orbit maintenance or long-distance transfer phases. This flexibility is essential to lower the duration of transfer and the consumption of propellant leading to optimize the global efficiency of the mission. The efficiency of the system is remarkable, reaching 53% efficiency at maximum specific thrust, meaning that 53% of electric power is transfer in Kinetic Power.
This means that the propellant is used very efficiently, reducing the overall mass of the spacecraft and therefore the launch cost. These solutions are particularly interesting for telecommunications satellites. For example, for spacecraft with a total mass of 3 tonnes, the use of the RIT2X system results in a significant reduction in the required xenon mass from 950 kg to just 600 kg. For heavier spacecraft with a total mass of 5 tonnes, the reduction in xenon mass is even more significant, from 1100 kg to just 700 kg. These benefits enable more efficient and cost-effective design and launch of telecommunications space missions, significantly improving the overall performance of the space sector.
Interest of the solution: what are the performances?
With the introduction of this new type of technology, we can see that the End of Rendezvous (EOR) duration is approximately 200 days, slightly longer than the typical threshold of 180 days, which has a significant impact on our operations. The recurring costs are affected by the estimated price of the Grid-Ion chain, but there’s good news – these costs can be offset by savings in Xenon mass (Xe) and a 30% reduction in RIT2X and PPU costs. When considering Grid-Ion, PPS is critical due to its close relationship with launch capability. Its performance depends on
- launch altitude,
- spacecraft mass,
- launch cost.
Therefore, these factors must be evaluated when assessing the effectiveness of our solution. Another critical aspect is the price of xenon (Xe). However, it’s important to carefully weigh up the cost savings on RIT-2X, Radio Frequency Generator (RFG) and PPU against our overall budget, and to decide whether to extend the life of the system beyond the standard 15 years plus EOR if necessary. It’s important to be aware of EOR duration, recurring costs and the key factors that influence the competitiveness of grid-ion PPS.
Author of the article Lorenzo Iacopino
Lorenzo Iacopino is currently dedicated to his Master’s program in Aerospace Engineering at the prestigious University of Bologna. His academic journey is propelled by an enduring fascination with spacecraft and astronomy, motivating his determination to delve into the expansive realms of these fields. In addition to his academic pursuits, Lorenzo derives immense gratification from playing a role in the progression and dissemination of scientific knowledge. He eagerly anticipates the opportunity to absorb wisdom from leaders in the space sector while also imparting his own insights and expertise to fellow scholars and a wider audience.
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