Electric and Ion Propulsion: Igniting a New Space Race for Mars, Mercury, and Beyond

Rajesh Uppal April 29, 2024 Energy & Propulsion, Geopolitics, Space Comments Off on Electric and Ion Propulsion: Igniting a New Space Race for Mars, Mercury, and Beyond 1,453 Views

The vastness of space has always beckoned humanity to explore its mysteries, and as technology advances, the race to conquer new frontiers intensifies. The roar of chemical rockets is fading into the annals of history. A new, electrifying era is dawning, fueled by silent thrusters and the unyielding ambition of nations locked in a thrilling race for the cosmos. In this era of space exploration, countries worldwide are engaged in a fervent competition to develop cutting-edge electric and ion propulsion technologies. These advancements hold the key to unlocking the potential for future Mars and Mercury missions, space planes, and Anti-Satellite (ASAT) capabilities.

Electric Propulsion: Revolutionizing Space Travel

The primary function of the space propulsion system is to provide thrust, which helps in the functioning of the launch vehicle or satellite. In propulsion systems, the fluid (either solid, liquid, or electric) reacts to initiate acceleration and provide force in the system.

An ion thruster, ion drive, or ion engine is a form of electric propulsion used for spacecraft propulsion. It creates thrust by accelerating ions using electricity. As the ionised particles escape from the aircraft, they generate a force moving in the other direction. Power supplies for ion thrusters are usually electric solar panels, but at sufficiently large distances from the sun, nuclear power is used.

Ion Propulsion Vs Chemical propulsion

As NASA explain: “An ion thruster ionizes propellant by adding or removing electrons to produce ions. Most thrusters ionize propellant by electron bombardment: a high-energy electron (negative charge) collides with a propellant atom (neutral charge), releasing electrons from the propellant atom and resulting in a positively charged ion. ” The gas produced consists of positive ions and negative electrons in proportions that result in no over-all electric charge. This is called a plasma. Plasma has some of the properties of a gas, but it is affected by electric and magnetic fields. Common examples are lightning and the substance inside fluorescent light bulbs. Ion thrusters have an input power need of 1–7 kW, exhaust velocity 20–50 km/s, thrust 25–250 millinewtons and efficiency 65–80%.

These thrusters have high specific impulses—ratio of thrust to the rate of propellant consumption, so they require significantly less propellant for a given mission than would be needed with chemical propulsion,” says NASA. These can be more than 10 times as fuel efficient as other rocket engines. Another attraction of using this kind of thruster is that it does not need the kind of high temperatures required by forms of chemical propulsion. This kind of electric propulsion system is also lighter in weight, meaning that future space trips could be more feasible. A xenon based EPS can be five to six times more efficient than chemical-based propulsion on spacecraft and has many uses, according to Dr Annadurai, whose centre assembles all Indian spacecraft. A 3,500-kg EPS-based satellite, for example, can do the work of a conventional spacecraft weighing 5,000 kg, but cost far less.

The advantages include : Highest specific impulse offers substantial mass saving (>3000s); High performance at low complexity; Reduced power processing unit mass; Narrow beam divergence; Robust design concept with a large domain of operational stability; Large throttle range and adaptable to available electric power; Excellent thrust stability and fast thrust response and Highest growth potential with increasing electric power in near and medium-term future

However Ion thrust engines create small thrust levels (the thrust of Deep Space 1 is approximately equal to the weight of one sheet of paper ) compared to conventional chemical rockets. They are practical only in the vacuum of space and cannot take vehicles through the atmosphere because ion engines do not work in the presence of ions outside the engine. Besides, the engine’s minuscule thrust would not matter when air resistance comes into play.

Michael Patterson, senior technologist for NASA’s In-Space Propulsion Technologies Program compared ion and chemical propulsion with “Tortoise and the Hare”. “The hare is a chemical propulsion system and a mission where you might fire the main engine for 30 minutes or an hour and then for most of the mission you coast.” “With electric propulsion, it’s like the tortoise, in that you go very slow in the initial spacecraft velocity but you continuously thrust over a very long duration — many thousands of hours — and then the spacecraft ends up picking up a very large delta to velocity.”

Ion Thruster technology

As NASA explain: “An ion thruster ionizes propellant by adding or removing electrons to produce ions. Most thrusters ionize propellant by electron bombardment: a high-energy electron (negative charge) collides with a propellant atom (neutral charge), releasing electrons from the propellant atom and resulting in a positively charged ion. ” The gas produced consists of positive ions and negative electrons in proportions that result in no over-all electric charge. This is called a plasma. Plasma has some of the properties of a gas, but it is affected by electric and magnetic fields. Common examples are lightning and the substance inside fluorescent light bulbs. Ion thrusters are categorized by how they accelerate the ions, using either electrostatic or electromagnetic force. Electrostatic thrusters use the Coulomb force and accelerate the ions in the direction of the electric field. Electromagnetic thrusters use the Lorentz force.

The most common propellant used in ion propulsion is xenon, which is easily ionized and has a high atomic mass, thus generating a desirable level of thrust when ions are accelerated. It also is inert and has a high storage density; therefore, it is well suited for storing on spacecraft. In most ion thrusters, electrons are generated with the discharge hollow cathode by a process called thermionic emission.

Electrons produced by the discharge cathode are attracted to the discharge chamber walls, which are charged to a high positive potential by the voltage applied by the thruster’s discharge power supply. Neutral propellant is injected into the discharge chamber, where the electrons bombard the propellant to produce positively charged ions and release more electrons. High-strength magnets prevent electrons from freely reaching the discharge channel walls. This lengthens the time that electrons reside in the discharge chamber and increases the probability of an ionizing event. The positively charged ions migrate toward grids that contain thousands of very precisely aligned holes (apertures) at the aft end of the ion thruster. The first grid is the positively charged electrode (screen grid). A very high positive voltage is applied to the screen grid, but it is configured to force the discharge plasma to reside at a high voltage. As ions pass between the grids, they are accelerated toward a negatively charged electrode (the accelerator grid) to very high speeds (up to 90,000 mph).

“The positively charged ions are accelerated out of the thruster as an ion beam, which produces thrust. The neutralizer, another hollow cathode, expels an equal amount of electrons to make the total charge of the exhaust beam neutral. Without a neutralizer, the spacecraft would build up a negative charge and eventually ions would be drawn back to the spacecraft, reducing thrust and causing spacecraft erosion.”

The primary parts of an ion propulsion system are the ion thruster, power processing unit (PPU),propellant management system (PMS), and digital control and interface unit (DCIU). The PPU converts the electrical power from a power source—usually solar cells or a nuclear heat source—into the voltages needed for the hollow cathodes to operate, to bias the grids,and to provide the currents needed to produce the ion beam. The PMS may be divided into a high-pressure assembly (HPA) that reduces the xenon pressure from the higher storage pressures in the tank to a level that is then metered with accuracy for the ion thruster components by a low-pressure assembly (LPA). The DCIU controls and monitors system performance,and performs communication functions with the spacecraft computer.

Generally, an ion thruster has a few advantages over a chemical-powered rocket. Ion thruster can drive a spacecraft to speeds of up to 40 kilometers per second; its chemical counterpart can only manage 5 kilometers per second. Secondly, an ion thruster has ten times more fuel efficiency which is ideal for space travel. Chemical rockets need to bring their fuel supply for the whole journey and that load means more mass and additional fuel requirement for take-off.

The use of electric propulsion (EP) for space applications is currently undergoing rapid expansion.

There are hundreds of operational spacecraft employing EP technologies with industry projections showing that nearly half of all commercial launches in the next decade will have a form of electric propulsion.

Current ion engines, predominantly solar-powered, represent a breakthrough in space propulsion technology, requiring minimal propellant for extended missions. Successfully employed in missions like Esa’s SMART-1 to the Moon and the ongoing Bepi-Colombo mission to Mercury, these engines showcase their reliability and efficiency. NASA is actively advancing ion propulsion, developing a high-power electric system tailored for the Lunar Gateway, an orbital station set to revolutionize lunar exploration.

Beyond their roles in attitude control and satellite deorbiting, ion thrusters are versatile tools, crucial for maintaining satellite positions and propelling spacecraft across the solar system. NASA emphasizes the mission-enabling potential of ion propulsion, envisioning applications where traditional chemical propellants fall short. With the prospect of fueling return trips to Mars without refueling and utilizing recycled space debris, ion propulsion stands poised as a transformative force in the future of space exploration.

Charging Toward Mars

Mars, the Red Planet, has long been a focal point for space exploration. Traditional chemical propulsion systems have their limitations, prompting a shift toward electric propulsion. Countries like the United States, China, and Russia are at the forefront of developing electric propulsion technologies that promise increased efficiency and extended mission durations.

Electric propulsion systems, such as ion drives, operate by expelling charged particles to generate thrust. This allows spacecraft to reach higher speeds with significantly less fuel consumption compared to conventional rocket engines. As nations gear up for future Mars missions, electric propulsion emerges as a game-changer, enabling spacecraft to navigate the vast distances of interplanetary space more efficiently.

Mercury’s Mysteries Unveiled

While Mars captures our imagination, Mercury, the closest planet to the Sun, remains a tantalizing target for exploration. The extreme conditions near the Sun pose challenges for spacecraft, making electric propulsion particularly advantageous. Countries envision utilizing ion drives and other electric propulsion systems to navigate the intense solar environment and unravel the secrets hidden within Mercury’s scorching atmosphere.

Ion Propulsion: Pioneering Interstellar Travel

Space Planes: Taking Flight Beyond Earth’s Boundaries

The concept of space planes, once relegated to the realm of science fiction, is gaining traction as countries strive to develop ion propulsion technologies capable of powering these futuristic vehicles. Ion drives, with their ability to provide continuous, low-thrust propulsion, open up new possibilities for sustained and efficient space plane operations.

As nations explore the potential of space planes, the ability to take off from conventional runways, enter orbit, and navigate beyond Earth’s atmosphere becomes a realistic vision. This paradigm shift in space transportation could revolutionize the way we approach travel within our planet’s gravitational embrace.

New Space: Ion Propulsion Powers Smaller, More Affordable Satellites

The traditionally expensive realm of space exploration has witnessed a dramatic shift with the emergence of “New Space” companies. These private ventures prioritize cost-effectiveness and shorter development cycles, aiming to democratize access to space. This has led to a surge in smaller, more affordable satellites, creating a demand for efficient and low-cost propulsion solutions.

Enter ion propulsion. Unlike traditional chemical rockets, ion thrusters use electricity to accelerate charged ions, resulting in significant fuel savings and extended mission durations. This technology is perfectly suited for smaller satellites, enabling them to maneuver efficiently and maintain their positions in large orbital constellations.

New Space companies are driving the demand for smaller, cheaper satellites, creating a market for efficient and cost-effective propulsion solutions. Ion thrusters, with their fuel-efficient and maneuverable capabilities, are ideally suited for these smaller spacecraft, paving the way for a new era of accessible and affordable space exploration.

Companies like SENER, in collaboration with ESA, are actively developing compact, electrodeless ion thrusters like the Helicon Plasma Thruster. This innovative design promises low voltage operation and minimal thruster erosion, making it ideal for small satellite applications. The success of such initiatives paves the way for a future where smaller, more affordable satellites equipped with advanced ion propulsion systems become the norm, revolutionizing space exploration and pushing the boundaries of scientific discovery.

Race to develop Ion Thrusters

Many countries led by US are developing Ion thrusters. University of Michigan researchers have developed an ion thruster that has the potential to power manned missions to Mars. Dubbed the X3, the ion thruster has already surpassed current thrusters in its category in terms of power output, thrust and operating current. China has finished building the world’s most powerful ion thruster and will soon use it to improve the mobility and lifespan of its space assets, according to a state media report. India has launched a 2,195-kg, GSAT-9 or the South Asia Satellite om May 5 carrying an electric propulsion or EP system, the first on an Indian spacecraft. The European Space Agency (ESA) has successfully tested a prototype ion engine powered by air that could provide propulsion for orbiting satellites almost indefinitely, and could even help power future missions to Mars.

An Australian-designed ion thruster, developed by Dr. Paddy Neumann and two professors, is embarking on a transformative journey to the International Space Station (ISS) for a critical year-long experiment. Fueled by magnesium using a “cathodic arc” process akin to welding, this innovative engine holds the promise of revolutionizing space travel, particularly for future Mars missions. The thruster boasts advantages such as remarkable fuel efficiency due to magnesium’s high specific impulse, accessibility of abundant fuel in aerospace materials, and minimal emissions, contributing to a cleaner space environment. The year-long ISS experiment aims to rigorously assess the thruster’s performance and endurance in space, with success potentially paving the way for expedited and cost-effective Mars voyages and ushering in a new era of efficient and sustainable space exploration.

Europe: ESA’s Solar Electric Propulsion Leads the Way

The European Space Agency (ESA) reigns supreme in the realm of Solar Electric Propulsion (SEP). Missions like BepiColombo to Mercury and Smart-1 to the Moon showcase the power of harnessing the sun’s energy for efficient, long-duration space travel. Powering missions like BepiColombo to Mercury and the ongoing Smart-1 lunar mission, SEP utilizes solar panels to generate electricity for thrusters, achieving high fuel efficiency and longer mission durations.

But ESA isn’t resting on its laurels. NEXT-STEP, its ambitious project, seeks to develop high-power electric engines capable of slashing travel times to Mars, making it a mere months-long journey.

United States: NASA Chases Speed with Ion Engines

NASA, the eternal rival, counters with its mastery of ion engines. The Dawn mission, a testament to their prowess, used ion thrust to meticulously explore the asteroid belt, proving the technology’s versatility and fuel efficiency.

• Dawn Mission: This successful exploration of Vesta and Ceres utilized ion engines, showcasing their ability for complex, low-thrust maneuvers and efficient travel over long distances.

• EmDrive Project: This controversial project investigated a purported propellantless propulsion system, though independent testing has not yet validated its claims.

• DARPA’s XS-1 Experimental Spaceplane: Aimed at developing a reusable, hypersonic spaceplane for rapid global transportation, this project explores electric and combined propulsion options.

In August 2022, NASA’s Psyche spacecraft embarked on a trailblazing mission, powered not by fiery chemical propulsion, but by the sun’s boundless energy.

This mission targets Psyche 16, a giant metallic asteroid, promising to unlock secrets of planetary formation and redefine deep space exploration through audacious solar electric propulsion (SEP) technology.

Harnessing Sunlight for Thrust: Eschewing traditional propellants, Psyche boasts two mammoth solar arrays – the largest ever flown – that convert sunlight into electricity. This energy feeds four high-efficiency ion thrusters, descendants of those employed on Dawn and Deep Space 1. By harnessing the sun’s inexhaustible power, Psyche achieves exceptional fuel efficiency, enabling extended missions and deeper ventures into the cosmos.

Tripling Thrust, Expanding Horizons: Compared to its predecessors, Psyche’s ion thrusters pack a punch, generating three times the thrust. This translates to faster travel and the ability to explore multiple celestial objects within a single mission. Imagine a fleet of solar-powered probes flitting between asteroids, gathering data on diverse environments, a testament to Psyche’s pioneering spirit.

The success of Psyche holds immense potential. Imagine a future where solar-powered probes swarm the asteroid belt, mining resources for space infrastructure. Envision sun-driven spacecraft orbiting distant planets for years, searching for biosignatures and unraveling the mysteries of distant worlds.

Private Sector: SpaceX and Blue Origin Push Innovation

SpaceX, the disruptor, has already begun rewriting the rules with its Starlink satellites. These marvels of miniaturization use electric propulsion for orbit maintenance, providing internet access to even the remotest corners of the globe. Meanwhile, Blue Origin, with its methane-powered BE-4 engine, offers a potentially cheaper and reusable alternative to traditional rockets, fueling its New Shepard spaceplane and future lunar ambitions.

Asian Advancements: China and Japan Join the Race

China, the rising star, is making waves with its Plasma Drive prototype. This clean and sustainable technology utilizes microwaves to ionize air for thrust, though it’s still in its early stages. Japan, the tech giant, isn’t far behind. Its Ikeda Thruster, another microwave-powered marvel, uses heated helium to generate thrust, pushing the boundaries of electric propulsion design.

• China’s Plasma Drive Prototype: While still in its infancy, this prototype utilizes microwaves to ionize air for propulsion, offering a potential clean and sustainable option.

China’s Tiangong space station boasts a futuristic feature: ion propulsion. This technology ditches fiery chemical rockets for electrically charged ions, offering major benefits like extended missions, reduced fuel needs, and even lower costs. The station’s four ion thrusters adjust its orbit and keep it stable, showcasing China’s technological prowess.

Tiangong’s Ion Thrusters:

The Tianhe core module of the Tiangong station is equipped with four ion thrusters, offering a total thrust of 50 mN (millinewtons). These thrusters are primarily used for station-keeping, adjusting the station’s orbit and counteracting the effects of atmospheric drag. During its testing phase, one of the thrusters ran continuously for over 8,240 hours without issue, demonstrating its reliability and durability.

• Japan’s Ikeda Thruster: This unique design uses microwaves to heat helium, creating thrust through plasma expansion, showcasing another innovative approach to electric propulsion.

Russia plan to use a nuclear reactor to power an electric ion propulsion system

Engineers, seeking to enhance the scalability of power-demanding electric thrusters, have explored the replacement of traditional heavy solar panels with nuclear power sources. Unlike solar-dependent systems, nuclear sources offer a sustained and reliable power supply, making them advantageous for prolonged missions in remote and cold regions of the Solar System. The Transport and Energy Module (TEM), a large space tug project revealed in 2020 by KB Arsenal, integrates a nuclear reactor at its core to generate heat, which is then converted into electrical power. The TEM concept, rooted in the early days of the Space Age, aims to marry a nuclear reactor with an electric rocket engine for efficient and enduring space travel.

Nuclear energy can be used in two ways in powering propulsion systems: either its energy can be used to generate heat that is turned into energy or it may provide power directly. Russia is targeting this latter technology for development. They plan to use a nuclear reactor to power an electric ion propulsion system.

The TEM tug employs a nuclear reactor to produce heat, with heat-to-electricity conversion achieved through a mechanical turbine or the thermo-emission method. While less efficient than a turbine, the thermo-emission method, simpler and familiar to the Russian industry, was observed in the 2020 TEM vehicle. Excess heat generated during reactor operation is dissipated into space through radiators, equipped with technologies to function in weightlessness. Russia’s pursuit of nuclear energy for powering electric ion propulsion systems positions it strategically in the space race, aiming to overcome the limitations of fuel-carrying capacity for extended deep space missions, where solar power becomes impractical due to distance from the Sun. If successful, this technology could give Russia a significant edge in space exploration by 2025.

If Russia is able to harness nuclear energy to power long-duration space missions by 2025, it would give them a significant lead in the modern space race. “Nuclear energy has significant advantages for deep space missions, in which the ability to carry fuel is a limiting factor in determining a mission’s duration. Solar power can be used for extended missions within the inner Solar System, but outer system missions are too far from the Sun to make this a practical energy source,” writes Ines Hernandez

ISRO Embraces Electric Propulsion for Lighter, More Efficient Satellites

Marking a significant shift in its approach, the Indian Space Research Organisation (ISRO) is actively developing electric propulsion systems (EPS) for its satellites. This technology, unlike traditional chemical rockets, utilizes electric fields to accelerate ions, offering several advantages:

Reduced fuel dependence: Electric propulsion requires significantly less propellant compared to chemical rockets, leading to lighter satellites and potentially lower launch costs.
Extended mission duration: The low-thrust, continuous operation of EPS allows for longer satellite lifetimes, maximizing their effectiveness and return on investment.
Greater payload capacity: With less fuel onboard, satellites can accommodate more transponders and other equipment, boosting their functionality and value.

ISRO successfully tested its initial EPS implementation on the GSAT-9 satellite in 2017, demonstrating the technology’s viability. Now, the agency is focused on developing higher-thrust EPS systems, aiming to significantly reduce reliance on chemical propulsion and its limitations. This advancement could enable ISRO to:

Launch heavier satellites: With reduced fuel weight, ISRO’s rockets could carry heavier payloads, potentially eliminating dependence on foreign launch facilities and boosting India’s space independence.
Reach distant destinations faster: Higher-thrust EPS would shorten travel times to more distant locations in the solar system, opening up new exploration possibilities for ISRO.

Field-Emission Electric Propulsion (FEEP): A Precise Thrust for Small Satellites

What is FEEP?

FEEP, or Field-Emission Electric Propulsion, is a type of ion thruster that uses liquid metal (usually caesium, indium, or mercury) to generate thrust. This technology works by applying a strong electric field to the metal, causing ions to be emitted and then accelerated to high speeds.

Advantages of FEEP:

Highly precise: FEEP thrusters can produce very small thrust forces, making them ideal for fine-tuning the position and orientation of satellites.
Efficient: FEEP thrusters use very little fuel, allowing satellites to operate for longer periods with less propellant onboard.
Scalable: FEEP systems can be easily adapted to different sizes and applications, making them suitable for a wide range of small satellites.
Environmentally friendly: FEEP thrusters use non-toxic propellants and generate minimal emissions.

Challenges and Opportunities:

Low thrust: FEEP thrusters are not powerful enough for large-scale maneuvers, limiting their use to smaller satellites and specific applications.
Technical complexity: FEEP technology is still relatively new and complex, requiring careful design and manufacturing.
Commercialization potential: Austrian startup Enpulsion is leading the way in commercializing FEEP thrusters, offering solutions for small satellite manufacturers. Their “porous tungsten crown emitter” technology promises mass-production scalability and cost-effectiveness.

Future of FEEP:

With increasing demand for small satellites and the advancements made by Enpulsion, FEEP is poised to play a significant role in the future of space exploration. Its ability to provide precise and efficient thrust makes it ideal for applications like satellite constellation management, in-orbit servicing, and deep space missions.

ASAT Technology: Safeguarding Space Assets

In addition to advancements in propulsion for exploration and travel, the development of Anti-Satellite (ASAT) technology has emerged as a strategic focus for several countries. ASAT capabilities, utilizing electric and ion propulsion systems, provide the means to protect essential space assets by deterring potential threats.

Space-faring nations recognize the vulnerability of satellites to intentional or accidental collisions and attacks. As a result, the race is on to deploy sophisticated ASAT technologies capable of safeguarding vital communication, navigation, and Earth observation satellites that form the backbone of modern technological infrastructure.

Ion propulsion technology, while promising for deep space exploration and satellite operations, introduces complexities in the context of its potential application in anti-satellite (ASAT) weapons. The advantages of ion thrusters in this role include precise maneuverability for accurate satellite approach, stealth through quiet operation and low emissions, and extended mission duration, providing ample time for tracking and disabling enemy satellites.

However, the technology faces challenges such as low thrust compared to traditional rockets, limiting its effectiveness against highly maneuverable satellites. Moreover, the complex nature of ion thrusters and their susceptibility to damage from lasers or other countermeasures pose vulnerabilities. Advances in space surveillance technology may also counteract the stealth advantage of ion-powered ASAT systems by enabling detection and prediction of their movements. Balancing the capabilities and limitations of ion propulsion in ASAT applications is essential for responsible development and fostering international collaboration.

Challenges and Collaborations: Navigating the Cosmos Together

The pursuit of electric and ion propulsion technologies comes with its share of challenges. Power scalability, efficiency improvements, and overcoming the constraints of current technologies are paramount concerns. However, the shared goal of unraveling the cosmos has sparked collaborations among nations and space agencies.

International partnerships, such as those witnessed in the International Space Station (ISS) program, exemplify the collaborative spirit that propels humanity into the cosmos. As countries pool their resources and expertise, the race to develop advanced propulsion technologies becomes a collective endeavor, transcending geopolitical boundaries.

Beyond Mars and Mercury: A Universe Awaits

Electric and ion propulsion technologies hold the key to unlocking the true potential of space travel, propelling us beyond the limitations of our current era.

In the race to develop electric and ion propulsion technologies, countries are not merely competing; they are pioneering a new era of space exploration. Whether the destination is Mars, Mercury, the far reaches of interstellar space, or the safeguarding of critical space assets, the technologies being developed today hold the promise of reshaping our understanding of the cosmos.