Sylvie Willis
Plasma thrusters are a type of electric propulsion engine that generates thrust from quasi-neutral plasma. They are more fuel-efficient than conventional rocket engines, using around 100 million times less fuel. Plasma thrusters accelerate gradually and can reach a maximum speed of 34 miles per second over 23 days, which is four times faster than any chemical rocket. Despite their high speed, they only provide around 2 pounds of thrust maximum, so they are not suitable for launch-to-Earth-orbit. Pulsed plasma thrusters (PPTs) are a type of plasma thruster that has been used by NASA and the Soviet Union. They have a much smaller fuel flow rate than chemical propulsion engines, but they can achieve a proportionally higher final velocity.
| Characteristics | Values |
|---|---|
| Fuel efficiency | Plasma thrusters are more fuel-efficient than conventional engines, using 100 million times less fuel. |
| Fuel type | Teflon, polypropylene, Delrin, argon, krypton, xenon, lithium vapour, hydrogen, ammonia, nitrogen, astronaut urine, and other gases. |
| Fuel flow rate | Pulsed plasma thrusters have a much smaller fuel flow rate than chemical propulsion engines. |
| Power requirement | The VX-200 engine requires 200 kW electrical power to produce 5 N of thrust. |
| Thrust | Plasma thrusters have a very low thrust, with an average maximum of about 2 pounds. |
| Thrust velocity | Pulsed plasma thrusters have exhaust velocities in the range of 20-70 km/s, with NASA's research PPT achieving 13,700 m/s. |
| Speed | Plasma thrusters can reach a maximum speed of 34 miles (55 km) per second over 23 days, four times faster than chemical rockets. |
| Energy storage | The energy used in each pulse of a pulsed plasma thruster is stored in a capacitor. |
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What You'll Learn
Plasma thrusters are more fuel-efficient than chemical rockets
Plasma thrusters are a type of electric propulsion that generates thrust from quasi-neutral plasma. They are more fuel-efficient than chemical rockets, using around 100 million times less fuel. Plasma thrusters accelerate gradually and can reach a maximum speed of 34 miles (55 kilometres) per second over 23 days, which is four times faster than any chemical rocket. This increased speed means less time spent travelling, reducing the risk of mechanical failure and astronauts suffering ill health effects.
The first use of plasma engines was a Pulsed Plasma Thruster (PPT) on the Soviet Zond 2 space probe in 1964. PPTs are a type of plasma thruster that has a simple design and uses less fuel than traditional chemical rockets. They have a lower fuel flow rate, resulting in a higher final velocity. NASA has also experimented with PPTs, achieving an exhaust velocity of 13,700 m/s, a thrust of 860 μN, and consuming just 70 W of electrical power.
Plasma thrusters do not use high-voltage grids or anodes/cathodes to accelerate charged particles. Instead, they use internally generated currents and potentials to accelerate ions, resulting in a lower exhaust velocity. This design removes a possible limiting factor due to grid ion erosion. Plasma thrusters can also use a wide variety of propellants, from argon to carbon dioxide air mixtures to astronaut urine.
However, plasma thrusters do have some challenges. They require a lot of power, and while this can be met by fission reactors, the reactor mass may be prohibitive. Plasma thrusters are also susceptible to plasma erosion, which can lead to system failure. They are not suitable for launch-to-Earth-orbit due to their low thrust.
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They use 100 million times less fuel
Plasma thrusters are a type of electric propulsion that generates thrust from a quasi-neutral plasma. They are used in rockets, where the fuel is converted into kinetic energy through the use of a de Laval nozzle. Plasma thrusters have been used in space missions, with the first use being a Pulsed Plasma Thruster (PPT) on the Soviet Zond 2 space probe.
Plasma thrusters offer several advantages over conventional chemical propulsion engines. One of the most significant benefits is their extremely high fuel efficiency. Plasma rockets use 100 million times less fuel than conventional engines. This remarkable efficiency means that a trip from Earth's orbit to the moon's orbit requires only about 30 gallons (113 liters) of gas. The low fuel consumption of plasma thrusters reduces launch mass and costs, making them a more economical option for space travel.
The high fuel efficiency of plasma thrusters is due to their unique method of generating thrust. In a plasma thruster, electric and magnetic fields are set up perpendicularly within the chamber. When electricity is applied, electrons move rapidly in circles. As propellant gas is introduced, high-speed electrons knock electrons off the propellant atoms, creating a plasma consisting of free electrons and positively charged ions. These ions are then expelled from the engine, creating the thrust needed to propel the rocket forward.
While plasma thrusters excel in fuel efficiency, they have lower thrust capabilities compared to conventional engines. Plasma thrusters have extremely low thrust, with an average maximum of about 2 pounds of thrust. Due to their low thrust, plasma engines are not suitable for launch-to-Earth orbit. However, they are highly efficient in open space and can achieve a maximum speed of 34 miles (55 kilometers) per second over 23 days, which is four times faster than chemical rockets.
Overall, plasma thrusters represent a significant advancement in propulsion technology, particularly for space exploration. Their extremely high fuel efficiency, with 100 million times less fuel consumption than conventional engines, makes them a more cost-effective and sustainable option for space travel. However, the low thrust capabilities of plasma thrusters also present limitations, making them unsuitable for certain applications such as launching to Earth orbit.
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Pulsed plasma thrusters (PPTs) have a smaller fuel flow rate
Pulsed Plasma Thrusters (PPTs) are a type of plasma propulsion engine that uses electromagnetic discharge to generate thrust. They are unique in that they can provide intense electromagnetic discharge by applying high currents in very short periods (microseconds).
PPTs have a smaller fuel flow rate compared to chemical propulsion engines. The Tsiolkovsky equation demonstrates that the lower fuel flow rate in PPTs results in a proportionally higher final velocity of the propelled craft. The exhaust velocity of a PPT is in the order of tens of km/s, while conventional chemical propulsion generates thermal velocities in the range of 2-4.5 km/s.
The reduced fuel consumption in PPTs is due to their inherent simplicity in design compared to other electric propulsion systems. The fuel used in PPTs, such as Teflon, is consumed slowly, and a spring forces the remaining solid propellant forward, providing a constant fuel source. This results in a continuous and smooth thrust, allowing the PPT to operate for extended periods and achieve a large final speed.
PPTs have been used in various space missions, including the Soviet Zond 2 space probe in 1964 and NASA's Earth Observing-1 spacecraft in 2000. NASA's research PPT achieved an exhaust velocity of 13,700 m/s, a thrust of 860 μN, and consumed only 70 W of electrical power. This demonstrates the fuel efficiency of PPTs, making them advantageous for interplanetary missions.
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PPTs use Teflon as fuel
Pulsed Plasma Thrusters (PPTs) are a form of electric propulsion for spacecraft. They are generally considered the simplest form of electric propulsion and were the first form of electric propulsion to be flown in space. PPTs are flown on spacecraft with a surplus of electricity from abundantly available solar energy.
PPTs use a solid material as a propellant, and most commonly, this is PTFE, or Teflon. PTFE is a synthetic fluoropolymer of tetrafluoroethylene, commonly known by the brand name Teflon. PTFE is chemically inert, hydrophobic, and has a very low coefficient of friction. Teflon is well-known for its use in non-stick pans and other cookware, but it is also used in pipework for reactive and corrosive chemicals, and in the aerospace industry in the production of carbon fibre composites.
In a PPT, an arc of electricity passes through the PTFE fuel, causing ablation and sublimation. The heat generated by the arc creates a charged gas cloud, turning the gas into plasma. The plasma is then propelled at low speed between two charged plates, and the fuel completes the circuit between the plates, allowing a current to flow through the plasma. This flow of electrons generates a strong electromagnetic field, which then exerts a Lorentz force on the plasma, accelerating it out of the PPT exhaust at high velocity.
PPTs have a much smaller fuel flow rate than chemical propulsion engines, and so benefit from reduced fuel consumption, reducing launch mass and therefore launch costs.
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Ion thrusters use Xenon as propellant
Plasma thrusters are a type of electric propulsion that generates thrust from a quasi-neutral plasma. They are highly efficient and use a lot less fuel than conventional engines—about 100 million times less. Plasma thrusters are well-suited for interplanetary missions due to their high specific impulse. However, they are not suitable for launch-to-Earth-orbit due to their low thrust.
Ion thrusters are a type of plasma thruster that generate thrust by extracting an ion current from the plasma source and accelerating it to high velocities. Ion thrusters typically use Xenon as a propellant. Xenon is easy to ionize, chemically inert, has a reasonably high atomic number, and causes low erosion. It is also easy to store in a compact form. The atoms are relatively heavy, so they provide a large thrust compared to other propellants.
NASA has used ion thrusters in several missions, including the Deep Space 1 space probe, which was powered by the NASA Solar Technology Application Readiness (NSTAR) ion engine. The Japanese Aerospace Exploration Agency's Hayabusa space probe used four xenon ion engines. The NASA Evolutionary Xenon Thruster (NEXT) project operated continuously for more than 48,000 hours, consuming approximately 870 kilograms of xenon propellant.
While Xenon is an effective propellant for ion thrusters, it is globally in short supply and expensive (approximately $3,000 per kg in 2021). Other propellants that have been used in ion thrusters include krypton, argon, bismuth, iodine, and mercury. However, mercury has been banned as a propellant due to its toxicity and tendency to contaminate spacecraft.
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Frequently asked questions
A plasma thruster uses 100 million times less fuel than a conventional engine.
A plasma thruster is a type of electric propulsion that generates thrust from a quasi-neutral plasma.
Plasma thrusters use electric and magnetic fields to accelerate electrons and create a plasma. This plasma is then propelled out of the engine to create thrust.
The fuel used in a plasma thruster can vary. The first use of a plasma engine was a Pulsed Plasma Thruster (PPT) which used Teflon as its fuel. Other propellants include polypropylene, Delrin, and argon.
Plasma thrusters are more fuel-efficient than conventional engines and other electric propulsion systems like Hall thrusters. However, they produce lower thrust, making them unsuitable for launch-to-Earth-orbit.
