Pulsed plasma thruster
Encyclopedia
Pulsed plasma thrusters are a method of spacecraft propulsion
also known as Plasma Jet Engines in general. They use an arc of electric current adjacent to a solid propellant, to produce a quick and repeatable burst of impulse. PPTs are excellent for attitude control, and for main propulsion on particularly small spacecraft
with a surplus of electricity (those in the hundred-kilogram or less category). However they are also one of the least efficient electric propulsion systems, with a thrust efficiency of less than 10%. At present they are deployed in space vehicles and probes as space does not offer any frictional force when compared to that on earth. The extremely quick and repetitive thrust accelerates the space probe continuously. Thus it eventually reaches and goes beyond the speeds of conventional propulsion systems. The electrical energy required to operate the arc mechanism is abundantly available by harnessing the solar energy via self adjusting solar panels on the probe.
PPTs have much higher exhaust velocity than chemical propulsion engines. According to the Tsiolkovsky equation this results in proportionally higher final velocity of propelled craft. The principle of operation is the electromagnetic acceleration of propellant via the Lorentz force
to velocities of the order of tens of km/s - which is much higher than the thermal velocity
of chemical engines. Chemical propulsion engines, with their limited rate of chemical reaction exhaust velocity (which is in the range of 2-4.5 km/s), become exponentially ineffective (see Tsiolkovsky equation) to achieve high interplanetary speeds (in the 20-70 km/s range, within the Solar System
).
Pulsed plasma thrusters were the first electric thrusters to be deployed in space, used for attitude control on the Soviet probes Zond 2
, from parking at Earth orbit to Mars on November 30, 1964, and Zond 3
in 1965. The active gases used in the Soviet plasma propulsion engines were argon
and helium
. Soviet engineers subsequently returned to the use of high-pressure nitrogen jets.
Pulsed plasma thrusters were flown in November, 2000 as a flight experiment on the Earth Observing-1
spacecraft. The thrusters successfully demonstrated the ability to perform roll control on the spacecraft and also demonstrated that the electromagnetic interference from the pulsed plasma did not affect other spacecraft systems. These experiments used Teflon
as the propellant.
Spacecraft propulsion
Spacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. There are many different methods. Each method has drawbacks and advantages, and spacecraft propulsion is an active area of research. However, most spacecraft today are propelled by forcing a gas from the...
also known as Plasma Jet Engines in general. They use an arc of electric current adjacent to a solid propellant, to produce a quick and repeatable burst of impulse. PPTs are excellent for attitude control, and for main propulsion on particularly small spacecraft
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
with a surplus of electricity (those in the hundred-kilogram or less category). However they are also one of the least efficient electric propulsion systems, with a thrust efficiency of less than 10%. At present they are deployed in space vehicles and probes as space does not offer any frictional force when compared to that on earth. The extremely quick and repetitive thrust accelerates the space probe continuously. Thus it eventually reaches and goes beyond the speeds of conventional propulsion systems. The electrical energy required to operate the arc mechanism is abundantly available by harnessing the solar energy via self adjusting solar panels on the probe.
PPTs have much higher exhaust velocity than chemical propulsion engines. According to the Tsiolkovsky equation this results in proportionally higher final velocity of propelled craft. The principle of operation is the electromagnetic acceleration of propellant via the Lorentz force
Lorentz force
In physics, the Lorentz force is the force on a point charge due to electromagnetic fields. It is given by the following equation in terms of the electric and magnetic fields:...
to velocities of the order of tens of km/s - which is much higher than the thermal velocity
Thermal velocity
The thermal velocity or thermal speed is a typical velocity of the thermal motion of particles which make up a gas, liquid, etc. Thus, indirectly, thermal velocity is a measure of temperature. Technically speaking it is a measure of the width of the peak in the Maxwell-Boltzmann particle velocity...
of chemical engines. Chemical propulsion engines, with their limited rate of chemical reaction exhaust velocity (which is in the range of 2-4.5 km/s), become exponentially ineffective (see Tsiolkovsky equation) to achieve high interplanetary speeds (in the 20-70 km/s range, within the Solar System
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
).
Pulsed plasma thrusters were the first electric thrusters to be deployed in space, used for attitude control on the Soviet probes Zond 2
Zond 2
Zond 2, a member of the Soviet Zond program, was the fifth Soviet spacecraft to attempt a flyby of Mars. Zond-2 carried a phototelevision camera of the same type later used to photograph the Moon on Zond 3. The camera system also included two ultraviolet spectrometers...
, from parking at Earth orbit to Mars on November 30, 1964, and Zond 3
Zond 3
Zond 3 was a member of the Soviet Zond program sharing designation Zond, while being part of Mars 3MV project. It was unrelated to Zond spacecraft designed for manned circumlunar mission . Zond 3 completed a successful Lunar flyby, taking a number of good quality photographs for its time...
in 1965. The active gases used in the Soviet plasma propulsion engines were argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...
and helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
. Soviet engineers subsequently returned to the use of high-pressure nitrogen jets.
Pulsed plasma thrusters were flown in November, 2000 as a flight experiment on the Earth Observing-1
Earth Observing-1
The Earth Observing-1 Mission is part of NASA's New Millennium Program , to develop and validate a number of instrument and spacecraft bus breakthrough technologies designed to enable the development of future earth imaging observatories that will have a significant increase in performance while...
spacecraft. The thrusters successfully demonstrated the ability to perform roll control on the spacecraft and also demonstrated that the electromagnetic interference from the pulsed plasma did not affect other spacecraft systems. These experiments used Teflon
Polytetrafluoroethylene
Polytetrafluoroethylene is a synthetic fluoropolymer of tetrafluoroethylene that finds numerous applications. PTFE is most well known by the DuPont brand name Teflon....
as the propellant.