Ion thruster
An ion engine cannot usually generate sufficient thrust to achieve initial liftoff from any celestial body with significant surface gravity.
For these reasons, spacecraft must rely on other methods such as conventional chemical rockets or non-rocket launch technologies to reach their initial orbit.
[8] The technique was recommended for near-vacuum conditions at high altitude, but thrust was demonstrated with ionized air streams at atmospheric pressure.
This low thrust makes ion thrusters unsuited for launching spacecraft into orbit, but effective for in-space propulsion over longer periods of time.
To keep the spacecraft from accumulating a charge, another cathode is placed near the engine to emit electrons into the ion beam, leaving the propellant electrically neutral.
However, the electrons produced near the end of the spike to create the cathode are trapped by the magnetic field and held in place by their attraction to the anode.
[35][36][37] In 2013, Russian company the Chemical Automatics Design Bureau successfully conducted a bench test of their MPD engine for long-distance space travel.
Neutral gas is first ionized by electromagnetic waves and then transferred to another chamber where it is accelerated by an oscillating electric and magnetic field, also known as the ponderomotive force.
This separation of the ionization and acceleration stages allows throttling of propellant flow, which then changes the thrust magnitude and specific impulse values.
Radio frequency AC power (at 13.56 MHz in the prototype design) is coupled into a specially shaped antenna wrapped around the chamber.
The VASIMR is currently being developed by Ad Astra Rocket Company, headquartered in Houston, Texas, with help from Canada-based Nautel, producing the 200 kW RF generators for ionizing propellant.
[42] In the discharge chamber, microwave (MW) energy flows into the center containing a high level of ions (I), causing neutral species in the gaseous propellant to ionize.
A theoretical propulsion system has been proposed, based on alpha particles (He2+ or 42He2+ indicating a helium ion with a +2 charge) emitted from a radioisotope uni-directionally through a hole in its chamber.
Ion thrusters' low thrust requires continuous operation for a long time to achieve the necessary change in velocity (delta-v) for a particular mission.
A test of the NASA Solar Technology Application Readiness (NSTAR) electrostatic ion thruster resulted in 30,472 hours (roughly 3.5 years) of continuous thrust at maximum power.
[80] Many current designs use xenon gas, as it is easy to ionize, has a reasonably high atomic number, is inert and causes low erosion.
[83] From 2018–2023, krypton was used to fuel the Hall-effect thrusters aboard Starlink internet satellites, in part due to its lower cost than conventional xenon propellant.
[86] Iodine was used as a propellant for the first time in space, in the NPT30-I2 gridded ion thruster by ThrustMe, on board the Beihangkongshi-1 mission launched in November 2020,[87][88][89] with an extensive report published a year later in the journal Nature.
Ion thruster efficiency is the kinetic energy of the exhaust jet emitted per second divided by the electrical power into the device.
Two geostationary satellites (ESA's Artemis in 2001–2003[92] and the United States military's AEHF-1 in 2010–2012[93]) used the ion thruster to change orbit after the chemical-propellant engine failed.
The development of the Hall-effect thrusters is considered a sensitive topic in China, with scientists "working to improve the technology without attracting attention".
Hall-effect thrusters are created with crewed mission safety in mind with effort to prevent erosion and damage caused by the accelerated ion particles.
A magnetic field and specially designed ceramic shield was created to repel damaging particles and maintain integrity of the thrusters.
[7] SpaceX's Starlink satellite constellation uses Hall-effect thrusters powered by krypton or argon to raise orbit, perform maneuvers, and de-orbit at the end of their use.
It used ion propulsion throughout its twenty-month mission to combat the air-drag it experienced in its low orbit (altitude of 255 kilometres) before intentionally deorbiting on 11 November 2013.
[25] Based on the NASA design criteria, Hughes Research Labs developed the Xenon Ion Propulsion System (XIPS) for performing station keeping on geosynchronous satellites.
It was powered by four xenon ion engines, which used microwave electron cyclotron resonance to ionize the propellant and an erosion-resistant carbon/carbon-composite material for its acceleration grid.
As of March 2011[update], a future launch of an Ad Astra VF-200 200 kW VASIMR electromagnetic thruster was under consideration for testing on the International Space Station (ISS).
[111] It would probably use the 50 kW Advanced Electric Propulsion System (AEPS) under development at NASA Glenn Research Center and Aerojet Rocketdyne.
[71] Geoffrey A. Landis proposed using an ion thruster powered by a space-based laser, in conjunction with a lightsail, to propel an interstellar probe.
