"Ion thrusters, the propulsion of choice for science fiction writers have become the propulsion of choice for scientists and engineers at NASA. The ion propulsion system's efficient use of fuel and electrical power enable modern spacecraft to travel farther, faster and cheaper than any other propulsion technology currently available. Chemical rockets have demonstrated fuel efficiencies up to 35 percent, but ion thrusters have demonstrated fuel efficiencies over 90 percent. Currently, ion thrusters are used to keep communication satellites in the proper position relative to Earth and for the main propulsion on deep space probes. Several thrusters can be used on a spacecraft, but they are often used just one at a time. Spacecraft powered by these thrusters can reach speeds up to 90,000 meters per second (over 200,000 mph). In comparison, the Space Shuttles can reach speeds around 18,000 mph."
https://www.nasa.gov/centers/glenn/technology/Ion_Propulsion1.html
"Scientists and engineers from the NASA Glenn Research Center and the Jet Propulsion Laboratory have worked for more than two years to build a high-power ion thruster that will help NASA realize the Vision for Space Exploration.
Dubbed Herakles, the new ion thruster is based on the Deep Space 1 system, but it will use electricity from a reactor to produce plasma from xenon -- the same gas found in photo flash bulbs. Ions from the plasma will be extracted and then accelerated at extremely high speeds. In space, as the xenon ion beam rushes from the thruster, it will propel the spacecraft in the opposite direction.
Although Herakles' thrust is as gentle as the force of 10 U.S. quarters in your hand, the speed of the spacecraft will constantly increase as it travels. That means Prometheus 1 could eventually reach speeds greater than 200,000 mph -- 10 times faster than the speed of Space Shuttles."
https://www.nasa.gov/vision/universe/features/nep_prometheus.html
"Electric propulsion systems are extraordinarily efficient. They use energy from external power sources like the sun or nuclear reactors to ionize—or positively charge—gas fuels like xenon. The ions are then accelerated and pushed out of the thruster, driving the spacecraft to speeds that can reach 200,000 mph, NASA describes. These systems can cost less, carry more, and use up to 90% less fuel than typical chemical propulsion approaches. They are currently used in satellites and robotic missions, but NASA’s eyeing more high-powered versions for human exploration of the solar system."
https://aero.engin.umich.edu/2021/05/12/testing-advanced-space-engines-here-on-earth/
"NASA has announced that its NEXT ion drive — NASA’s Evolutionary Xenon Thruster — has operated continually for over 43,000 hours (five years). This is an important development, as ion thrusters are pegged as one of the best ways to power long-term deep-space missions to other planets and solar systems. With a proven life time of at least five years, NEXT engines just made a very big step towards powering NASA’s next-gen spacecraft.
Ion thrusters work, as the name suggests, by firing ions (charged atoms or molecules) out of a nozzle at high speed (pictured above). In the case of NEXT, operation is fairly simple."
https://www.extremetech.com/extreme/144296-nasas-next-ion-drive-breaks-world-record-will-eventually-power-interplanetary-missions
"supersonic nozzle"
https://theeventchronicle.com/secret-plane-tr-3b-patent/#
"Ion propulsion systems generate a tiny amount of thrust. Hold nine quarters in your hand, feel Earth's gravity pull on them, and you have an idea how little thrust they generate. They can't be used for launching spacecraft from bodies with strong gravity. Their strength lies in continuing to generate thrust over time. This means that they can achieve very high top speeds. Ion thrusters can propel spacecraft to speeds over 320,000 kp/h (200,000 mph), but they must be in operation for a long time to achieve that speed."
https://phys.org/news/2015-11-ion-propulsionthe-key-deep-space.html
"In reality, satellites powered by these nts can travel speeds in excess of 200,000 mph as measured by speed up to 90,000 meters per second."
https://www.eclipseaviation.com/how-much-thrust-does-nasa-ion-engines-produce/
" The new ion thruster is designed to last seven to 10 years in space and is about 15 times more efficient than the Space Shuttle Main Engines.
"The more efficient the engine, the less fuel the spacecraft has to carry," said Dr. John Foster, NASA Glenn research engineer."
https://www.spacedaily.com/news/rocketscience-05ze.html
"These ions are then accelerated by high voltage grids and expelled into space as an ion beam, leaving behind a ghostly blue trail.
Although the thrust from the engine is less pressure than the weight of a single sheet of paper in the hand, each day it will add between 15 mph to 20 mph to the probe's speed.
In 300 days it will have accelerated the Deep Space One by 60,000 mph.
"I like to call it 'acceleration with patience,'" says Marc Rayman, the mission's chief engineer.
The ion propulsion system is powered by electricity from solar panels and a supply of xenon gas.
Nasa says it is 10 times more efficient than conventional rockets."
http://news.bbc.co.uk/2/hi/science/nature/200504.stm