How Ion thrusters power spacecraft

The incredible sci-fi technology made a reality

Ion propulsion studies began In the 1950s, with NASA's Glenn Research Center engineering the earliest ion thrusters for rocket propulsion.

In the system, electrons get pushed into the thruster via a cathode tube. These electrons, which have an innate negative charge, come into contact with the propellant - typically the noble gas xenon - In the discharge chamber, drawn by strong electromagnets. When a free electron hits a neutral atom from the propellant, the xenon breaks into two negative electrons and a positive ion.

The ions then get forced Into Ion optics, which are electrodes that contain thousands of coaxial apertures. The end that is closer to the exit is negatively charged and the end closer to the rocket is positively charged. The positive ions stream toward the negatively charged end of the apertures, get compressed and form an ion stream. This ion stream then shoots out of the end of the thruster, providing the force to propel the rocket.

In order to keep the overall system neither positive nor negative, a cathode tube called a neutraliser pumps a stream of negatively charged electrons into the ion stream once it has been expelled to mix with the positively charged Ions and balance out the whole process so the exhaust remains neutral.

The main benefit of ion thrusters is that they are able to propel rockets at a much faster pace than a chemically powered rocket. The now-retired Space Shuttle could travel at a top speed of 28,000 kilometres (17,400 miles) per hour, but an ion thruster allows for a speed of 322,000 kilometres (200,000 miles) per hour! 

The downside is that, unfortunately, the amount of thrust generated by ion propulsion is minuscule. An ion thruster can only create as much as 0.5 Newtons (0,1 pounds) of force, which is about as much as holding ten small coins (20 pence or quarter dollar) in your hand. Therefore, acceleration Is extremely slow but it can continue over a very long period of time.

Longer, stronger and faster

The two key benefits of an ion thruster are its longevity and its ability to propel rockets much faster than it has ever been possible to do. 

NASA's Evolutionary Xenon Thruster (NEXT) is one of the most advanced thrusters around. It ran continuously for 48,000 hours - more than five and a half years - in a test to discover just how long these units can provide energy. 

Over the course of the mat, NEXT only used 870 kilograms (1,900 pounds) of fuel, which is less than a tenth of the fuel consurnption of a traditional thruster, which would have used in the range of 10,000 kilograms (22,000 pounds) of fuel. 

The weight saving will allow either smaller spacecraft to undertake missions or larger craft to run for much longer than ever before.