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NASA's Ion Thruster Sets Continuous Operation Record
cylonlover writes "NASA's Evolutionary Xenon Thruster (NEXT) ion engine has set a new world record by clocking 43,000 hours of continuous operation at NASA's Glenn Research Center's Electric Propulsion Laboratory. The seven-kilowatt thruster is intended to propel future NASA deep space probes on missions where chemical rockets aren't a practical option. The NEXT is one of NASA's latest generation of engines. With a power output of seven kilowatts, it's over twice as powerful as the ones used aboard the unmanned Dawn space probe, yet it is simpler in design, lighter and more efficient, and is also designed for very high endurance. Its current record of 43,000 hours is the equivalent of nearly five years of continuous operation while consuming only 770 kg (1697.5 lbs) of xenon propellant. The NEXT engine (PDF) would provide 30 million newton-seconds of total impulse to a spacecraft. What this means in simple terms is that the NEXT engine can make a spacecraft go (eventually) very far and very fast."
lots and lots and lots. just expensive to separate as it is widely distributed.
Xenon is a trace gas in Earth's atmosphere, occurring at 87±1 parts per billion (nL/L)
(wikipedia is fun)
being heavy it doesn't escape the atmosphere.
It is very dense as a liquid, stores compactly, and can used as a heatsink for the engine.
for fun:
770kg of xenon is 130641 L at STP
it is 252 L at xenon boiling point (as liquid)
it is also ~2% of total xenon production (in 1998)
Xenon is easy to ionise - it's a large, diffuse atom with the outer electrons far from the nucleus. It's also inert and heavy, giving you a non-toxic, non-corrosive fuel with a high mass/charge ratio; ideal for an ion thruster.
If only it were cheaper to buy!
It's also not true that "nothing reacts with it". The lower end of group 18 does react with strong oxidisers and you can form (and isolate) crystals of XeO4 and so on. The closest to being truly "noble" gasses are helium and neon.