For example, keeping geostationary satellites in their correct orbit, to counteract the aerodynamic drag from the very tenuous atmosphere 200km above the Earth.
Hmm. Not sure geostationary satellites orbit at that distance, more like... 36,000km.
I'm pretty sure it was meant to be parsed like this:
> [Real applications like] For example, (keeping geostationary satellites in their correct orbit), (to counteract the aerodynamic drag from the very tenuous atmosphere 200km above the Earth).
Of course there isn't any significant drag at GEO, but you still need to use engines to do station keeping, thanks to things like Earth's shape, other planets and solar winds messing up with your orbit in tiny ways that tend to accumulate. You can't keep a stable orbit forever without correction burns the way you can in Kerbal Space Program (because it doesn't do full n-body simulation).
Is this a good ripost to the hand wringing articles bemoaning the end of technology development; a breakthrough technology taking man's instruments and machines to a place that they couldn't previously have got to?
This explains a lot of the recent interest in LEO for telecoms I guess, I should imagine that the control that this gives you coupled with the longevity would enable you to do a lot more for a lot less than is currently the case.
I don't think it's really a breakthrough - Hall Effect Thrusters and similar ion propulsion have been around for a while. The Soviets used them in the 70's. Its more the technology has reached a level of maturity and relability that it is now a good choice.
Mention saving fuel as a cost saving. But the real issue is, what is the maximum mission delta-v? Fuel needs grow geometrically with needed acceleration over the mission. The ion engine can quadruple the mission possibilities or duration.
For those curious: Exhaust velocity is linearly related to impulse per fuel mass, so if you double the exhaust velocity, you double the engine's total impulse (force*burn time).
Ion drives are pretty amazing. I'm curious about what the fuel availability's like though. Xenon's not very abundant on Earth, and it's really not very abundant in space, as mentioned in the article.
Its properities are highly useful: exceptionally nonreactive, not radioactive (e.g., Radon), but a heavy atom (so good specific impulse for this class of drive, and a high mass/volume ratio).
Wikipedia says Bismuth looks promising for Hall Effect-based thrusters, and VASIMR has been tested using both Xenon and Argon, the latter of which is in abundant supply, at least on Earth. (http://en.wikipedia.org/wiki/Ion_thruster#Propellants)
Argon does make sense -- it's higher up the table than xenon -- by two rows, which tends to mean higher abundance. It's also a Nobel gas (largely inert). But a lot lighter -- atomic weight ~40 vs. 131 -- only 30% the mass per atom.
But found with natural gas as a result of nuclear decay within the Earth's crust / mantel.
The only down shot is the acceleration of an ion engine is god awful. But seems the best way to go if you don't care about time needed to get going (and slow down).
Hmm. Not sure geostationary satellites orbit at that distance, more like... 36,000km.