

The revolutionary ion engine that took spacecraft to Ceres - jgrahamc
http://phys.org/news/2015-03-revolutionary-ion-spacecraft-ceres.html

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jgrahamc
_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.

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TeMPOraL
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).

More at [http://en.wikipedia.org/wiki/Orbital_station-
keeping](http://en.wikipedia.org/wiki/Orbital_station-keeping).

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grownseed
An interesting description of Dawn's ion engine and its pros and cons:
[http://dawn.jpl.nasa.gov/mission/journal_12_06.asp#ips](http://dawn.jpl.nasa.gov/mission/journal_12_06.asp#ips)
(Marc Rayman, Chief Engineer, NASA's Jet Propulsion Lab, 2006).

~~~
everyone
"The force of the ion thruster on the spacecraft is comparable to the weight
of a single sheet of paper."

That is magnificent.

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sgt101
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.

~~~
bigger_cheese
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.

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JoeAltmaier
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.

~~~
wyager
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).

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dredmorbius
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).

Anyone know what practical alternatives _do_ exist?

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curtis
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](http://en.wikipedia.org/wiki/Ion_thruster#Propellants))

~~~
dredmorbius
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.

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curtis
There is a proposal for a manned mission to Ceres using nuclear powered ion
engines:
[http://news.nationalgeographic.com/news/2013/11/131118-ceres...](http://news.nationalgeographic.com/news/2013/11/131118-ceres-
asteroid-solar-system-space-science/).

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jjwiseman
Deep Space 1, the first spacecraft to use an ion drive, also had Lisp on
board: [https://baltazaar.wordpress.com/2009/07/20/a-story-about-
lis...](https://baltazaar.wordpress.com/2009/07/20/a-story-about-lisp-remote-
debugging/)

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LaneRendell
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).

