
Neumann Space Ion Engine Sets Record for Specific Impulse - jcr
http://www.neumannspace.com/p/science.html
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Gravityloss
One big note up front! Electric propulsion engines are usually not specific
impulse limited!

Your power source mass dwarfs the reaction mass ("fuel") really quickly.

Basically, for equivalent thrust, with twice the specific impulse you require
half the fuel but double the power.

So often with electric propulsion you get a better, lower spacecraft mass by
using lower specific impulse! This means more reaction mass but smaller solar
panels / power electronics.

That's why things like hall thrusters are used, with ISP around 1000s compared
to 3000 s gridded ion engines.

Maybe for a Venus or Mercury mission where you have plenty of power and need
large delta vees...

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Symmetry
That just what I was going to say, but probably put better. Another important
metric for electric propulsion is how reliable they are - that is how long you
can run them before they burn out. The fact that they're eroding the cathode
intentionally might mean this form of propulsion could do well on that metric
but only testing will tell.

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Symmetry
I guess that means that it would be good for satellite station keeping?

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personjerry
In case it wasn't clear, specific impulse is more or less equal to fuel
efficiency for spacecrafts (higher is better).

My experience playing Kerbal Space Program, if accurate, suggests that such an
engine is more effective for longer term missions, because the increased SI
comes at a cost of lower max thrust (I.e. it takes longer to accelerate); I
suspect this is not very accurate IRL as all our missions take a very long
time so this problem may be irrelevant. Also looking below it seems such an
engine is limited by electric power (solar panel/battery).

Hence this leads me to believe this type of engine allows us to extend the
range of our missions but at the cost of longer mission durations.

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outworlder
> My experience playing Kerbal Space Program

KSP's ion engines are WAY overpowered to make for better gameplay.IRL thurst
is lower by orders of magnitude.

If we are talking about probes in the solar system, then the mission durations
are already long to begin with. Instead of firing a conventional hydrazine-
based thruster for a few minutes, we'll fire an ion engine for months. But, if
it takes years to get where you are going, who cares?

There are things we can't do yet, such as orbital insertions, with ion
engines. In these cases, conventional engines are better.

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david-given
Plus, as real life ion engines have burn times on the order of years, and as
KSP can't do (adequate) time acceleration while the engine is running, there's
a bit of an incentive to build high-thrust short-burn spacecraft --- I don't
really want to have to babysit a burn in real time for six months.

(This also disqualifies solar sails, which is a shame, because I'd love to
play with them.)

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outworlder
Sort of. People have figured out a way to simulate constant acceleration while
the spacecrafts are "on-rails". I believe the KSPi mod has solar sails. They
are not very realistic, but probably good enough for a game.

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robbiep
I read about this earlier this week in the campus newspaper [0] which contains
a bit more background information including that the university declined any
ownership of the invention. Good for him!

[0] [http://honisoit.com/2015/09/university-of-sydney-student-
sma...](http://honisoit.com/2015/09/university-of-sydney-student-smashes-nasa-
record-for-fuel-efficiency-mars-and-back-on-a-tank-of-fuel/)

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zump
This invention came from my former place of study. Congratulations!

