[extropy-chat] next generation of ion engines

[deimtee]

Adrian Tymes wrote:

>Hmm.  The stats on it as listed at
>http://www.estec.esa.nl/conferences/FPD/info/eui-act20051215.pdf
>suggest that you could get up to a full Newton of thrust with
>100 cm^2 of grid.  I wonder how light one could build an engine
>that size?  If one could also find a battery or capacitor
>capable of delivering 100 kW over 10-15 minutes, such that
>battery/capacitor plus grid was less than a kilogram total mass,
>one could use this for ground launches.  (Some googling seems
>to indicate that said amount for the energy storage alone - at
>about 17-25 kWh/kg - it either well beyond or about at the limit
>of current technology, and that's not including the engine's
>mass.)
>  
>

Uh, no.

It takes about 10 newtons to lift a kilo against 1 gee.
You would have to get the mass under 100 grams just to lift off.

However,  how about if you dropped it off SpaceShipOne at apogee?
How much time have you got to give it orbital velocity before drag 
exceeds thrust?

also,
I think you are a bit optimistic on the battery too.

100kW * 10 min = 16.666 kWHrs
Thats about the same as a 12 volt battery delivering 1400 amps for an hour.

I want some of those for my electric car.   : )
 
- deimtee.