[extropy-chat] next generation of ion engines

Adrian Tymes wingcat at pacbell.net
Sat Jan 14 07:57:09 UTC 2006

--- deimtee <deimtee at optusnet.com.au> wrote:
> It takes about 10 newtons to lift a kilo against 1 gee.

...right, forgot to factor in G.

> 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?

>From http://en.wikipedia.org/wiki/SpaceShipOne_flight_17P we
know that SSO only took 24 minutes between detaching from White
Knight through apogee to landing, of which just over 80 seconds
was spent under thrust.  So the apogee-to-landing phase probably
took about 12 minutes.  Most orbital rocket launches I've
studied seem to take about 10 minutes to get to orbital
velocity.  So, you'd probably need wings or something to gain
lift while going at hypersonic speeds - and the wings would need
to be thermally protected (probably made out of solid heat
shields), because as you get towards Mach 25 you're flying not
through air but through plasma.  Which is not to say it can't be
done, just that a proper analysis is probably way in excess of
simple back-of-the-envelope equations.

I wonder, though: what would be the physics of flying through
plasma?  Could you use an M2P2-type magnetic bubble to shield
the craft from direct contact with the atmosphere, while still
maintaining enough of an airfoil shape (in the bubble, which
seems to be the shape that would then matter for lift and drag
calculations) to gain lift?

> 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.   : )

Actually, some of the sources were advanced batteries being
developed for cars.  But I did caution that that was the
optimistic end of the figures I was seeing: quite a few of the
"most advanced" figures were quite a bit more conservative than
that.  ;)

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