[ExI] specific thrust

[Adrian Tymes]

On Sat, Dec 11, 2010 at 1:10 AM, Eugen Leitl <eugen at leitl.org> wrote:
> On Fri, Dec 10, 2010 at 10:57:35PM -0800, Adrian Tymes wrote:
>> IIRC, the main problem was a heavy power source - and there's been much
>> research since then into lighter weight power sources.  So I wonder if it would
>
> About the lightest power source is an almost unshielded reactor
> running at close to self-destruction temperature. That is a nasty,
> nasty thing.

Well yeah.  But that aside, there are lighter safe power sources
available today.

Also, the arguments about needing a lot of power for an ion engine skip the
fact that, today, we can get systems of (ion engine + power source) that deliver
positive thrust.  So why not just strap a bunch of those together?  That the
rocket might be 90+% engine is not all that different from today - and some of
that would likely be reusable as the structure of a reusable rocket.

>> be possible, using today's technology, to build an ion engine that could
>> deliver 1G+ of thrust - again, including something to power said ion engine for
>> about 10 minutes.
>
> You realize that ion engines don't work much below 100 km?

Ah, now that I did not know.  Is it not possible to evacuate the
engine long enough
to gain that much altitude?  (Though, one could use balloons to gain
mere altitude
and launch from there, using ion engines to get up to orbital speed.)