[ExI] specific thrust

spike spike66 at att.net
Sat Dec 11 04:06:36 UTC 2010

> ... On Behalf Of Adrian Tymes
>>If it's just a matter of exhaust velocity, what about ejecting stuff at
100+ km/s?
>> Sure, but where do you get all the energy?

>Bring a lightweight nuclear power plant?  (Shielded from the exhaust,

Feynman suggested the concept in 1941.  NASA has managed to get drives that
could be hauled into orbit that are capable of sending an ion stream all in
the same direction with a velocity at around 30 km/sec.  This would provide
enormous *specific* thrust, but the total thrust is in the milli-newton
range.  So you could eventually use something like that to navigate in
space, but it requires patience.  It could be scaled up, but everything
scales together.  So haul this up to LEO, then use the ion drive to
accelerate to escape velocity, which might take a couple years, then off you

We have orbited experimental ion drives.  They work as advertised, but as I
vaguely recall the solar cycle of 1990 peaked a little higher than expected,
which expanded the upper atmosphere, causing a bit more drag on the
satellite than anticipated, so it ended up re-entering with ion drives
screaming full throttle continuously for several months before the fiery
end.  That ion drive was an experimental tag along on another satellite as I
recall, don't have a reference.



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