[ExI] specific thrust
deimtee at optusnet.com.au
Sat Dec 11 08:15:56 UTC 2010
On Fri, 10 Dec 2010 23:39:19 -0800
Adrian Tymes <atymes at gmail.com> wrote:
> On Fri, Dec 10, 2010 at 11:10 PM, spike <spike66 at att.net> wrote:
> > Ja, ion engines are only good for enormous specific thrust.
> Why is this?
> extropy-chat mailing list
> extropy-chat at lists.extropy.org
E = 0.5* M * V * V
Enormous specific thrust means very high exhaust velocity. That means
large amounts of energy per unit mass of exhaust. To go from an
exhaust velocity of 3km/s (good chemical rocket) to 30km/s (low end ion
engine) increases your energy requirements by a factor of 100, while
only increasing your thrust by a factor of 10.
You can't do it with chemical based power. The energy simply isn't
there. You need either nuclear, solar, or ground-based beamed power.
To get above 1G on an ion rocket would require a staggering amount of
100 ton liftoff mass
30 km/s exhaust
65 kg/s exhaust mass
300 Gigawatts energy requirement
It gets worse as your ion drive gets better.
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