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Re: starship-design: Hitching a Ride on a Magnetic Bubble
In a message dated 10/5/00 10:24:13 AM Pacific Daylight Time,
> I thought you'd be interested in this story from Science@NASA:
> NASA-funded scientists are experimenting with miniature magnetospheres as
> an innovative means of space transportation. If the group succeeds,
> next-generation spacecraft may come equipped with fuel-efficient magnetic
> bubbles that speed their occupants from planet to planet and ward off the
> worst solar flares.
> <A HREF="http://science.nasa.gov/headlines/y2000/ast04oct_1.htm?friend">
> Hitching a Ride on a Magnetic Bubble </A>.)
Partial quote from link
"The solar wind's force per unit area decreases as the square of the distance
from the Sun. Doubling the distance, for instance, decreases the solar wind
pressure by a factor of four. "The solar wind is weaker far from the Sun, but
the bubble is bigger, too (precisely because the solar wind pressure is
lower)," he continued. "It so happens that the cross section of the bubble
increases by the same factor that the solar wind pressure declines. The two
effects completely cancel." It seems amazing, but the propulsive thrust of an
M2P2-powered craft remains the same whether the spacecraft is near the Sun or
in the outer reaches of the solar system.
" end partial quote
I would have to examine the math. On the surface It seems to violate the laws
of conservation of momentum. P=mv, so the momentum of the push force must
equal the momentum of the accelerating object. I do not see how the bubble
getting bigger cancels the inverse square law that determines the push force
in relation to the acclerating object bubble field size. In other words, I am
not convinced the area exposed to the solar wind by increased bubble size is
an equal size inverse square function as claimed. Bubble size may indeed have
some linear effect, but not to the exponential extent claimed.
Do you have any more math data on the subject?
It seems clear to me using the powering energy of the sun being it light,
electro or magnetectic field providing the energy. The inverse square law
limits the practicality as the observed sun grows dimmer and smaller wrt to
the bubble. For the conservation of energy or momentum to balance on both
sides of the equation, an added energy source would be in order.
Energy added to the bubble from internally aboard the craft may be required
to cancel the remainder of the inverse square function. If so, that energy
must come from an increased mass aboard the ship which puts you back to
square one and a decrease in velocity as P remains equal to mv.
Until I am shown the error of my ways I will stick to action/reaction engines
blowing exhaust out the back as they are practical for star journeys. Solar
power just fizzles out any signifigant distance from the sun.