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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, 
curtismanges@netscape.net writes:

> Hi!
>  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.
>   http://science.nasa.gov/headlines/y2000/ast04oct_1.htm?friend
>  (or
>  <A HREF="http://science.nasa.gov/headlines/y2000/ast04oct_1.htm?friend">
>  Hitching a Ride on a Magnetic Bubble </A>.)

Hi Curtis,
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.