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In article ,
"Jon Berndt" wrote:

In this article on MSNBC.com:

http://www.msnbc.msn.com/id/3217961/

"At the start of the trip, the [near-] Earth station would focus
its particle beam on the magnetic sail of a Mars-bound space taxi,
pushing it to speeds of tens of thousands of miles an hour. During
the approach to Mars, the Red Planet station would fire its own
beam to decelerate the spacecraft."

Nowhere is mention made that this particle beam causes any "equal
and opposite" action at the particle-beam source. If this
near-Earth station is blasting a particle beam into space that
causes a spaceship to accelerate (momentum transfer) to "tens of
thousands" of mph ... what is the source doing to maintain position
or orbital velocity? Am I missing something?

Jon

One of the summaries I saw made mention of an interaction between the
particle beams, a type of solar sail and the solar wind. Perhaps that
is the key.

Alternately, the developers - as theoreticians rather than engineers,
forgot that inconvenient little F=ma thing . . . :-)
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--
Herb Schaltegger, B.S., J.D.
"Never underestimate the power of human stupidity."
~ Robert A. Heinlein
http://www.angryherb.net