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Mag-beam to Mars?



 
 
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  #11  
Old October 21st 04, 06:18 PM
Paul F. Dietz
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Geoffrey A. Landis wrote:

It's cool to see that Robert Winglee has been awarded a NASA Institute
for Advanced Concepts (NIAC) project to develop a plasma beam to push
a M2P2 magnetic plasma sail for space propulsion. It sounds like an
excellent project which has the potential to revolutionize high
delta-V space propulsion.

I do want to mention that, in part, the concept develops out of my
previous study of a particle-beam pushed magnetic sail, presented at
the 2001 STAIF Conference:

G. A. Landis, "Interstellar Flight by Particle Beam," presented at the
Space Technology and Applications Intenational Forum Albuquerque NM,
Feb. 11-15, 2001. American Institute of Physics Conference
Proceedings Volume 552, pp. 393-396.

Coincidentally, the refereed-journal version of this article has just
come out:
G. Landis, "Interstellar Flight by Particle Beam," Acta Astronautica.
Vol 55, No. 11, 931-934 (Dec. 2004). [Copies available by request.]
It is published online via ScienceDirect: (
http://authors.elsevier.com/sd/artic...9457650400133X )



What keeps the beam from spreading, and how are plasma instabilities
(due to the energy available from the motion of the plasma beam
relative to the ambient plasma) addressed?

Paul

  #12  
Old October 25th 04, 01:32 AM
Terry
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No John, I don't think you're missing anything. There is nothing special
about Earth orbit which might magically stop Newtons Third Law "For every
action there is an equal and opposite reaction" from applying to an orbiting
M2P2 source. I too paused over this when I first heard the of proposal. A
reaction force applied to the M2P2 source might eventually slow and
potentially de-orbit the spacecraft but this is *NOT* a problem. Newton's
Third Law actually helps to keep the M2P2 source satellite in orbit.

Consider the M2P2 source satellite in circular/elliptical orbit about the
Earth (or Sun or Moon or any L1-L5 LaGrange point in the Sun-Earth or
Earth-Moon system for that matter).

For one half of the orbit the M2P2 source will have a measurable component
of velocity in a direction *towards* the magnetic sail equipped target
spacecraft at which the M2P2 source fires the magnetised plasma beam (in the
current proposal this force is in the order of a few Newtons). So a
*negative* reaction force acts on the source lowering it's radius of orbit.
(Negative because this reaction force is acting in the opposite direction of
M2P2 beam.

During the other half of the orbit the M2P2 source will have a measurable
component of velocity in the direction *away from* the target. The reaction
force still has the same direction and magnitude, but since M2P2 source has
now changed direction away from the target, this reaction force is
accelerating the source increasing the radius of orbit.

So for a complete orbit, the net effect is a (possibly sinusoidal?)
oscillation in the orbital radius of the M2P2 source about some mean orbit
radius.
Such oscillations could be attenuated by giving the M2P2 source a larger
mass, thanks to Newtons second Law "The relationship between an object's
mass m, its acceleration a, and the applied force F is F = ma. Acceleration
and force are vectors. The direction of the force vector is the same as the
direction of the acceleration vector" .

Further reading is about M2P2 can be found at
http://www.niac.usra.edu/files/libra...ee/winglee.pdf, and Newtons
Laws can be found at
http://csep10.phys.utk.edu/astr161/l...wton3laws.html

I wonder (flame retardant suit on stand by....) if the magnetic sail about
the target spacecraft can be given some airfoil like shape so that the M2P2
beam becomes akin a laminar air flow over an airfoil or wing. Achieve this
and the target spacecraft might not be restricted to a direction of travel
determined by the direction of the M2P2 beam.

Now is that right or am I missing something?

Best regards,
Terry

"Jon Berndt" wrote in message
...
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


 




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