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Re: RE: RE: starship-design: Re: Perihelion Maneuver

KellySt@aol.com wrote:

>>> Why?  I thought everyone was prewtty comfortable with a phased array
>>> emmiter
>>> cluster?  (See details in recent Fuel/Sail is dumb responce)

>>Its not that I don't think it will work as advertised as far as beaming 
>>power to a sail,

It doesn't work as advertised.  If you have a bunch of emitters, they
are most effective when "shoulder to shoulder".  Spreading them apart
in an attempt to decrease spot size will _reduce_ the amount of power
reaching the target.

>>what I am not comfortable with is station keeping, ALL of 
>>the components of the system will experience thrust as a direct result of 
>>the power being transmitted. The laws of physics can't be thwarted, it will 
>>still require as much or more reaction mass as any other concept (probably 
>>more) the only difference is that it isn't necessary for the fuel to be 
>>aboard the vehicle.

This actually isn't a concern.  The effect of thrust is inversely
proportional to mass, and the emitters are VERY HEAVY compared to
the thrust they emit in beams.

This should be intuitively obvious.  If you had a laser emitter which
could impart decent thrust on itself, you could use _that_ as a photon
rocket.  (Then you wouldn't even have to worry about focussing the
beams and you could use it for deceleration also.)

The real concern is whether you can build that the huge honking
emitter (or emitter array) in the first place.  It's dizzyingly
massive and big.  If you can build it, then it's not going to go
anywhere just because of the (relatively) puny beam it emits.

>At least the fuel/sail system itself seems prety solid and relyable.  No cryo
>tanks or unstable fuels.  Pretty simple brute force tech.

You can say Forwards pure sail system is also "simple brute force tech".
Actually, it requires much less technology than this "fuel/sail" idea.
It doesn't require exotic fusion technology.

However, the sheer size of that "brute force" is inconceivably massive.

Especially when you consider that a modified design would only require
a fraction of a percent of the effort.
    _____     Isaac Kuo kuo@bit.csc.lsu.edu http://www.csc.lsu.edu/~kuo
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