starship-design: Beamed Power (was: Perihelion Maneuver)

["L. Parker" <lparker@cacaphony.net>]

On Monday, December 01, 1997 7:50 AM, Isaac Kuo [SMTP:kuo@bit.csc.lsu.edu] 
wrote:
>
> 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.

I don't recall having ever seen anybody claim that the array was as 
powerful or as efficient as a single huge emitter, then again I have never 
seen anyone suggest that we should build a single large emitter either. 
Just exactly what point are you arguing? That we should build one large 
emitter? Or that we should give up the whole idea just because the 
efficiency of the array is less than a single large emitter?

> 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.

Isaac, this isn't like you, you didn't do the math!

> 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.)

Ibid. (What is intuitive is that if it can impart decent thrust to the 
sail, then it must also be imparting an equal amount of thrust to itself. 
Total net acceleration in the system has to be zero.)

> 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.

Ibid.

Isaac, I can rarely fault the technical correctness of your arguments (you 
usually take the time to at least do the math), but you seem to take off on 
minor tangents that really have no bearing on the original topic. NASA, JPL 
and a host of others seem thoroughly convinced that the concept will work. 
All of these people are specialists in this field with published papers and 
the respect of their peers, I see no reason for us (a bunch of amateurs) to 
pursue this argument any further.


Lee

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"Extraordinary claims require extraordinary evidence." - Carl Sagan