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RE: starship-design: Timothy's beamed power paper


> The beaming concept looks nice, but its most essential problem is
> deceleration. Using the "sail" as an energy collector to power some engine
> (Kelly has a "simple" solution for that too) is the only option besides a
> retro-reflection-mirror.

[L. Parker]  I was assuming that the first trip would use some other method 
of braking, perhaps a combination of magnetic and solar sail braking. 
Subsequent trips could use lasers built by the first trip.

> The power density of the beam should compensate for this. I believe that I
> did some calculations when we thought about scooping hydrogen. I remember
> that even using rediculous big scoops we could not scoop more than a few 100 kg.
> To this problem more transparant: Even if we encounter as much mass per
> second as the ship itself, it will only half the acceleration.
> And if we encounter that much mass, then I'd rather not be in that ship.

[L. Parker]  Transmitted power density is measured in one frame of 
reference but impact density on the leading edge of the sail is in 
a different frame of reference where "mass per second" is measured 
with a relativistic shift. You will have a laser behind you and the 
equivalent of an x-ray laser in front of you (I know, its not really 
a laser because it isn't coherent) for that matter there will be an 
opposite relativistic shift on the beam which will further lower the 
terminal velocity.

> My suggestion was to use part of the beam to blow clear the path. We may
> re-route a part of the beam to a more divergent beam which will push the few
> atoms in our way to the side.

[L. Parker]  Not a bad idea. They use a similar technique with high 
energy lasers in the military, a short burst in front of the main 
shot creates a sort of temporary vacuum which reduces beam scattering 
in atmosphere.

Lee Parker
                                                          (o o)
When I die, I want to go peacefully, in my sleep, like my grandfather...
not screaming like the people in his car.