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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.

Solar braking is out of the question, the beam we use is much more
concentrated than solar light at a save distance.
Magnetic braking will need thousants (probably much much more) of miles of
(heavy?) conductive wires, and you'll probably not be in a strong enough
magnetic field for a long enough time.
I'd think this has been said several times before.

>[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.

True there is that reverse dopplershift, but I don't think the impacting
molecules at the front will form anything like a dense wall, unless we get
very close to the speed of light. For our vessels, the doppler shift is not
likely to exceed a factor 10.

>> 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.

Bummer, I thought I was the first to think of this ;)
Glad to know it works though.