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

In a message dated 11/18/97 4:03:33 AM, lparker@cacaphony.net wrote:

>On Monday, November 17, 1997 11:23 PM, Isaac Kuo [SMTP:kuo@bit.csc.lsu.edu] 
>> No, it still needs a fresnel lens.  Without it, diffraction limits
>> are too severe.  The beam needs to fall on a spot 1km wide at a
>> range of 30,000,000,000km.  With a wavelength of 1mm, that requires
>> an aperture around 30,000km wide.  Don't tell me you're going to
>> make a microwave laser that big.
>Unless, I totally misremember, a Fresnel lens is a diffraction device not a 
>reflection device. It won't work with microwaves unless you are going to 
>make it out of about a zillion miniature waveguides...
>Its irrelevant anyway, a Fresnel lens cannot be built that will function as 
>advertised, so if you are correct about the aperture (and I suspect you 
>are, but I will run the equations when I have more time) then you can 
>forget a maser powered sail. Or a maser powered anything for that matter.

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