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

KellySt@aol.com wrote:
>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.

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

It doesn't work.  I came up with the idea (and if I wasn't the one
who suggested it, then I came up with the idea independently).

However, it doesn't work.  This is actually pretty obvious when you
do the numbers.

A cluster of in phase emitters can only acheive the emitted power/m^2
equivalent to a single emitter with an aperture of the same total
aperture area.  However, this cluster is less effective than that single
emitter in that this power/m^2 is emitted onto a smaller spot (the
rest is lost in sidelobes).

If you wanted an array to take the place of the single emitter, the
best way would be to have an array of emitters sitting "shoulder to
shoulder" in a hexagonal grid.  It still needs to be 30,000,000,000km
in diameter, with lenses flush against each other.
    _____     Isaac Kuo kuo@bit.csc.lsu.edu http://www.csc.lsu.edu/~kuo
/___________\ "Mari-san...  Yokatta...
\=\)-----(/=/  ...Yokatta go-buji de..." - Karigari Hiroshi