🚀 go-pugleaf

In article <990@devvax.JPL.NASA.GOV> lwall@devvax.JPL.NASA.GOV (Larry Wall) writes:

>>        [I and others pointed out diffraction, etc, limit resolution
>>         to about 5 inches]

>You guys are all assuming a big round mirror.  Now, it's true that for looking
>at faint stars you need a lot of mirror acreage, but there's plenty of light
>bouncing off of Lebanon.  You don't need a huge round mirror to get the
>aperature you want--just build a frame that will stay rigid in microgravity
>and hang several smaller mirrors on it with a common focus.  What's the
>resolution for a mirror with an effective aperature of, say 20 meters?  How
>many 1 meter mirrors would it take to get the interferometry to come out right?

Another posting suggests a larger conventional mirror.  The reason I used
2 meters in my article instead of (1) assuming a larger single mirror or
(2) assuming an interferometer is that I think neither practical.
I do not believe that the technology is available to do the right kind 
of interferometry at optical wavelengths with non-coherent sources.
A more likely method would be to launch a 3 meter mirror in 3 1.5 meter
pieces, then fit them together in orbit.  I doubt that the required accuracy
is possible now (a telescope is being built in Hawaii (??) which has 6
mirrors fitted together into one large mirror; I have heard that the 
technology to build it is quite recent and that it is not known if it 
will work).  Unless the mirror array were solid, the gaps would cause
diffraction and the result would be no better than a single mirror of 
the size of the individual components.
I chose 2 meters because I am not aware that we can launch anything bigger.
Does anyone know what the size of the Titan II(I) is?  
Does anyone know what the diffraction limit is for 3 mirrors, in an
equilateral triangle [so no preferred direction], with a common focus ?



  --John Carr