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Re: starship-design: Re: Go Starwisps

In a message dated 6/30/97 4:14:42 AM, TLG.van.der.Linden@tip.nl (Timothy van
der Linden) wrote:

>>>>I used to agree with this.  But given you can probably gain about the
>>>>amount of info via super sized telescopes, and the robots would report
>>>>for decades (by then the whole projects likely to be obsolete).  I'm
>>>>woundering if robot probes aer very usefull?
>>>First of all you'd need rather big telescopes to resolve something like a
>>>meter. Note that big can also mean two telescopes far apart (big means
>>>something like 1E10 meters).
>>>This number doesn't take into account that the telescope has to gather
>>>enough light to make a visible image. It is likely that the two telescopes
>>>that are far apart still need to be much bigger than anything we have on
>>>Earth to give a bright enough image.
>>How about thousands of scopes over hundreds or thousands of miles?  ;)  If
>>can mass produce striped down hubble telescopes.  ( Say simple optics for a
>>couple million dollars each?  Like clemmintine technology.)  Launch a
>>thousand scattered over hundreds of thousands of miles of space.
>OK let me show:
>sin(theta)=1.22 lambda/a
>sin(theta) is approximately equal to theta
>theta is apparoximately equal to d/R
>d/R=1.22 lambda/a -> d=1.22 R lambda/a
> theta =diffraction limited beam convergence angle
> r     =separation between light source and telescope
> d     =detail you like to be able to resolve (meters)
> a     =diameter of the aperture
> lambda=wavelength to be observed
>You suggest an aperture of say 3000 miles = 5.556E6 meters
>lambda of green light 530 nm= 5.3E-7 meters
>distance of 10 ly = 9.46E16 m
>d=1.22 * 9.45E16 * 5.3E-7 / 5.556E6 = 1.1E4 metres
>So the maximum detail would be roughly 11 kilometers. Enough to see clouds,
>mountains, lakes, (cities). But not enough to see trees, (villages).
>>>Besides that having more detail is useful for the mission, it might spark
>>>imagination of Earth's population and get some extra money.
>>The photos would spark public interest.  
>Well, with your huge telescope, the best picture they could produce for an
>Earth sized planet would be a total planet image of about 1200x1200 pixels.

Actually The largest scope I mentioned was Hundreds of thousands of miles
across.  Thou the calculations are a good Idea.  To a degree you could scale
up the scopes to any size nessisary.  How big would it need to be?