# starship-design: Re: Go Starwisps

```Kelly,

>>>I used to agree with this.  But given you can probably gain about the same
>>>amount of info via super sized telescopes, and the robots would report back
>>>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 we
>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:

RAYLEIGH'S CRITERIA:

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.

Timothy

```