Re: Resolution of synthetic aperature telescope?
- From: Jim Klein <jameseklein@xxxxxxxxxxxxx>
- Date: Thu, 08 Mar 2007 19:59:24 GMT
Phil Hobbs <pcdh@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
Brian Huether wrote:
Let's say money wasn't an object and that you could build a huge number of
large telescopes and deploy them in space to create a stable array. Would it
be possible to create such a high resolution telecope that you could
actually see the surface of distance planets? I am not necessarily talkng
about optical. I am just wondering if it is theoretically possible to 'see'
a planet with enough detail to make out features (like plantlife, etc). And
I am talking about very distant planets.
A useful rule for resolution is that to see an object of size S at a
distance R,
S/R >~ 10*D/lambda
where D is the diameter of the telescope and lambda is the wavelength of
the radiation.
Thus to see an object the size of a dog (1 m) on a nonexistent planet of
Alpha Centauri (~40 trillion metres away), using light of 1 micron
wavelength, you'd need a diffraction limited system of aperture ~ 10,000 km.
As you scale an optical design up in size, the diffraction blur for a
point source (PSF) becomes smaller, in object space, but since no
optical design has zero residual geometrical abberrations over a
non-zero field of view, these residual abberrations scale up and so
given zero mfg errors and zero alignment errors, the design, as it
scales up, becomes less diffraction limited.
Add that to the reality that there will always be mfg errors and
alignment errors and that they become more difficult to handle as the
design gets bigger, there will be a point when no $ budget large
enough will exist to pay for a large design which can keep giving you
higher resolution.
As time passes and technology improves, we get the same built design
for a smaller fraction of the GNP but there will be a limit when even
that stops yielding resolution.
James Webb is IR and not visible and that helps some as the wavelength
gets longer.
At some point in time, it will be cheaper to build a warp drive and
just go there. My guess is that this will be some time between 2100 to
2400 AD :-)
The fact that our lives are not long enough to see some of this really
cool future stuff really sucks.
Jim Klein
James E. Klein
jameseklein@xxxxxxxxxxxxx
Engineering Calculations
http://www.ecalculations.com
ecalculations@xxxxxxxxxxxxxxxxx
Engineering Calculations is the home of
the KDP-2 Optical Design Program
for Windows.
1-818-507-5706 (Voice and Fax)
1-818-823-4121
.
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