[amsat-bb] Re: Malaysian airliner puzzle

[Franklin Antonio]

At 12:40 PM 3/17/2014, Bruce wrote:
>i am sure that the u.s. as well as other countries have spy 
>satellites that have been taking pictures 24/7 with resolution that 
>can see a person on the ground. that being said, i would further 
>venture to say that none of them will want to show pictures of the 
>jet as it would give away their secret ability.

Hey, good to see a post that's on topic.  Satellites!

Actually, the capability is not very secret.  Its pretty much out in 
the open.  Although every nation keeps the details secret, but you 
don't need details to understand what kind of a picture is 
possible.  Physics will tell you that.

You can calculate the resolution of a spy satellite.  Its just 
physics.  You know the diameter of the aperture (lens or 
mirror).  You know that because dimensions for many classified 
objects have been published.  Also you know the diameter of the space 
shuttle's payload bay.  You know the wavelength of light.  Simple 
formula gives you the resolving power as an angle.  To turn that into 
the size of an object you need to know a distance.  You can look up 
the orbits of many classified satellites, so know how far away they 
are.  But because you get more resolution by being closer, you know 
the best pictures will come from low orbit, and here the limit is the 
Earth's atmosphere.  No need to know classified orbit data.  Just 
presume there are some spy satellites in low but stable orbits, 
perhaps 300 to 500 km.

So, yes, they should be able to see something smaller than a person, 
but here's the kicker... They can't do that everywhere at 
once.  Because they are in orbit close to the earth, they can only 
see stuff that's under them.  This is a tiny fraction of the 
earth.  Also, within that area, you have to tell them where to 
point.  A simple number-of-pixels thing.  Looking at the whole 
footprint at max resolution would be an enormous # of pixels.  We 
would have to guess the limit, but its not hard to guess that the 
maximum image is way smaller than the footprint.  This is great for 
taking pictures of your opponent's military installations, and maybe 
even seeing what assets there come and go over time, but it is 
unlikely to be of help in tracking an airplane that unexpectedly 
flies some unknown path to some unknown location.

Also, the plane flew at night, in the dark.

I'm sure the big boys are thinking about new capabilities as we 
speak, and writing them into next year's budget!