[amsat-bb] On the possibility of imaging AO-40 with earth bound telescopes...

Mark VandeWettering kf6kyi at gmail.com
Wed Oct 14 23:57:40 PDT 2009

> Has there been any serious attempt to take a photograph of the damaged
> bird using ground based optical telescopes while it is in sunlight ?

It's not going to work.   AO-40 just isn't big enough.   For fun,
let's worth through
some of the details.

> With modern telescopes such as
> http://www.refractortelescopes.co.uk/reviews/orion/orion-shorttube-80-a-refractor-telescope/
> or similiar and a modern digital camera and a known RA/DEC co-ordinate
> of the satellite at any point in its orbit, it should be possible get
> a fairly decent picture of what is still up there...

> Note RA / DEC are astronomy co-ordinates which should be able to be
> calculated from AZ/EL or TLE, but I may not be able to do it myself.

> We don't need to track it, but just to image it in several consecutive
> frames. From: http://www.emergentspace.com/pubs/AIAA_GNC_2002_AMSAT_A040.pdf

Table 1. Nominal Orbit Parameters for AO-40
Orbit Parameter Value
Semimajor Axis (km) 36,245
Perigee Height (km) 1,042
Apogee Height (km) 58,691
Eccentricity 0.797
Inclination (deg) 6.04
Period (hours) 19.1

Let's look at a couple of potential telescopes.  The short tube
refractor that you linked to has an 80 mm (roughly 3 inch) aperature.
According to the Rayleigh criterion, that scope should be able to
resolve angles as small as about 1.5 arc seconds.    At perigee, the
resolving power is 1042000 * tan(1.5 arc seconds), or about 7.5 meters
(or 25 feet).    To increase the resolution by a factor of 2, you need
to to double the  aperature.   To get resolutions down to 1/2 a foot,
you need an aperature 50x larger, or 150 inches.

This doesn't take into account any effects of atmosphere either.
it's actually fairly rare to get sub arcsecond resolution from any
earthbound telescope without using adaptive optics.   This limits the
practicality of high resolution imaging.

Impressive photos of the space shuttle, ISS and HST have been taken
using amateur equipment, but these objects are both closer and an
order of magnitude larger than AO-40.   While we might be able to
measure spin rate and the like by measuring the brightness curve,
actual imaging of the satellite isn't likely.

73 Mark K6HX

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