This is interesting; I've learned stuff because of this.

Not that it's practical, but what could Hubble see? The first question would be can it be positioned to stare "down", and then how well would it see something that close and fast?

--STeve Andre' wb8wsf en82

On Thursday 15 October 2009 08:57:59 Tim - N3TL wrote:

Please see Page 19 of the May-June 2008 issue of The AMSAT Journal.

Patrick Seitzer, WA4DSR, provided a photo of AO-40 taken by the University of Michigan's Curtis-Schmidt Telescope at Cerro Tololo Inter-American Observatory in Chile. Following is information from a University of Michigan Web page about the telescope:

"The Curtis-Schmidt telescope is a 0.61 meter aperture f/3.5 Schmidt telescope located at the Cerro Tololo Inter-American Observatory, about 500 km north of Santiago, Chile. This telescope was originally installed at the University of Michigan's Portage Lake Observatory in 1950, and moved to the much clearer skies of north central Chile in 1966. It is named for Heber D. Curtis, Director of the University of Michigan Observatories from 1930 until 1942. The telescope is dedicated to optical studies of artificial space debris for NASA's Orbital Debris Program Office at the Johnson Space Center. Projects include optical surveys for debris and follow-up observations to determine orbits and photometric properties of recently discovered debris."   If you find the Journal photo, you'll see a field with dozens of blurred stars and one sharp litttle white dot, which is AO-40.  I believe it's safe to say that obtaining an image with the detail necessary to try assess damage is impossible.   73 to all,

Tim - N3TL

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From: Mark VandeWettering [email protected] To: [email protected] Sent: Thursday, October 15, 2009 2:57:40 AM Subject: [amsat-bb] On the possibility of imaging AO-40 with earth bound telescopes...

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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.

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With modern telescopes such as http://www.refractortelescopes.co.uk/reviews/orion/orion-shorttube-80-a-refr... 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...

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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.

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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 _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb

At 04:56 AM 10/16/2009, Alan P. Biddle wrote:

Getting an image is clearly possible, but only if you can get a certain agency known by its initials to do it.

I offer a different opinion. We know how large the primary mirror (optical aperture) of these spy satellites are, because we know how big the launch vehicles are, and the satellites had to fit into the launch vehicles. Therefore, I believe they are no larger than Hubble. Therefore, I figure the spook agencies can't actually help us.

Someone earlier offered a calculation of the resolution Hubble could achieve when imaging AO40, based on the aperture, and the minimum possible distance, given the orbits of Hubble and AO40. The answer was 5", which just isn't really good enough to see what may have happened.

Because the distances are large, and because we have no hope of any telescope that's gonna fly up next to AO40 to take a close look (unless we build & launch it ourselves!), all existing single-aperture telescopes seem to be unable to do the job.

Seems to me that the only technique which could have a chance is interferometry. At radio frequencies we're familiar with phased array antennas where signals from multiple antennas are combined coherently. Doing this at optical frequencies always seemed impossibly difficult to me, so I figured I would never see it.

In recent years however those darn astronomers have started doing optical interferometry. They've imaged the surface of stars, measured the sizes of extrasolar planets, etc. Some of their images appear to indicate sub-milli-arcsecond resolution.

Two of these instruments are CHARA and COAST.

CHARA... http://www.chara.gsu.edu/CHARA/ See the two detailed documents on CHARA by clicking on the links labelled "here and here" about half way down the page.

COAST... http://www.mrao.cam.ac.uk/telescopes/coast/handout.html

I wonder if this sort of instrument could image a satellite?

There are of course a large number of practical engineering considerations. These machines require bright objects. A satellite in sunlight is pretty bright. Enough? Satellites require rapid tracking. I doubt they designed these machines to do that. The satellite is likely tumbling, so maybe you can't correlate or average data taken over a few minutes or even seconds apart. I don't know what exposure times would be required. Etc etc. I don't know the answer to any of these questions, or even how to go about figuring out the answers.

Having said all this, I suppose it is possible that the spooks have done the engineering to make multiple optical satellites work together as an optical interferometer, and therefore have the high resolution capability that we need, but I am guessing that they have not (yet). (Just look at all the work the ground-based astronomers have done to make this work with a huge machine nailed down to the ground. Just doesn't look ready for space yet!) And even if the spooks had done this work, they wouldn't give it away (yet) by showing us pictures.

So, back to the non-spook world, could a machine like CHARA or COAST image a satellite?