Help with maths on ISS imaging please.

[michaelmorris]

I've just read an article in the April/May edition as AstroPhoto Insight magazine about imaging the ISS.

AstroPhoto Insight

It talks about tracking the ISS to image it. I wondered if I should start off by trying to simply capture it with my Toucam Pro II as it whizzes through the field of view on my 8" LX200. However, by my (probably very shaky) maths I reckon that this will give me a maximum of 1 frame containing the ISS in the capture if I capture at 10 frames per second.

Here is how I've calculated this.

The ISS is approximately 40 arc seconds across.

The field of view of my Toucam Pro II at prime focus on my 8" f10 LX200 is 4.7 x 6.3 arc minutes (taken for CCDcalc software). At 0.58 arc seconds per pixel, this will give me an image of the ISS approximately 40/0.58 = 69 pixels across - not bad.

The apparent motion of the ISS across the sky is around 67 arcminutes per second.

Thus, if one assumes that the ISS passes through the short axis of the chip (4.7 arc minutes), the ISS will pass through this axis in 4.7/67 = 0.07 seconds. As the frame rate is 10 fps (1 frame in 0.1 seconds), it is entirely possible that no frames will be captured.

If I add my f6.3 focal reducer the field of view for the Toucam Pro II in my 8" LX200 widens to 7.5 x 10.1 arc minutes. At 0.92 arc seconds per pixel, this will give me an image of the ISS approximately 40/0.92 = 43 pixels across – still quite good.

Again, if one assumes that the ISS passes through the short axis of the chip (7.5 arc minutes), The ISS will pass through this axis in 7.5/67 = 0.11 seconds. At the 10 FPS frame rate (1 frame in 0.1 seconds), it should be guaranteed that I will get at least 1 frame.

Does this maths stand up?

I know that going for a higher frame rate will give me more images, but with a Toucam Pro II image quality falls off a cliff at frame rates above 10 fps.

[Psychobilly]

Join the sattracker yahoo group to get the software and be prepared to be amazed how fast your scope can move...

Good cable managment add nerves of steel required... oh and a few dry runs in advance to make sure nothings going to get snagged up...

Make sure your pc is time synced and you update the TLE's about an hour before the pass...

All good fun...

Peter...