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How accurate are satellite location predictions?

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#1 azure1961p

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Posted 11 September 2013 - 01:08 PM

Say Satellite XYZ is said to be passing Vega at 9:00pm - just how close to Vega are these typical predictions? Can I "hang out" by a star waiting at 100x and then follow from there or do I need to spot it first in my finders 8x50 wide field?

Thanks in advance guys!!!

Pete

#2 David Knisely

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Posted 11 September 2013 - 05:40 PM

Say Satellite XYZ is said to be passing Vega at 9:00pm - just how close to Vega are these typical predictions? Can I "hang out" by a star waiting at 100x and then follow from there or do I need to spot it first in my finders 8x50 wide field?

Thanks in advance guys!!!

Pete


With good current orbital elements, a good set of location coordinates (your latitude and longitude to the nearest arc second or so), and the proper software, the predictions are pretty much spot-on (usually well within a degree or so of where they are predicted to pass and within a minute of the stated times). I have used Heavens-above.com for Iridium flares and they agree pretty closely in both position and magnitude to what I see with my eyes. In fact, if the brightest location for the flare is shown to be within a few miles of me, I like to travel right to "the centerline" to get the maximum flare effect (it is a little like a small searchlight being thrown at you). A magnitude -8.6 Iridium flare has to be experienced to be believed! The ISS passes I have used to view the station in my telescope have also been well predicted by Heavens-above. I would still recommend using a wide-field eyepiece or the finderscope to get on the track of the satellite rather than just waiting for it to go through the field, but otherwise, the predictions tend to be pretty good. Clear skies to you.

#3 obin robinson

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Posted 11 September 2013 - 06:32 PM

The accuracy of the predictions depends often on the accuracy of your location input. I have my lat/long and altitude down to within 1 meter accuracy. If i go to a remote site I adjust my location information to correspond to where i am observing satellites that night. I have found the information to be exact within a second or so. The TLEs for some satellites are computed very exactly and updated on a regular basis. As long as your TLEs are fresh and your location info is exact you will find your satellite obervations to be exact as well.

Have you ever wondered how some of these TLEs, especially for classified satellites, are obtained offhand? There are observers in the southern parts of africa, south america, and australia that use very sensitive cameras in large newtonian telescopes. They just aim at the celestial pole and keep track of everything that zips by that night. Using some fairly straightforward plate solving software they can generate TLEs that are extremely precise. Much to the disappointment of intelligence agencies and militaries worldwide: satellites have to follow the rules of physics. Not even stealth features can hide a satellite as long as the laws of physics are in motion.

obin ;)

#4 azure1961p

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Posted 11 September 2013 - 10:05 PM

Obin,

First - thank you very much for a very informative reply. And - yes I HAVE wondered how the classified stuff gets its predictions for orbital passes overhead. Its a little funny quite frankly. I'm slowly wading into say observation. I will say Im floored that done days are magnitude 32!!!!! I've got a vision of some small tabling box tens of thousands if miles away spray painted flat black. Magnitude 32 - that's astounding.

The faintest Ive seen are around 13 with my 8" and moving along at a good clip. The ones that fluctuate are particularly captivating.

Thank you very much for the tips and tricks of positional accuracy!

Pete

#5 obin robinson

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Posted 12 September 2013 - 07:31 AM

No problem at all. If you want to get an idea of how accurate and powerful the software and cameras are take a peek into these posts:

http://www.satobs.or...-2012/0142.html

http://www.satobs.or...-2009/0117.html

That is just a typical "data dump" from the people who track satellites on a nightly basis. Nothing can hide from a camera, telescope, computer software, and the laws of physics.

obin :cool:

#6 azure1961p

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Posted 12 September 2013 - 09:43 PM

David,

Thank you for your input here , its greatly appreciated. Ill probably try with my Ranger first at 18x and go from there. I've to date never seen an Iridium sat flash. It'd be accidental if I chanced upon it as I have nt yet tried for them. The ISS was dumb luck on my part . Flew straight over head and I happened to have my 8x42s. The serendipity of the zenith pass is an observing buddy from years back actually imaged it as I was watching it and emailed the confirmation to me. With 8x42s - you knew it wasn't stellar appearing but actual shape was elusive - extended but unear.

Again thanks!

Pete

#7 Muffin

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Posted 28 September 2013 - 03:10 AM

Morning Obin
If you follow classified satellites then you will know who I am - Im the observer in South Africa that you see posting to SeeSat from time to time - incidentally we dont have a classified satellite observer in South America and the one in Australia who observes fairly seldom. Afraid you have the technique wrong as regards aiming at the celestial pole - I think you meant celestial equator since this is where the geostationary and near geostationary satellites may be found. For leo sats one of course observes where ever the satellite will be in the sky. As regards plate solving software I use a very sophisticated program that is not in general use by western observers since it was designed for the ISON network ( International Satellite Observing Network) for use with their systems - I have one of the CCD cameras used. As to accuracy of the amateur classified tracking network - depends to a great deal on how often the satellites are observed. Since we are spread pretty thin around the world some seasonal satellites might not be observed for sometimes months so time accuracy will be very poor - especially if the satellite should execute any orbit changes. Then we have the more "difficult" satellites in highly eccentric orbits and low inclinations that cannot be tracked by the US Radar fence stretching across the United States at about latitude 33 degrees N or so (NAVSPASUR) - any satellite with an inclination less than 33 degrees cannot pass through the fence, and with very low perigees - sometimes as low as 100 kms or so, the atmospheric drag plays havoc with predictions and then we have problems with lunar perturbations etc out at apogee -- all in all a fascinating hobby ! Cheers Greg Roberts Cospar station 0433 near Cape Town,South Africa.

#8 obin robinson

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Posted 28 September 2013 - 06:14 AM

Morning Obin
If you follow classified satellites then you will know who I am - Im the observer in South Africa that you see posting to SeeSat from time to time - incidentally we dont have a classified satellite observer in South America and the one in Australia who observes fairly seldom. Afraid you have the technique wrong as regards aiming at the celestial pole - I think you meant celestial equator since this is where the geostationary and near geostationary satellites may be found. For leo sats one of course observes where ever the satellite will be in the sky. As regards plate solving software I use a very sophisticated program that is not in general use by western observers since it was designed for the ISON network ( International Satellite Observing Network) for use with their systems - I have one of the CCD cameras used. As to accuracy of the amateur classified tracking network - depends to a great deal on how often the satellites are observed. Since we are spread pretty thin around the world some seasonal satellites might not be observed for sometimes months so time accuracy will be very poor - especially if the satellite should execute any orbit changes. Then we have the more "difficult" satellites in highly eccentric orbits and low inclinations that cannot be tracked by the US Radar fence stretching across the United States at about latitude 33 degrees N or so (NAVSPASUR) - any satellite with an inclination less than 33 degrees cannot pass through the fence, and with very low perigees - sometimes as low as 100 kms or so, the atmospheric drag plays havoc with predictions and then we have problems with lunar perturbations etc out at apogee -- all in all a fascinating hobby ! Cheers Greg Roberts Cospar station 0433 near Cape Town,South Africa.


Thanks for posting that! I can't believe I wrote celestial pole. I meant celestial equator! Brain and fingers were on two different channels. :foreheadslap:

Cheers from Space Center Houston and home of the ISS.

obin :cool:

#9 azure1961p

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Posted 05 October 2013 - 10:37 PM

Greg,

Thank you for a very informative post. I look forward to reading more.

Pete






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