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SS5 Pro | Telescope Tracking Satellites?

Originally from ticket #27348.

Dear Sir, dear Madame,

I have the SKY SAFARI 5 PRO version 5.0.2.11 on my I-pad + SkyWire and i would like to know if with this version it is possible to track the ISS with my 8" Skywatcher Dobson Go-To telescope.

 

Bill Tschumy replies:

Freddy,

Sorry, but no. Tracking satellites is hard, in part because they can move so fast. Most mounts just can't keep up with them. We have put a bit of effort into adding satellite tracking for some mounts, but it has not been released.

Bill Tschumy
SkySafari Developer

14 comments

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    Martin A. Sebestyen

    Bill,

    what are the mounts that will be supported by Skysafari for satellite tracking and when will this function be released ?

    Regards

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    Bill Tschumy

    We are making no promises that this will every be released.  It is just some experimental code right now.  I think Tim was trying this with one of the Celestron mounts but I don't know which.

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    Tim Campbell

    This is an older post, but I thought I'd add to it.  There are are a few issues that make this a bit difficult.

    First... most telescope mounts have tracking rates designed to track at standard sidereal rate (about 15 arc-seconds per second) because that's the the rate at which the Earth spins... so as the Earth spins one direction, the telescope mount rotates in the opposite direction and at the exact same rate and this cancels out the spin of the Earth leaving your telescope fixed on your target.  

    But since the moon is relatively close, actually makes noticeable progress (relative to the background stars) over the night.  So if you are studying the moon, a standard sidereal tracking rate would cause the moon to eventually drift out of view.  So most mounts have a lunar tracking rate as well.  

    If you pick any deep-space object, you get 'sidereal' speed and if you pick the moon you get 'lunar' speed.  

    But satellites are a problem because they have different tracking rates depending on their orbit.  The majority of mounts do not have programmable tracking rates... but some mounts do have programmable tracking rates.  

    There's a PC program called "Satellite Tracker" (it's very old - designed to work with Windows XP and I have no idea if it was updated to work in newer versions of Windows) and IF your mount has programmable tracking speeds, then it can use that to track the ISS.  It is able to use my LX-200GPS telescope (which does have programmable tracking rates).  Also, some mounts have variable slew speeds and the computer can program a series of successive go-to commands... it's sort of a connect-the-dots way of tracking the satellite by picking several points in the sky that on the satellite's orbit and telling the scope to go-to each of them.  This causes the mount to basically "leap frog" it's way across the sky... the scope moves a little faster than the ISS and the ISS then catches up and passes that point, then the scope "leap frogs" to the next point, and so on.  

    The next problem has to do with the accuracy of the orbit data itself.   The orbit of satellites isn't quite as stable as you might guess.  The ISS orbit regularly decays, and when a service module docks with the ISS to bring up more supplies or fresh astronauts, they can give the ISS a bit of a push to take it back into a higher orbit and cancel out the decay.  Without these periodic pushes the ISS would eventually crash back into the Earth.   The point is, the ISS orbit is ever-changing.  If you're going to try to view the ISS with a telescope and at high power, you've got to nail the position of the ISS accurately, to within a very tiny tolerance of time.  If you try to use orbit data that hasn't been updated in months, you're almost certain to miss the ISS.

    To get accurate data, you have to register with space-track.org.  The data is updated by NASA/Norad frequently.  If I wanted to view the ISS and I noticed that there will be a nice pass -- say a week from now -- I would update my TLE (two-line elements) data for the ISS literally within an hour of the predicted pass to make sure my scope is using up-to-date information.  Otherwise the ISS may have moved enough that you could miss it completely when viewed through a telescope at high power.  

    When you register with Space Track, they (the US government) wants to know "why" you are interested in the obtaining the data.  I can only presume that this is in response to terrorism threats (e.g. are you trying to get highly precise orbit data because you are up to no good.)  With the Satellite Tracker program that I use, the instructions explain that we have to go register on our own, wait to be approved, and then program our login information into the application so that the program can pull the TLE data when needed.  Usually they pull the data for the specific object you want to track (they don't update the whole database.)

    Third, because it's moving fairly rapidly across the sky, trying to put your eye to the eyepiece of a constantly slewing telescope may be a bit of a challenge.  Most observers suggest one of the webcam module type eyepieces that lets you view the image on a monitor.

    Fourth, there's the way the software actually works.  Unlike most objects in the night sky, when you want to see a satellite, that object is probably not currently visible to you in the night sky.   The scope has to move to the location in the sky where the object is first likely to appear... and then at the precise moment, the scope has to start moving to track the object.  But of course we all know that in practical use, when you tell your "go to" scope to move to an object, that object will probably _not_ be precisely in the center of the field of view.  Depending on the quality of your alignment (and several other factors such as orthogonality of the axes and wether or not you have "cone error", etc.) your object may not be in the field of view at all.  This means when your scope does a 'go to' that initial position where the satellite should appear, the scope may not really be pointing at the correct spot in the sky.  So you definitely need a very good alignment otherwise even with the best software and best orbit elements, you may *still* miss seeing your object.

    Tracking a satellite is one of those things that sounds like it should probably be easy, and when you get into it, you start to realize that it's a bit harder than you might have guessed.  The satellite is only visible for a couple of minutes and it's moving at a rate that makes it extremely difficult for you to correct on-the-fly.  So if everything wasn't already perfect when you begin, the chances of fixing it before the satellite is out of view are slim.

     

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    Bill Tschumy

    Tim,

    Thanks for a more detailed explanation than I was willing to type.  As he said, there are numerous reasons why satellite tracking is hard.  We've experimented with it a bit but don't have anything close to being shippable.  The effort is currently on hold while we attend to more strategic things.

     

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    Dvader

    Yes, I know it is hard.

    But I will very happy to have this function in SS (or Satellite Safari). I have used before years the mentioned Satellite Tracker, but I have now Mac computer and tracker doesnt run properly in virtual machine.

    And also I would like to have this function in iPhone/iPad - so no needs to have computer at observing.

    I have very good experience with satellite tracking with my Celestron CPC-1100. It was perfect and accurate with the Satellite Tracker.

    Thanks for your attention!

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    bfeinner

    I've been using Satellite Tracker for many years with my Celestron 8SE. It works perfectly in continuous mode, it doesn't have to leap frog. It also works with Meade scopes. I used an earlier version with my LX-200 many, many years ago. Anyone who wants to track sats in their scope should check it out at heavenscape.com. Get the free version, it's all you need. You should also get a USB joystick, you can use it to keep the sat centered in your eyepiece.

    You don't have to go to Spacetrack.com to get updated orbital data (TLEs), you can get it from celestrak.com without having to register or anything.

    I would love to see this as a feature in Skysafari, but it looks like we'll have to wait a while.

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    John Bush

    Bfeinner, I just purchased a 6SE, but always get a Slew Error on the Satellite tracker program. 

    Now do I rectify that? 

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    bfeinner

    Please describe your setup. Interface Protocol must be set to: NexstarGPS Continuous Tracking, Alt-Az. Which version of Satellite Tracker are you using?

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    Bill Tschumy

    Can we please *not* have a discussion of SatelliteTracker on this forum?  This is for Simulation Curriculum products.

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    John Bush

    Sorry Bill. Found this Forum was talking about an issue I have (New to Telescope Tracking) and saw the post. Now realizing it's not the right spot for discussing other vendors. I would like to know after reading about Sky Safari 5 (for my Android phone) if it does track satellites.  Thank you    John Bush

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    Bill Tschumy

    John,

    Sorry, SkySafari does not track satellites.

    Bill

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    bfeinner

    IMO, satellite tracking should not be added to SkySafari. If SC wants to release such a thing, It should be a separate app.

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    John Bush

    I think I might get SkySafari for the convenience of using a handheld device to pick and choose instead of a laptop. My Celestron 6SE now has USB for the hand controller. I'm guessing I can just plug my Android mini-usb into the Celestron without any special adapters?!

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    Bill Tschumy

    Sorry, no.  Currently SkySafari on Android can only control a mount wirelessly.  We can't talk out of the USB port on Android.  You would have to get a wireless adapter such as our SkyFi.

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