Satellite Observing

In addition to all the heavenly objects available for observation there are a host of man made objects orbiting the Earth that can be viewed either with the naked eye, binoculars or a telescope.  Things like rocket boosters, weather and navigation satellites, even the Hubble Space Telescope and the International Space Station.  Viewing these objects can be fun, and there are many objects visible on a clear night even with your naked eye, once you know what to look for.   The movie in this link shows a European geosynchronous television satellite Astra 1KR as controllers place it into its orbital slot.  The image is courtesy of  Hugues Laroche who captured the movie using a C14 and a SBIG ST-8 CCD camera.

In order to track an object orbiting the earth with a telescope a number obstacles have to be overcome. The first is knowing where and when to look for the orbiting object.  Fortunately NASA and NORAD can help  with this problem. Between the two of them, pretty much everything in size ranging from the smallest nut and bolt all the way up to the International Space Station is tracked.  The information about the object is contained in what is referred to a Two Line Element, or TLE for short. The TLE has all the stuff you need to know about the orbiting object and for the most part follows a standard format.  For an example and a explanation of a TLE click here.  It is common for individual TLEs to be grouped together in files that contain TLEs for many objects. Usually the objects are grouped with other objects that  have something in common, like weather satellites or navigation satellites.  All TLEs used by the observatory are obtained  from the Air Force Space Command CFE Space-Track .org website.

In order for the file to be useful it needs to be read by a program that understands the TLE file. The program will provide a prediction of what satellites (or objects) will be visible by the observer based on their longitude and latitude.  With most programs the observer has the option of choosing the time they want to observe objects, or what objects (by name or ID) they want to observe.  Then, depending on which option the observer decided upon the program will either tell them what will be visible for a given time, or tell them the time the particular object they are interested in will pass over their location within their line of sight. Most programs will also provide the object's speed, direction of travel and duration of visibility.  The other useful feature of these programs is they can help identify object an observer may have seen. If the user supplies the date, time and the location, the program will search the supplied file and display a list of satellites that would have been visible within the window defined.  (One thing to remember is that TLE files don't last forever. The older the file is the less accurate it becomes, so you need to update your TLEs at least every 30 days).

The above process works very well for naked eye observing or even wide field binoculars, because once you locate the object using the predict data it is easy to keep the object in view (even fast moving ones).  But when you want to use a telescope to observe orbiting objects, the telescope must be able to locate and follow the object at the speed and direction the object is traveling.   This is not always an easy task. Depending on the orbit of the object and the mounting geometry of the telescope this may require the telescope to use both axis in order to track the object.  This means the telescope must be able to ingest the TLE as well as precisely control the movement of the scope in order to track the object. One way to do this is to use software that will accept a TLE file, generate a predicts file and send commands to the scope that will precisely control both axis' to keep the object in view based on the predicts file. 

The combination of TheSky6 and the Paramount ME German Equatorial used at the  JATObservatory allows satellite tracking without the need for any other software. TheSky6 will download TLE files from the Space-Track.org website.  But to make things a bit easier I use a 3rd party piece of software Space Track TLE Retriever written by Dr. T. S. Kelso to automatically download TLEs daily.  That way there is a fresh set of TLE files available for any tracking session.  Once the start tracking radio button is clicked the Paramount will begin tracking the satellite.  Because the telescope is housed in a dome, and because some man made orbiting objects travel at a fairly fast rate across the sky, the telescope's aperture still has to remain within the opening of the dome's shutter. This required the update frequency of the script that checks the dome and telescope's alignment position to be increased to approx every 2 seconds.  This page show an image of a communications satellite orbiting at over 35,000 km. 

For more information about observing man made objects check out the Heavens-Above , The High Altitude Satellite Observers Home Page , CelesTrak and NASA's J-Track 3D website.

The software below will help you in locating satellites visible from your location. Some are freeware some are not, but it is by no means a complete list. Remember Google is your friend.

Satellite Tracker       WinTrak      WXTrack      WinOrbit   
Here is a screen shot of the Sat Tracker software during a actual sat track at the observatory. (The Sat Tracker software was used to control the LX200GPS for satellite  tracking before the Paramount ME was installed.)


Go to the JATObservatory Home page

Updated 07/11/2015 - Please report broken links webmaster@jatobservatory.org