International Space Station - Hubble Space Telescope
Plotting and Tracking with the
Paramount ME
In order to plot satellites you need
to supply accurate two line orbital elements* first. Secondly you must ensure
that the date and time are also set accordingly in TheSky. Two Line Elements (known
as TLE's) are readily available for the
International Space Station (ISS) along with many other types
of man-made satellites like Iridium
Flares, Weather, Geosynchronous, and so forth. Keep in mind that TLE's are only good for about
45 days. After that period they become invalid and TheSky will not use them
indicating they have been DATE REJECTED. Personally I try to archive the TLE's
for the ISS and Shuttle.
So why are there three satellite components
plotted in
TheSky when using the
TLE's for the ISS? The answer is the set of TLE's from the
web page
NORAD Two-Line Element Sets at the writing
of this page has three separate entries in the data set as follows (SUBJECT
TO CHANGE).
Data | Satellites
Import from web
Categories listed
Select International Space Station (ISS)
Note there are several "modules" that end up
making the International Space Station and these modules will change over time.
Components are added and subtracted. Currently there are three individual
objects being plotted in
TheSky when the two line
elements for the ISS are being used (date July 21, 2004). The components
are the Zarya module, Soyuz-TMA 4 module, and currently the Progress-M 49
module. Each of these are currently interconnected to each other (AGAIN
SUBJECT TO CHANGE!). See below showing this for
June 27. 2007.
Related links:
For information on using TLE's with
TheSky please refer to
TheSky's documentation for
details Without current updated TLE's you simply cannot plot satellites.
Also note that the two line elements are
constantly being refined so it is best to update the elements on a very regular
basis. You can easily label all three objects when using the ISS TLE's in
TheSky display using View
| Display Explorer as shown. The entry is under Solar System then Satellites. Under
labels
check the ID as shown to plot the name of the satellite.
View | Display Explorer
under Solar System - Satellites
Check the fields you want labeled
By labeling the objects on screen it makes
identifying satellites (any and all satellites) much easier to see, especially
at wider fields. In the case of the ISS you must zoom into a very small field of
view to separate the three or 4 in the following case labels because they are in very close proximity.
4 objects identified June
28, 2007
NOTE: Very narrow field of view!
There are three objects being
plotted directly on top of each other. The TLE's were downloaded from Celestrak
today June 28, 2007
The RAW TLE data from the
Celestrak site for June 28 2007.
ISS (ZARYA)
1 25544U 98067A 07179.20820721 .00014343 00000-0 84641-4 0 4803
2 25544 51.6345 46.9454 0008226 9.9082 89.7659 15.78430680492511
PROGRESS-M 59
1 29714U 07002A 07178.25948115 .00015106 00000-0 89040-4 0 1248
2 29714 51.6340 51.8499 0008028 6.2695 98.8168 15.78405176 25276
SOYUZ-TMA 10
1 31100U 07008A 07178.25948115 .00015106 00000-0 89040-4 0 717
2 31100 51.6340 51.8499 0008028 6.2695 98.8168 15.78405176 12690
PROGRESS-M 60
1 31393U 07017A 07178.25948115 .00015106 00000-0 89040-4 0 687
2 31393 51.6340 51.8499 0008028 6.2695 98.8168 15.78405176 7294
NOTE! Because the Soyuz-TMA
10 spacecraft and the Progress M-59 AND Progress-M 60 module today have the EXACT same
TLE's the two objects are plotting directly on top of each other! Also see
here for why TLE's cannot be fully trusted to a
high degree of accuracy.
Why are these objects so far
apart?
Good question! The link below
explains this using the ISS and Shuttle TLE's at
the time of docking as an example in 3D space. Even though the spacecraft
are physically joined (docked) the TLE's do not reflect this!
To search for the ISS use
Edit | Find in
TheSky and expand the
group Solar System | Satellites as shown below. The individual satellites
are listed. This list is provided by the
Special Interest satellites found on the
Celestrak page.
ISS is shown here
Center and Frame
Use group Space & Earth Science
TLE's for the Hubble Space Telescope
Edit Find Sat HST
Sat HST
Dr. T.S. Kelso's site
NOTE: Above you can download a text
file with the proper TLE's for both the ISS and Shuttle and then IMPORT them into TheSky directly by using
Import from File option. See below. This site does not require the user to login and
the source of the elements can be edited easily enough. As in if you want
you could edit the text file and remove all other entries leaving only
the ISS when there are more than 1 set of TLE's present.
From the Celestrak site select the option
"Current Data" then
Current US Space
Shuttle Mission (STS 117) at the time of this writing June 18th 2007. Use the option File Save As and save the
text file on your local drive then Import the TLE's directly from the
file using Data | Satellites | Import from the Web and then Browse the
file with the TLE's by name to import the ISS and Shuttle assuming there is a
Shuttle mission
present..
Import the ISS
Browse the TLE's in the text file saved to
plot
The Celestrak site above
(at the time of this writing June 18 2007) will supply ONLY two sets of TLE's the ISS
and the Shuttle STS 117.
But Wait!
The Shuttle and ISS are not shown in the exact
same position even though they are docked! So if the two spacecraft are docked how can this be?? Why is
TheSky not plotting them extremely accurately?
Of course these two objects
physically do not occupy the same space when docked so there will be a small
difference in their plotted positions. However, note that the accuracy of the
TLE's is only good to a few kilometers! That being said neither the position for
the Shuttle or the ISS is ever extremely accurate! Take note. This means that even a
perfectly built and perfectly pointing telescope cannot simply place the objects
accurately in a very small field of view, that is smaller than ~15 arcminutes
which is quite common for small video chips! Errors on the order of arcminutes is common because the
TLE datasets are only good on the order of several kilometers (5 to 20
kilometers or worse).
Margin of error in TLE's
1.79 " (arcseconds) angular separation
ISS to Shuttle!
Now to demonstrate the inaccuracies that exist
in the TLE's supplied at Celestrak (BTW: there is no "better source" to the lay
person). I picture is worth a thousand words.
For another
example see here.
If we use the current TLE's for the Shuttle and
the TLE's for the ISS on June 18th 2007 from Celestrak
that is while the craft are docked look at the Shuttle's position is in 3D space!
And because the TLE's are only updated daily over several hours their accuracy
changes, i.e. 6 hours later the objects are separated by 4 arcseconds, and 12
hours later 7 arcseconds!
To see the change in positions over the course
of a single day use either TheSky or Seeker and step several minutes in time
noting the position of the two craft over the course of the day!
Here is the contents of the file "Satellites.txt" used by Seeker
found in the "\Seeker\Objects" folder for the above screen shot on June 18th 2007.
; All earth satellites Use TLEs from Space-Track
;Name,modelfile,mass,size in meters, vector towards earth (3 components), best view date
;2454269.75290936 Julian Day June 18 07
;
;June 18 07 - 2454270.19142361 Julian Day
;
ISS (ZARYA),iss.iva,0.0,1100.0, 0.0, 0.0, -1.0, 2454270.19142361
1 25544U 98067A 07169.32910034 .00013048 00000-0 77918-4 0 4150
2 25544 51.6362 98.0024 0008104 335.3435 115.0878 15.78270239490958
STS 117, endeavour.iva, 0.0, 25.55, 0.0, 0.0, 1.0, 2454270.19142361
1 31600U 07024A 07169.39454981 .00012591 00000-0 75324-4 0 195
2 31600 51.6368 97.6651 0008082 335.3918 127.1586 15.78270984 1502
While docked note how similar the TLE's are
for both satellites but not the same!
HINT: If you
EDIT | FIND the ISS in Seeker first by using the Point to button you can easily
find the location of the Shuttle. Also, label the satellites using Display
Labels (CONTROL+L).
Again, note the Julian Day being used here for
the docking date June 18th 2007 - 2454270.19142361. Make sure you have
this date entered in Seeker when using these TLE's. You can save the above text
as satellites.txt in the Seeker/Objects folder. BUT first make sure you backup
the existing default "satellites.txt" file first so you can go back a step!
And now for some fun! Use the EXACT same TLE's for both
the ISS and the Shuttle. This will plot both spacecraft at the exact same location!
Houston we have a problem!
Using identical TLE's for both craft!
; All earth satellites Use TLEs from Space-Track
;Name,modelfile,mass,size in meters, vector towards earth (3 components), best view date
;2454269.75290936 Julian Day June 18 07
;
;ISS (ZARYA),iss.iva,0.0,1100.0, 0.0, 0.0, -1.0, 2454270.19142361
1 25544U 98067A 07169.32910034 .00013048 00000-0 77918-4 0 4150
2 25544 51.6362 98.0024 0008104 335.3435 115.0878 15.78270239490958
STS 117, endeavour.iva, 0.0, 25.55, 0.0, 0.0, 1.0, 2454270.19142361
1 25544U 98067A 07169.32910034 .00013048 00000-0 77918-4 0 4150
2 25544 51.6362 98.0024 0008104 335.3435 115.0878 15.78270239490958
Seeker
showing the completed Space Station
Location of the Soyuz module indicated plotted without using TLE's!
(Click on image for details about Seeker)
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