Updating ISS Position

[cljohnston108]

Hey, All! Absolutely lovin' the new 1.5.1 build!
The question was once asked about having the current position of ISS displayed, and the answer from selden was that you'd have to do that manually... but didn't give any tips on how to go about it.
Okay, so, I opened up the spacecraft.ssc file...

Code: Select all

"ISS" "Sol/Earth"
{
   Class "spacecraft"
   Mesh "iss.3ds"
   Radius 0.040
   Beginning           2451138    # Zarya module launched 20 Nov 1998
   # Ending ????

   EllipticalOrbit {
      Period          0.064176392
      SemiMajorAxis   6767
      Eccentricity    0.0016886
      Inclination      51.5684
      AscendingNode   343.1518
      ArgOfPericenter 346.2476
      MeanAnomaly      13.8216
      Epoch           2452028.18381755
   }

   UniformRotation
   {
   Inclination    51.5684          #
   MeridianAngle  90           # orientation corrections by Matt McIrvin
   AscendingNode 343.1518        #
   }

   Albedo        0.10
}

...and then I went to Heavens Above...

1 25544U 98067A 08183.83463292 .00011154 00000-0 77774-4 0 7757
2 25544 051.6412 301.0484 0008682 320.4813 178.9640 15.74891896550830

Epoch (UTC): 8:01:52 PM, Tuesday, July 01, 2008
Eccentricity: 0.0008682
Inclination: 051.6412°
Perigee Height: 339 km
Apogee Height: 351 km
Right Ascension of Ascending Node: 301.0484°
Argument of Perigee: 320.4813°
Revolutions per Day: 15.74891896
Mean Anomaly at Epoch: 178.9640°
Orbit Number at Epoch: 55083

Several items are self-explanatory (Eccentricity, Inclination, Ascending Node, Mean Anomaly), and I'm assuming that "Argument of Pericenter" is the same as "Argument of Perigee".
I'm also assuming that Epoch needs to be converted to Julian Date. (I've got 2454648.83463)

Now, I think I just need to know how to get the Period and the Semi-major Axis, and find out what to set as "Beginning".
Is the Period just 1/(Revs per Day)? That would be 0.0634964217, then.
Why is Semi-major Axis not listed anywhere? Isn't it one of the most important bits of orbital info?
I know that it's half the distance between Perigee (339 km) and Apogee (351 km), but the radius of the Earth varies a bit between the Equator (6,378.1 km) and the Poles (6,356.8 km).
When I average the two Earth radii, I get 6367.45, but the Mean Radius (according to Wikipedia) is listed as 6,371.0 km, which would make the diameter 12742 km.
Other sites give the diameter of the Earth as 12756.3 km. Obviously they just went with the Equatorial value.
So, (12756.3 + (339 + 351))/2 = 6723.15 km is what I get for Semi-major Axis.

Now then, what to do with this line...
Beginning 2451138 # Zarya module launched 20 Nov 1998

Hmmmm, any thoughts?
I so hope I'm doin' this all right!

[selden]

1 25544U 98067A 08183.83463292 .00011154 00000-0 77774-4 0 7757
2 25544 051.6412 301.0484 0008682 320.4813 178.9640 15.74891896550830

Epoch (UTC): 8:01:52 PM, Tuesday, July 01, 2008
Eccentricity: 0.0008682
Inclination: 051.6412°
Perigee Height: 339 km
Apogee Height: 351 km
Right Ascension of Ascending Node: 301.0484°
Argument of Perigee: 320.4813°
Revolutions per Day: 15.74891896
Mean Anomaly at Epoch: 178.9640°
Orbit Number at Epoch: 55083

Several items are self-explanatory (Eccentricity, Inclination, Ascending Node, Mean Anomaly), and I'm assuming that "Argument of Pericenter" is the same as "Argument of Perigee".

right.

I'm also assuming that Epoch needs to be converted to Julian Date. (I've got 2454648.83463)

Note that the time is PM. You calculated it for AM.
http://www.calendarhome.com/converter/ yields
2454649.3346296297 but you can use the Gregorian date in quotes:
Epoch "2008 7 1 20:01:52"

Now, I think I just need to know how to get the Period and the Semi-major Axis, and find out what to set as "Beginning".
Is the Period just 1/(Revs per Day)? That would be 0.0634964217, then.

right

Why is Semi-major Axis not listed anywhere? Isn't it one of the most important bits of orbital info.I know that it's half the distance between Perigee (339 km) and Apogee (351 km), but the radius of the Earth varies a bit between the Equator (6,378.1 km) and the Poles (6,356.8 km).
When I average the two Earth radii, I get 6367.45, but the Mean Radius (according to Wikipedia) is listed as 6,371.0 km, which would make the diameter 12742 km.
Other sites give the diameter of the Earth as 12756.3 km. Obviously they just went with the Equatorial value.
So, (12756.3 + (339 + 351))/2 = 6723.15 km is what I get for Semi-major Axis.

probably close enough

Now then, what to do with this line...
Beginning 2451138 # Zarya module launched 20 Nov 1998

That's when the first ISS module was launched. Celestia draws the ISS after that date but not before then. It's not an orbital parameter.

Hmmmm, any thoughts?
I so hope I'm doin' this all right!

[cljohnston108]

Hey! Thanks for the quick reply!
Yep, I spaced on the PM in the Julian date. Thanks for the link! I was using the USNO converter, but there's so much more goin' on at the page you pointed me to. Lookit all that!

Good to know I got almost everything else right!

EDIT: Annnnnd... It works!! Woohooo!
Now for Hubble!

[selden]

You're very welcome.

[cljohnston108]

Even though I have the little ISS Locator widget for my iMac (which doesn't show the night side), and links to the NASA HSF locator (which doesn't seem to animate these days) and the n2yo tracker, this is so much better because you can look at it from any angle and distance.
I just installed krisci3's add-on, showing ISS in its current configuration... Oh, that reminds me: I also have OSXplanet as my desktop, which shows current weather patterns and day/night, as well as positions of ISS & Hubble. I just made a new ISS icon to show its current config because OSXplanet showed it in its initial Zarya phase, like the ISS Locator widget does.

I now have 5, count 'em, 5 different sources for knowing where the Station is!
Man I love technology!

[cljohnston108]

I just watched a nice orbital sunrise a few minutes ago...



I can hardly wait until the next shuttle mission, so I can be looking at Celestia with NASA-TV audio during an EVA, when the PAO says, "...the astronauts are now enjoying an orbital sunrise..."
Coolness!

[bh]

Lovely shot...

[cljohnston108]

Lovely shot...

Thank you kindly!

[shalom]

How can I get the ISS position on September 15, 2006 at 12:00:00 UT? I mean the Velocity and Position, I have the two line elements, but I don't know how to do it.
Regards!

[selden]

Shalom,

converting TLEs to Celestia's SSC format is described in the FAQ:

1.
Start here: FAQs, features, news & collections
viewtopic.php?f=2&t=11031

2.
+ A Preliminary Celestia User's FAQ
http://www.celestiaproject.net/forum/viewtopic.php?t=2291

3.
Q23: Celestia's orbit for the ISS is out of date. How can I get a better one?
http://www.celestiaproject.net/forum/viewtopic ... 1069#41069

[fly_space]

umm.... This code is understand very hard to me, But I know It's hard work. Good...


P.S- The capture ISS's figure very good! rainbow is very good, too.

[cljohnston108]

Okay, with this beautiful new version 1.6.0, I'm not sure how to access the spacecraft.ssc file, since the standard data files needed to run Celestia are now included inside the application package instead of provided as a separate folder.
What might be cool in a future version is for the program to automatically update that file from the Celestrak site!

[selden]

cljohnston,

You don't need to edit Celestia's official catalog entry in order to change the orbit of the ISS.

Instead, you should put an SSC file in the same extras directory where you put other Addons. It would contain a Modify directive to update the orbital definition appropriately.

For example, a catalog file named ISS_update.ssc could contain

Code: Select all

Modify "ISS" "Sol/Earth"
{
EllipticalOrbit { ...revised parameters here...}
}


[cljohnston108]

Ahhhh! Thank you kindly!

[david_lexicon]

Where can I find the parameters?

[selden]

Where can I find the parameters?

One place is the "Heavens Above" web site at
http://www.heavens-above.com/orbitdispl ... atid=25544

[david_lexicon]

Where can I find the parameters?

One place is the "Heavens Above" web site at
http://www.heavens-above.com/orbitdispl ... atid=25544

THanks for your reply. I do not know what to do with the parameters. I am new to Celestia.

[selden]

You'll need to edit Celestia's SSC catalog for the ISS.
If you're running Celestia v1.6.0, that file is
Celestia\extras-standard\iss\iss.ssc

It's a plain text file.
If you're running Windows, please take a look at
http://www.lepp.cornell.edu/~seb/celest ... html#2.1.1
That section of the Web page describes some of the issues related to editing under Windows:
a. you can use Notepad to edit Celestia's catalog files
b. you'll need to disable "hide known file types"
c. you should associate .SSC, STC and DSC with the Notepad editor.

http://www.lepp.cornell.edu/~seb/celest ... eters.html
describes the standard names for orbital parameters and their equivalent Celestia parameter names.

Documentation of SSC catalog files are on the documentation page on the MotherLode at
http://www.celestiamotherlode.net/catal ... ation.html
and in the Celestia WikiBook at
http://en.wikibooks.org/wiki/Celestia/SSC_File

Does this help?

[david_lexicon]

A bit complicated but I'll try.

Thanks.

[david_lexicon]

You'll need to edit Celestia's SSC catalog for the ISS.
If you're running Celestia v1.6.0, that file is
Celestia\extras-standard\iss\iss.ssc

It's a plain text file.
If you're running Windows, please take a look at
http://www.lepp.cornell.edu/~seb/celest ... html#2.1.1
That section of the Web page describes some of the issues related to editing under Windows:
a. you can use Notepad to edit Celestia's catalog files
b. you'll need to disable "hide known file types"
c. you should associate .SSC, STC and DSC with the Notepad editor.

http://www.lepp.cornell.edu/~seb/celest ... eters.html
describes the standard names for orbital parameters and their equivalent Celestia parameter names.

Documentation of SSC catalog files are on the documentation page on the MotherLode at
http://www.celestiamotherlode.net/catal ... ation.html
and in the Celestia WikiBook at
http://en.wikibooks.org/wiki/Celestia/SSC_File

Does this help?

I have two questions:

1) Can I edit the text files in WordPad? The Notepad does not put neatly the text.

2) Does ISS parameters change often ?