Correct orbital elements for Skylab (in extras on CVS)

[revent]

Shrox's Skylab add-on is in the extras dir on CVS, but without the correct orbital elements (as he notes in the file). Here they are, with launch and deorbit dates.

SKYLAB 1 Launched: 1973/05/14 Decayed: 1979/07/11
1 06633U 73027 A 79185.88914720 .01109374 +00000-0 +00000-0 0 00194
2 06633 050.0279 012.4010 0004938 264.3626 095.7798 16.18386537348710
SKYLAB 2 Launched: 1973/05/25 Decayed: 1973/06/22
1 06655U 73032 A 73169.60155385 .00003303 +10994-5 +00000-0 00163
2 06655 050.0417 210.1316 0011671 054.4825 305.7185 15.44463920003739
SKYLAB 3 Launched: 1973/07/28 Decayed: 1973/09/25
1 06757U 73050 A 73268.70598970 .00006016 +01798-5 +00000-0 0 00096
2 06757 050.0405 066.0497 0011296 095.7173 264.5039 15.44957924009103
SKYLAB 4 Launched: 1973/11/16 Decayed: 1974/02/08
1 06936U 73090 A 74021.81572529 .00000000 +00000-0 +00000-0 0 00087
2 06936 050.0381 185.1450 0017748 226.6031 133.3415 15.44489098010197

Skylab 1 was the actual station, while Skylabs 2-4 were the Apollo capsules carrying the manned missions to it. These TLEs are from GSFC, and should be correct for the Epoch.

Hopefully Shrox'll spot this topic.

[granthutchison]

Here's a definition prepared from the elements given. Like all these Earth-satellite orbits it'll be correct for only a few revolutions either side of Epoch, but I guess that's better than nothing.

Code: Select all

# Skylab model created by Shrox -- http://www.shrox.com/

"Skylab" "Sol/Earth" {
   
   Class "spacecraft"
   Mesh "skylab.3ds"
   Radius 0.015

   Beginning       2441817     # 14 May 1973
   Ending          2444066     # 11 Jul 1979

   EllipticalOrbit {      
      Epoch        2448342.38914720      
      Period             0.06178994      
      SemiMajorAxis   6602.066      
      Eccentricity       0.0004938      
      Inclination       50.0279      
      AscendingNode     12.4010      
      ArgOfPericenter  264.3626      
      MeanAnomaly       95.7798      
   }      
   
   Obliquity        23.45       # Sun-synchronous orientation
   RotationPeriod 8766.15265008 # by Matt McIrvin
   RotationOffset  191          #

   Albedo          0.10

}

Skylab kept its solar panels orientated towards the Sun, according to Matt McIrvin on this thread: http://www.shatters.net/forum/viewtopic.php?t=427
So I've used Matt's orientation parameters to keep Skylab sun-synchronous.

Grant

[TERRIER]

Wow!, this certainly is alot different to the old Skylab orbit. The distance is much closer to Earth now - around 225km compared to over 400km previously. This orbit helps show off the high res VT of Florida very nicely. Check out the orbit on 14th May 1973 at around 16:35 UTC for a good example.

regards
TERRIER

[revent]

Er, that's not right, then (I gave the TLE, but didn't install it). That's what happens when you use a TLE from the wrong epoch, I guess. An orbit that low would be essentially IN the atmosphere, and not at all stable.

When Skylab was operational, it was in a 268.1x269.5 mile (431.5x433.7 km) orbit, according to NASA. That was in 1973, and the TLE I gave was for 1979, so apparently the orbit decayed pretty quickly. Fortunately, I know where to get older TLEs.

(These are the actual TLEs for the lab, not the Apollo CSMs that carried the astronauts up)

Launch was on 14 May 1973...here's the TLE from 15 May...

1 06633U 73027 A 73135.30828343 .00050000 퍍0 퍍0 00027
2 06633 050.0459 024.3850 0009421 272.0174 087.9670 15.44172945000092

It's in the old format, but the second line is the same and it's all that Celestia needs.

Skylab 2 (1st manned mission) was launched on 25 May....here's 26 May

1 06633U 73027 A 73146.11491442 .00030714 �4 퍍0 00115
2 06633 050.0371 329.5361 0007618 323.8544 036.1864 15.44261313001768

Skylab 3 (2nd manned mission) was launched on 28 July...

1 06633U 73027 A 73209.64835188 .00003303 흏5 퍍0 00427
2 06633 050.0425 006.4831 0012008 209.5953 150.4293 15.44614935011606

and finally, Skylab 4 (last manned mission) was launched on November 16...here's the 19th

1 06633U 73027 A 73323.28583330 .00003421 퍝6 퍍0 0 01015
2 06633 050.0379 148.2353 0010544 321.3613 038.6556 15.45458031029160

As you can see (easier if you can read TLEs) the orbit was pretty perturbed even over this few month period. Here's a SSC using the TLE for the last mission(Nov 19th)

Code: Select all

# Skylab model created by Shrox -- http://www.shrox.com/

"Skylab" "Sol/Earth" {
  Class "spacecraft"
  Mesh "skylab.3ds"
  Radius 0.015

   Beginning       2441817     # 14 May 1973
   Ending          2444066     # 11 Jul 1979

  EllipticalOrbit {
    Epoch  2442005.78583330
    Period  0.06470574
    SemiMajorAxis  6808.162
    Eccentricity  0.0010544
    Inclination  050.0379
    AscendingNode  148.2353
    ArgOfPericenter  321.3613
    MeanAnomaly  038.6556
  }
   
   Obliquity        23.45       # Sun-synchronous orientation
   RotationPeriod 8766.15265008 # by Matt McIrvin
   RotationOffset  191          #

   Albedo          0.10

}


This gives a 430x437.2 km orbit, and is accurate for late 1973. Sorry my earlier post was so useless. Thanks for trying to use it, tho.

**blatant SGP4 plug**

[granthutchison]

I've just revised skylab.ssc on the CVS tree to incorporate the elements revent gives for 15 May 1973, as well as Matt McIrvin's sun-synchronous orientation.
I have no idea if this early date is appropriate for the appearance of shrox's model - I recall there were some ad hoc modifications to Skylab at a later date - so if anyone has solid info on this, let me know.

Grant