Double Body Problem

[Dollan]

Okay **sighs** What am I doing wrong?

Code: Select all

"ScyllaCharybdis" "Tau Ceti"

   {
   Class    "Invisible"
   EllipticalOrbit
      {
      Period      3.4
      SemiMajorAxis   2.24
      }
   }

"Scylla" "Tau Ceti/ScyllaCharybdis"

   {
   Class      "Planet"
   Texture       "Scylla.jpg"
   Radius       4758
   # Mass
   EllipticalOrbit
      {
      Period      3.4
      SemiMajorAxis   2.24
      Eccentricity   0.0036
      Inclination   3.568
      }
   RotationPeriod   305.76
   Obliquity                  26.72
   Albedo      0.55
   }

"Charybdis" "Tau Ceti/ScyllaCharybdis"

   {
   Class      "Moon"
   Texture      "Charybdis.jpg"
   Radius      3116
   # Mass      
   EllipticalOrbit
      {
      Period      305.76
      SemiMajorAxis   10087
      Eccentricity   0.00
      Inclination   0.00
      }
   RotationPeriod   305.76
   Obliquity      26.72
   Albedo      0.35
   }

I'm trying to have two rocky worlds orbit one another so that each faces the other eternally. At the moment, I'm not worried about realism.

My big problem, I can't get the thing to display at all. I used the Pluto-Charon code at for reference, but obviously I'm still doing something wrong.

Probably something absurdly simple, knowing me. I'm using the latest pre release, too.

...John...

[Spaceman Spiff]

Dollan,

try this:

Code: Select all

"ScyllaCharybdis2" "Tau Ceti"
{
  Class "Invisible"
  EllipticalOrbit
  {
    Period 3.4
    SemiMajorAxis 2.24
    MeanLongitude 10
  }
}

"Scylla2" "Tau Ceti/ScyllaCharybdis2"
{
  Class "Planet"
  Texture "Scylla.jpg"
  Radius 4758
# Mass 0.373 # Earth masses.
  EllipticalOrbit
  {
    Period 1.069375 # = 27.321661 ?— sqrt( ( 4 ?— pi ^ 2 ?— ( 10087 / 384400 ) ^ 3 ) / ( 0.373 + 0.093 ) )
    SemiMajorAxis 2013.071 # = 10,087 ?— ( 0.373 / ( 0.373 + 0.093 ) )
    Eccentricity   0.0036
    Inclination 26.72
    MeanLongitude 0
  }
  RotationPeriod 25.665 # = 24 ?— 1.069375
  Obliquity 26.72
  Albedo 0.55
}

"Charybdis2" "Tau Ceti/ScyllaCharybdis2"
{
  Class "Moon"
  Texture "Charybdis.jpg"
  Radius 3116
  # Mass 0.093 # Earth masses.
  EllipticalOrbit
  {
    Period 1.069375 # = 27.321661 ?— sqrt( ( 4 ?— pi ^ 2 ?— ( 10087 / 384400 ) ^ 3 ) / ( 0.373 + 0.093 ) )
    SemiMajorAxis 8073.929  # = 10,087 ?— ( 0.373 / ( 0.373 + 0.093 ) )
    Eccentricity 0.0036
    Inclination 26.72
    MeanLongitude 180
  }
  RotationPeriod 25.665 # = 24 ?— 1.069375
  Obliquity 26.72
  Albedo 0.35
}


It will set up a copy 10?° along orbit from your original...

Spiff.

[Dollan]

I'll try it out when I get to work this evening, thanks!

But I have to ask... where did all the math come from in the orbital parameters? I've never seen that before in an ssc file.

Also, for my own education in this, exactly what is the change that will make the planets register with Celestia? If I can figure that out, I shouldn't have this problem again **knocking furiously on the wooden desk here**.

Much appreciation for your help!

...John...

[Spaceman Spiff]

The maths comes from me - I added it as comments so you can see how you might work out the general orbital dynamics of a double planet. Just match up the similar numbers, and you'll see what must equal what.

I'm not sure why you couldn't see anything from how Celestia is supposed to interpret SSC terms, but I did see that the double planet was missing. I just kept working at it until I got it right. It wasn't easy though, and sometimes it just wouldn't work:


( http://img290.imageshack.us/img290/3774 ... 7488vg.png ).

I know the Scylla and the Charybdis were scary things, but...


Spiff.

[Dollan]

Ah, I see the math now. I usually don't bother figuring out the exact parameters until I have the rough "sketch" of the system completed.

And thank you for getting the two bodies to orbit each other so that each faces the same spot on the other.

But you know what? I am an idiot. Turns out that, since I defined these worlds around a barycenter, the orbit didn't show up when I checked the system, and that was why I thought that my code wasn't working. But low and behold, I check the solar system browser because YOUR version wasn't showing either.... and there was both mine AND yours.

Yes, I feel the fool. **sighs**

Nonetheless, thanks! Now to go and figure out the Roche limits for this planetary pair, and make certain that they *can* orbit this close.

...John...

[bdm]

I have also created a pair of locked worlds like Pluto/Charon and I would like to share a few thoughts.

If the worlds are not showing up, try using the HIP catalogue number instead of the star name as "HIP xxxxxx".

The worlds will tend to drift out of alignment over long periods of time: one or both will appear to rotate slowly if the simulation is sped up greatly. To minimise the chances of this, don't specify a rotation period for the moon because that will lock it to the planet by default. To minimise the wandering of the planet's axis, specify the rotation period of the planet (which is in hours) to be 24 times the period of revolution of the satellite (which is in days).