Orient spacecraft by RA/Dec or ecliptic coordinates

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Topic author
j13r
Posts: 2
Joined: 15.10.2019
With us: 1 year

Orient spacecraft by RA/Dec or ecliptic coordinates

Post #1by j13r » 30.10.2019, 16:57

Dear all,

I am trying to find a way to point my spacecraft to a specific star. Lets say, Vega for example, has ecliptic J2000 coordinates 285.31638779° +61.73286467°.

I tried:

Code: Select all

    BodyFrame {
        EclipticJ2000 {
            Center "Sol"
        }
    }
    FixedRotation
    {
        MeridianAngle 61.73286467
        Inclination 285.31638779
    }


However, this does not point in the correct direction.

I see that choosing "MeridianAngle 0 Inclination 0" the spacecraft is aligned with the ecliptic plane, as expected.

What am I doing wrong? Do I need to set AscendingNode, and if yes, to what value?

Added after 36 minutes 12 seconds:
Switching to "Inclination 61.73286467 MeridianAngle 285.31638779" did not help.

Looking at stars in the ecliptic, I seem to need to need to add 90° to the ecliptic RA of a star to match the pointing.

Avatar
Art Blos M
Moderator
Posts: 829
Joined: 31.08.2017
Age: 28
With us: 3 years 1 month
Location: Volgodonsk, Rostov Oblast, Russia

Post #2by Art Blos » 30.10.2019, 19:22

Why indicate the coordinates when you can specify a star by name?

Code: Select all

BodyFrame
{
   TwoVector
   {
      Center   "Sol/Kepler"
      Primary
      {
         Axis   "y"
         RelativePosition
         {
            Observer   "Sol/Kepler"
            Target   "Kepler-1000"
         }
      }
      Secondary
      {
         Axis   "x"
         RelativeVelocity
         {
            Observer   "Sol/Kepler"
            Target   "Kepler-1000"
         }
      }
   }
}
Founder and head of the project "Celestia Origin"

Topic author
j13r
Posts: 2
Joined: 15.10.2019
With us: 1 year

Orient spacecraft by RA/Dec or ecliptic coordinates

Post #3by j13r » 31.10.2019, 01:07

Thank you, Art Blos. Making a STC file with Barycenters combined with your solution helped me.

Ultimately, I want to point the spacecraft at different stars over time. Avoiding quaternion transforms, at the moment I solved this by defining a auxiliary spacecraft with the orbit, and then adding spacecrafts with the right orientation and time segments, with positions at the auxiliary spacecraft. This allows following of the orbit continuously (using the auxiliary spacecraft name). However I can't make a smooth transition in pointing.


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