How to use Epoch ?

[Cham]

I need to place two spaceships on the same orbit, close from each other (about 50 meters).

Is there a way to do this without using the Epoch command in an orbit definition ?

If not, how can I set an Epoch number (in which units, anyway ?) to make two ships very close ?

[granthutchison]

You don't need to use Epoch. Just make the MeanAnomaly slightly different for the two ships. If you want them 50m (=0.05km) apart, then you need to divide 0.05 by (SemiMajorAxis*2*pi), and multiply by 360 ... that should give you the fraction of a degree difference required in MeanAnomaly. If your orbit is circular they should stay exactly 50m apart, if it's elliptical, they'll move back and forth relative to each other as they orbit.
(This assumes you're in orbit round a planet - if your ships are orbiting a star the SemiMajorAxis will be in AU, and you'll need to convert to kilometres before doing the sum.)

Grant

[Cham]

Thanks a lot for the fast reply !

Ok, I'll use that trick (my orbit is circular). But what if I want my ships to be at a constant distance on the same elliptical orbit ?

[granthutchison]

But what if I want my ships to be at a constant distance on the same elliptical orbit ?

They couldn't do that in the real world without constantly firing manoeuvring jets.
You could place one ship in a 50m-radius orbit around the other with the same period as they orbit the planet ... the distance will remain the same, but now their orientation relative to the planet will shift back and forth a little, since the constant motion in the small circular orbit won't match the varying speed in the large elliptical orbit.

Grant

[Cham]

This reminds me the epicycles of Ptolemea ! LOL