Celestia Forums

My question... Can I delineate an orbit for a spacecraft from some asteroid in the Belt, to Mars, then to Earth, and back to the original asteroid, and have it NOT matter what the time of year it is (thinking of planetary orbital changes here)?

Is that the gist of an XYZ file (which I have never messed with before)? If so, what tutorial would be recomended to learn this?

Okay, so it was three questions....

...John...

Unfortunately, the quick answer is "no" if I'm understanding your question.

xyz trajectories are fixed in space and time.

Also, don't forget that orbital transfer trajectories change as both the origin and destination bodies move. A trajectory which is appropriate one month can't work at all a month later. A lot goes into deciding when to go and how much acceleration has to be used to make the orbital transfers. Even a simplified version of calculating how to get to Mars usually is the topic of a semester-long course. If it helps, "patched conics" is one popular method of calculating orbital transfers.

A google search for
asteroid patched conic
turns up some interesting pages. The one I found most fascinating, although maybe not so helpful for your situation, is
http://www.lpi.usra.edu/publications/re ... tech01.pdf
"Asteroid Rescue Mission." It describes how one might attempt to rescue a Mars mission that failed to decelerate in time.

Hi John,you can use Toti's xyz builder script to just sketch out an orbit as you want ,but it will then only work once as Selden has pointed out-it is time specific,so if you want it to happen over and over you would have to repeat the orbit for the different time periods,Jestr
ps it only seems to work in Celestia 1.3.2

Hmm. Okay, what I might try then is to pick an asteroid from the Belt, and have the _Almucantar_ in an absurdly large orbit about it, stretching perhaps to the rough orbital position of Mars. It won't have the same effect as if a ship were going from one true destination to another, but it will give that feeling of "having travelled", as it were.

A further question: I can delineate, in an orbit, the near and far points of the orbital path, can't I? Say, if I want the ship to pass within a few kilometers of the asteroid's surface, and as far as whatever it would take to reach Mars' orbit (but, of course, not Mars itself)?

...John...

Sort of.

Celestia does not (yet?) support precession of orbits, so they're always at the same orientation relative to the "fixed stars". In other words, an elliptical orbit (e.g. around an asteroid) with its semi-major axis pointing toward the sun at one time of "year" will be pointing away from the sun after a half-year of the asteroid.

In other words, it'd probably be better to define an orbit around the sun with its aphelion near the asteroid's orbit and its perihelion near the orbit of Mars. It'll only pass by them both at one particular time, but I think it'll look reasonable more of the time.