Celestia Forums

Hi,

does anyone know how i could calculate the relative velocity (or speed, to make things simpler) of an object relative to another object ?

I guess the orbital elements of both are enough, but i am not too much into formulas...

Any hint ?

thankx
Amaury

forgot to mention that both objects would be orbiting the sun...

I think you're going to have to study up on keplerian mechanics and vector maths. Objects in Celestia are in elliptical orbits, so they're not always moving at the same orbital velocity.
You'll need to work out the velocity and direction of each object at a point in time, each expressed as a 3-dimensional vector, then you should be able to subtract one vector from the other to give the relative velocity.
Here's a reference for the Vector math:
http://www.sparknotes.com/physics/vecto ... tion1.html
You should also find what you need on the keplerian stuff at that site as well.

I don't know of any way in Celestia to just plug in orbital elements and get out relative velocity, so you might have to do the math (I suggest a spreadsheet, once you've worked out the formulae you need, to make it easier on yourself.)

Sorry I can't be more help, but that's how I'd attack it. If anyone knows a better way, jump in!

Thanks a lot ! I'll check it out right away!!

I finally managed to find time to dig into vectors and stuff.

It took me a while, but i think i now have a relative velocity (Vinfinity) display script. I checked solar planets velocities and some asteroid-Earth close approaches and it seems accurate.

If anyone thinks it is not right, please tell me, my understanding of motion physics is limited.

There you go:

relative velocity calculator (largely based on Toti's orbitalspeeds.celx script, and still beta)

amaury

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