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Modding Orbital Mechanics
Posted: 13.03.2005, 22:01
by droscoe
This is one hell of a simulator!
Can I change the orbital mechanics of Celestia to use a different value for G, and to change the masses? Are all mass values described as ratios with Earth's mass as 1?
Long live open source!
-Dave
Posted: 14.03.2005, 12:06
by selden
Dave,
Celestia ignores masses.
You define the celestial mechanics in the objects' "EllipticalOribit" declarations. Celestia puts no constraints on the period or semi-major axes of the orbits.
Posted: 15.03.2005, 23:48
by t00fri
selden wrote:Dave,
Celestia ignores masses.
You define the celestial mechanics in the objects' "EllipticalOribit" declarations. Celestia puts no constraints on the period or semi-major axes of the orbits.
How about all the expansion terms in VSOP87??
These depend of course on the other masses around the body under consideration...Since the polynomial terms are given as numerical values, it appears /quite probable/ that they cannot be easily scaled to another value of G....
In Celestia, VSOP87 is used for most (inner) planets...
Bye Fridger
Posted: 16.03.2005, 14:47
by selden
Fridger,
My point is that the terms of the polynomials used in VSOP87 have been precalculated to take into account the gravitational effects of the major planets and a few of the minor ones. As a result, the objects for which Celestia provides CustomOrbits follow fixed paths. Celestia doesn't change the terms or the paths if you add an SSC file which defines a "Planet X" with a large mass, for example.
In principle, Celestia could be modified to load at runtime new object definitions with different trajectory definitions. I suspect it would be rather difficult to provide a smooth transition between the old and new trajectories, though.