Will GRAVITY ever be added?

[chris]

My point is that we must not get carried away by having too high tolerances. Celestia uses preset orbits for all the Jovian moons, and no one of these moons is affected by any other body than Jupiter itself. Therefore we are already giving away a lot of precision, but that's fine with everybody.

The orbital models that Celestia uses for the Galilean satellites in fact do account for mutual perturbations. So, no we're not giving away a lot of precision.

--Chris

[t00fri]

I believe that currently in Celestia, the observer's motion is "outside of time" with respect to the cosmic simulation. Thus if the user slows, or stops, or reverses the simulation time, it affects the motion of the planets and other objects, but it does not affect the motion of the observer. So how gravitational effects would apply to observer motion in Celestia is perhaps not entirely obvious.

- Hank

Hank,

I largely agree with you. The role of the observer in Celestia is that of a socalled test-body, a familiar concept it theoretical physics. It means that the test object is considered not to be dynamically coupled into the system that is probed. So observers are not subject to the usual laws of physics. They can move with a speed larger than the speed of light and have no gravitational interactions unlike satellites for example.

Bye Fridger

[t00fri]

My point is that we must not get carried away by having too high tolerances. Celestia uses preset orbits for all the Jovian moons, and no one of these moons is affected by any other body than Jupiter itself. Therefore we are already giving away a lot of precision, but that's fine with everybody.

The orbital models that Celestia uses for the Galilean satellites in fact do account for mutual perturbations. So, no we're not giving away a lot of precision.

--Chris

I was about to write the same thing;-). The VSOP87 theory that is used in Celestia is about the analogue of the Hatree-Fock method in atomic physics. The perturbations due to all those surrounding atoms onto a given one are reduced mathematically into an effective interaction that is parametrized somehow. In Vsop87 one uses complicated (Chebychev polynomial) expansions with partly hundreds of terms...I advice XNK to look into the respective code before making his claims of the contrary...


Bye Fridger

[xnk]

Sorry, I didn't read into the details of CustomOrbit very carefully. I assumed it was a marker for a predefined ellipse.

I still stand by my idea.

[selden]

xnk,

The relevant physics course is often called "intermediate mechanics". If you're at the University of Oregon, I think that corresponds to one of the courses in the sequence 411-412-413, although it might be 421. I'm rashly assuming that what they're calling "Newtonian mechanics" is what's also known as "Hamiltonian mechanics".

An online introduction is at http://alamos.math.arizona.edu/~rychlik/557-dir/mechanics/mechanics.html

[xnk]

Thanks. I'll be at Oregon State for the third year of my degree though.

[selden]

In that case, it looks like it'd be 435 -- classical mechanics.

[marc]

I suspect that most of you that want gravity have not tried out my mod, its hard enough to get in an orbit let alone think about a slingshot. The algorithm I used breaks down at high time compressions anyway.

Have you tried orbiter? Thats got gravity, and even with all its fancy readouts it is still very hard to fly.
Without thrusters, readouts, fuel usage, etc etc there really isnt much point.

Celestia does not need gravity, get over it.

[chris]

Aside from the philosophical points about whether or not gravity belongs in Celestia, I don't bloody feel like writing a gravity simulation. I'm just not interested. There are lots of enhancements I do want to work on, and gravity is not among them. I think I speak for the other Celestia developers as well. All of this discussion is moot. If you want gravity, start a Celestia-based project and add it yourself. I apologize if I come across as bratty, but the matter has been discussed to death in this and other threads.

--Chris

[jrobert]

The gravity of the situation is that Celestia needs no gravity. This isn't a physics simulator! The planetary orbits are actually calculated from VSOP87 data which basically computes the position of a planet or satellite in the solar system according to a specified date and time. No physics involved there. Here are some limitations of Celestia: The galaxies don't spin let alone move thru the cosmos. (The Milky Way galaxy will never meet the Andromida Galaxy) The stars are fixed points and don't move in relation to the galaxy. The whole galaxy isn't even populated with stars -- only our small corner of the galaxy is. There's no room to add gravity, IMHO.