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This is a fun game. But... I'm pretty sure the toggle to turn the gravity model from "Oblate Spheroid" to "Flat" is just cosmetic/trolling. I don't think it changes the gravity model. I submit the following as evidence... 1/7 https://twitter.com/SpaceX/status/1260269423090208768
With the Oblate Spheroid model, let's maneuver to 200m away and null our other rates (Should look something like this.) Then let's close at 0.5 m/s. After that, we won't make any other corrections or maneuvers.
Who thinks they know what is going to happen? 2/7
Who thinks they know what is going to happen? 2/7
Intuitively, you might think the spacecraft would close distance in a straight line. And it would... assuming a Flat Earth gravity model. But in reality, in this orbit, at this closing velocity, the spacecraft would drift almost 15m out of the corridor unless corrected! 3/7
So let's try it in the simulator. Again, this is with the Oblate Spheroid gravity model, starting 200m prograde of the station and an initial impulsive burn of ~0.5 m/s. 100m out, and we can see that no drift is apparent. We are still in line. 4/7
50m out and we've only drifted ~1m out of line. And it's here the pilot/engineer in me overwhelms the astrodynamicist, and I'll give it a short corrective burn. Because I *never* want to see a spacecraft crash into the ISS, not even in a simulator! 5/7
After that, bring the closing rate down, recenter, and dock without issue. Out of curiosity, I tried it again with the Flat Earth gravity model, but the behavior was the same. No ~15m drift. 6/7
So SpaceX: What gives? If only that toggle had been real, this could be a great way to help people develop an intuition for the complicated dynamics of proximity ops and why they are so counter-intuitive!
I would *love* to finally see a game get this right. Why not this one?
I would *love* to finally see a game get this right. Why not this one?
I checked it with different code, and I'm now certain that the gravity model toggle doesn't do anything. It's always flat earth gravity.
How bad an approximation is that? Well, it's the difference between the red line (game data) and the green line (Clohessy-Wiltshire equations)
How bad an approximation is that? Well, it's the difference between the red line (game data) and the green line (Clohessy-Wiltshire equations)
One more addendum: Here is what would really happen if you started from the game's initial conditions r=[200,12,30]m and v=[0,0,0]m/s and did *nothing*.
After just 12 minutes, should have drifted ~50m above the station's VN plane (unlike in the game, where you remain ~fixed).
![One more addendum: Here is what would really happen if you started from the game's initial conditions r=[200,12,30]m and v=[0,0,0]m/s and did *nothing*.After just 12 minutes, should have drifted ~50m above the station's VN plane (unlike in the game, where you remain ~fixed).](https://pbs.twimg.com/media/EX7r5sqXYAEpzN6.jpg "One more addendum: Here is what would really happen if you started from the game's initial conditions r=[200,12,30]m and v=[0,0,0]m/s and did *nothing*.After just 12 minutes, should have drifted ~50m above the station's VN plane (unlike in the game, where you remain ~fixed).")
After just 12 minutes, should have drifted ~50m above the station's VN plane (unlike in the game, where you remain ~fixed).
