Gravity based on Unity's rigid body physics and trajectory is simulated(meaning I run my physics 1000 ticks ahead of actual astronaut position and record all 1000 points astronaut hits, then draw line connecting those points). I also simulate other parts of game mechanics like amount of O2 changing by breathing and thrust, so I can mark different parts of trajectory with green(under the thrust), blue(gravitation only), and grey(still gravitation only but astronaut is dead already :) )