Effects on performance when setting Time.fixedDeltaTime = 0.005?

Questions & Answers
1

I’m building a simulation of satellites orbiting Earth. The simulation requires a high level of accuracy. I use real-world scale values for physics calculations, and then scale them down for Unity.

The operative code:

public void FixedUpdate()
{
  // Calculate gravity using Fg = G*m1*m2/r^2. Result is scaled down for Unity
  float gravity = G * massEarth * massSat / Distance() / Distance();
  gravity = gravity / meterScale * timeScale * timeScale;

  Vector3 gravityVector = (GravityDirection() * gravity);
  _rigidbody.AddForce(gravityVector);
}

In a perfect world the distance of a satellite in circular orbit should not change, so the goal is to minimize |position(t) - position(0)|.

The problem: because I am scaling the force by a time scale (in my own calculations, not using Time.timeScale), the satellite moves a significant distance in between FixedUpdate calls, and error accumulates. I need FixedUpdate to run more frequently.

The solution: I am able to reduce error to acceptable levels by setting Time.fixedDeltaTime to 0.005, though 0.0005 would be ideal.

My question: As a result of setting fixedDeltaTime so low, what kind of performance issues should I expect as I scale my scene by adding more satellites and custom assets? Is it advisable to use an alternate way of increasing frequency of physics updates?

The target device will be Hololens.

2

Physics usually don’t take much, but of course it depend on how much you do (how many rigidbodys you have I guess, and how much collisions there are). I run at 0.01 (100Hz) in a VR 2D platformer with a few moving objects and a fixed collider for the map . Don’t think 200Hz is problematic. Test it out in the Profiler (Window/Analysis/Profiler). Physics time used is shown on the main thread.