SpaceEngineer! Hi! I've always been interested in procedural generation. Have you ever thought about implementing Simplex noise? Ken Perlin designed it to be faster than his Perlin noise algorithm.
Simplex noise could be used in the tg_common.glsl shader. But it would lead to complete change of the planet surface of course. I didn't saw much acceleration after switch on the simplex noise. Modern GPUs are so fast so differecу is negliegable. So I switched back to perlin noise, because I have working functions of perlin noise derivatives, which are used in some fractals.
p.s. I'm not sure, but is it possible for SpaceEngine to use a noise function like this to generate volumetric clouds?
Volumetric clouds is a rendering system on the first place. It is not implemented yet and cannot be implemented easily, so it is too early to talk about which noise functions to use for clouds.