I've made experiments with a logarithmic depth buffer. Results is pretty cool, but there is a lot of work to do. On these screenshots I used astronaut and Discovery model from Doc's 2001 ships pack. Their sizes are real, not exaggerated as Doc originally made. No near plane clipping and no z-fighting.
This will be not enabled in next patch by default, because full supporting of a log Z-buffer requires a lot of changes in the engine. There are two ways of using logarithmic Z-buffer: in a vertex shader and in a pixel shader. First gives artifacts on close or long triangles - their Z value interpolated incorrectly (perspectively). The second method fixes that, but kills FPS to almost zero: SpaceEngine have a huge overdraw on planets, so disabling fast Z test (that required for this method) makes complex planetary surface shader with atmospheric effect to apply to huge amount of pixels.
Anyway, I plan implement a deferred shading pipeline in SpaceEngine, and logarithmic Z-buffer is a first step to it. Deferred pipeline have a lot of benefits: fast Z-pass (that will speedup logarithmic Z buffer in a pixel shader), atmosphere as a post effect (that will speedup it a lot, because there will be no overdraw, and apply it to a planetary surface and ships that are in the atmosphere simultaneously), hundreds of lights (requires for ships at first place), proper lens flare occlusion, and many other.