Acquisition, Historical Context, and Installation of Legacy KSP Version 0.25 (Demo/Legacy Build)
Many older, classic mods were optimized for this specific version. If a specific mod hasn't been updated in years, 0.25.0.642 is often the best "legacy" environment to run it, as noted by community members on the Kerbal Space Program Forums . Kerbal Space Program -KSP- 0.25.0.642 download for computer