Relativity

Relativity adds the sub-light half of special relativity to KSP, as a gameplay layer and the view out the window.

As your vessel approaches the speed of light, effective engine thrust falls as 1/γ³. The same engine pushes less and less the faster you go, so c becomes a barrier you can approach but never cross. Propellant still burns at its normal rate; what degrades is efficiency, not the fuel bookkeeping. Meanwhile time dilation slows the crew's clock, so they age and consume life support (food, water, oxygen) slower by 1/γ. Radiation dose, however, keeps ticking on coordinate time. Getting fast is hard, but a fast crew endures, and radiation is what actually limits the trip.

Since v1.0 there is also an optional visual layer showing what the crew would actually see: the sky ahead blueshifts and brightens (Planck-exact Doppler colour and beaming), the sky behind reddens and dims, the starfield bunches toward your heading (the "starbow", with a live rear camera keeping the magnified aft sky sharp), and planets, sun and sunflare shift to their aberrated bearings. Purely cosmetic, gated like the physics, off in map view so navigation stays truthful. Costs about +1.7 ms/frame on a light craft.

The mod modulates force and consumption rate only. It never rewrites the physics integrator, which is what makes it safe alongside Principia and identical on the stock flight model.

Features

• Relativistic thrust correction (net thrust F/γ³), verified in flight.
• The relativistic visual layer, verified in-game at β ≈ 0.98. Scatterer optional (exact sunflare separation); TextureReplacer skyboxes picked up automatically.
• A toolbar flight dashboard: β, γ, effective thrust %, supply-rate %.
• A two-clock counter: mission (coordinate) time vs crew (proper) time, per vessel.
• A VAB/SPH trip planner: cruise β, mission vs crew time, and accel/coast breakdown for a target distance.
• Kerbalism life-support dilation (radiation excluded), RP-1 relativistic-retirement crediting, and reaction-wheel/RCS attitude slowdown near c.

Requirements

• Harmony2

Status

v1.0.0: core relativistic flight and the visual layer are verified in-game. Some integrations (two-clock counter, trip planner, Kerbalism dilation, RP-1) are built and compile-clean but not yet play-tested; reports on the GitHub issue tracker are very welcome. Back up your save before a long relativistic mission.

Source, changelog, and full docs: https://github.com/Vannadin/Relativity Wiki: https://github.com/Vannadin/Relativity/wiki License: MIT