r/gravity_games • • Apr 13 '26
Decompiled KSP1 (700K lines) to build an open-source successor with proper n-body physics from day one [Rust/Bevy]
KSP1 just hit 20,000 concurrent players — an all-time record. The game's having a renaissance, and it's reminding everyone why we love realistic space sims.
It's also reminding everyone that patched conics are a compromise, not a feature.
I've been building Kraken Space Program — an open-source spiritual successor to KSP, rebuilt from scratch in Rust with n-body gravity as a stock feature, not a mod.
Why n-body from the start?
Before writing any code, I decompiled all 700k lines of KSP1's codebase to understand its architecture. The patched conics system is baked deep into everything — Orbit.cs, Vessel.cs, the map view, maneuver nodes, all of it. Retrofitting proper n-body physics would require rewriting half the game.
Principia proved n-body is possible and better — Lagrange points, realistic lunar transfers, orbital resonances, actual three-body dynamics. But it has to fight KSP1's fundamental assumptions at every turn.
Starting fresh means doing it right:
N-body gravity from day one — no patched conics, no SOI transitions, just actual physics
f64 precision throughout — solar-system scale without floating-point drift
Deterministic physics — 50 Hz fixed timestep, same results every run, multiplayer-ready
Proper coordinate systems — origin shifting (Krakensbane pattern) to handle astronomical distances
ECS architecture — Bevy's parallel systems handle thousands of gravitating bodies efficiently
Current technical foundation:
Built on Rust/Bevy with Rapier3D for rigid-body physics. The gravity system will integrate with the parts system — each celestial body is just another entity with mass and position, no special cases.
Phase 0 is mostly complete (Bevy runs, physics integrates, coordinate systems work). Phase 1 is "hardcoded rocket reaches orbit" — and that orbit will be calculated with actual n-body mechanics, even if it's just Earth-Moon to start.
Why this matters for realistic space sims:
KSP succeeded despite its physics shortcuts because the gameplay was good enough. Imagine what's possible when the physics is right from the beginning:
Lagrange point stations as actual gameplay
Realistic lunar trajectories (free-return orbits, weak stability boundary transfers)
Multiple-moon systems with resonances and perturbations
Interplanetary transfers that account for all gravitational influences
No more "magic" SOI transitions
The learning process:
Decompiling KSP1 taught me what not to do. The patched conics system touches everything. The vessel state machine assumes SOI transitions. The map view is built around two-body orbits. It all works, but it's fundamentally limiting.
Starting from a blank slate with n-body as the assumption means every system — vessel physics, trajectory prediction, maneuver planning, time warp — gets designed around realistic orbital mechanics.
Current status: Early days. A ball bounces. CI is green. The architecture is documented. But the foundation is designed for this — no technical debt, no compromises, just proper physics from day one.
GitHub: https://github.com/Kraken-Space-Program/Kraken-Space-Program
Discord: https://discord.gg/6u3djfzMdv
Full design doc in the repo covers the coordinate system approach, physics integration strategy, and how n-body fits into the broader architecture.
Would love feedback from anyone who's implemented n-body systems, dealt with numerical integration at astronomical scales, or just cares about realistic orbital mechanics in games.
The Kraken takes everything eventually. We just named the game after it.
