FA-69533 / Orbital propagation / Member archive

Fixed-step RK4 two-body propagation: Acceleration uses |r|^2 in the vector form · case 03

Gravity has the wrong falloff and scales with distance.

Member previewVariant 3 · 3 implementations · 7 checks per implementation

Case contract

Input [r0, v0, mu, T, steps] for a planar two-body orbit. Integrate state [x,y,vx,vy] with acceleration -mu r/|r|^3 using classical RK4 with h=T/steps for exactly steps steps. Return the final state rounded to 6 decimals.

Why this case matters

Orbit determination and mission planning chain many small conversions; one wrong branch or unit silently moves a spacecraft by kilometres.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
fixed-step rk4 two-body propagation [[0.0, 9000.0], [-6.2, 0.8], 398600.4418, 1200.0, 15]	`[18550.875826, -1065213.845329, 10.634364, -570.845461]`	`[-6593.162659, 6759.502773, -4.170281, -4.18782]`	Failed

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