FA-69527 / Orbital propagation / Member archive

Fixed-step RK4 two-body propagation: RK4 stages are averaged equally · case 02

Energy drifts much faster than expected for the step size.

Member previewVariant 2 · 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 [[7000.0, 0.0], [0.0, 8.5], 398600.4418, 900.0, 20]	`[4101.502929, 6610.326481, -5.692359, 5.333101]`	`[4101.15166, 6610.394483, -5.692596, 5.332573]`	Failed

MEMBER ARCHIVE

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This record includes three runnable implementations, regression fixtures, execution results, and source hashes.

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