FA-69549 / Orbital propagation / Member archive

Velocity Verlet two-body propagation: Position drift omits the one-half acceleration factor · case 04

Positions overshoot toward the central body every step.

Member previewVariant 4 · 3 implementations · 7 checks per implementation

Case contract

Input [r0, v0, mu, T, steps]; planar two-body. Velocity Verlet with h=T/steps: p += h v + h^2 a/2; a_new = a(p); v += h (a + a_new)/2; carry a_new. Return final [x,y,vx,vy] rounded to 6 plus specific energy v^2/2-mu/|r| rounded to 6.

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
velocity verlet two-body propagation [[1.0, 0.0], [0.0, 1.0], 1.0, 3.0, 30]	`[-0.496093, -0.374943, 0.867143, -0.913719, -0.814709]`	`[-0.993552, 0.151005, -0.14987, -0.983712, -0.499988]`	Failed

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