FA-69404 / Orbital propagation / Member archive

Mean anomaly propagation between epochs: Backward propagation leaves a negative mean anomaly · case 04

Propagating to an earlier epoch returns negative angles.

Member previewVariant 4 · 3 implementations · 7 checks per implementation

Case contract

Input [[y1,d1],[y2,d2],M0,n,ndot2]: epochs as calendar year and fractional 1-based day of year; M0 degrees at epoch 1; n revolutions per day; ndot2 is the published first derivative divided by two (rev/day^2). dt = epoch2-epoch1 in days (Gregorian calendar). M = (M0 + 360*(n*dt + ndot2*dt^2)) mod 360. Return [dt rounded 6, M rounded 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
mean anomaly propagation between epochs [[2026, 50.7], [2026, 50.2], 270.0, 16.0, 0.0]	`[-0.5, -90.0]`	`[-0.5, 270.0]`	Failed

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