FA-69444 / Orbital propagation / Member archive

Two-line element set line 1: Two-digit epoch years pivot at 50 · case 04

Element sets from 1950-1956 or 2050-2056 are placed in the wrong century.

Member previewVariant 4 · 3 implementations · 7 checks per implementation

Case contract

Input one TLE line-1 string (exactly 69 characters, starting "1", else None). Epoch year from columns 19-20 (57-99 -> 1900s, 00-56 -> 2000s), epoch day 21-32, ndot/2 34-43, BSTAR 54-61 in assumed-decimal exponent form (" 34123-4" = 0.34123e-4, sign first), checksum column 69 (digits plus 1 per "-", mod 10). Return [year, day, ndot2, bstar rounded 14, checksum_ok].

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
two-line element set line 1 "1 45555U 19050Z 50200.12500000 -.00000001 00000-0 99999-9 0 12343"	`[1950, 200.125, -1e-08, 9.9999e-10, true]`	`[2050, 200.125, -1e-08, 9.9999e-10, true]`	Failed

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