FA-69452 / Orbital propagation / Member archive

Two-line element set line 1: Negative BSTAR loses its sign · case 02

Negative drag terms become positive.

Member previewVariant 2 · 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 33333U 99025B 99032.25000000 .00012345 00000-0 -50000-3 0 176"	`[1999, 32.25, 0.00012345, 0.0005, false]`	`[1999, 32.25, 0.00012345, -0.0005, false]`	Failed

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