The massive airlock doors in the granite walls parted with a loud hydraulic hiss, and a small gush of water poured out onto the ferroconcrete floor. Trundling in on rusty rails, the cargo box clanked and rattled through the locks and on deep into the maze of machinery before coming to rest at a padded buffer. The double doors closed with a strident boom and then hissed again, prominent wall gauges showing pressure being reestablished on the other side.