The plane’s crew started talking about Séparation de l’Atmosphère, and Sax listened closely. Although these people had been concerned with the revolution’s armaments and with basic materials research, while “Sep” as they called it had dealt with the more mundane world of mesocosm management, they still had a healthy respect for it. Designing strong tents and keeping them functioning was a task with very severe consequences for failure, as one of them said. Criticalities everywhere, and every day a potential adventure.

Sep was associated with Praxis, apparently, and each tent or covered canyon was run by a separate organization. They pooled information and shared roving consultants and construction teams. Since they deemed themselves necessary services, they ran on a cooperative basis— on the Mondragon plan, one said, nonprofit version— though they made sure to provide their members with very nice living situations and lots of free time. “They think they deserve it, too. Because when something goes wrong they have to act fast or else.” Many of the covered canyons had had close calls, sometimes the result of meteor strike or other drama, other times more ordinary mechanical failures. The usual format for covered canyons had the physical plant consolidated at the higher end of the canyon, and this plant sucked in the appropriate amounts of nitrogen, oxygen and trace gases from the surface winds. The proportions of gases and the pressure range they were kept at varied from mesocosm to mesocosm, but they averaged around five hundred millibars, which gave some lift to the tent roofs, and was pretty much the norm for indoor spaces on Mars, in a kind of invocation of the eventual goal for the surface at the datum. On sunny days, however, the expansion of air inside the tents was very significant, and the standard procedures for dealing with it included simply releasing air back into the atmosphere, or else saving it by compressing it into huge container chambers hollowed out of the canyon cliffs. “So one time I was in Dao Vallis,” one of the techs said, “and the excess air chamber blew up, shattering the plateau and causing a big landslide that fell down onto Reullgate and tore open the tent roof. Pressures dropped to the local ambient, which was about two hundred and sixty, and everything started to freeze, and they had the old emergency bulkheads,” which were clear curtains only a few molecules thick but very strong, as Sax recalled, “and when they deployed automatically around the break, this one woman got pinned to the ground by the supersticky at the bottom of the bulkhead, with her head on the wrong side! We ran over to her and did some quick cut and paste and got her loose, but she almost died.”