The execute package wasn’t so much a detailed time line, as the first generations of astronauts had had to follow, but a “shopping list” of objectives. Mission planning was a lot more laid-back, compared to the days when moonwalks had been choreographed down to the minute. The shopping list approach had evolved during the long-duration Skylab flights of the 1970s. York was relieved; she was a senior professional, after all — they all were — and she didn’t need her activities handheld by some remote roomful of experts down in Houston.

In her pocket, to help her with the timing, she carried a small personal alarm clock, a cute clockwork thing she’d picked up from a five-and-dime in a mall in Nassau Bay. Its crudity and lack of accuracy appealed to her, in the midst of all that high technology.

Her main objective for the day was going to be powering up the Ares Transfer-Orbit Science Platform. She drifted upward, along the cylindrical length of the Mission Module.

The Mission Module was based on the design of the Skylabs, which had been in use for more than a decade. Such was the lifting capacity of the Saturn VB that the Mission Module had been delivered to Earth orbit “dry” — carrying no fuel — and with interior partitions and equipment already fitted. The crew occupied what had been the hydrogen tank, all forty-eight feet of it, with its domed ceiling and floor. Hidden under the floor was the lox tank, much smaller, a cramped, squashed sphere. The lox tank was used to hold stores, and with its thicker walls it would serve as the crew’s storm shelter — shielding them from solar flares, if any blew up in the course of the mission.

The hydrogen tank was split into three levels by partitions of triangular metal mesh. York was wearing Dutch shoes, with V-flanges in the sole, to enable her to cling to either side of the floors. There was a fireman’s pole running down the middle of the workshop, and there were straps and guide ropes and harnesses everywhere.

The tank’s bottom level was “home” — the wardroom, sleep and waste compartments. The middle belt doubled as a command and control area, covering all of the spacecraft’s subsystems, environmental processes, and flight operations, and as an experiment and exercise area, with a running strip around the tank’s circular wall. The exercise machines, still in their launch configuration, were strapped against the pressure hull. And the top level, closest to the prow of the Ares cluster, was the Science Platform.

The whole module was something like a big engine room, York thought, with clunky tanks and storage boxes stuck to the curved walls, and cables and pipes running everywhere, under smooth covers of yellow plastic.