Chapter 18

On Sol 197, Mark Watney accepts he has lost communications and must design the rover/trailer for the Ares 4 trek alone. Confronting power limits, he drops the water reclaimer to save energy and analyzes the Big Three loads, discovering the oxygenator actually draws far less due to his single-person CO2 load.

On Sols 198–199, Watney details the atmospheric regulator’s supercooling cycle and realizes most of its power heats return air. He plans to run the regulator continuously and use stored liquid oxygen to backfill O2, dedicating occasional “air sols” to run the oxygenator. He repurposes the RTG’s heat to warm return air, reducing the regulator’s power from 21.5 to about 1 “pirate-ninja,” validating the approach with tests.

On Sol 200, he load-tests the rover and trailer with rocks to simulate mass, achieving only 57 km per charge and projecting a 92-sol journey if stopping frequently for oxygen—a duration he deems intolerable. On Sols 201–207, after injuring his back, he uses Vicodin and constructs an RTG-heated bathtub from Johanssen’s cot to recuperate. He also refines plans to carry far more solar panels and to add extra battery capacity to reduce air-sol frequency and increase daily range. He informs NASA via rock Morse that he was injured but is continuing work.

On Sols 208–209, he experiments with panel stowage, then fabricates L-bracket shelves from MAV struts to mount panels along the rover and trailer sides. He successfully secures twenty-eight panels after road tests and restores them to the farm overnight.

By Sol 211, Watney strips nonessential gear from the rover and trailer, reinstalls the trailer’s battery, and fits two large Hab batteries inside the trailer, wiring them into the system. With 29 panels and 36 kWh storage, he expects roughly 100 km per sol four days out of five, significantly shortening the trip. He closes with anxiety over the upcoming Chinese resupply launch that Hermes needs.