Watney continues on his drive, as everyone on Earth—including NASA and those watching the Watney Report—follows along. Everyone except Watney knows, from NASA’s Mars satellites, that Watney is approaching, then soon engulfed in, a low-level dust storm. Watney doesn’t see this for many days, although he does notice the terrain getting rougher, as he attempts to navigate without a nav system (using a makeshift instrument of his own). Somewhere in a long, shallow crater en route to Schiaparelli, Watney begins to see that his rover has been moving more slowly, and that the visibility outside is “asymmetric.” He deduces that a dust storm is approaching him, which would account for the sluggishness of the vehicle. And he understands quickly that, in order to survive, he must “outrun” the storm by picking the correct, “shorter” edge of it, and hoping he has enough power, on that longer route, still to make Schiaparelli by the appointed time.
As always, Watney comes up with a brilliant plan to measure the dust storm and avoid its worst effects. He places solar panels in a row, many kilometers apart, and sets up cameras to measure their charging potential during a solar day. He realizes, after doing this, that the storm is moving to the north, because the southernmost panel absorbs the most solar energy. Thus, he correctly adjusts his course to the south, then back east, to reach Schiaparelli crater with only a small disruption to his schedule. If he had stayed pat and continued on a straight line for the crater, he would’ve run out of power for the panels and been stuck; but Watney’s ingenuity once again comes to his rescue. On approaching Schiaparelli crater, however, Watney’s rover strikes an uneven, soft-hard patch of Martian soil, causing the rover to flip on its side.
Watney is able to escape the roll unhurt by “curling himself into a ball.” He breaks a few solar panels on the rover, and the trailer attached to the rover is bent with its coupling broken (although there’s another hitch as backup). Watney spends four days making sure the rover is back in shape, and he tacks a backup solar panel onto the side to help make up for some of the lost power. Watney resolves to drive at 5 kph for the rest of the trip to Schiaparelli, which is painstaking but safe. NASA turns on the homing beacon on the Ares 4 MAV site, so that, as Watney approaches, he no longer needs to navigate by site, but can follow his rover’s own nav system. When he reaches the Ares 4 MAV, his rocket into space to rendezvous with the Hermes crew, he is overjoyed, and finally admits to himself that he just might manage to escape Mars alive.
Watney spends nearly a month making the “invasive modifications” that NASA requests for the MAV, allowing it to blast off into space for rendezvous effectively. Essentially, Watney needs to use extra water to generate extra fuel (some of his urine goes to this purpose); he also rips out unneeded Ares 4 material, bringing the weight of the MAV down significantly. In the leadup to the rendezvous launch, Watney is extremely nervous, perhaps more scared than he’s been at any point on the Ares 3 mission and its aftermath. But he also knows he’s very close to a final meeting with Ares 3, and a trip home.
Watney doesn’t need to steer the MAV, as NASA will take care of all navigation. He only needs to survive the many Gs he’ll pull on rocketing off the surface of Mars. The liftoff goes well, but as the MAV rises into Mars’s atmosphere (and with much of Earth’s television audience watching), the quickly-redesigned ship teeters somewhat off its planned course for the Hermes, winding up over 60 km away. The Hermes crew doesn’t want to burn any excess fuel, nor to overshoot the MAV with Watney inside, as they’ll only have one chance to meet up with him and pull him back into the Hermes. Fortunately, the Ares 3 crew has a clever idea, and Vogel creates a small “bomb,” which the crew uses to blow a hole in an airlocked portion of the Hermes. This hole allows the Hermes to redirect toward Watney, and Beck leaps out of the vessel (with his navigational spacesuit on), to pry Watney from the MAV and bring him back to Hermes alive.
Watney has been unconscious for much of his rocket flight back into space, and he remarks that he’s cracked some ribs owing to the gravitational force. But he’s beyond happy to be alive and back with his crew. Commander Lewis reports to Houston that Watney has been recovered, and as the entire crew celebrates together, with Watney recovering, they begin their journey back to Earth. The novel ends.
The novel’s conclusion has a mood of slowly ramping-up tension, as Watney first reaches the Ares 4 MAV, then goes about gutting it to make it space-ready in a short period of time. The novel itself seems to accelerate once it reaches this stage. Watney can’t wait to reunite with the Hermes crew and begin his trip back home, and the reader can’t wait for the same things to happen. Watney and the reader, by this stage of the novel, are united in a common project: making sure he gets home safe. Once again, the motif of small deviations (with big results) is evident here. Tiny variations in Watney’s blast-off from Mars, in the MAV, result in his being far away from Hermes once he reaches outer space. But the Hermes crew, like Watney, is resourceful and patient, and the improvised, controlled “explosion” that redirects Hermes saves Watney’s life (although it also damages an extraordinarily expensive ship).
By the end of the novel, the reader can take stock of the costs and, of course, the benefits of Watney’s rescue. As throughout, Watney himself, the crew, and NASA raise the question of just how much help one human deserves in making his or her way back home. NASA has demonstrated that they are willing to spend any amount to bring Watney home alive. But as Weir realistically renders the NASA bureaucracy, this decision—to rescue Watney regardless of cost—has an implicit benefit to NASA’s public relations strategy, perhaps making it easier, down the line, for the organization to secure funding from Congress.
Indeed, by the end of the text, a final theme is present: that of “cost-benefit analysis.” No decision is without its costs, and even successful decisions can have side effects that are difficult to accept. Lewis leaves Watney behind because it’s the right move for the rest of the crew—but she has abandoned a shipmate whom she goes on to rescue. Watney’s many small decisions on Mars—especially his more experimental efforts to make water, irrigate, and farm—occasionally result in dangerous situations that imperil his living space, even as he tries to improve it. Back on Earth, NASA is willing to spend enormously, as is the American government, but a perceptive reader understands that a fraction of this money could help lift a large number of American citizens to escape earthly dangers, like poverty and illness. With all that said, Watney’s joy, on rejoining his crewmates, is a pure and exciting one, and the novel captures, in thrilling detail, the practical, scientific decision-making that’s brought him home.