It's Day 63 and things are looking up—well, as much as they can be, given the circumstances. The water has been produced, the potatoes are "growing nicely" and there has been a distinct lack of explosions (7.1). What a dream, eh?
Although Mark doesn't know that NASA's watching, he also sees Ares 4 as his only chance for escape. Of course, that'll still require him to drive about 3,200 km to Schiaparelli Crater, where the Ares 4 Hab is located. (And he'll still have to wait four years.)
In order to make perilous trip possible, Mark will have to modify one of his rovers as if he were on Pimp My Ride: Mars Edition.
First, he takes Rover 1's battery and installs it in Rover 2. This helps, but it's not enough—especially because he has to expend a ton of energy on heat. Mars is freezing, and Mark's suit is getting cold. He gets himself a bit of extra charge by attaching a few of the Hab's solar cells as well.
Now that Rover 2 is completed, Mark prepares to test out his newfangled contraption in a mission he dubs "Sirius 1." He still hasn't solved the heat problem, so he throws on a few extra sweaters and calls it a day.
Sirius 1 doesn't go great. Though the rover runs like a Lamborghini, it's way too chilly out on the Martian surface for him to make it all the way to the Ares 4 site.
Enter the RTG. Before Mark and his crewmates arrived, the MAV was powered by something called the RTG, a "big box of plutonium" more dangerous than a nuke (7.83). As per mission protocol, Commander Lewis buried it south of the Hab and marked it with a giant green flag.
So why does this matter? Well, being a highly dangerous ball of energy, the RTG is hotter than the Fourth of July in South Florida.
All praises be to that giant green flag, because it only take Mark a few minutes to locate the buried RTG. This thing is hot—so hot, in fact, that Mark has to tear out some of the rover's insulation in order to stay temperate.
After running a successful test, looting the Hab's backup oxygen tanks, and prepping the Hab to self-water his potato field, Mark prepares for his most ambitious test yet. Wish him luck, guys.