It's been 60 days since we last checked in with Mark and his rover modifications have been completed.
Now comes the hard part—actually planning the course. While the journey to Pathfinder was on smooth, flat ground, this 3200 kilometer journey is filled with "massive elevation changes" and rough terrain (20.34).
To combat this, Mark charts a course down the Mawrth Valley, a long valley formed by an ancient river. That'll get him half of the way there, but that's when things will get tricky.
In the meantime, Mark continues "prepping the rover" (20.112). He uses a pop-tent to make a bigger camping area for himself and hooks up the oxygenator. With 59 days left until that fateful journey, Mark is finally ready to go.