Now that Mark has reached the MAV, he can finally reconnect with NASA. That's a good thing because the MAV will need to "lose some weight" to reach Hermes in orbit (25.8)
As it turns out, that's going to be quite the challenge. The first step will be ditching every life support and navigational system on the ship—after all, Mark will be wearing his suit and the MAV will be remotely piloted by Martinez.
The next step—which is more like a Superman-sized leap—is to essentially remove "the front of the ship (25.45). All they'll have to do is slap on a piece of Hab canvas with a little duct tape and it'll be perfect!
As Mark gets to work chopping up the MAV, Martinez is running through launch simulations—and failing. If he can't manage to steer it directly into the ship, Beck will have to go out into space and retrieve Mark manually.
It's now the eve of the mission and everyone—whether they're on Mars, Earth, or Hermes—is prepping for what will surely be the craziest day of their lives.