Urine is mostly water. Separating hydrogen and oxygen only requires a couple of electrodes and some current. The problem is collecting the hydrogen. I don't have any equipment for pulling hydrogen out of the air. The Atmospheric Regulator doesn't even know how. The last time I had to get hydrogen out of the air (back when I turned the Hab in to a bomb) I burned it to turn it in to water. Obviously that would be counter-productive.

But NASA thought everything through and gave me a process. First, I disconnected the rover and trailer from each other. Then, while wearing my EVA suit, I depressurized the trailer and back-filled it with pure oxygen at one fourth of an atmosphere. Then I opened a plastic box full of urine and put a couple of electrodes in. That's why I needed the atmosphere. Without it, the urine would just boil immediately and I'd be hanging around in an piss-based atmosphere.

The electrolysis separated the hydrogen and oxygen from each other. Over time, it reduced the urine to a really gross sludge as it pulled the water out. Now the trailer was full of even more oxygen and also hydrogen. Pretty dangerous, actually.

Then I fired up the Atmospheric Regulator. It doesn't even recognize hydrogen, but it knows how to yank oxygen out of the air. I broke all the safeties and set it to pull 100% of the oxygen out. After it was done, all that was left was hydrogen. That's why I started out with an atmosphere of pure oxygen. So the regulator could separate it later.

Then I opened the inner airlock door and had it evacuate the trailer. It pumped all the air in to the airlock's holding tank. And there you have it, a tank of pure hydrogen.

The final step was to take the airlock's holding tank to the MAV and transfer the contents to the MAV's hydrogen tanks. I've said this many times before but: Hurray for standardized valve systems!

Once I fed it the hydrogen, I fired up the fuel plant and it got to work making the additional fuel I'd need.

I'll need to go through this process several more times as the launch date approaches. I could have done this all at once, but NASA doesn't want me to run low on water until we're close to launch. They'd rather I electrolyze urine over time because I've already “used” that water.

If I survive this, I'll tell people I pissed my way in to orbit.

[19:22]JOHANSSEN: Hello, Mark.

[19:23]MAV: Johanssen!? Holy crap! They finally letting you talk to me directly?

[19:24]JOHANSSEN: Yes, NASA gave the OK for direct communication an hour ago. We're only 35 light-seconds apart, so we can talk in near-realtime. I just set up the system and I'm testing it out.

[19:24]MAV: What took them so long to let us talk?

[19:25]JOHANSSEN: The psych team was worried about personality conflicts.

[19:25]MAV: What? Just cause you guys abandoned me on a godforsaken planet with no chance of survival?

[19:26]JOHANSSEN: Funny. Don't make that kind of joke with Lewis.

[19:27]MAV: Roger. So uh... thanks for coming back to get me.

[19:27]JOHANSSEN: It's the least we could do. How is the MAV retrofit going?

[19:28]MAV: So far, so good. NASA put a lot of thought into the procedures. They work. That's not to say they're easy. I spent the last 3 days removing Hull Panel 19 and the front window. Even in Mars-G they're heavy motherfuckers.

[19:29]JOHANSSEN: When we pick you up, I will make wild, passionate love to you. Prepare your body.

[19:29]JOHANSSEN: I didn't type that! That was Martinez! I stepped away from the console for like 10 seconds!

[19:29]MAV: I've really missed you guys.

LOG ENTRY: SOL 543

I'm... done?

I think I'm done.

I did everything on the list. The MAV is ready to fly. And in 6 sols, that's just what it'll do. I hope.

It might not launch at all. I did remove an engine, after all. I could have fucked up all sorts of things during that process. And there's no way to test the ascent stage. Once you light it, it's lit.

Everything else, however, will go through tests from now until launch. Some done by me, some done remotely by NASA. They're not telling me the failure odds, but I'm guessing they're the highest in history. Yuri Gagarin had a much more reliable and safe ship than I do.

And Soviet ships were fucking deathtraps.

“All right,” Lewis said, “tomorrow's the big day.”

The crew floated in the Rec. They had halted the rotation of the ship in preparation for the upcoming operation.

“I'm ready,” Martinez said. “Johanssen threw everything she could at me. I got all scenarios to orbit.”

“Everything other than catastrophic failures,” Johanssen corrected.

“Well yeah,” Martinez said. “Kind of pointless to simulate an ascent explosion. Nothing we can do.”

“Vogel,” Lewis said, “How's our course.”

“It is perfect,” Vogel said. “We are within one meter of projected path and two centimeters per second of projected velocity.”

“Good,” she said. “Beck, how about you?”

“Everything's all set up, Commander,” Beck said. “I linked all the tethers I could find and spooled them up in Airlock 2. My suit and MMU are prepped and ready.”

“Ok,” Lewis said. “The battle plan is pretty obvious. Martinez will fly the MAV, Johanssen will sysop the ascent. Beck and Vogel, I want you in Airlock 2 with the outer door open before the MAV even launches. You'll have to wait 52 minutes, but I don't want to risk any technical glitches with the airlock or your suits. Once we reach intercept, it'll be Beck's job to get Watney.”

“He might be in bad shape when I get him,” Beck said. “The stripped-down MAV will get up to 12 g's during the launch. He could be unconscious and may even have internal bleeding.”

“Just as well you're our doctor,” Lewis said. “Vogel, if all goes according to plan, you're pulling Beck and Watney back aboard with the tether. If things go wrong, you're Beck's backup.”

“Ja,” Vogel said.

“I wish there was more we could do right now,” Lewis said. “But all we have left is the wait. Your work schedules are cleared. All scientific experiments are suspended. Sleep if you can, run diagnostics on your equipment if you can't.”

“We'll get him, Commander,” Martinez said. “24 hours from now, Mark Watney will be right here in this room.”

“Let's hope so, Major.” Lewis said. “Dismissed.”

“Final checks for this shift are complete,” Mitch said in to his headset. “Timekeeper.”

“Go, flight,” said the Timekeeper.

“Time until MAV launch?”

“16 hours, 9 minutes, 40 seconds... mark.”