Fortunately, I have accurate clocks. There are four computers in my immediate line of sight right now. And I have Phobos.

Because Phobos is ridiculously close to Mars, it orbits the planet in less than one Martian day. So it travels west to east (unlike the sun and Deimos) and sets every 11 hours. And naturally, it moves in a very predictable pattern.

I spend 13 hours every sol just sitting around while the solar panels charge the batteries. Phobos is guaranteed to set at least once during that time. I note the time when it does. Then I plug it in to a nasty formula I worked out and I know my longitude.

So, working out longitude requires Phobos to set, and working out latitude requires it to be night so I can sight Deneb. It's not a very fast system. But I only need it once a day. I work out my location when I'm parked, and account for it in the next day's travel. It's kind of a successive approximation thing. So far, it's been working.

Mindy Park zoomed in on the latest satellite photo with practiced ease. Watney's encampment was visible in the center, the solar cells laid out in a circular pattern as was his habit.

The bedroom was inflated. Checking the timestamp on the image, it was from noon local time. She quickly found the status report; Watney always placed it close to the rover when rocks were in abundance, usually to the north.

To save time, Mindy had taught herself Morse Code so she wouldn't have to look each letter up every morning. Opening an email, she addressed it to the ever-growing list of people who wanted Watney's daily status message.

“ON TRACK FOR SOL 495 ARRIVAL.”

She frowned and added “Note: 5 sols until Tau Event entry.”

LOG ENTRY: SOL 466

Mawrth Vallis was fun while it lasted. I'm in Arabia Terra now.

I just entered the edge of it, if my latitude and longitude calculations are correct. But even without the math, it's pretty obvious the terrain is changing.

For the last two sols, I've spent almost all my time on an incline, working my way up the back wall of Mawrth Vallis. It was a gentle rise, but a constant one. I'm at a much higher altitude now. Adicalia Planitia (where the lonely Hab is hanging out) is 3000m below elevation zero, and Arabia Terra is 500m below. So I've gone up two and a half kilometers.

Want to know what's at elevation zero? On Earth, it's sea level. Obviously, that won't work on Mars. So lab-coated geeks got together and decided Mars's elevation zero is wherever the air pressure is 610.5 Pascals. That's about 500 meters up from where I am right now.

Now things get tricky. In Acidalia Planitia, if I got off-course, I could just point in the right direction based on new data. Later, in Mawrth Vallis, it was impossible to fuck it up. I just had to follow the canyon.

Now I'm in a rougher neighborhood. The kind of neighborhood where you keep your rover doors locked, and never come to a complete stop at intersections. Well, not really, but it's bad to get off-course here.

Arabia Terra has large, brutal craters that I have to drive around. If I navigate poorly, I'll end up at the edge of one. I can't just drive down one side and up the other. Rising in elevation costs a ton of energy. On flat ground, I can make 90km per day. On a steep slope, I'd be lucky to get 40km. Plus, driving on a slope is dangerous. One mistake and I could roll the rover. I don't even want to think about that.

Yes, I'll eventually have to drive down in to Schiaparelli. No way around that. I'll have to be really careful.

Anyway, if I end up at the edge of a crater I'll have to backtrack to somewhere useful. And it's a damn maze of craters out here. I'll have to be on my guard; observant at all times. I'll need to navigate with landmarks as well as latitude and longitude.

My first challenge is to pass between the craters Rutherford and Trouvelot. It shouldn't be too hard. They're 100km apart. Even I can't fuck that up, right?

Right?

LOG ENTRY: SOL 468

I managed to thread the needle between Rutherford and Trouvelot nicely. Admittedly, the needle was a 100km wide, but hey.

I'm now enjoying my fourth Air Day of the trip. I've been on the road for 20 sols. So far, I'm right on schedule. According to my maps, I've traveled 1,440km. Not quite halfway there, but almost.

I've been gathering soil and rock samples from each place I camp. I did the same thing on my way to Pathfinder. But this time, I know NASA's watching me. So I'm labeling each sample by the current sol. They'll know my location a hell of a lot more accurately than I do. They can correlate the samples with their locations later.

It might be a wasted effort. The MAV isn't going to have much weight allowance when I launch. To intercept Hermes, it'll have to reach escape velocity, but it was only designed to get to orbit. The only way to get it going fast enough is to lose a lot of weight.

At least that jury-rigging will be NASA's job to work out, not mine. Once I get to the MAV, I'll be back in contact with them and they can tell me what modifications to make.

They'll probably say “Thanks for gathering samples. But leave them behind. And one of your arms, too. Whichever one you like least.” But on the off-chance I can bring them, I'm gathering them.

The next few days travel should be easy. The next major obstacle is Marth Crater. It's right in my straight-line path toward Schiaparelli. It'll cost me a hundred kilometers or so to go around, but it can't be helped. I'll try to aim for the southern edge. The closer I get to the rim the less time I waste going around it.

“Did you read today's updates?” Lewis asked, pulling her meal from the microwave.

“Yeah,” Martinez said, sipping his drink.

She sat across the Rec table from him. Carefully opening the steaming package, she let it cool for a moment before eating. “Mark entered the dust storm yesterday.”

“Yeah, I saw that,” he said.

“We need to face the possibility that he won't make it to Schiaparelli,” Lewis said. “If that happens, we need to keep morale up. We still have a long way to go before we get home.”

“He was dead before,” Martinez said. “It was rough on morale, but we soldiered on. Besides, he won't die.”

“It's pretty bleak, Rick,” Lewis said. “He's already 50km in to the storm, and he'll go another 90km per sol. He'll get in too deep to recover soon.”

Martinez shook his head. “He'll pull through, Commander. Have faith.”

She smiled forlornly. “Rick, you know I'm not religious.”

“I know,” he said. “I'm not talking about faith in God, I'm talking about faith in Mark Watney. Look at all the shit Mars has thrown at him, and he's still alive. He'll survive this. I don't know how, but he will. He's a clever son-of-a-bitch.”