I’m on the clock. I have to figure out how to figure out what I need to know about the storm. And I have to do it now.

And right this second nothing comes to mind.

• • •

MINDY TRUDGED to her computer. Today’s shift began at 2:10 p. m. Her schedule matched Watney’s every day. She slept when he slept. Watney simply slept at night on Mars, while Mindy had to drift forty minutes forward every day, taping aluminum foil to her windows to get any sleep at all.

She brought up the most recent satellite images. She cocked an eyebrow. He had not broken camp yet. Usually he drove in the early morning, as soon as it was light enough to navigate. Then he capitalized on the midday sun to maximize recharging.

But today, he had not moved, and it was well past morning.

She checked around the rovers and the bedroom for a message. She found it in the usual place (north of the campsite). As she read the Morse code, her eyes widened.

“DUST STORM. MAKING PLAN.”

Fumbling with her cell phone, she dialed Venkat’s personal number.

CHAPTER 23

LOG ENTRY: SOL 476

I think I can work this out.

I’m on the very edge of a storm. I don’t know its size or heading. But it’s moving, and that’s something I can take advantage of. I don’t have to wander around exploring it. It’ll come to me.

The storm is just dust in the air; it’s not dangerous to the rovers. I can think of it as “percent power loss.” I checked yesterday’s power generation, and it was 97 percent of optimal. So right now, it’s a 3 percent storm.

I need to make progress and I need to regenerate oxygen. Those are my two main goals. I use 20 percent of my overall power to reclaim oxygen (when I stop for Air Days). If I end up in an 81 percent part of the storm, I’ll be in real trouble. I’ll run out of oxygen even if I dedicate all available power to producing it. That’s the fatal scenario. But really, it’s fatal much earlier than that. I need power to move or I’ll be stranded until the storm passes or dissipates. That could be months.

The more power I generate, the more I’ll have for movement. With clear skies, I dedicate 80 percent of my total power toward movement. I get 90 kilometers per sol this way. So right now, at 3 percent loss, I’m getting 2.7 kilometers less than I should.

It’s okay to lose some driving distance per sol. I have plenty of time, but I can’t let myself get too deep in the storm or I’ll never be able to get out.

At the very least, I need to travel faster than the storm. If I can go faster, I can maneuver around it without being enveloped. So I need to find out how fast it’s moving.

I can do that by sitting here for a sol. I can compare tomorrow’s wattage to today’s. All I have to do is make sure to compare at the same times of day. Then I’ll know how fast the storm is moving, at least in terms of percent power loss.