As winter gave way to spring in the northern hemisphere of Mars, the prevailing winds of the latitude of the Ares III Hab began to shift. What during the winter ran west to east fluctuated, becoming east to west, with what passed for strong gusts in Mars's attenuated atmosphere.

What is winter in a planet's northern hemisphere is summer in its southern hemisphere. Just before the arrival of the Ares III crew on Mars, the warming of the surface in the south produced an unusually strong dust storm, strong enough to cross the equator. By a series of coincidences and unintended consequences, the ESA Amicitas’s unplanned entry into the Martian atmosphere had amplified this storm to levels not seen on the planet since the last major volcanic eruption. These winds had battered the eastern face of the Hab, in particular Airlock 1. Airlocks 2 and 3, facing southwest and northwest respectively, had been sheltered by the rest of the Hab.

Two much smaller dust storms, brief and feeble, had visited the Hab since the day of the Ares III abort and the Amicitas crash-landing. Smaller events, like the dust devil witnessed by two of Amicitas’s crew on Ares III Sol 84, hit the hab almost all the time. By freaks of the gradually warming northern weather, these almost invariably struck the Hab on its eastern face.

Under normal circumstances none of this should have been cause for alarm. The materials the Hab was constructed of, and the methods of assembly, had been tested by NASA engineers in an Earth environment as well as simulated Martian environments. The canvas which made up the inflatable dome of the Hab, in particular, had been tested to withstand wind forces up to Category 1 hurricane levels in an Earth atmosphere. Even the freak storm of Sol 6 posed only a relatively minor danger to the Hab, and the other storms no danger at all.

But the stress tests had never taken into consideration the constant use and abuse the Hab canvas, particularly near its seams with hard metallic edges, would see over a mission extended beyond the planned 60-day maximum. Just as a man can wear a hole into granite with feathers given infinite time and patience, so also can repeated long-term strain on a particular point break down something tested and proven to hold up to abuse in the short term.

The Sol 6 storm had opened a tiny flaw in the canvas, hidden by the two-piece clamp that held it in place around Airlock 1. The flaw flexed with every airlock use, stretching and relaxing as the airlock pressurized and depressurized. The hab’s final human inhabitant preferred that airlock because it was adjacent to the rover recharge station. Its alien inhabitants preferred it because it was the most direct route to Site Epsilon and its massive crystal cave. Thus Airlock 1 saw repeated use almost every sol, with Airlock 3 used solely for visits to the remaining portion of Amicitas and Airlock 2 relegated to the status of storage closet.

No visual search would have turned up the leak. The flange it was glued to hid it from the outside, and a metal gasket that clamped it against the flange hid it from the inside. But even with metal pressing it on both sides, it allowed air to escape through the canvas’s multiple layers into the vastly lower pressure Martian atmosphere outside, a few molecules at a time. The leak was too slow to trigger the atmospheric regulator’s pressure warning alarms. Furthermore, with the pony space suits being used to replace the oxygenator, the tiny fraction of lost air was constantly replaced. Thus, no obvious warning sign existed to cause the occupants of the Hab to take action.

Even when the leak became noticeable to the most sensitive of the alien crew, she couldn’t even identify it as a leak, let alone locate it. She could only tell that the operation of Airlock 1 seemed to make it worse. In response to her worries the aliens discontinued use of that airlock. They then used airtight sample bins to transfer vacuum-sensitive materials from the Hab to their ship and its independent air supply.

But despite the caution, the aliens had no warning other than a vague premonition of danger- so vague that none of them remembered to pass that warning on to the owner of the Hab.

Thus he, and his sole alien companion on his overland trip, returned in the Martian dawn of Sol 88 without a clue that his preferred airlock might be dangerous in any way.

“Finally!” Mark cheered as a brownish lump rose on the foreshortened Martian horizon. “Home sweet home!”

Starlight Glimmer couldn’t quite believe she’d heard properly. “I thought Earth is your home,” she said.

“It is,” Mark said. His face went pale- well, paler than usual. “Oh my God. Did I just call the Hab home?”

“Yes.”

“I have got to get out of this rover.”

“Yes,” Starlight said firmly. “We have to get out of this rover.”

Mark had put the rover into motion shortly before dawn, picking up the solar panels from their final campsite and securing them to the rover’s roof in record time. Now, barely an hour later, he slowed down for the final approach to the Hab.

There had been a few changes. The MAV’s descent stage had lost its engine bells. The MDV had been moved much closer to the Hab, with only a bit of it visible beyond Rover 1. The remaining debris from the Sol 6 storm had been cleared away. But the Hab itself looked the same as ever- maybe a little dustier, but otherwise just as Mark and Starlight had left it twenty-two sols before.

The rover came to a stop. The instant Mark shut down the rover systems he grabbed his spacesuit, slipping it on with the ease and speed of long practice and urgent need. Starlight followed his lead, digging out her own suit and shutting down its environmental system long enough for her to step into its legs and seal it up.

Her suit had held up extremely well for the wear and abuse it had seen. The rubber soles were beginning to wear down a little- she’d have to talk with Dragonfly about re-soling the suits for everypony. But the joints were still sound, with no sign of fabric wear, much less rips that might lead to air leaks. Starlight wondered, idly, if the other ponies’ spacesuits were holding up as well.

Mark sealed his helmet, activated his life support, and picked up his huge toolbox, which had hardly been opened the entire trip. Starlight was a little surprised that Mark was bringing anything with him at all. A little, but not much; after watching him interact with Dragonfly, she knew that the tools were Mark’s greatest treasure on the planet.

Speaking of… Her own suit secure and active, Starlight used her magic to lift the mostly depleted mana battery onto her back. She secured its carrying harness, wriggled her body to test it, and nodded. “Ready to go, Mark,” she said.

“I’m past ready,” Mark replied, stepping into the rover airlock. “Let’s go.”

Starlight squeezed in beside him, and the inner airlock door closed behind them.

Spitfire set the remaining half of her breakfast food pack in Mark’s refrigerator and shut and latched its airtight door. Nineteen food packs remained of the entire Amicitas supply, counting Fireball’s remaining inedible-by-pony meals. Dinner of day after tomorrow, she figured, would be the last meal with food brought from Equestria.

The crops in the cave were coming along quite well, but the first alfalfa harvest in bulk lay weeks in the future- weeks during which the ponies would have no choice but to steal from Mark’s supply of food. She’d already inspected some of his food packs, with the help of a dictionary Dragonfly had found on the computer used for their nightly television viewing. She wished she hadn’t, and she hoped the harvest came in before she learned the flavors of things that, back home, she would have greeted by name.

The thought gave her more incentive to work hard that day. It was another day for working the cave farm, and it was her turn to walk out with Cherry Berry to the cave. By the time they returned Mark and Starlight would finally be back from their long trip, and-

The air pumps on Airlock 1 began to whirr.

Almost instantly, Spitfire felt the air inside the Hab change in that subtle, disturbing way.

She looked around the Hab interior for the others. None of them stood anywhere near Airlock 1; Fireball was finishing off his breakfast of plain quartz, Cherry Berry was putting on her spacesuit undergarment, and Dragonfly was at the computer staring at diagrams she’d found for the MDV, trying again to make sense of them. Obviously they didn’t activate the airlock controls.

Obviously Mark and Starlight were early. They hadn't announced their arrival on the suit comms- and why would they, since nopony had their suit on yet? But Spitfire had counted on their arriving while her suit was on, so she could steer them away from Airlock 1.

They had activated the airlock, depressurizing it in preparation for entering the Hab.

And, equally obviously, neither of them had been warned not to use the airlock.

The pumps continued to whirr, drawing air out of the airlock and back into the Hab. Spitfire watched the canvas wall around the airlock. Was it flexing? Was it shifting, or was her imagination making her see things that weren’t there? Every instinct screamed at her that she and her crewmates were in danger, deadly danger, deadly and immediate danger.

But she didn’t want to panic. She still couldn’t be sure of herself. Nopony else could feel the air current, and everypony had had a try at finding possible leaks in the hab.

It wasn’t even her hab. The person who knew the most about the hab was about to come in by the airlock. If he didn’t find anything wrong-

Spitfire’s frantic chain of thought ceased as she felt the air current, stronger than ever before, ruffling the fur on her back.

No more thought. No more doubt. Time to act.

“SUIT UP!!!”

The airlock door opened. Mark and Starlight stepped inside.

“Suit clear!”

“Suit clear!”

“Suit clear!”

“Suit clear!”

Starlight blinked at the series of suit-clear calls flooding her headphones. “Amicitas, Starlight,” she replied. “Guys, we appreciate the welcome home, but shouldn’t the suit drill wait until we’re inside?”

“This is no drill,” Spitfire’s voice replied over the comms. “Does Mark have that crystal you made him on?”

“Yes, he does. What’s going on here?” Starlight looked up at Mark, who had just finished securing the outer airlock door.

“Mark, danger. Maybe hole in Hab. Careful.”

Mark stiffened. “Hole in the Hab?” he asked. “Where? Hold on, we’re coming in.” His hand reached across the small airlock and hit the button to pump air into the chamber.

The Hab canvas was a triumph of NASA engineering, layers of complex polymers reinforced with a weave of carbon fibers. The material combined unprecedented strength, insulation, radiation reflectivity, and lightness. It had been assembled with care by the Ares III crew on Sol 1, using an equally miraculous resin on convenient seal-strips that formed an airtight seal even stronger than the canvas itself.

As miraculous as the canvas was, it was not indestructible.

As Airlock 1 depressurized, two of the fibers around the flaw in the fabric stretched and failed, snapping apart, making the gap in the weave larger. The rest held, under the tension of more than five thousand kilograms per square meter, as the airlock finished depressurizing.

But as the astronaut began the repressurization process, the airlock began to expand again, causing the flawed canvas to slacken for a fraction of a second. The air pressure of the interior of the Hab pulled it taut again almost instantly, tugging harder on the remaining fibers in the process.

This slight tug, atop the strain already present, proved too much. More fibers parted. The failures propagated up and down the edge where canvas met airlock metal. Without its reinforcement, and with thirteen point nine pounds per square inch of differential pressure backing it, the canvas failed, parting enough for an actual hole, visible to the eye, to appear along the edge of the airlock’s flange.

In less time than it would take that eye to blink, the hole propagated around the entire perimeter of the airlock.

On Sol 88, the Ares III Hab suffered sudden eruptive decompression. The wind generated lasted for only a fraction of a second, but for that second thousands of pounds of force exerted themselves against the metal canister which was Airlock 1.

The airlock, and its two occupants, went flying, soaring for twenty meters before tumbling across the Martian surface for thirty more, beating and battering the people inside before finally coming to rest.

The Hab systems, sensing the sudden and total loss of air pressure, enacted an emergency shutdown. Breakers snapped open. Valves snapped shut. Electrical supply died.

Inside the now all-but-airless Hab, things were chaos.

Inside the airlock, things were worse.

RECORDING…

Ooooh… oh, my head… what the hell happened?

….

You fucking kidding me?

For the record, since my suit is recording all of this, Mars has just given me a wonderful welcome-back-fuck-you gift by waiting until the moment I got back to the Hab to have it breach. And by breach I mean send Airlock 1 flying a good fifty meters, with Starlight and I tumbled like socks in a dryer. I’m having to wipe a trickle of blood from my forehead because my stupid fucking idiotic safety-glass faceplate took the brunt of my impact with the airlock inner door when the thing went flying.

The good news is, my suit had more than enough air in it- fresh O2 and N2 tanks- to fill the airlock. The bad news is, I’m hearing a hissing sound, and I’m really hoping it’s a leak in Starlight’s suit. If it’s not, we’re in real trouble.

Checking my suit air tank levels… yeah, we’re fucked. My suit is still backfilling air. The airlock has a small leak somewhere. I know it’s a small leak because if it was a large leak we’d already be dead.

I’m hearing a lot of pony voices over their comm channel. There’s a real sore spot on my chest where the battery for the crystal communicator Starlight made for me rests. In the bouncing around we took I must have banged my chest against something- maybe my arms. Doesn’t feel too bad, though. I don’t think anything’s broken.

I hear Cherry’s voice now. She’s taking charge.

Watney here, Cherry. I mean Mark here. The glass on my helmet is broken, but I think I’m okay.

I don’t know. I’ll check. Starlight? Starlight, are you awake?

Oh. Oh, this is bad. Cherry, Starlight was carrying her battery when the Hab blew out.

Dragonfly, do you understand me? Good, explain it to Cherry. Starlight was carrying the battery. When the Hab blew out we got shaken up hard. The harness shifted on her and pinned one of her legs. The metal on the battery cut a hole in her suit. Also I think her leg is broken. And she’s out cold. Unconscious. Not awake.

That’s right, she has a hole in her suit.

Also, the airlock is leaking.

Leaking. It has a hole in it. Either that or there’s another Dragonfly in here with me.

No, there isn’t really another Dragonfly in here. I just meant it hisses.

Look, I have to find that leak while I still have air in my suit. My suit has a hole in it too.

The lights? The lights on Starlight’s suit are all green.

She does? Good. I’m turning my air off, then.

What? Okay, I’m waiting.

Oh. Okay, I’ll leave it on. But that means I need to find that leak really quick.

No, I don’t want to wake Starlight. We both took a beating. If her leg is broken, she’s really going to hurt.

Okay. I’m going to turn my crystal off now. I’ll call you when I have something to say. Mark out.

Okay. Have to think fast. Starlight’s life depends on it. If the air pressure drops too low in here her life support will shut down automatically. I have to fix the leak while my suit still has air in its tanks.

So. How can I find that leak?

I need a visible vapor of some kind. The only kind I can think of is smoke. What have I got in here that can burn?

Hair. My hair and Starlight’s hair. But I don’t want to disturb her until I have to, so my hair will have to do.

First step, get out of this suit.

RECORDING ENDED

“I found the magic battery, Cherry!” Fireball shouted. His head poked through a curtain of half-collapsed canvas.

“We can hear you fine,” Cherry replied. “Good work. Dragonfly, what about a helmet for Mark?”

“I’m digging out a whole suit for him,” Dragonfly called, her suit barely visible under a collapsed pile of canvas and poles near the bunks. “Just because we know his helmet is shot doesn’t mean there isn’t damage elsewhere. Plus he’ll need more air.”

“Good call,” Cherry replied. “Spitfire, how about first aid?”

“Nothing doing until we can get Starlight somewhere safe,” Spitfire replied from the hole where the airlock had been. “I’ve got our medical kit here, but I’m taking it back to the ship. That should still have air.” Without pausing for permission, she half-trotted, half-bounced out into the Martian morning light.

“It’ll have power, too,” Dragonfly said. “We kept the electrical batteries charged. They should be good for a few hours.”

“Okay. Fireball, give me the magic battery. What’s the charge?”

“One-third, looks like,” Fireball said.

“Good. You take Mark’s new suit and helmet once Dragonfly digs it out. Dragonfly, I want you in the ship. Make sure it can handle all of us. We need to get Starlight and Mark over there as quickly as possible.”

“Okay,” Dragonfly responded. “Fireball, can you give me a claw over here? I’m having trouble getting the suit off its rack. I can’t disconnect the recharge harness.”

“Just a minute. I’ll be with you once I’ve got the battery harnessed to Cherry.”

“Spitfire here.”

“Go ahead, Spitfire,” Cherry said.

“I’m carrying the medical kit up to the Amicitas crew airlock,” Spitfire said. “Just a reminder, we’re probably going to need both Fireball and Mark to get Starlight up the ladder.”

“Got it. Dragonfly, do you think you can patch Starlight’s suit?”

“If it’s only the fabric, sure. But I can’t do it in vacuum. Also, I’ll need a meal pack to make enough goo for the patch.”

“Can you use one of Fireball’s?”

“Hey!” Fireball protested.

“Have something to say, Fireball?” Cherry asked.

“No, ma’am.” The dragon’s voice softened immediately. “Sorry. Force of habit.”

“So long as the gem bits aren’t too large, yeah,” Dragonfly, said. “I can use it.”

“Grab the one marked ‘Rubblerito with Chococoal Fudge,’” Fireball said, seating the battered mana battery on Cherry’s back and fastening the harness around her. “The burrito’s mostly beans and peppers.”

“Will do. Done with the bossmare yet?”

“Yes, he is. Go get that suit, Fireball. Then let’s go help Mark.”

I owe Dragonfly a great big thank you. If she hadn’t made me paranoid about my tools with all her poking and prying, I wouldn’t have grabbed them first thing when I left the rover, and I wouldn’t have them in the airlock with me. The toolbox came through the tumbling intact, as did everything inside, including the shears I used to cut several locks of hair and the flashlight I’ve just finished breaking so I can make a spark.

If I hadn’t had the tool box… well, I could have pulled a couple of wires on my space suit for the spark. And I could have removed Starlight’s helmet and bit some of her mane hairs off. But the tools make things much easier. Of course, this might get us both killed, so the tools might just be assisting my suicide here. There is that to consider. Mixed blessings and all that.

Anyway, here’s the plan. I’ve closed the nitrogen valve on my suit completely, so it’s now backfilling the airlock with pure oxygen. The higher the oxygen level in the airlock, the more easily my hair will burn. I’ve removed an LED from the flashlight and used a couple short lengths of wire from the supply in the tool box. Now when I switch the flashlight on, I get a little spark. That’s plenty. With enough oxygen, any spark will ignite almost any fuel.

Thing is, I’ve just described Apollo One. Not the parallel I’d like to have here.

Starlight just groaned. She’ll be waking up soon, I think. I need to hurry up and do this. My air levels are dropping pretty rapidly.

Wish me luck…

END RECORDING

Starlight Glimmer opened her eyes. Her head hurt. Her horn really hurt. And her right foreleg…

Starlight opened her eyes again. This time she tried not to think of the leg.

And failed.

For the third time in as many minutes, Starlight opened her eyes again, just in time to hear Mark behind her saying, “Goddammit! Five times!”

“Mark?” she asked, unable to raise her voice much above a croak.

“Starlight, stay absolutely still,” Mark said sternly. “And when I tell you, turn off your suit air and hold your breath. It’s important.”

“What happened?” Starlight asked.

“Starlight, is that you?” a voice asked in her ear.

“The Hab blew out,” Mark said. “We’re in the airlock and it’s leaking.” She heard the sound of a pair of shears working. “Okay. Attempt number six. Suit air off. Starlight, hold your breath now.”

“Starlight, if you’re awake, please respond,” the voice in her ears said.

Starlight, caught between conflicting orders, decided to follow the orders of the person actually in the chamber with her. She pulled her left forehoof under herself and hit the shutoff switch for her suit life support. This done, she held her breath, trying to ignore the gradual ache in her ears as the air pressure in the airlock began to drop.

Silence. More silence. Starlight could hear her heartbeat in her ears.

“Gotcha!” Starlight heard the sound of Mark’s boot hitting the airlock floor. “Starlight, breathe! Air! Now!”

Starlight switched on her suit air again. A warning beep echoed in her headset; the suit sensed the air pressure was below standard pressure. But between her suit and Mark’s the air pressure returned to normal in a few seconds, and the beep cut out.

“Amicitas, Starlight Glimmer,” she said, now that the need for silence was past. “I’m awake. Not happy about it, though.”

“Report,” Cherry said bluntly.

“My right foreleg hurts a lot,” Starlight said. “I think it’s broken. It’s pinned by the mana battery. I can feel air blowing through a gash in the suit there. My head also hurts, but my helmet seems to be intact, I think. We’re losing air, but I think Mark is working on that.”

“Yes, Mark told us that,” Cherry replied. “How much magic is left in the battery?”

“Less than ten percent,” Starlight said. “I used most of it when we recovered Mark’s robot, and I’ve tapped it once or twice for translation spells. I’ve really been working on learning his language.”

“Understood. Now this is important,” Cherry said. “Are you able to cast a forcefield spell to hold the air in for about a minute? We can get Mark a fresh suit if you do. We can also give you the other battery- it’s up to thirty-five percent power.”

The sound of Mark unspooling gray tape from his tool kit echoed through the airlock, momentarily drowning out all other sound.

“I think I can,” Starlight said. “But there’s no point in bringing the other battery. I can’t cast a mending spell on my suit while wearing it.”

“Okay. Dragonfly says she can patch the suit. Are you familiar with changeling goo?”

Starlight found the strength to groan. “I suspect I’m going to be a lot more familiar in a few minutes,” she said.

Before Cherry could continue, Mark spoke up, and his voice echoed in Starlight’s ears as she heard it both from in the room and over her headset. “Watney here,” he said. “Air leak secured for now… I mean, I stopped the leak. Are all of you all right?”

“We are all right,” Cherry said, very carefully, in English. “We have plan. Get you in our ship. Starlight will tell you. Okay?”

“Okay,” Mark said. “I’ll shut up and let you talk.”

“Good. Thank you.” Cherry switched back to Equestrian. “Starlight, when I give the signal you put the air retention forcefield around the inner airlock door. Then tell Mark to open it. Fireball will pass the new spacesuit in for Mark, and Dragonfly will come inside with it. She’ll patch up your suit well enough to hold air. Then Mark and Fireball will carry you over to Amicitas. It still has power and air, and Spitfire’s waiting there to splint your leg. Once we’re all in the ship safe, we can discuss what to do next.”

“Got it,” Starlight said. “I’ll explain it to Mark.”

It’s been a very long, very bad day, but it could have been oh so much worse.

It took two-thirds of the remaining spare hab canvas, but the hole where Airlock 1 was has been patched. Starlight tells me that, once a magic battery is fully recharged, she could properly fix the leak in the airlock, but that could take weeks. We need the hole patched now, so we patched it now. Maybe we’ll find some use for Airlock 1 somewhere down the line, but for now we just have to make do with the two remaining airlocks.

The assembly of the Hab on Sol 1 took four people most of the day. Fortunately I didn’t have to reassemble it by myself; most of it, including the heavy equipment, didn’t move very far. Airlock 1 took most of the blow, with the rest of the debris being small objects like all the open markers we’d been using for whiteboards. I checked four of them; all dead, dried out under their non-airtight caps by the Martian air. Fortunately we have the backup supply, never opened, plus the bundle Starlight brought on the Pathfinder trip.

I owe a lot to the ponies’ foresight, particularly Spitfire. She was the one who first knew something was wrong, or so Cherry tells me. None of the others had a clue that the airlock was about to go, but they were careful enough to move a lot of the potentially air-sensitive material, including most of the medical stores, over to their ship. That included the unused alfalfa seeds, which is a very good thing.

All in all, the hab was open to the Martian environment for about seven hours before we verified a good seal on the repaired canvas. That was more than long enough to kill all the plants in the Hab farm. It’s possible some of the bacteria survived at the bottom of the dirt, but it’ll be days before we know for sure. But the original alfalfa stand is dead at least to the top of the roots, and the potato plants are all goners. The new spuds had just begun sprouting, too. Fuck, what a waste.

It’s not disaster. We have the cave farm. Most of the conditioned soil remained in the Hab, with only the loosest dirt blowing out. We can revive that soil a lot more easily than the effort required to condition it in the first place. We have some spare alfalfa seeds, and we can take some potatoes from the first cave harvest to replant those. But it’s a huge setback.

Every piece of equipment survived the sudden decompression except the computer Dragonfly was using at the time (it took a ten-meter flight across the Hab and hit the ground hard, breaking the monitor) and the water reclaimer. I suspect ice formed in the lines, causing them to burst. That’s not a big problem: I have a lot of hose specifically to repair problems like that. Everything else is working fine, which is how I’m able to type this on a computer plugged into Hab power.

The most serious problem is Starlight. Spitfire did the best she could to splint the broken leg, but that’s all she knows how to do. We haven’t got a doctor to do it properly. The ponies apparently had some magic medicines which accelerate healing, but Spitfire says they’re not working nearly as well as they should. She’s going to be bedridden- all but immobile- for three weeks minimum. Fireball and I are going to get a lot of practice carrying her to and from the john, and I guarantee you all three of us are looking forward to that SO much.

And Starlight’s suit is… well, it’ll still hold air. I got to watch Dragonfly hork up the world’s biggest, blackest loogie right onto the rip in her suit. The suit’s absolutely rigid at that point now- the stuff hardened almost instantly. Starlight tells me it’s permanently bonded to the suit, quoting her, “and magic can’t fix it anymore.” Apparently there are spells that can fix broken things, but not beyond a certain point. Trying the spell now with that goo on would just rip off the patch and make a bigger hole, if I understand correctly.

So, even after Starlight gets out of bed again, her suit is permanently scratched for any further heavy labor. She’s going to be limited to the absolute minimum EVA time. Her suit is compromised, and if it fails irreparably she probably dies here. We can’t risk that.

I need an explanation for how Dragonfly can do things like that suit patch that doesn’t begin or end with the word “magic”. But I haven’t got the time now. I want to get the water reclaimer fixed before bed tonight so I can begin trying to fix Pathfinder tomorrow. That’s going to be a long job if it’s even possible at all, so I don’t want anything else on my plate.

Anyway, summary: today was the worst sol I’ve had on Mars since Sol 6. But it could have been worse. Working together, we got Starlight out of the airlock safely and repaired the Hab in a few hours instead of the couple of days it would take me alone. The Hab farm is dead, but it can be revived- and at least some of the alfalfa will be edible, although freeze-dried alfalfa is going to be a taste pleasure for absolutely nobody.

Mars didn’t kill us today. Life goes on, until tomorrow.

And I’ve taught Spitfire the English words for “suit up.” From now on, when she calls a suit drill, I’m joining in.

Author's Notes:

Two days ago, not a word of this existed. I wrote nine hundred words Thursday night, deleted two hundred of them Saturday afternoon, and kept pressing on when I could until the chapter was completed.

And today I wrote another 2150 words, so hey! I have a buffer again!

So, for those who haven't read the book, there was no sign or warning of a Hab failure until the chapter opening, which began with a detailed description of the manufacture of one particular canvas panel. The sequence just screams, "This is the thing that's going to kill Mark Watney!" That kind of annoyed me, so although I do something similar here, instead of hammering the reader over the head with it in one chapter, I dropped hints in previous chapters to foreshadow it properly.

Today, as part of writing the next chapter, I did a bit of calculation using the Web. Air flowing from a compressed area to a non-compressed area can't travel faster than the speed of sound (approx. 350 meters per second in Earth's atmosphere), because that's the point where air stops being compressible. Escaping air hits that speed if it's roughly twice or more as dense/compressed as the air where it's escaping to, if I understand the math correctly. There are complications including the size of the hole connecting the two zones of air. But it was enough to go on with.

Suppose that the Hab, instead of being basically an inflatable tent with a rigid floor, was an air cannon with barrel precisely fitted for the airlock. On the inside you have one standard Earth-sea-level atmospheric pressure; on the outside, Mars's barely-there atmosphere. What happens when you pull the trigger and release the air inside the Hab?

What happens is, at least in the first instant, the sudden imbalance of air pressure on the system puts a whopping 172 G's of acceleration on the airlock. To put it mildly, that's not survivable.

I've given a few more words on this in-story to Venkat Kapoor next chapter, but despite all the problems with the scenario and the shakiness of my own math, I now find the ejection of the airlock a lot more plausible than I did before.

This is, again, a moment where the crossover becomes much easier than the original book. On the one hand it's a bit of a dramatic letdown by comparison, but on the other it let me show the Amicitas crew working together as an efficient team under Cherry Berry. Yes, she slipped up. But under the circumstances it was an understandable slip. This, also, will be explored a bit more next chapter.

Note: Amicitas is hooked up to Hab power, but not to Hab air. It was refilled (not including the engine bay) during the tow, and when the ponies are in the ship they leave their suits on except for helmets, so the air stays fresh. Thus the ponies weren't dependent on the rover for shelter when the Hab blew.

The pop-tents, on the other hand, were hooked directly to Hab air. They depressurized too, just like in the book.

So: why did the Hab blow (besides the explanation that Andy Weir and I are both dicks)? The weak spot in the canvas was caused by the Sol 6 freak storm. After that it was a matter of wear... and the ponies have been using the airlock a LOT more than Watney would have done by himself. So the surprise is not that it blew, but that it conveniently waited for the one person who knew how to repair it to get back before doing so. Had it blown earlier Mark and Starlight would have been safe short-term, but the ponies would have had to retreat to Amicitas or the crystal cave, and the Hab would have been exposed to Mars for days or even weeks at a time.

Mark's karma swings tend to peg the needle on both sides of the gauge.