6
Building
Will and Ethel watched the Sunwing jet into the air and climb into the pink morning sky. Then it banked northward and headed for the expedition, some 1,200 kilometers north of the outpost. Ethel automatically waved to Sebastian and Roger, even though it was unlikely either of them would see the gesture.
“There they go,” she said to Will on a private channel. “So, we’ve got six to eight weeks before they return.”
“Probably. Sebastian said he might come back for a few days on one of the supply flights.”
“I bet he’ll get into the exploration and won’t bother. I’m still surprised he appointed you interim commander of the Outpost.”
“I was a bit surprised as well. But I suppose since he’s European, he had to appoint an American.”
“I wish we didn’t have to think that way. It’s silly.”
“I agree. It won’t be six weeks with unchanging staff, though. Armando will go down to replace Shinji in two weeks, and Paul will be back here in four weeks, followed by Monika. At some point Roger will be back, too.” Will turned to the Sunwing hanger, which was nearby. “Say, let’s go look at the hanger again. I want to think about construction options.”
“Sebastian did give a green light for an unpressurized geology building for sample storage,” agreed Ethel. “The hanger has used every technique imaginable.”
Will nodded and they turned toward the hanger, which was a scant sixty meters away. It had only one Sunwing in it at the time; they pulled back a flap of parachute material forming the roof and front wall to enter. Since the parachutes were a translucent white, it was bright inside the hanger; it was even twenty degrees Centigrade warmer than outside, which they soon noticed through their pressure suits. Will walked under the remaining Sunwing and reached the hanger’s sixty-five meter long back wall; it was nearly as long as a football field. Representing a history of their construction efforts, the wall had taken months of intermittent work to complete.
At the end they had entered, the hanger was excavated into the Martian ground in order to make its floor flat. They had used both rangers to bulldozer the regolith out of the way and build a berm that helped support the back wall, which was built of unmortared fieldstone. Will had done much of the stacking of the rocks himself; he had a knack for it. Fines had sifted into the cracks between the rocks and helped fill them up.
Ten meters of fieldstone was followed by plastic sandbags; a lot of work to fill, but they made a tighter wall. Fifteen meters of sandbags were followed by plastic sheets held in place by vertical iron beams they had buried in the ground and frozen in place. It had proved much faster to build because the rangers could push regolith—carefully—against the lower meter of the plastic sheets to hold them in place. But the blank white plastic wall was ugly.
Thirty meters of plastic was followed by ten meters of duricrete, made by mixing Martian dust with water and letting it set inside plastic forms. It had a bit more strength than plaster of Paris, partly because it had solidified and frozen at the same time; had it been able to solidify without freezing it would have been stronger. The wall looked like concrete, but was orange-red-brown, just like the dust it was made of.
Finally, they turned the corner and walked along the twelve-meter side wall, which was made of real concrete. They had taken duricrust—the hard crust that forms on the Martian surface because of water percolating upward through the ancient crust—crushed it, washed the salts out of it, then roasted the remainder, dehydrating the calcium sulfate and converting the calcium and magnesium carbonates into lime. Then they mixed the result with sand, added water, and let it set in forms. The result was not as good as terrestrial concrete, but it wasn’t bad.
“Which would you recommend?”
Ethel pointed at the orange-red section of the wall. “Of everything we’ve tried, the duricrete is fastest and easiest. The engineers in Houston have proposed a mixing device that I think we can put together from items we have here. We’d start with a hopper, which we’d fill with dust, which would flow under gravity into a pipe in the bottom. Warmed Martian air and a spray of water would flow into the pipe, mix with the dust, and blow the mixture into a form, gradually filling it. The form would have to be airtight enough to build up some air pressure so the mix could set slowly, above the freezing point of water. The form would have to be reinforced with metal ribs.”
Will nodded. “It sounds a little like a snow maker at a ski resort.”
“Yes, it’s similar. We have the compressors, the solar power units make plenty of heated Martian air, we have the piping, we can make plastic and metal forms, and we have something we can use as a hopper. The big problems, after we put the pieces together, are making sure the hopper stays full of dust and making sure the mix is right. Too much dust and it’ll be too cold and dry; too warm and the water will vaporize. Too much water is less of a problem. We’ll have to open the form periodically to check how we’re doing, too.”
“Can we make walls for a pressurized building?”
“Will, we only have permission to build an open building.”
“I know, but duricrete walls could be pretty thick, strong, and airtight.”
“Yes, they could be. The walls of a pressurized building would be thicker and we’d have to spray them with a plastic coating to make them more airtight. A pressurized building probably should have heavier piles of regolith outside to counter the interior air pressure, and if the regolith pile were frozen hard it would be even better.”
Will shrugged. “We’ve got plenty of water; dozens of tonnes of it. That’s not a problem. Could we make duricrete walls thick enough to hold in air pressure?”
“And get away with it?” Ethel considered. “No. A duricrete wall for a pressurized building should have iron reinforcing rods in it and should be thicker. But we could eliminate the reinforcing rods and build the walls thicker, and tell Houston that we’re constructing something that later could be pressurized. Actually, I think we could justify some reinforcing rods for safety purposes. Let me talk to the construction experts in Houston; I don’t need to run any of that past Sebastian.”
“Okay. I’m willing to do my ordinary work at all sorts of odd hours in order to help. I really think we need to build a pressurized building. Mars will never expand if it has to import all pressurized space. We’ve got to learn how to build here.”
“I agree. We know the rough size of the building, so you can start excavating the foundation with a buggy. That’ll take three or four days. By then I’ll have a better idea how to make the walls.”
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The next three days were quite busy for Will and Ethel. Will ran the buggy—a small, one-person vehicle about the size of an all-terrain vehicle—with a little bulldozer blade every day for as many hours as he could; it was not easy to operate the machine in a pressure suit, but all the pressurized vehicles were on the expedition. Meanwhile, he postponed breakfast every morning so that he could get an hour of lab work done starting about dawn; the various tests on rock samples ran for as long as three hours autonomously, so he was able to get a substantial amount of work done in the morning while he ran the rover. Before and after supper he worked four hours more in the lab. The arrangement gave him about six hours a day outside. Unfortunately, the hard physical labor required a lot of eating and a lot of rest.
Meanwhile, Ethel ran the metal and plastic making equipment twelve hours a day to make the materials while exchanging emails and voice mails with the construction experts in Houston. Among the dozens of designs available to her on the web was a design for a duricrete building twenty meters long and ten wide, with a row of three pillars down the middle to support a roof of welded metal sheets covered by two meters of regolith. The weight of the reg overhead counteracted the three tonnes per square meter of upward pressure from the interior air; the pillars guaranteed the roof would not collapse if the building lost pressure. An ice layer in the middle of the reg gave it concrete-like hardness. A spray-on plastic sealant would reduce the air leakage through the duricrete walls, which had a light network of reinforcing rebars. The rebars could be woven together in units inside the suit donning facility in standard atmosphere, which could then be depressurized and the units could be hauled outside for installation; that simplified construction.
The morning of the fourth day of work, Will and Ethel awoke to find an email from Houston giving the complete plan; the web site’s plan had been tentatively modified to fit their situation. But they noted with a sinking heart that the email had been copied to Sebastian. He called Will a few minutes later.
“Will, good sol. What’s this email I just received about a building? Is this the Geology Storage Facility?”
“Yes. We’ve been in consultation with the construction experts in Houston, and they’ve recommended a design that we can accomplish in about eight weeks. We’ve either got all the equipment needed or can press into service some equipment designed for other purposes. The folks in Houston are already hard at work testing construction techniques for us.”
Sebastian hesitated. “This was approved by Dr. Mann?” Rafael Mann was the head of the construction team.
“Yes, we’ve been in touch with him several times every sol about it.”
“But this is for an unpressurized building?”
Will chose his words carefully. “Yes, but the building can be outfitted for pressurization as well. It’s the design the team recommended.” He didn’t add that he and Ethel were the members of the construction “team” initially advocating the pressurization aspect. The folks in Houston had become keen on it as well; it was an important development for Mars settlement.
“I see. Well, I just hope you can do this and the regular duties we outlined before I left.”
“Sebastian, we will get everything finished, don’t worry.”
Sebastian hesitated. “Okay, have it your way. I’m looking forward to seeing this so-called unpressurized building. Have a good sol.”
“You, too. Bye.”
“Bye.” Will closed the circuit with relief.
“Congratulations; you did it,” said Ethel, who had been listening.
“Thank you. Sebastian seems to have decided to look the other way. Maybe he’s curious to see how we do both, so he can give us more work!”
“I wouldn’t put it past him!”
They headed down to breakfast a few minutes later. The call had made them a bit late; Armando, Madhu, and Monika were already eating. Monika had just gotten back from the expedition two nights before.
“Good sol,” said Will, greeting everyone. “Interesting news. Mission Control sent the final design for the Geology Storage Building during the night. They copied Sebastian as well.”
“And he said no?” asked Madhu.
“No; he asked whether it was a pressurized building and when we said yes, and that Houston was recommending it, he growled and said he’d be interested in seeing it.”
“And that we had to be sure to get our regular work done,” added Ethel.
Madhu was surprised. “Really? He’s slipping.”
“You’re going to build a pressurizable building?” asked Monika, surprised.
Will nodded. “It can be either, of course. The walls and roof are heavy enough to hold in air pressure; the key is piling regolith on them and building them so that they distribute the various forces adequately. Iron rebars inside sixty centimeters of duricrete will do it.”
“How much eolian dust will you have to move!” she asked.
“About two hundred fifty tonnes,” replied Ethel. “But we can do that in seven weeks at the rate of four tonnes per day. We’ll need to pile a lot more on the roof and against the walls; maybe two thousand tonnes. But the buggy and the reg blowers can do that pretty efficiently.”
“And until we add the weight, we can use the building without pressurizing it,” added Will. “It can accommodate all the rock samples we’ll recover for about four years.”
“That’ll help a lot,” said Monika.
“Meanwhile, we can leave a large open area in the middle of the building where larger structures can be assembled,” added Ethel. “We can assemble things inside without a pressure suit, then depressurize the building and open the doors to carry the thing outside where it can be used. I really am very limited in the suit donning area.”
“I bet,” agreed Madhu. “So, I guess we can still thumb our noses at Sebastian in a creative way by helping you.”
“I’m not sure that’s the right reason to help!” exclaimed Will.
“Let me clarify. Sebastian’s too anal. He micromanages. So I want to help because this will make a statement, at least to me. How can I help?”
“We could use a lot of help,” agreed Ethel. “The main way all of you can help is to structure your time inside so you can keep an eye on the plastic and metal making equipment while you’re doing other duties. Madhu, when you’re in the greenhouses you can run into the manufacturing facility in a matter of seconds, so you can help monitor the equipment while I’m outside.”
“And I need help with the geological analysis,” added Will. “I can set samples up and log them into the computer, but I need someone to physically place them in the machines, turn the machines on, and afterwards turn the machines off and remove the samples.”
“That’s easy; I can do that,” said Armando. “I need to spend about two or three hours a day running medical tests, but the rest of the time when I’m doing medical work I could do it in the Geo Lab.”
“That would really help,” agreed Will.
“I’d like to get outside and help with the construction,” said Monika. “When I was down with the expedition for the last two weeks, I was amazed how tired and weak I felt at first. I’m not getting enough exercise.”
“Your bones are decalcifying as a result,” added Armando. “You really do need more exercise, Monika.”
“Especially if I’m going to stay,” she added. “I signed up for four years, but my health is not cooperating. I need a good reason to be outside walking around with a fifty-kilogram pressure suit weighing down my legs.”
“We can give that to you!” exclaimed Will.
“Then you can count on me for four hours a day. I’ll extend my workday from nine hours to eleven; with Paul away, I really don’t have much to do.”
“Thank you, that’ll help a lot!” said Ethel.
“I think we can keep the two of you outside six or eight hours a day,” suggested Armando. “I’ll rearrange my schedule and postpone a few tasks that were optional. If we cut back to the ‘nominal’ work, I bet we can get that building put up in seven weeks.”
“I’m counting on it,” replied Will.