“Agreed.”
I turned the air-shelter valve and let air from the tunnel into the shelter. We listened to the hiss closely. If it stopped, that meant the skirt weld was airtight. If it just kept hissing that meant there was a leak and we’d have to go back out there and find it.
The hiss grew more and more quiet, eventually coming to a stop. I cranked the valve open all the way and there was no change. “Seal’s good,” I said.
“Well done!” Dad exclaimed over the radio.
“Thanks.”
“No, seriously,” he said. “You made a three-meter-long airtight weld while wearing an EVA suit. You really could have been a master.”
“Dad…” I said, a note of warning in my voice.
“All right, all right.”
He couldn’t see my smile, though. It really was a hell of a weld.
I cranked the hatch open and stepped in. The metal tube was freezing cold. Water condensed on the walls. I gestured Dale to the front. He turned on his helmet lights and got close to the weld site so Dad could see it through the camera.
“The inside edge of the weld looks good to me,” I said.
“Agreed,” said Dad. “Make sure Mr. Shapiro stays nearby, though.”
“I’ll be right behind her,” Dale said. He stepped back into the connector.
I craned my head back to Dale. “Are we sure the pressure in here is exactly twenty point four kPa?”
Dale checked his arm readouts. “Yes. Twenty point four kPa.”
We had pressurized to 20.4 kPa instead of Artemis’s standard 21. Why? Because of how double-hull systems work.
Between the two hulls, there’s a bunch of crushed rock (you knew that). But there’s also air. And that air is at 20.4 kPa—about 90 percent of Artemis pressure. Also, the space between the hulls isn’t a giant empty shell. It’s partitioned into hundreds of equilateral triangles, two meters on a side. Each of those compartments has a pressure sensor inside.
So outside there’s vacuum, between the hulls there’s 90 percent Artemis pressure, and inside the bubble there’s full Artemis pressure.
If there’s a breach in the outer hull, the compartment’s air will leak out to the vacuum outside. But if there’s a breach in the inner hull, the compartment will be flooded with higher-pressure air from inside the bubble.
It’s an elegant system. If the compartment pressure goes down, you know there’s a leak in the outer hull. If it goes up, you know there’s a leak in the inner hull.
But I didn’t want a hull-breach alarm going off in the middle of my operation, so we made damn sure our air pressure matched the insi
de-hull pressure.
I made a quick inspection of my torch nozzle to make sure it hadn’t warped in the temperature changes it had just been exposed to. I didn’t see any problems.
“Dad, according to the specs, this will be the same as a city bubble hull—six centimeters of aluminum, a meter of crushed regolith, then another six centimeters of aluminum.”
“All right,” said Dad. “The initial breakthrough will be messy because of the thickness of the material. Just stay with it and try not to wobble. The steadier your hand the faster it’ll breach.”
I pulled the oxygen and acetylene tanks into the shelter and prepped the torch.
“Don’t forget your breather mask,” said Dad.
“I know, I know.” I’d completely forgotten. Oxyacetylene fills the air with toxic smoke. Normally it’s not enough to matter, but in a confined pressure vessel you need your own breathing apparatus. Hey, I would have remembered once I started coughing uncontrollably.
I reached into my duffel and pulled out a mask. The attached air tank had a little backpack rig to keep it out of the way. I put it on and took a few breaths just to make sure it worked. “I’m ready to fire up. Any other advice?”
“Yes,” he said. “The regolith has a high iron content. Try not to linger in one place for too long or it might clump up around the cut site. Too much of that and you’ll have a very hard time pulling the plug out.”