And that’s where I am now. Wondering what the hell happened.

After all that work and getting blown up, I’m exhausted. Tomorrow I’ll have to do a million equipment checks and try to figure out what exploded, but for now I just want to sleep.

I’m in the rover again tonight. Even with the hydrogen gone, I’m reluctant to hang out in a Hab that has a history of exploding for no reason. Plus, I can’t be sure there isn’t a leak.

This time, I brought a proper meal, and something to listen to that isn’t disco.

LOG ENTRY: SOL 41

I spent the day running full diagnostics on every system in the Hab. It was incredibly boring, but my survival depends on these machines, so it had to be done. I can’t just assume an explosion did no long-term damage.

I did the most critical tests first. Number one was the integrity of the Hab canvas. I felt pretty confident it was in good shape, because I’d spent a few hours asleep in the rover before returning to the Hab, and the pressure was still good. The computer reported no change in pressure over that time, other than a minor fluctuation based on temperature.

Then I checked the oxygenator. If that stops working and I can’t fix it, I’m a dead man. No problems.

Then the atmospheric regulator. Again, no problem.

Heating unit, primary battery array, O₂ and N₂ storage tanks, water reclaimer, all three airlocks, lighting systems, main computer… on and on I went, feeling better and better as each system proved to be in perfect working order.

Got to hand it to NASA. They don’t screw around when making this stuff.

Then came the critical part… checking the dirt. I took a few samples from all over the Hab (remember, it’s all dirt flooring now) and made slides.

With shaking hands, I put a slide into the microscope and brought the image up on-screen. There they were! Healthy, active bacteria doing their thing! Looks like I won’t be starving to death on Sol 400 after all. I plopped down in a chair and let my breathing return to normal.

Then I set about cleaning up the mess. And I had a lot of time to think about what had happened.

So what happened? Well, I have a theory.

According to the main computer, during the blast, the internal pressure spiked to 1.4 atmospheres, and the temperature rose to 15°C in under a second. But the pressure quickly subsided back to 1 atm. This would make sense if the atmospheric regulator were on, but I’d cut power to it.

The temperature remained at 15°C for some time afterward, so any heat expansion should still have been present. But the pressure dropped down again, so where did that extra pressure go? Raising the temperature and keeping the same number of atoms inside should permanently raise the pressure. But it didn’t.

I quickly realized the answer. The hydrogen (the only available thing to burn) combined with oxygen (hence combustion) and became water. Water is a thousand times as dense as a gas. So the heat added to the pressure, and the transformation of hydrogen and oxygen into water brought it back down again.