As commander of the return mission, Krikalev had to deal with a lot of anxiety the night before our return to earth. The Soyuz must be packed very carefully since the center of mass actually affects where the capsule lands.
We also had very little room to spare. During launch the vehicle has three sections, so there’s some extra space. But the descending Soyuz is missing two thirds of that volume, and space is at a premium. Krikalev carefully balanced the vehicle, with much communication from the ground. All I could do was watch.
One issue arose around me and my medicines. The Russians had insisted that I take “Spiriva,” which is an inhaler to aid lung capacity for people with chronic obstructive pulmonary disorder (COPD). This was packed in a container about the size of two books—not a lot of volume on earth, but a considerable size on Soyuz.
Ground control was insisting that it be included in the descending payload and the commander was having trouble finding room for it. We’re talking about the kind of space you find under a car seat, in an economy car! I kept telling him that it really wasn't necessary but the people on the ground kept insisting that it was. I was embarrassed that so much time was being spent on my behalf on such an insignificant issue. Finally, I suggested that I keep enough in my spacesuit for the descent and landing (it was only three hours for Chrissake! The inhaler was once a day). They agreed—problem solved. I think they were worried that if we had an emergency landing and were stranded for awhile, I would need my medicine. I’m glad that reason prevailed here. In fact, it was no big deal even if I didn't have that inhaler for several days.
I don’t think Krikalev got much sleep before we left. None of us did. When we got ready to undock, we had trouble balancing the pressure between two modules, which could indicate a potential leak. We checked and rechecked everything, and finally the ground decided that the pressure difference was small enough to ignore. Slowly, we pulled away from the ISS, first aided only by the springs in the docking mechanism, then by our thrusters, which fired once we got far enough away from the ISS. We completed a little over one orbit and then began the descent process, jettisoning the instrument module below our seats and the habitat module above our heads. From time to time I would glance at the instrument panel to try to see our position, velocity, g-forces and cabin pressure. I don't remember exactly when, but I began to notice the total air pressure in the capsule (normally 760 mm) was starting to drop. It went from 740 ... to 730 ... then 700 over several minutes. Commander Krikalev's eyes showed he was also picking up on this and I could see him checking this readout more frequently, in addition to the thousand other tasks he had to do. This was a slow decompression, a situation we had simulated many times during training.
I thought I knew what to do, and I was grateful to the Russian instructors who had drilled us on how to respond during training and reprimanded us if we didn't do it exactly right. When ordered to do so by Krikalev, I was to open the oxygen valve and keep it open until the total pressure got back near 760 or Krikalev commanded me to close it. It was down by my right foot, and I was the only one who could reach it easily. So I kept my eye on that gauge and my ears open for Krikalev's command. When the pressure got below 650 I knew it wouldn't be long. At 630 mm, as best as I can remember, Krikalev shouted “Olsen—kislarod!” I opened the valve.
It wasn’t easy. Spring tension in the valve, combined with the thick glove on my hand, made it difficult to hold open. But it was my duty and I was not going to fail, even if my arm fell off! I watched hopefully as the pressure began to increase. When it got somewhere above 730 Krikalev told me to close it. Thankful for the reprieve, I pushed the valve back in, and breathed another sigh of relief as the pressure seemed to hold steady.
However, opening the oxygen valve can create another problem: too high an oxygen content. If there is more than 40% oxygen in the atmosphere of the Soyuz capsule, it will automatically depressurize, and the emergency oxygen supply will feed into our spacesuits to pressurize them instead. (That's why you wear them—without pressure your blood will literally boil.)
This safety measure stems from the Apollo 1 disaster in 1967, when three astronauts died in a fire during training. They were using 100% oxygen, which is very flammable—if there’s a spark or electrical short the situation turns deadly in a hurry. I nervously glanced at the partial pressure for oxygen: we were at about 34%. Enough of a safety margin not to have the emergency oxygen turned on in our spacesuits, assuming things stabilized.
Fortunately they did stabilize, and there were no further incidents during our descent and landing. Unlike the NASA Shuttle, the Soyuz spacecraft’s re-entry capsule has little flight capability. Parachutes lower it through the atmosphere to a landing spot, so we had little control over our direction during descent. But we landed right on target, with a helicopter circling around us during our final descent. A Russian recovery team was waiting to pick us up as the capsule’s parachutes lowered us through that precious layer of atmosphere down onto the ground in Kazakhstan.