Because our undock time was in the middle of the night, we ended up with one of those strange sleep shifts where we are just supposed to magically sleep about 18 hours all at once. I managed to sleep in until about 9:30 in the morning of the day we were to leave. Since I tried to stay up late the night before, it netted me about seven and a half hours of sleep. Not as much as I would have liked, but enough that I felt reasonably rested. The last thing I wanted was to feel tired before I needed all my brains to get us home.

Since our official work day had not yet started when I got up, I used to the time to finish up a few last minute items that I wanted to do as well as prepare my electronic files for downlink. Next I proceeded to throw away whatever stuff I had remaining on board and deleted my files from the laptop I was using in my crew quarters. On the one hand that was a little sad as it truly marked the end of my stay. But, on the other hand, I was excited about the trip home. And, I was excited about being home.

Then I spent time looking out the window. The views continued to amaze. It was especially interesting now because the orbit that the Station had over the Earth was basically lined up so that we did not really see night time. The sun would have barely set before it would be rising again. It is nice to see so much of the Earth in daylight, but you do not get to see the fantastic light shows that appear at night - the lightening from the storms, the aurora, or all the city lights.

Along about 3:30 in the afternoon we had our "morning" conference with the ground. I did not have a lot of official work scheduled for my day. About the only thing I had to do was to remove some experiment samples from one of the Japanese experiment racks and get them packed for the Soyuz ride home. Once that was complete, I just enjoyed my last bit of time on the Station and waited for the fun to start.

Around 9:30 in the evening I got into my Kentavr suit. Much like a "g-suit" or pressure suit, the Kentavr is designed to keep pressure on your lower half in order to keep fluids up in your head to prevent you from passing out during the high g-loads during entry. It is not the most stylish or comfortable thing to wear, but a necessity. I also put on the long underwear that I would be wearing under my Sokol suit.

Suited up and ready for the trip home.

At 10:15 p.m. it was time to get into the Soyuz. Because we were now docked on one of the Russian research modules, there was not a lot of room to say goodbye to our colleagues who would be staying on the Station. But, we managed to have hugs all around which was nice. As soon as we were inside the Soyuz, the hatches were shut. We then proceeded to start the lengthy leak check process. While we were waiting for the leak checks to be completed, we got into our Sokol suits. Once again, I needed to be in my seat first, so I was the first to get into my suit. And, once again, I just floated there and let Wheels and Fyodor dress me like a doll. By my estimate, I was in my seat about five and a half hours before our expected landing time. Shortly thereafter we determined that the leak check of the hatches between the Soyuz and the Station had been completed successfully. We were getting closer to being able to undock. By and large, all the undocking preparations proceeded as they were supposed to up until the point that we were to leak check the hatch that is between the descent module, where we were in our seats, and the orbital compartment over our heads, which would not be making the entire trip back with us.

We check that hatch's integrity by venting about twenty percent of the atmosphere of the orbital compartment overboard and then check to see if the atmosphere in the descent capsule leaks across the hatch between the two compartments. As it turned out, our hatch failed the leak check which indicated either the hatch was not closed properly or there was something across the hatch (dirt, schmutz, a strap, whatever) that would have prevented the hatch seals from sealing properly.

So, roughly twenty-eight minutes before we are to undock from the Station, our hatch is under suspicion. This is not good news as not only is it getting close to the time of undock, but we could not guarantee that our capsule would hold its pressure during the trip home. Nominally a proper leak check of that hatch takes twenty-five minutes so we did not have much time to correct the situation. Fyodor unstrapped from his seat and re-opened the hatch to ensure that nothing had gotten trapped or inadvertently shut in it when we closed the hatch originally. None of us could see anything. We carefully checked all the seals, saw no issues, and reclosed the hatch.

At almost exactly twenty-five minutes before our designated undock time, we got the hatch closed again and began a second leak check. Fyodor was hurriedly getting strapped back into his seat and I was keeping my eye on the time and the capsule pressure. It was my job to send the command to undo the latches so we could separate from the Station. I knew it was going to be a very close call as to whether the leak check would be finished by that time or not. If we did not unlatch at precisely the right time, we would either have to wait an orbit before we could try again or run the risk of not landing in the right location.

After about fifteen minutes into the leak check, the ground gave us the go to undock on time. Normally, we would not have expected a go so soon, but it was fairly obvious that this time around, we did not have a leak. Or, at least not one that was significant. The pressure was holding reasonably steady given the expected fluctuations due to temperature changes as the sun moved while we continued around in our orbit. At the appointed time, Fyodor was strapped back in his seat and I sent the command to undock. Whew! We were on our way. It takes a little over four minutes for the latches to completely unlatch. When they were finally undone, we felt a little bump as springs pushed us away from the Station.

Shortly after we separated (three minutes later, to be accurate), our small jets fired to move us farther away from the Station. That went very smoothly. Now we had about an hour to wait until we were in the proper location for our deorbit burn. This was a nice, quiet time. I was able to watch the Earth drift by underneath us and I got to see the most gorgeous sunset just before we fired our engine. At one point as we were drifting along we were out of range for communication with the Russian Control Center, but we still had a communication link with the Station. The crew there gave us a call and wished us well on our trip home. That was neat.

As we got closer to our deorbit burn time, Fyodor and I checked out the Soyuz systems and got ready for the action. If everything goes according to plan, we should basically not have to do anything except monitor the engine burn because just about everything is supposed to happen via time tagged commands that the ground has uplinked to the Soyuz computers. I had to do a few preparation steps to ensure that our computers were on and ready to go as well as to ensure the information uplinked from the ground was correct. I also transferred data between the two computers that we have to ensure that they are both working with the same information. Normally one computer controls the activities going on and the other is lurking in the background to take over should the first computer have issues. At any rate, at the appointed time, I had my finger on the button to start the engine just in case it did not start automatically. But, all happened as it should and the engine started up just when it was supposed to.

To return from space we have to fire our main engine for just under four and a half minutes to slow us down just the right amount. When the engine starts up you can feel the kick as you are thrust forward. You also can hear a very low rumbling boom when the engine starts and stops. What you do not hear very loudly is the engine as it is firing away. That surprised me. You can sort of hear the engine when it is on, but it was not nearly as loud as I would have expected. Actually, you sort of feel it more than you hear it. It is interesting. At any rate, during the entire burn I was helping Fyodor monitor all the parameters of the engine as it was firing, so it was entirely possible that I was not paying that much attention to what my ears were hearing since I was concentrating on watching what was going on. Happily the engine operated perfectly, fired for just the right amount of time and turned off automatically when it was supposed to. But, I was ready to hit the button to cut it off manually, if needed.

It was at this point things did not quite go as planned. They did mostly, but we had an added twist. When the engine cuts off after the deorbit burn, there are three things that are supposed to happen automatically. The first is that some thermal sensors are put into service. These sensors are used as a last resort to separate the Soyuz compartments as you are coming into the atmosphere. You need the compartments to separate because the only one that is to make it all the way to the ground is the one the crew is sitting in. The other two burn up in the atmosphere. Normally, the compartments will separate automatically well before these thermal sensors would trip. But, if for whatever reason that does not happen and the crew does not separate the compartments manually, as the Soyuz goes through the atmosphere and begins to heat up, the thermal sensors will force the command to separate the compartments to be sent.

The second thing that is to happen is that the main computer starts the program to separate the compartments based on the time that the ground has uplinked. And, the third thing that happens is that a valve is opened to completely depress the orbital compartment. It gets depressurized so that when the compartments do separate, there is no force of air making it spin off in an unknown or undesired direction. You do not want your orbital compartment coming back and hitting you after you get rid of it. All three of these things happened as they were supposed to. We could tell that they did because we got the expected alarm and indicator light for each activity; we nominally expect three alarms in short succession after the engine cuts off. What also happened and what we did not expect was that we got a fourth alarm that said our cabin pressure was decreasing. Needless to say that was a surprise to all of us.

When the alarm went off a lot of things went through my head at the same time. The first was something along the lines of, "well, gee, that is not supposed to happen." Then I wondered if it was because of the hatch problem we had before we undocked. While I was pondering this, I was estimating the leak rate and realized it was small-ish. What I mean by small-ish was that we clearly did not have a big gaping hole in our decent capsule and I knew that we would have more than enough oxygen in our tanks to get us home.

Actually, I already knew that. The Soyuz is designed so that you can have the descent capsule be completely depressurized and there is still plenty of oxygen in the tanks to get you home safely. So, I really was not worried about that. I did not particularly want our capsule to depressurize because when that happens your pressure suits fill up with flowing oxygen from the tanks. This makes the suits puff up and become rather stiff so they are hard to work in. But, it beats the alternative.

We had communication with the ground at this point and Fyodor called them and told them what we were seeing. We suggested that we "feed the leak" by introducing oxygen from our tanks into the cabin. This would keep the cabin pressure up and delay our need to deal with a depressurization situation. The ground concurred and we proceeded to do add oxygen to our atmosphere. Doug was the actual valve operator in this case. The valve to introduce oxygen into the cabin is in front of his seat, so Fyodor told him when to open and close it. It was great teamwork in action.

None of us in the Soyuz knew why our decent capsule was leaking. We found out a couple days later that it was because there was a valve misconfigured in the capsule. One of the things that we do during our preparation for entry is pump water that has been removed from the atmosphere into a tank that is situated in the orbital compartment. After that pumping is done there is a valve that is to be moved in order to direct the water into a tank that is inside the descent capsule. For whatever reason, this valve did not get moved to its entry position. The water tank in the orbital compartment essentially has an open top so that you cannot overfill the tank. So, when the orbital compartment was depressurized, there was a leak path from our cabin to space through open water tank.

At any rate, we had to add oxygen into our cabin three or four times to keep our pressure up. Each time we would increase the oxygen amount up to the usual limit of how much oxygen is normally in the atmosphere. You do not want to add too much oxygen into the cabin because at a certain point you will have too much oxygen in your atmosphere and not enough nitrogen. When this happens, you can breathe just fine but you have a flammability concern with your atmosphere. But, we never got to that limit.

Roughly fifteen minutes after the main engine cuts off is when we got ready for the automatic separation of the compartments. It is at this point we closed the visors on our suits and prepared for the trip through the Earth's atmosphere. Once again, I checked the various systems and parameters to ensure that all was in order for the separation. And, I had my fingers on the buttons to separate the compartments manually if it did not happen automatically. But it did - right on time. And, interestingly enough, our cabin leak stopped. Of course, we had no idea why, but who was I to argue with that? It was just one less thing to think about during the trip home. As it turned out, the leak stopped because when the compartments separated, there was a pyro-valve that blew to close the line where the water flows to the orbital compartment. So, our leak path was automatically closed by design. How clever.

The separation of the compartments is very interesting. The three compartments of the Soyuz - the orbital compartment above us, the descent capsule where we are sitting, and the propulsion module below us which contains the main engine and fuel tanks - are held together with bolts that have pyrotechnic devices attached to them. At the time of separation, these pyros fire all at once to sever the bolts. When they fire we can hear and feel the explosion inside our capsule. You definitely know something has happened. I made sure to look out my window to see what I could see. That was an interesting show. I was able to see a very large piece of a thermal blanket that had been covering the outside of the Soyuz float away from us. What I did not see was either of the two other compartments. But if I had seen them it would have meant something was not going quite right, so I was perfectly happy to only see the thermal blanket.

It is after the separation of the compartments that the trip home gets very interesting. This is when you start going through the atmosphere. At first not much happens. The Soyuz is gently turning so that we are tumbling head over feet. But, since we are essentially still in space, you cannot tell that much is going on. But, this phase does not last long. It takes about four minutes for you to be decidedly inside the atmosphere.

The shape of the Soyuz is such that it automatically ends up in the right orientation with the bottom side pointing in the direction of travel. You can think of it as sort of a weather vane; when the atmosphere starts rushing past you, the aerodynamic forces on the Soyuz will move it so that you stop tumbling and become positioned in the right way. This is needed because the way the Soyuz protects the crew and capsule from burning up is that there is a thermal shield on the bottom of the Soyuz decent capsule. In fact, this thermal shield is actually designed to slowly burn away as you come through the atmosphere.

We hit the point where we are considered inside the atmosphere roughly a second off from the pre-entry calculations from the ground. I have to say, this is very impressive. The atmosphere is constantly changing. It is expanding or contracting depending on what the sun is up to. The ground specialists have to model what the atmosphere will be doing, use that to predict when we will be entering it, back off of that time to determine when we need to separate the compartments and use that time to back off and decide when we need to fire our engine and, ultimately, when we need to undock from the Station. All of this is calculated to create the condition so that we will land at the appointed location in Kazakhstan at the appointed time. It is amazingly complex. And, to have us enter the atmosphere that precisely is a testament to some incredibly smart people on the ground. Being only a second or so off from the prediction meant that the Soyuz entry navigation system could easily get us to precise landing location. I forget how many kilometers off from the target you are for each second your engine burn starts early or late, but it is a lot. But, then again, that is also one reason we land in the middle of "nowhere." If you are off a bit, there is plenty of open space to touch down.

You may be wondering how the Soyuz controls its flight path once the three compartments have been separated and the fuel tanks have been tossed away. The Soyuz descent capsule is actually quite self-contained. The main computer that was used to control our deorbit burn does actually leave with the propulsion module. But, the "back-up" computer is situated in the bottom of the descent module beneath our seats. It now becomes the main computer for our trip home. In addition, the descent module has a number of jets and a fuel system to control the Soyuz when going through the atmosphere.

So, what is it like going through the atmosphere? It is one crazy, wild ride! It is a little bit rough and it sounds sort of like you are in the middle of a blow torch. You can definitely hear and feel everything. Plus, if you happen to look outside the window, you can see bits of flaming and charred material fly past. There is no question that you are moving fast and that the capsule is heating up. At this point, you are a shooting star coming in.

Fyodor and I had to do some checking to ensure that the entry systems were working correctly and they were. We have all the appropriate indications that the vehicle's attitude is being controlled and our life support systems are working correctly. At this point you are not just willy, nilly hurtling through the atmosphere. The navigation system is organizing things so that you land where you are supposed do. It does this by controlling the lift of the vehicle. The lift of the vehicle is controlled by how much and which direction the vehicle is rolled to one side or the other. So, our ride through the atmosphere is bumpy, noisy, and under automatic control.

The thickness of the atmosphere and our descent profile determined how many g's we experienced. The nominal profile, which is what we had, is such that we actually have two "g peaks," meaning that there are two times when we had relatively high g-loads. For both of those times we saw about four and a half g's. Not too bad - certainly light enough to breathe reasonably comfortably, but heavy enough that it got your attention. The first peak went as expected, but the second one lasted longer than either Fyodor or I thought it should based on our training. That was not a problem at all but I am not sure why it was. I suppose the atmospheric conditions could have been different than predicted. Or maybe it was because we entered the atmosphere at a slightly different location than planned which affected our entry profile. Or the training simulators do not quite accurately reflect a real entry. Whatever the case, it was no big deal - just an interesting thing to experience.

It takes about eight minutes to get through the main part of the atmosphere. You are bumping along the entire way watching and listening to parts of your capsule burn off while the atmosphere inside the Soyuz is heating up because the outside of the Soyuz has become ridiculously hot. I think this is one of the few times that I started to feel a little warm in my pressure suit. Usually the guys are always sweating up a storm in our simulations, but I was never much bothered. However, coming home I could definitely tell the Soyuz was hot. In addition, the two windows we have are slowly charring over. Well, actually, the entire Soyuz is charring, but the windows slowly get covered over so that eventually you cannot see anything outside of them.

After the eight minutes or so, you are at the right spot in the atmosphere for the parachute to be deployed. This is about ten kilometers above the ground - roughly the altitude where commercial airlines fly. I have to say, this was the most unexpected and surprising part of our entry. I knew that we would feel it when the cover to the parachute compartment blew open. And, I knew that we would feel some healthy jerks when the pilot and drogue chutes came out (the small parachutes that come out first before the large main one). I also knew that we would feel a very big jerk when the main parachute deployed. Indeed, all of this happened as I expected. And, let us just say for the record that these are definitely not small jerks at all. You know when the parachute is put into operation. But, what I was not expecting was what a crazy ride it is when the parachute first deploys. I had been told that this was "a very dynamic phase." That phrase does not quite do it justice.

I am not even sure how describe what it felt like. The best I can do (and, what actually went through my mind as I was experiencing it) was that it was like we were riding on a mechanical bull. Or, even a real bull. The Soyuz capsule is bouncing and jerking around like nobody's business. There is no way to tell how big the next bounce is going to be or in what direction you are going to be jerked. It is insane. And, it went on for a lot longer than I would have expected. I estimate that this "dynamic phase" lasted a good twenty or thirty seconds. It definitely can rattle your brains. One of the things that you need to do as you are coming in through the atmosphere and experiencing the high g loads is to tighten your seat belt and shoulder harnesses. The tighter the better. I can definitely say that if you did not have all your belts tight by the time the parachute opened, you could have been seriously injured. It is total craziness.

Finally, finally, things started settling down. The bouncing became less and the capsule started to spin. This spin is by design (another thing that Fyodor and I had to check to ensure it happened as planned). The capsule spins to stabilize the Soyuz underneath the parachute. I knew that the spin had started not only because the bucking bronco had been pacified, but because my eyes started their familiar jitter that I experienced whenever I was in the centrifuge. In fact, I did not even need to look at the data we were receiving to know that the spin had started. Just as in the centrifuge, I could not really feel the spin with my body, but I could feel it in my eyes. It was pretty nifty. And then everything calmed down. We were peacefully floating underneath our parachute.

Roughly four minutes after the parachute opens, the thermal cover that has been protecting us as we have been coming through the atmosphere is blown off. There are also some covers on the windows that are blown off as well, so we can once again see outside. And, a valve to equalize the pressure between the inside of our cabin and the outside is opened. You know all of this happens by the explosions and by the fact that the pressure in the Soyuz decreases. We were about five kilometers above ground at this point (the height of a tall mountain). The pressure inside decreases because the atmospheric pressure outside is less than that inside our cabin. The equalization of pressure must occur so that the Soyuz does not rip apart due to the higher pressure inside. Even though the pressure inside the Soyuz decreases, oxygen is flowing through our suits and there is actually enough air pressure to breathe in the cabin without the extra oxygen. And, as we continue down towards the ground, the pressure increases inside.

One of the other things that happen at this time is that our seats are raised up to prepare the shock absorbers underneath our seat for landing. This also was a very interesting event. During our fit check of the Soyuz before we flew the specialists raise our seats so that we could see what it felt like and see how close you get to the panel in front of you when it happens. The real raising of the seats is a much more lively event. They pop up quite quickly. One second you are nice and happy in your usual configuration in your seat and the next second your face is just inches from the panel in front of you. It definitely gets your attention. This is another time that you could get hurt if you did not have all your arms and legs appropriately tucked in.

After Fyodor and I checked once more to ensure that all the systems were still operating automatically and according to plan, there was nothing for us to do except sit and wait for the ground. It is about this time that the search and rescue forces start to make contact with us. They let us know that they had us in sight and all was good. At this point they pretty much keep up a constant stream of chatter to us. They call out our altitude as we are descending and want us to respond so that they know we are all right. I have information on the display in front of me as to what altitude the Soyuz thinks it is at. This is based on some atmospheric pressure data we input to the computer before we undock, but the Soyuz altimeter is only a good approximation. The altitudes that the search and rescue guys tell us are more accurate. Because Doug does not have a display in front of him I translated the altitude information from the search and rescue forces to ensure he knew where we were.

The total time under the parachute after it opens and before we hit the ground is about fifteen minutes. When we started to get close (about a kilometer from touchdown), the search and rescue forces tell us to begin get ready. This means we need to make sure our seat and shoulder belts are as tight as they can possibly be. When we are about three hundred meters (a football field) away from the ground they tell us to prepare for landing. This means that we are supposed to essentially quit talking, so that we do not accidentally bite our tongues, and to brace ourselves for impact. Less than a second before we hit the ground our "soft landing" rockets fire. These jets are pointing towards the bottom of the Soyuz and are designed to slow us down at the last second. I do not recall the exact numbers, but I think when we are under the parachute, we are descending at a rate equal to just under twenty miles and hour. I believe that the soft landing rockets slow us down to about six miles an hour.

However, make no mistake about it, when we hit the ground, it is like being in a car crash. I am sure the soft landing rockets and the seat shock absorbers do a good job, but the fact of the matter is you have gone from moving reasonably quickly to not moving at all in a fraction of a second. You hit the ground hard.

When we landed, we bounced at least once and then ended up on our side. Basically we were tilting forward in our shoulder harnesses and I was on the low side. My head felt like it was crammed up against the front panel and I could just barely peek out my window. I could see that one of the search and rescue helicopters was landing and I knew that we were in good hands. All was well. We were back on terra firma once again and it was good to be home.

© Shannon Walker   2010 - 2011

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Credits - The above pictures were downloaded from NASA's Website at http://www.nasa.gov/

Posted 03-09-11