Soyuz undocking, reentry and landing explained
Soyuz undocking, reentry and landing explained
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00:30Every day since November 1998, the International Space Station has been orbiting the Earth
00:43at a speed of 28,000 km per hour.
00:50Having spent several months on board the International Space Station, the time has come for three
00:54of its crew members to travel back to Earth.
00:58The return journey aboard a Soyuz capsule takes three and a half hours.
01:03Before it can start, there's a lot of preparation to do, both in space and on the ground.
01:13The normal landing site for the Soyuz is Kazakhstan.
01:17A group of ground-based experts prepare meticulously for this operation.
01:21They take into account the current orbit of the station and then select the most appropriate
01:25landing site on the ground.
01:29The landing site is checked by the search-and-rescue team to make sure that the terrain is flat
01:34and free from any obstructions that could complicate the landing.
01:39The search-and-rescue team is able to operate even in extreme weather conditions.
01:47When all the information has been analyzed, the optimal return trajectory is calculated.
01:58One week before the Soyuz undocks from the station, the instructors and controllers located
02:02in the Mission Control Center near Moscow conduct a remote training session with the
02:06crew and the onboard simulator.
02:10During this session, the crew are reminded about the most important actions they will
02:13have to perform during the re-entry.
02:16They carefully run through the procedures for each critical step, including the scenarios
02:20that could lead to an emergency descent.
02:23They are also briefed on the latest details of their trip back, such as landing conditions
02:28and the precise timelines for the activation of vehicle systems.
02:33The onboard crew runs a test of the Soyuz vehicle and begins packing items that will
02:38travel with them back to the ground.
02:41The Soyuz is then activated and the crew starts preparing it for undocking.
02:46When instructed by the ground controllers, the crew say their goodbyes to the colleagues
02:50staying behind and close the hatch that separates the Soyuz orbital module from the station.
02:57The hatch is carefully checked to make sure there are no leaks that could cause an unexpected
03:02cabin depressurization.
03:05The crew members put on their spacesuits and enter the descent module that they will occupy
03:10for the ultimate rollercoaster ride back to Earth.
03:16Former astronaut Frank de Wiener is now head of the European Astronaut Centre in Cologne.
03:21He remembers clearly the emotions he felt as he was about to leave the International
03:26Space Station.
03:28Wow, today I'm really going home.
03:31Because of course, the days before, you're preparing for the descent, you're reviewing
03:36all the procedures, you're going through all the radiograms, but it's only at the moment
03:40that you're in your spacesuit and that the hatches are closing that you know that four
03:45hours later you will be back on Earth.
03:50Both crew and vehicle are now ready for the undocking sequence.
03:55The Russian segments of the station have several docking ports for hosting Soyuz vehicles.
04:01In this example, the vehicle is going to undock from the so-called service module.
04:08In this case, the undocked Soyuz reaches an orbit below the station.
04:13The orbital velocity of the Soyuz also increases.
04:16Sometimes, however, the Soyuz is docked to a port underneath the station.
04:22In these situations, approximately 40 minutes before the undocking, the station changes
04:27its orientation.
04:31The Soyuz then undocks and joins a higher orbit, and its velocity decreases.
04:38In both cases, after one revolution of the Earth, the orbits intersect, but because of
04:43their now different velocities, the station and the Soyuz arrive at the intersection point
04:49at different times.
04:50This prevents any possibility of a collision between the two vehicles.
05:01When the flight director is ready, a GO is given to the crew to initiate the undocking.
05:07The crew commander issues the command to open the Soyuz hooks.
05:11These are the only mechanical devices holding the vehicles together.
05:15After approximately 3-4 minutes, the hooks are fully opened and the Soyuz is no longer
05:20firmly attached to the station.
05:22A set of pushers that were kept mechanically compressed while docked gently ease the Soyuz
05:27away from the station at a relative speed of 12-15 cm per second.
05:38Being so close to the station, the Soyuz propulsion system is inhibited in order to avoid contamination
05:44of the station with residual chemical dust produced by the Soyuz thrusters.
05:50The crew gets visual confirmation of the separation through the image provided by the external
05:55TV camera, and also from indications displayed on their monitors.
06:03ESA astronaut Paolo Nespoli returned to Earth aboard a Soyuz spacecraft at the end of Expedition 27.
06:10I didn't actually felt the detach when we detached from the station.
06:16Physically I didn't feel it.
06:18The physical departure of the station is done because of a push of some spring that there
06:23are inside.
06:24You don't want to start your engines close to the station because you are going to plume
06:28everything.
06:29So you are just kind of drifting away and what you are doing there, what we were doing
06:33was just looking at the instruments, looking at the camera outside and checking that the
06:38Soyuz would be inside the departure corridor.
06:42This is what we were doing.
06:44Did not really felt anything.
06:46The only thing is that we felt we started this long journey back to Earth.
06:55Three minutes later, when the spacecraft has moved about 20 meters, the crew monitors the
06:5915-second burn that increases the separation speed up to 2 km per hour.
07:05This leads the Soyuz to a safe position relative to the space station.
07:12After the undocking, the ground controllers upload the data needed by the onboard computer
07:17to autonomously perform the descent.
07:20The crew is in constant communication with the ground.
07:23They verify the validity of the data before allowing the computer to use it.
07:30At this stage, the crew must pay special attention to prepare for the next critical operation,
07:35the de-orbit burn.
07:38As can be seen, although the Soyuz is now far away from the station, it is still orbiting
07:43the Earth at an altitude close to that of the ISS.
07:47The purpose of the de-orbit burn is to force the Soyuz to decrease its speed.
07:53As a result, the trajectory of the vehicle changes and it re-enters the atmosphere.
07:58The atmosphere acts as a natural brake and does most of the work in slowing the Soyuz
08:03down until a set of parachutes opens and ensures a relatively soft landing.
08:10This braking is achieved by using the main engine located in the rear side of the spacecraft
08:15to push against the direction of travel.
08:18The required orientation and duration of the braking impulse must be precisely calculated
08:23and achieved because it directly influences the steepness of the re-entry path.
08:29If we don't burn enough, then we have still too much speed and we will still be too high
08:34in the atmosphere and we can actually skip over the atmosphere and then go further into
08:39space and that of course would not be a successful re-entry.
08:43On the other hand, if we burn too much and we come in too steep, then we will have too
08:47much speed when we are in the lower parts of the atmosphere.
08:51The heat that is normally around 2000 degrees Celsius will be much higher and we have a
08:56risk of burning up.
08:58So also therefore it is very critical that we do the correct de-orbit burn and that we
09:03really fix this around 120 meters per second.
09:09To achieve the correct burn, the main engine fires for exactly 4 minutes and 45 seconds.
09:23The Soyuz now follows a trajectory that will lead it to intercept the dense layers of the
09:27atmosphere leading to a safe re-entry and landing about 55 minutes later.
09:36As the vehicle travels along its trajectory, about 30 minutes before landing and at an
09:41altitude of roughly 140 kilometers, it separates into three parts, the orbital module, the
09:48descent module and the instrument compartment.
09:52There is no chance of the individual modules colliding with each other.
09:55This is called impactless separation.
09:59Only the descent module hosting the crew will make it back safely to Earth.
10:03The other two will disintegrate and burn up in the atmosphere.
10:08The separation of the spacecraft in the three parts is happening through several seconds
10:15because there are several parts that get detached after one or the other.
10:19All of these actions are done with explosive bolts or explosive implements.
10:26Seen from inside of the spacecraft, it felt like there was somebody outside the spacecraft
10:32with a sledgehammer that was hammering here and there, up and down, and so every few milliseconds
10:38the spacecraft was shaking with this bang, bang, bang, bang, bang, bang.
10:43It felt really interesting actually.
10:52The descent module experiences extreme high temperatures during re-entry, so to protect
10:57it and the crew inside, it's fitted with a special protective coating and has a heat
11:02shield on its base.
11:04As the atmosphere becomes more dense, the descent module positions itself so that its
11:09heat shield points forward.
11:11The capsule is about to enter the Earth's atmosphere.
11:15This will be the most stressful part of its journey home.
11:19By the time we were supposed to re-enter the atmosphere, I actually looked out from our
11:24window and I actually looked and we were tumbling.
11:27I was a little bit puzzled because I thought we need to re-enter in a special angle.
11:32So I started looking at procedure, we did a few things, and when I looked out again,
11:38I saw that we were already inside this plasma, it was getting really red, and actually the
11:45window was getting pretty dark.
11:48It was happening that a plasma stream is actually burning the outside layer of the window, which
11:54has a protective cover.
11:56So it was kind of interesting, at that point I really did not feel that much, I mean the
12:01gravity starts grabbing you, but it's very gentle at the beginning and you actually use
12:08it to feel or go into the seat and buckle up, pull your straps so that you really lay
12:16into the seat.
12:17It was an interesting feeling.
12:20The descent module follows a path that is similar in shape to that made by a surfer
12:24riding a big wave.
12:26Like a surfer, the Soyuz is able to make small adjustments to keep itself on track.
12:32So how is the trajectory of a free-falling capsule controlled?
12:38Even though it doesn't have wings, the Soyuz capsule is able to change the way it flies
12:43through the air.
12:44The design of the Soyuz enables it to do this.
12:47The capsule's lift increases when it rotates in one direction and decreases if it rotates
12:52in the opposite direction.
12:54In this way, the capsule is able to keep to its planned trajectory.
12:58As a side effect, this rotation also induces a sideways displacement of the module.
13:04This effect is very useful because it gives more flexibility for the selection of the
13:09landing site.
13:10This sideways maneuver has already been taken into account when selecting the optimum trajectory.
13:20During the descent in the atmosphere, a crew feels the effect of the deceleration when
13:25their weight exceeds several times their own weight on the ground.
13:29The maximum G-load, 4G, is experienced when the capsule reaches an altitude of roughly
13:3435 kilometers when it's already been traveling for 6-7 minutes in the atmosphere.
13:40Gravity is a very, very strong force.
13:43We do not understand here on Earth how gravity has such a hold on our body and what is around
13:49us.
13:51You do feel it when you come back from space because now you have been in a non-gravity
13:57environment for a long time and then you see all these forces grabbing you.
14:04You look at stuff and you feel your hands are heavy, you feel your watch weighs a ton,
14:08your books, the materials around you, your head, it's extremely heavy.
14:13And it's really, really, really a very strong feeling.
14:17In the unlikely event that the automatic control system fails, the crew is able to use a manual
14:23hand controller as a backup.
14:25They train extensively to prepare for this possibility.
14:29Another option is the ballistic descent.
14:32The spacecraft starts spinning and flies a much steeper trajectory without any additional
14:37sideways displacement.
14:39The G-load, in this case, will increase up to 9.
14:45When the capsule reaches an altitude of 10.5 kilometers, its speed has already decreased
14:50from 28,000 to 800 kilometers an hour.
14:55In order to further decrease the speed, the parachute cover is jettisoned and a series
14:59of parachutes are deployed.
15:02At the end of the atmospheric re-entry, you really start hearing the noise of the wind
15:07and the sound.
15:08You're almost breaking the sound barrier.
15:10Then in the opposite direction, of course, you're coming back into the normal area of
15:15flying.
15:23And this is around 30,000 feet that the parachute has to open.
15:27This is actually a very critical moment, and it's one of the only things in the Soyuz
15:31where the crew does not have a manual override.
15:34So this is only an automated system.
15:36So far it has always worked, and we also have a backup parachute that can help us in case
15:41that the main would not open.
15:42But it's also a very violent moment.
15:44You can imagine this 2,000 kilogram capsule that is soaring at the speed of sound through
15:50the atmosphere, and then all of a sudden you have a parachute that opens on the side and
15:55that pulls on you like with a little string.
15:58It's almost like a yo-yo, and you see the capsule going all around.
16:01It's much worse than in a roller coaster because it motions in all directions.
16:07And it's a little bit scary for some of us.
16:09For some others, it can also be fun to say like, oh, this is the best ride I ever had.
16:14Then, a few minutes later, at a height of 8.5 kilometers, the drogue chute finally deploys
16:20the 1,000 square meter canopy of the main parachute.
16:27This slows the capsule down to a speed of 22 kilometers per hour.
16:32The capsule is suspended under the parachute with a specific angle relative to the ground.
16:37This angle helps the capsule to dissipate the heat accumulated on its surface and structure
16:42during the reentry.
16:45But then everything calms down, of course, once the main parachute has deployed.
16:50You really get to the calm air after this whole violent reentry, the violent opening
16:54of the parachute, then you're hanging safely, slowly descending to the earth underneath
17:00your parachute.
17:01And this is actually the first time that you know, yes, I'm safe, we're going to make it.
17:09At an altitude of roughly 5.5 kilometers, the frontal heat shield and external window
17:14glass are jettisoned.
17:16This capsule vents excess fuel and oxygen from pressurized tanks to reduce any chance
17:22of an explosion when it hits the ground.
17:24In order to position the spacecraft adequately for the landing, the main canopy switches
17:29to symmetric suspension.
17:31This setup ensures the cosmonaut seats are now perfectly positioned to absorb the landing
17:36impact shock.
17:38The retro rockets that were hidden behind the heat shield are prepared for firing.
17:44Inside the capsule, the crew seats automatically raise in order to prepare shock absorbers.
17:50Usually, the search and rescue team equipped with aircraft and helicopters start tracking
17:56the Soyuz capsule even before the very first parachute is deployed.
18:00The helicopters land next to the capsule shortly after touchdown and the team help the crew
18:05to exit.
18:06Finally, 70 centimeters above the ground, the six retro rockets fire to further reduce
18:12the capsule speed to approximately 5 kilometers per hour.
18:16The capsule hits the ground, but the crew seats continue moving down and shock absorbers
18:21help to make the landing softer for the crew.
18:27The soft landing is not really soft.
18:30You prepare for it by putting your arms against your body, not touching any of the metallic
18:36parts, all your books against you.
18:39You're not talking, not to put the tongue in the middle of your teeth, and you're laying
18:43there trying to be as inside your seat as well as you can.
18:49And you're waiting for this soft landing to happen, which for me felt like a head-on collision
18:56between a truck and a small car.
18:59And of course, I was in the small car.
19:01So when this happened, it was like, bada boom, everything shook.
19:06I was kind of shaking in there.
19:08And then silence, everything was stopped.
19:12So I looked a little bit around, I looked at my crew members, and then I said, hey guys,
19:18welcome back to Earth.
19:21Once landed, one of the first actions of the crew commander is to release one of the two
19:25ropes that connect the capsule to the parachute.
19:28This is important as in windy conditions, it prevents the capsule from being dragged
19:33away on the ground by the inflated parachute.
19:38You know that you're on the ground.
19:39You hear the voices of the rescue troops that are next to you.
19:43And you know that five minutes later, they will open up the hatch and you can breathe
19:47fresh air.
19:50The crew is now safely back on Earth.
19:52They will soon be reunited with their families and begin the rehabilitation process after
19:57their extraordinary journey.
20:33NASA Jet Propulsion Laboratory, California Institute of Technology