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A Brief Description of How the Soyuz Capsule Returns from the International Space Station: Expedition 40 Returns Sunday, November 9th, 2014
  Posted: 9 November 2014  
Soyuz capsule
Above: The Soyuz capsule is a little spec with solar panel arrays for electrical power- Expedition 40 crew inside. November 9th, 2014. Photo credit: NASA

Baikonur Cosmodrome, located in Kazakhstan and owned by Russia, is the same facility from where Yuri Gagarin lifted off and made his orbit around the Earth over 50 years ago.  Today Baikonur is used as the launch facility for the Soyuz capsule when it goes to the International Space station.  Currently Russia's cosmodrome is the only location in the whole world from where manned spacecraft depart for the International Space Station. (China also has a space laboratory and astronauts ride into orbit on Shenzhou-10 spacecraft from a launch pad in China to go there. The Chinese space laboratory can currently sustain 3 astronauts with resources for 20 days). On Sunday, November 9th, 2014, the Soyuz capsule will be returning Expedition 40 to the the uninhabited steppes of Kazakhstan by a parachute landed assist 3.5 hours after undocking from the International Space Station. Expedition 40 consists of Russian Commander Maxim Suraev, and astronauts (also called Flight Engineers) Reid Wiseman from NASA and Alexander Gerst from ESA.

Expedition 40 after landing in Soyuz in Kazakhstan
Above: The 3 astronauts of Expedition 40 after landing. The Soyuz capsule is the gum drop shaped object behind them.

The International Space Station (ISS) is orbiting at 400 km above the Earth and it has been in use since November 1998. The ISS orbits the Earth at a speed of 28,000 km/hr.

The journey back to Earth from the ISS in a Soyuz capsule takes approximately 3.5 hours. So from the time flight engineers are on the ISS in low Earth orbit, to the time they are seeing human faces back on Earth in Kazakhstan, is about 4 hours. That is shorter than a plane ride from San Diego to New York.

A Brief Description of How the Soyuz Capsule Works to Bring Astronauts Home

For the Soyuz capsule to return from the ISS, weather info must be analyzed so that the optimal return trajectory for the Soyuz can be calculated.

Expedition 40 crew will say goodbye to their colleagues staying behind (expedition 41), the hatch to the module will be closed, and the flight engineers on ISS will check to see that there are no leaks that could cause a cabin destabilization. Inside the closed off area, the expedition 40 crew will put on their space suits and enter the descent module for the “ultimate roller coaster ride back to Earth.”

The main engine of the Soyuz is located in the rear side of the spacecraft. The duration of the “breaking impulse”must be precisely calculated and achieved.

The Russian segment of the ISS has several docking ports from which a Soyuz capsule can dock. Undocking from different ports results in different trajectories. For example, undocking from the so-called service module port, the Soyuz reaches  orbit above the ISS and it’s orbital velocity slows down.  There is another port below the ISS- and the ISS changes orientation- so that the Soyuz can undock from that port, and it would join a higher orbit and speed up. When it is time to undock the Flight Director on the ground gives the signal, to open the Soyuz hooks, which are the only mechanical devices holding the capsule to the ISS.

The Soyuz does not fall like something dropped on Earth, as it separates from the International space station- because there is no gravity to pull it away.  Instead it floats away from the ISS at a slow rate like an object on the surface of water.  A set of mechanical pushes gently moves the Soyuz capsule away from the ISS. A de-orbit burn is initiated to decrease the speed and to change trajectory of the capsule so the vehicle re-enters the atmosphere, which acts as a natural break. 

As the vehicle travels its trajectory about 30 minutes till landing, at an altitude of roughly 140 km, the Soyuz capsule spacecraft separates into 3 parts; the orbital module, the descent module, and the instrument compartment.  There is no chance of the pieces colliding with one another- this is called impact less separation; only the descent module where the crew is located, is designed make it safely back to Earth. The other 2 pieces of the Soyuz spacecraft that come off break up and disintegrate in the atmosphere.

Photo by NASA astronaut Reid Wiseman from the ISS in November of 2014
Above: Sunrise on ISS. Photo by: NASA astronaut Reid Wiseman.

As the atmosphere becomes more dense the descent module gains speed. Its velocity traveling through the atmosphere is parallel to the velocity of a surfer traveling on a wave. At first it paddles into a wave slowly, but when the board catches onto the wave, the surfer feels himself gain more and more speed. Also like a surfer, the Soyuz has maneuvering capabilities to allow it to stay on its trajectory.

The Maximum G load of 4-G is experienced when the capsule reaches an altitude of 35 km above the surface of the Earth, when it has already been traveling for 6 of 7 minutes in the atmosphere. During a ballistic descent which is a different type of descent, the G-load may increase up to 9G.

The Soyuz capsule is about to enter the Earth’s atmosphere which will be the most stressful part of its journey for the capsule. The descent module experiences extreme high temperatures during re-entry so it is painted with a special protective coating and has a heat shield over its base. As the atmosphere becomes dense the descent module positions itself so that its heat shield points forward.

Supersonic-parachute-assisted landing
At an altitude of 5.5 km the frontal heat shield and external window glass are jettisoned. The parachute cover is jettisoned and parachutes are deployed at 30,000 feet.

Around 30,000 feet the parachute has to open. This is only an automated system with no manual override so it must go right. It does have a back up parachute.  It is a very violent moment when a 2,000 kg capsule soaring at the speed of sound suddenly is jerked by the string of a parachute opening from the side. The parachute slows the module to 22 km/h. This is the part of the ride compared to a roller coaster, but one astronaut said it’s worse because you are being pulled in all directions, however others might say it was the best ride of their lives. 

The capsule vents excess fuel and oxygen from pressurized tanks to reduce any chance of an explosion when the descent module hits the ground.Retro-rockets that were hidden beneath the heat shield are fired. Retro rockets fire forward to slow the descent module as it nears the surface of the landing zone.

Planet Earth by NASA astronaut Reid Wiseman
Above: Planet Earth, by NASA astronaut Reid Wiseman.

Back on the ground the astronauts are pulled out from descent module by the rescue and recovery team and they are carried to the vehicle that will transport them to the press conference in Kazakhstan, since their muscles are too weak to walk after landing in Earth’s gravity upon their immediate return.

Expedition 42 will be heading up on November 23rd which consists of the flight engineers Terry W. Virts; Russian Air Force pilot Anton Shkaplerov; and ESA astronaut Samantha Crisotoforetti. 

- Andrea Boggs

Reference list

  1. European Space Agency (Nov. 11, 2013) Soyuz undocking, re-entry & landing explained. [ ]
  2. European Space Agency (Date/year) Soyuz Launch sequence explained. [ ]
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