Soyuz (Союз) is a series of spacecraft designed by the Soviet Union. The Soyuz spacecraft succeeded the Voskhod design and were originally built as part of the Luna program. The spacecraft are launched by the Soyuz launch vehicle. They were later used to carry cosmonauts to and from the Salyut space stations, Mir and the International Space Station.
A Soyuz spacecraft consists of three parts, an orbital module, a reentry module, and a service module. By moving equipment into an orbital module which does not reenter the atmosphere, the Soyuz vastly increases the space available to the cosmonauts, because the orbital module does not need to be shielded for reentry into the Earth's atmosphere. In the Command Module of the Apollo spaceceft there six cubic metres of living space for a mass of 5000 kg, the Soyuz provided the same crew with 9 cubic meters of living space, an airlock, and the service module for the mass of the Apollo capsule alone.
It could carry up to three cosmonauts. The vehicle is protected during launch by a nose faring, which is jettisoned after passing through the atmosphere. It has an automatic docking system. The ship can be operated automatically, or by a pilot independently of ground control.
The fore part of the spacecraft is the Orbital module. It houses all the equipment that will not be needed for reentry, such as experiments or photographic cameras. It also contains the docking port and can act as an airlock if needed.
The descent module is used for the journey back to Earth. It is covered by a heat-resistant covering to protect it during re-entry. It is slowed initially by the atmosphere, then by a braking parachute, followed by the main parachute which slows the craft for landing. At 1 metre above the ground, solid-fuel braking engines are fired to give a soft landing. One of the design requirements for the reentry module was for it to have the highest possible volumetric efficiency (internal volume divided by hull area). The best shape for this is a sphere, but this has no ability to bank a little, to generate lift and 'fly' to some extent. That is why it was decided to go with the 'headlight' shape that the Soyuz uses - a hemispherical forward area joined by a barely angled cone (7 degrees) to a classic spherical section heat shield.
At the back of the vehicle is the service module. It has a pressurized container with systems for temperature control, electric power supply, long-range radio communications, radio telemetry, instruments for orientation and control. A non-pressurized part of the service module contains the main engine and a spare: liquid-fuel propulsion systemss for maneuvering in orbit and initiating the descent back to Earth. The ship also has a system of low-thrust engines for orientation. Outside the service module are the sensors for the orientation system and the solar array, which is oriented towards the sun by rotating the ship.
The Soyuz spacecraft has gone through several incarnations. The first manned version was the 7K-OK. This could support up to three crews in a shirt sleeve environment. Although it could feature a docking port this was passive and only allowed the two spacecraft to be joined, with the facility for internal transfer. Cosmonauts had to spacewalk to the other spacecraft, as done on Soyuz 4 and 5. This spacecraft was also designed to fly the moon.
The next manned version of the Soyuz was the 7K-OKS. This was designed for space station flights and now had a docking port that allowed internal transfer between spacecraft. In the end it only flew twice manned after the fatal end to Soyuz 11 where the crew were killed when the capsule depressurised during reentry.
The complete redesign that resulted lead to the 7K-T. It deleted one crew space so that all cosmonauts could wear spacesuits during launch and reentry. It also had batteries instead of solar panels meaning it could only fly undocked for about two days.
A modified version of this spacecraft flew on Soyuz 13 were instead of the docking system was a large Orion 2 astrophysical camera for imaging the sky and Earth.
Another modification was the 7K-T/A9 used for the flights to the military Almaz space station. This featured the ability for remote control of the space station and a new parachute system but other than that the changes are still classified and unknown.
The Soyuz ASTP spacecraft was designed for use during the Apollo Soyuz Test Project. It featured design changes mandated by the Americans to make the spacecraft safer. The Soyuz ASTP featured new solar panels for increased mission length, an androgynous universal docking mechanism instead of the standard male mechanism and modifications to the environmental control system to lower the cabin pressure to 0.68 atmospheres prior to docking with Apollo. The last flight this version, Soyuz 22 again featured a camera instead of the docking port.
The next major redesign was the Soyuz T version. It featured solar panels allowing longer missions, a revised Igla rendezvous system and new translation/attitude thuster system on the Service module.
The Soyuz TM crew transports were introduced in 1986 to service the Mir space station. It was a modernised version of the Soyuz T, for use with the Mir Space Station. It has new docking and rendezvous, radio communications, emergency and integrated parachute/landing engine systems. The new Kurs rendezvous and docking system permitted the Soyuz TM to maneuver independently of the station, without the station making "mirror image" maneuvers to match unwanted translations introduced by earlier models' aft-mounted attitude control.
A slightly modified Soyuz TMA is now also being used. This features several changes to accommodate NASA requirements, including more latitude in the height and weight of the crew and improved parachute systems.
The unmanned Progress spacecraft were derived from Soyuz and are used for servicing space stations. The Chinese Shenzhou spacecraft is also heavily influenced by the design of the Soyuz, although, contrary to some media reports, it is not a derivative of the Soyuz.
See also: space exploration