Science Fair Project Encyclopedia
Soyuz (Союз, union) is a series of spacecraft designed by Sergey Korolev for the Soviet Union's space program. The Soyuz succeeded the Voskhod spacecraft design and were originally built as part of the Luna program. The spacecraft are launched by the Soyuz launch vehicle, as part of the Soyuz program and the later missions of the Zond program. They were later used to carry cosmonauts to and from the Salyut space stations, Mir and the International Space Station. The first unmanned launch of the Soyuz was on 28 November 1966. The first manned launch of the Soyuz was on 23 April 1967.
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 spacecraft there were 6 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.
Soyuz can carry up to three cosmonauts. The vehicle is protected during launch by a nose fairing, 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 forepart of the spacecraft is the Orbital module. It houses all the equipment that will not be needed for reentry, such as experiments, cameras or cargo. It also contains the docking port and can be isolated from the descent module to act as an airlock if needed.
The descent module is used for launch and 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 mounted behind the heat shield 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 such a shape can provide no lift, which results in a purely ballistic reentry . Ballistic reentries are hard on the occupants due to high deceleration and can't be steered beyond their initial deorbit burn. 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. This shape allows a small amount of lift to be generated due to the unequal weight distribution. The nickname was thought up at a time when nearly every headlight was circular.
At the back of the vehicle is the service module. It has a pressurized container shaped like a bulging can that contains 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 systems 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 many incarnations of the Soyuz
The first manned version of the Soyuz was called 7K-OK. It could support up to three crewmembers in a shirt-sleeve environment. Although it could feature a docking fixture, this was passive and only allowed the two spacecraft to be joined, with no 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 to the moon.
The 7K-L1 was designed to launch men from the Earth to circle the moon. It was based on the 7K-OK with several components stripped out to reduce the vehicle weight. The most notable modifications included the removal of the orbital module (extra space for living quarters or equipment) and reserve parachute. It was the primary hope for Soviet circumlunar flight. Tests in the Zond program from 1968-1970 produced multiple failures in the 7K-L1's re-entry systems. Apollo 8 won the race to circle the moon and the goal was scrapped, along with the two remaining 7K-L1s.
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. It flew only twice manned. During the reentry of the second flight, Soyuz 11, the crew were killed when the capsule depressurised.
The complete redesign that resulted led to the 7K-T. It deleted one crew space so that all cosmonauts could wear spacesuits during launch and reentry. The replacement of solar panels with batteries limited it to about two days of undocked flight.
A modified version of this spacecraft flew on Soyuz 13 where 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 (69 kPa) prior to docking with Apollo. The last flight of this version, Soyuz 22 again replaced the docking port with a camera.
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 added to the Soyuz T 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.
See also: space exploration
- David S.F. Portree, Mir Hardware Heritage, NASA RP-1357, 1995
- Information on Soyuz spacecraft (search for Soyuz on that page for links to every spacecraft imaginable)
- OMWorld's ASTP Docking Trainer Page
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