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| - A Soyuz spacecraft consists of three parts. From front to back, a roughly spherical orbital module, a small smooth reentry module, and a cylindrical service module with solar panels attached. The first two portions are habitable living space. By moving as much as possible into the orbital module, which does not have to be shielded or decelerated during atmospheric reentry, the Soyuz is both larger and lighter than the Apollo spacecraft's command module. The Apollo command module had 6 cubic meters of living space and a mass of 5000 kg; the 3-part 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.
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| abstract
| - A Soyuz spacecraft consists of three parts. From front to back, a roughly spherical orbital module, a small smooth reentry module, and a cylindrical service module with solar panels attached. The first two portions are habitable living space. By moving as much as possible into the orbital module, which does not have to be shielded or decelerated during atmospheric reentry, the Soyuz is both larger and lighter than the Apollo spacecraft's command module. The Apollo command module had 6 cubic meters of living space and a mass of 5000 kg; the 3-part 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 and provide life support for them for up to 3.2 days. The life support system provides a nitrogen/oxygen atmosphere at sea level partial pressures. The atmosphere is regenerated through KO2 cylinders which absorbs most of the CO2 and water produced by the crew and regenerates the oxygen, and LiOH cylinders which absorb leftover CO2. 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. This separation also lets the orbital module be customized to the mission with less risk to the life-critical descent module. 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.
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