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The Russian Soyuz spacecraft has been the longest-lived, most adaptable, and most successful manned spacecraft design. In production for forty years, more than 230 have been built and flown on a wide range of missions. The design will remain in use with the international space station well into the next century.
The fundamental concept of the design can easily be summarized as obtaining minimum overall vehicle mass for the mission. This is accomplished by minimizing the mass of the re-entry vehicle. There were two major design elements to achieve this:
Put all systems and space not necessary for re-entry and recovery outside of the re-entry vehicle, into a separate jettisonable ‘living section’, joined to the re-entry vehicle by a hatch. Every gram saved in this way saves two or more grams in overall spacecraft mass - for it does not need to be protected by heat shields, supported by parachutes, or braked on landing.
Use a re-entry vehicle of the highest possible volumetric efficiency (internal volume divided by hull area). Theoretically this would be a sphere. But re-entry from lunar distances required that the capsule be able to bank a little, to generate lift and ‘fly’ a bit. This was needed to reduce the G forces on the crew to tolerable levels. Such a maneuver is impossible with a spherical capsule. After considerable study, the optimum shape was found to be the Soyuz ‘headlight’ shape - a hemispherical forward area joined by a barely angled cone (7 degrees) to a classic spherical section heat shield.
This design concept meant splitting the living area into two modules - the re-entry vehicle, with just enough space, equipment, and supplies to sustain the crew during re-entry; and a living module. As a bonus the living module provided an airlock for exit into space and a mounting area for rendezvous electronics.
The end result of this design approach was remarkable. The Apollo capsule designed by NASA had a mass of 5,000 kg and provided the crew with six cubic meters of living space. A service module, providing propulsion, electricity, radio, and other equipment would add at least 1,800 kg to this mass for the circumlunar mission. The Soyuz spacecraft for the same mission 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!
The modular concept was also inherently adaptable. By changing the fuel load in the service module, and the type of equipment in the living module, a wide variety of missions could be performed. The superiority of this approach is clear to see: the Soyuz will remains in use at least 70 years later, while the Apollo was quickly abandoned. After studying a range of designs, the Chinese elected to copy the Soyuz layout for their Shenzhou spacecraft, rather than Apollo. Perversely, NASA copied the Apollo spacecraft layout for their Orion CEV, set to replace the shuttle after 2015. Will Soyuz still be flying when Orion is retired?
Alla pagina ( http://www.astronautix.com/craftfam/soyuz.htm ) inoltre si può vedere un esplicativo schema della quantità di versioni progettate che derivano dal design Soyuz…si arriva fino al Kliper.Per quanto riguarda la specializzazione dipende da quali obbiettivi e risorse si hanno, nel 60 i russi avevano bisogno di un’astronave che potesse gareggiare nella gara per andare sulla luna (nn voluta però dai russi nei termini e scadenze americane) e che consentisse di poter svolgere varie tipologie di missioni orbitali sostituendo o cambiando parti della soyuz,questo è molto utile quando una missione singola richiede un design particolare che serve solo per quella missione,per cui sarebbe illogico costruire una astronave specializzata solo per una o due missioni (ASTP per esempio).La specializzazione porta a grandi capacità in un ridotto campo d’azione e questo genera più veicoli da mantenere.Come ogni problema ingegneristico nn vi è soluzione giusta o sbagliata a prescindere ma bisogna esaminare obiettivi e risorse e dare una risposta a questi.
