The new manned space exploration initiative announced by the United States in 1989 will involve the design and development of advanced manned spacecraft to transport crews from Earth orbit to the orbits of the Moon and Mars and back on a regular basis. Though the Moon is only a few days distant, a typical round trip to Mars will take about 500 days during which time crews will be confined to a spacecraft environment for two periods of about 235 days each. Under these exceptional circumstances, the crews must be provided with spacecraft habitability standards and accommodation facilities which are as comfortable, efficient and spacious as possible. However, the substantial mission propellant needs will dictate that crew facilities are minimized to help to limit overall spacecraft mass and complexity. This will conflict with the need to provide improved habitability and accommodation for such a long mission. Therefore, new design strategies must be developed in which maximum architectural opportunity is achieved with minimum pressurized volume.Several strategies are possible: internal spaciousness can be increased by in-flight modifications to recover residual volume from other completed applications; accommodation efficiency can be improved by adaptation to changes in shifts and schedules as and when they occur; sleeping quarters and exercise facilities can be optimized as deployable and expandable compartments which are retracted when unoccupied; in-flight training facilities can be developed to serve a dual-purpose as a semi-private crew library during leisure hours; inflatable pressurized structures can be used to provide an exterior annexed accommodation capability during certain portions of the mission. The combined impact of these strategies will substantially benefit the spacecraft habitability standards and crew accommodation facilities without reducing spacecraft mass or volume efficiencies.