Multi-faceted Approach for Initial Volume Determination for Smaller Lightweight 2 ^nd Generation Space Planes

The SLI proposed requirements for a Crew Transfer Vehicle, CTV, have evolved from a Shuttle-like multipurpose vehicle concept to a vehicle with a requirement to merely transport 3-5 crewmembers (a space taxi) to the International Space Station. In an effort to minimize the weight and cost of this Orbital Space Plane, OSP (previously known as CTV) and to optimize the total 2^nd Generation Reusable Launch Vehicle approach, the requirements for OSP have dictated a much smaller crew cabin than the Shuttle astronauts have utilized. The challenge to the human factors engineers is to develop a set of derived requirements for the crew volume. Several analysis approaches have been used, compared, and evaluated against the key drivers. The drivers of these approaches are the physical and psychological limits of humans, operational requirements, time on orbit, task requirements, crew accommodations/technologies, packaging, volume layout and application of lessons learned. This paper both describes the approaches and rationales used to develop initial crew volume requirements for the various OSP design reference missions and summarizes the resulting requirements identified. While significantly smaller, the recommended volume requirements will aid vehicle designers during the concept development and insure enough volume is allocated for humans. An additional benefit is the pushing back on questionable/soft system requirements for trade decisions affected by vehicle size and weight.