Orbiter radiator performance provides the most variance in determining the amount of Shuttle Transportation System (STS) Orbiter water available for transfer to the International Space Station (ISS). As radiator performance decreases, dependence upon the Flash Evaporator System (FES), which requires Fuel Cell (FC) water to reject the Orbiter's waste heat, increases. Generally, radiator performance decreases as the ISS assembly size increases (especially as solar arrays are added), and also as beta angle increases.
A parametric study has been accomplished that provides a quick-reference table for determining the amount of Orbiter water available for transfer during ISS missions 2A.2 through 7A.1. An hourly Orbiter net water generation rate is reported according to variations in ISS assembly configuration, beta angle, ISS attitude, Orbiter radiator configuration, and Orbiter heat load. Those permutations of higher probability of occurrence than others have been identified. It appears very likely that the Orbiter will be able to accommodate the amounts of water required by the ISS Program (ISSP) for these early missions, even for high beta angles.
Another parametric study has been accomplished that provides a quick-reference table for determining expected water generation rates for ISS assembly complete missions, with similar parametric variations investigated as for the early mission study. Although ISSP requirements for water transfer have not yet been fully defined, it appears that most of the flight attitudes, especially at high beta angles, yield very low water transfer rates. The Orbiter net water generation rate at some of the attitudes at higher beta angles could possibly preclude docking to the ISS during these flight configurations.