1. 2 analyzed a f i l l i n g technique based on maintaining separation of the liquid and vapor phases within the receiver tank during the entire fill process. This technique relies on favorable orientation of the receiver tank so that the very low acceleration environment generated by atmospheric drag w i l l position the liquid and allow direct venting from the vapor region of the tank t o maintain an acceptable pressure level. An alternate concept for providing the desired acceleration environment, the use of tethers between the Space Station and a Space Vehicle Servicing Facility, i s currently being studied by Martin Marietta under NASAfJSC contract 9-17059. I n general, for the "fluid dynamic" liquid transfer technique, extremely low liquid transfer flow rates or long tethers are required in order that the stability of the liquidvapor interface i s maintained.
2. The OTV payload transportation requirements dre anticipated to grow with the evolution of the Srme Station. As satellitelpayload placement requ ireinevf: become more demanding the on-orbi t topping O f ground based OTV propellant tanks a t the >pace Station w i l l become desirable to: (1) replenish Cryogenic propellant boil-off, and (2) overcome the launch weight restrictions associated with the Shuttle. Eventually, space-based reusable OTVs having higher energy capability w i l l be riiquired to meet the payload placement Capability riematids envisioned for the mid-1990s time frainr dnd beyond.