Another justification of this selection is found in the independent nature of the chemical COTV. The primary incentive for utilization of the chemical COTV would be to avoid the penalties associated with tapping the satellite power; yet operation of the 1iquification plant would require external power, largely negating the justification for choosing the chemical COTV. 1.2.3 REPRESENTATIVE CONFIGURATION The representative LO2/LH2 COTV was derived using the following constraints and assumptions: 0 KSC site for launch into LEO 0 two-per-day HLLV flights each carrying 1 million pounds payload for tanking propellant 0 earth-launch propellant tank is plugged into a structural and feed system array that becomes the "stage" (no propellant transfer) The general requirements for a LO2/LH2 COTV engine are primarily long life (1000 hrs), simplicity (minimum active controls), and high specific impulse. An expander cycle (like the RL-10) was selected because of its high performance combined with relatively low chamber pressures (600 - 800 psia) and corresponding pump speeds. The low temperature heated hydrogen turbine provides for long life and active controls are minimized by using a single shaft for the pumps and turbine. A thrust level of 25,000 lb^ was selected to provide maximum pump and turbine efficiencies at low speeds and minimize kinetic losses that occur at lower thrust levels. Engine weight is not nearly as important as performance so a very high nozzle area ratio was selected. The only technical issues are associated with the turbo-machinery. Low speed/heavy weight pumps will utilize advances in technology. The proposed engine characteristics are given in table VI-D-1-1. Tank-mounted zero NPSH electric driven boost pumps supply propellant to the engine. The concept envisioned for assembling the stage is illustrated in figure VI-D-1-5. The tanks employ series feed through connections made while the stage is being assembled. No reaction control capability is provided by the COTV; a greater than normal gimbal range will probably be required, but the attitude control system of the satellite is assumed to be capable of performing any orientation that cannot be done by differential gimballing of the COTV main engines. A weight statement for the O2/H2 COTV is included as table VI-D-1-2. The numbers provided must be regarded as highly preliminary since the COTV concept is somewhat unconventional and a large number of assumptions are required in order to calculate any weights. 1.2.4 TECHNOLOGY ISSUES Technology issues are not a significant problem with this COTV concept. The size of the stage, its manner of construction and operation, and its economic viability will inevitably give rise to a large number
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