Upper stage propellants

Upper stage propellant applications are usually based primarily on performance—i.e., high specific impulse. If the upper stage is a multistart vehicle, hypergolicity is usually required. Careful consideration is also given to the propellant physical and chemical stability as well as to the matching of the propellant s liquidus range to the space environmental temperature if the propellant system is to remain operational in space... 

Economic Factors. Economic factors are related to the availability and cost of the propellant as well as the cost of the equipment required to transport, store, and supply the propellant. Generally, low cost is a prime requisite for a propellant which will be utilized in large quantities and/or in multiunits (i.e., booster stages of launch vehicles and in military weapons). However, where utilization of a high-cost propellant may be required to complete the mission, the cost factor can be of secondary importance. This situation is usually associated with upper stages of a space launch vehicle. 

Butts, P.G., and Hammond, R.N., (1983) Inertial upper stage (IUS) propellant development and qualification, in JANNAF Propulsion Meeting, vol. I, (ed. 

M. Mochizuki, "Solid Motor and Propellant for Upper Stage of H-l Rocket 1." Industrial Explosives (Not yet printed)... 

The total figure of merit of propellant system performance is usually taken to be specific impulse multiplied by propellant bulk density to some exponent which may range from 0.05 to 1.0. The actual value of the exponent depends upon a complex relationship among the propellant, its properties, the mission, and design criteria. Thus, the high density of the propellant in a volume-limited application such as an air-launched missile is extremely important whereas for an upper-stage it is not nearly so critical. 

Propellant utilization systems have been used to attain minimum propellant residual at engine cutoff by controlling outflow of one of the propellants within the limits of mixture ratio tolerances. Signals from point level sensors, which are spaced at various percent full levels in both the fuel and oxidizer tanks, can be compared on a time basis and processed through a computer. The computer may then provide the necessary mixture ratio control commands to a flow control valve. Such a system is presently used on the Atlas Standard Space Launch Vehicle (SSLV) and has been proposed for upper stages of Saturn. 

While Centaur upper stages continue to be used for evolved expendable launch vehicles (EELV), start baskets were never installed into the propellant tanks. Several low-g CFM experiments were proposed (Chato, 2006) and modifications to convert the Centaur upper stage into a cryogenic test bed were conceived, but they never came to fruition (Kutter et al., 2006 Sakla et al., 2006 Gravlee et al., 2010). 

Another recently proposed small-scale depot demonstration of LH2 storage and transfer in LEO was the proposed Cryogenic Orbital Testbed (CRYOYE-LFTE) mission from the United Launch Alliance (ULA), which considered the transfer of propellant from a Centaur upper stage to the CRYOTE receiver tank. The CRYOTE tank would be launched empty as a secondary payload on Centaur once the primary payload has been delivered. Centaur and CRYOYE would detach, and Centaur would supply liquid to an empty CRYOTE tank. Once in orbit, CRYOTE could then conduct short term storage tests. Details and proposed experimental requirements for this test (Pikes et al., 2006 Gravlee et al., 2010 McLean et al., 2011), as well as older Centaur-based experiments (Schuster and Brown, 1987), are available in the literature. 

Behruzi, K.P., MichaeUs, M., 2006. Development of a propellant management device for restartable future cryogenic upper stages. In AIAA-2006-5053, 42nd Joint Propulsion Conference, Sacramento, CA, July 9 12. 

Behruzi, P, Dodd, C., Netter, G., 2007. Future propellant management device concepts for restartahle cryogenic upper stages. In AIAA-2007-5498,43rd Joint Propulsion Conference, Cincinnati, OH, July 8-11. 

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