Launcher Propulsion System Characteristics

Section 3.1 provides the governing equations and methodology for determining launcher size to achieve a given velocity increment with a given payload mass. The sizing process is the same. The difference is that, for a fixed-volume payload bay, each propellant combination has a different bulk density and therefore a different tank volume occupied for a fixed propellant mass. The role of the propel-lant delivery vehicle is analogous to that of an Air Force Tanker. Its role is to deliver fuel to in-flight operational vehicles on demand, and on a sustained operational basis. In this case the role of the LEO tanker is to routinely deliver propellant to an orbital refueling station in LEO. Being a dedicated tanker, the cargo container is a propellant tank, with provisions for transferring propellant in orbit. In micro-gravity special design considerations are necessary, e.g., that the propellant is adjacent to the transfer pumps, but this has been accomplished for some time in space and is a known design approach. In all cases, the LEO tanker is an automatic vehicle, that has sustained, frequent use and routinely exits and enters the atmosphere, and in not an expendable or a reusable expendable vehicle. So the configuration of the LEO tanker is that of a hypersonic glider or airbreathing launcher, as shown in Figures 2.16 and 2.17, and Figures 4.34 to 4.36. Four different launcher propulsion systems were evaluated for the tankers to LEO:

(1) Hydrogen/oxygen rocket, based on the Pratt & Whitney XLR-129.

(2) Hydrogen/oxygen LACE rocket based on the Pratt & Whitney XLR-129.

(3) Rocket ejector ram-scramjet airbreathing to Mach number 10, transitioning to a hydrogen/oxygen rocket, based on the Pratt & Whitney XLR-129.

(4) Rocket ejector ram-scramjet airbreathing to Mach number 12, transitioning to a hydrogen/oxygen rocket, based on the Pratt & Whitney XLR-129.

The design payload is 19 tons (41,895 lb) of propellant with a bulk density of 999.4 kg/m3 (62.4 lb/ft3). A launcher for the design payload was sized for each propulsion system. For different propellant densities, the size and weight of the launcher is different, and these corrections are discussed later in this chapter and are given in Figure 5.6.

0 0

Post a comment