241 t

375 t

The ejector ram-scramjet operating to airbreathing Mach numbers from 6 to 14 offers the ability to reduce the gross weight by more than half. (5) ACES-LACE ejector scramjet-rocket, ACES-deeply cooled ejector scramjet-rocket is another concept that dates back to the late 1950s, and, like the scramjet, has not proceeded beyond the ground test phase. This concept did have much more full-sized, flight-weight hardware built and tested very successfully in the 1960s. The difficulty has always been the sensitivity of SSTO space launchers to volume demands. This propulsion system is very attractive for TSTO launchers, with the air collection and separation system in the first stage [Rudakov et al., 1991b,c]. A number of these have been designed, but none have proceeded beyond the concepts stage. This will be discussed later in the chapter dealing with mission-sized launcher systems. If indeed there is a problem with this propulsion system concept, it is the volume required for the liquid air separator. For volume-limited applications the size and weight of the airframe increases. It remains to be designed and demonstrated that the volume reduction potential of the deeply cooled gaseous separation is real [Lee et al., 2003]. As a result both systems are being treated as equal size, weight and performance systems.

For a vehicle for a rocket OWE equal to 76 metric tons and the OWE of other propulsion systems also 76 t, plus any differential for the propulsion system, the TOGW for the this systems is:

Cycle WR O/F TOGW Savingsa

ACES-scramjet 2.90 0.50 2521 3641

a With respect to an all-rocket SSTO launcher.

Even though the weight ratio is less than for the ejector ram-scramjet-rocket, the gross weight is not, and that is result of the air separation system volume.

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