The 1966 Aeronautics and Astronautics Coordinating Board (AACB) report had concluded that "no single, most desirable vehicle concept could be identified…for satisfying future DoD and NASA objectives." So the search for a viable concept continued.
AACB and other previous studies had indicated that fully reusable "Class II" launch vehicles would have to be TSTOs since they would weigh too much at lift-off. But the need to develop two separate vehicles also greatly increased the DDTandE cost. "Class I" DynaSoar-like reusable mini-spaceplanes, on the other hand, would have a high recurring cost per flight since they would be launched on existing expendable launchers. The ILRV represented the best of both worlds since all the expensive components (engines, avionics, power and life support systems etc.) would be recovered and reused while only the relatively inexpensive propellant tanks would be discarded. The cost per launch would thus be lower than for "Class I" while the development cost would less than for the "Class II" TSTOs.
By this time (1968), the RLV plans had grown increasingly cautious and the ILRV was actually regarded as the most advanced of three manned spaceflight options, the others being a standard Apollo capsule and a new reusable lifting-body spacecraft plus existing or new expendable launchers.
Starclipper American winged orbital launch vehicle. Lockheed ILRV design created for the USAF in 1966. X-24B lifting body configuration orbiter with linear aerospike engine and wrap-around drop tank. Related to Lockheed Shuttle LS200 proposal. |
FDL ILRV American manned spaceplane. Study 1968. In late 1968 the USAF Flight Dynamics Laboratory proposed its Integrated Launch and Re-entry Vehicle. This was a 1.5 stage-to-orbit concept with an external drop tank. |
McDonnell-Douglas ILRV American winged orbital launch vehicle. The McDonnell-Douglas ILRV design featured fold-out wings for improved low-speed lift-to-drag ratio during final descent and landing. All of the vehicle's propellants were moved outside the orbiter into two large hydrogen tanks and two smaller oxygen tanks. The original concept was sized for an 11,340kg, 9.44m x 4.57m payload. |
Starclipper Light American winged orbital launch vehicle. Downsized version of the Starclipper, equipped with conventional bell nozzle engines, released by NASA for public consumption in 1968. |
Triamese American winged orbital launch vehicle. The General Dynamics proposed an ingenious "Triamese" concept for the US Air Force "Integral Launch & Re-entry Vehicle" program. This system (originally developed in 1965 for a classified USAF SAMSO study) would have utilized three virtually identical reusable booster/orbiter element vehicles rather than develop two different booster and orbiter spaceplanes. General Dynamics estimated that the Triamese only would cost $1-2 billion to develop (=$4.5-9B at 1999 economic conditions) and be operational by 1976. |