PanAero feels that one promising approach is to stage at about mach 2.5 at 30 km, using both water injection into the inlet and auxiliary rocket power.  We feel that this is much simpler and lower cost than trying to reach higher speeds and using a zoom climb to get to staging dynamic pressures below 50 Pa.  This latter approach was our goal as part of a Phase I DARPA / RASCAL (Responsive Access Small Cargo Affordable Launch) to Coleman Research last year.  PanAero had the lead for the first stage, with the support of Northrop Grumman and six subcontractors. We were not successful in obtaining a Phase II contract.  Our effortts to meet DARPA technical goals led to replacing the inlets with much larger, higher speed inlets and to forcing the engines to work at much higher thrust levels than the levels for which they were designed.  This was rightfully viewed as being too high risk.  However, our post-RASCAL concept is relatively low risk. Morover, the post-RASCAL concept should actually reduce operational costs per flight--relative to the RASCAL operational cost goal.

The DARPA / RASCAL goal is to stage at very low dynamic pressure to eliminate any need for an aerodynamic upper stage.  However, this goal is difficult to combine with a companion goal of using airbreathing engines with little or no reliance on rocket engines.  Our post-RASCAL approach is to use a reusable upper stage capable of withstanding moderate dynamic pressures.  Our current concept constrains dynamic pressures during captive flight to about 50,000 Pa--with staging at about 5000 Pa.  The second stage wing and other aerodynamic surfaces are braced until just before staging.

The F-14B and F-14D have two GE- F-110 engines.  It may be possible to avoid adding rocket engines to the F-14D (or B) by using water injection and other augmentation concepts.  However, only the less powerful TF-30 engines used earlier in the F-14A are likely to be availble in the near future.  Accordingly, we would likely use rocket engines for takeoff at full gross mass and for pullup before staging, should we obtain several F-14A's for conversion to a dual commercial/military launch system.

The figure below shows one concept for such a system.  This figure does not show any rocket engines on the F-14; however, we have a relatively straighforward conceptual idea of how to integrate the rocket engines.