7.1. FUTURE DEVELOPMENTS IN X-43 (Seminar Hyperplanes)

The future models of X-43 would also have almost similar design as X-43A , though the aircraft were expected to be moderately to significantly larger in size. The future models are

(i).X-43B
The X-43B was expected to be a full-size vehicle, incorporating a turbine-based combined cycle (TBCC) engine or a rocket-based combined cycle (RBCC) ISTAR engine. Jet turbines or rockets would initially propel the vehicle to supersonic speed. A ramjet might take over starting at Mach 2.5, with the engine converting to a scramjet configuration at approximately Mach 5

(ii).X-43C
The X-43C would have been somewhat larger than the X-43A and was expected to test the viability of hydrocarbon fuel, possibly with the Hi-Tech engine. While most scramjet designs have used hydrogen for fuel, HyTech runs with conventional kerosene-type hydrocarbon fuels, which are more practical for support of operational vehicles. The building of a full-scale engine was planned which would use its own fuel for cooling. The engine cooling system would have acted as a chemical reactor by breaking long-chain hydrocarbons into short-chain hydrocarbons for a rapid burn.
The X-43C was indefinitely suspended in March 2004. The linked story reports the project's indefinite suspension and the appearance of Rear Admiral (RADM) Craig Steidle before a House Space and Aeronautics subcommittee hearing on March 18, 2004.
According to a special feature article by Daryl Stephenson in the August 2005 online issue of Boeing Frontiers the X-43C appears to be funded through 2005. "Thanks to a funding request of $25 million for NASA sponsored by U.S. Rep. Jim Talent (R-Mo.), work on the X-43C program will continue through 2005.

(iii).X-43D
The X-43D would have been almost identical to the X-43A, but expanding the speed envelope to approximately Mach 15. As of September 2007, only a feasibility study has been conducted by Donald B. Johnson of The Boeing Company and Jeffrey S. Robinson of NASA Langley Research Centre, in Hampton, VA. According to the introduction of the study, "The purpose of the X-43D is to gather high Mach number flight environment and engine operability information which is difficult, if not impossible, to gather on the ground."