Current propulsion systems require such significant mass in order to obtain sustained orbit that conventional staging arrangements are necessary, and the potential loss of valuable vehicle structure is inevitable. Similarly, other companies pursue 'two-stage' vehicles with massive mother ships. A secondary spacecraft, which ‘piggy-backs’ the primary launch vehicle, is then subsequently released in order to achieve orbit. These two highly conventional approaches, however, have not yet solved the inherent mass problems associated with current propulsion systems. These arrangements typically require heavy takeoff weights, enormous developmental costs, and perhaps even more significantly, face potentially risky separation concerns and problems. Additionally, the touted weight savings of the vehicle structure derived from decreased safety margins and advanced materials amount to only a small fraction of the total propellant fuel mass, and thereby further increase risk factors. These issues and concerns are not entirely insurmountable, yet are they hardly economical or practical approaches either.
The need for a manned hypersonic research vehicle is paramount in developing the propulsion system that will give the United States economical access to space.
The optimum solution to economical earth surface to-orbit travel will ultimately be found in the discipline of hypersonic propulsion research.
In the coming years, a small manned test system, essentially consisting of a rocket-powered aircraft, will be required to solve this propulsion problem.