by John W. Hicks, BS ASE 1969
As a nine-year veteran on the X-30 NASP project, I came up with the original X-43 idea and flight configuration after the NASP program was cancelled by Congress in Nov. 1994. The NASP concept had suffered from trying to tackle too many very advanced technologies and complex system integration issues to ever succeed under its limited funding level and management setup. Many technical experts realized we needed to flight validate many component technologies before ever trying to create as advanced an integrated vehicle as the X-30. Chief among these was the need for the world's first flight test of a large-scale scramjet under real atmospheric conditions, integrated onto an actual airframe. Besides the question of whether a scramjet could be successfully airframe integrated, a major technical issue was to demonstrate that scramjets could actually produce positive levels of thrust at Mach conditions of up to at least Mach 10.
NASA held a meeting in late Jan. 1995 at NASA Hq to decide where to go from there with hypersonic air breathing technology within the Agency. Coming from NASA's primary flight research center (Dryden Flight Research Center located at Edwards A.F.B. in California), I still saw the need to flight validate an airframe-integrated scramjet under actual flight conditions, which was something that have never been successfully done since the earliest wind tunnel ground tests began in the early 1960s. My concept was to propose something that was solely focused on the scramjet operation and performance, was cost effective, and could be carried out as simply as possible with existing flight test technology.
My simple idea was based on the fact Dryden knew how to air launch vehicles of all kinds (from the X-15 on) on its B-52 carrier aircraft, and that they had successfully launched the first six three-stage Pegasus rockets to orbit in the past. So I just combined those two facts into a new concept and vehicle configuration that was meant to be “rude and crude” as I called it then and “cheap” in government terms – compared to the X-30 program to any extent. I limited my “Hyper-X” vehicle to a small, compact one of 10-15 ft. that would be cheap/easy to build and fit full-scale into existing wind tunnels. This would allow us to both ground test it and compare that for the first time directly to flight. I came up with the use of the first-stage only booster using the winged first-stage Pegasus (which had never been used that way before) because it could be carried by its wing on the B-52 pylon (already existing) and air-launched (which many types of rockets can’t be). I chose an overall configuration (first-stage Pegasus + interstage adapter + X-43 vehicle) that would be approximately the same weight, length and center-of-gravity as the three-stage Pegasus rocket, so the B-52 could handle it and launch it from the existing Pegasus pylon on the Mothership.
The mini-X-43 vehicle itself was to have a single, simple airframe-integrated scramjet engine that could be fired for a few seconds in flight using gaseous hydrogen and fly between Mach 5 and 10 – as simple as I could make it and still prove the scramjet technology. The scramjet configuration needed to be "simple" in that it was to have fixed flow path geometry and have no active cooling of the structure so as to avoid additional complex variable geometry mechanisms and advanced structural cooling technologies. The airframe integration was important to be able to demonstrate aerodynamic forebody compression and flow conditioning technology of the inlet airflow for use by the scramjet combustor. Integrated scramjet nozzle geometry was needed to validate proper flow expansion and positive thrust production.
This was considered “crazy” and was certainly fraught with many technical and developmental difficulties. Not only had the winged first-stage of the Pegasus never been launched by itself, but it had to fly a very different “depressed” trajectory instead of its usual ballistic one. Additionally the total configuration was highly “asymmetric” or non-symmetrical, unlike the nice cylindrical Pegasus rocket. To top it all off, we had to separate the X-43 from its booster and interstage adapter at hypersonic speeds, which is very tricky at best.
But armed with this “low-cost, simple” concept I was put on NASA Administrator Dan Goldin's new X-Plane Committee that began in March 1995 and was made up of representatives from all the NASA centers. Over the next few months I worked to promote my concept against nine other candidate concepts from the committee that included everything from flying cars (literally!) to 800+ passenger airliners to Mars airplanes. We were the technical arm of the effort and were called the Blue Committee. The financial/upper management arm from Hq was called the Bluer Committee (NASA tries to be clever sometimes) who were to select from the ten concepts based on technical viability, potential overall cost and time schedule to develop, and would find political support in Washington D.C.
The Hyper-X concept was considered “iffy” because of the negative fallout of the recently cancelled and very expensive $2.5 billion X-30 NASP development program. But we prevailed and the X-43 was the only concept from the ten that was selected in Dec.1995. The rest of 1996 and into 1997 as its first project manager I set about developing the program plan, getting contractor bids, getting NASA Langley on our team, etc., so we could begin the arduous effort of developing a “hair-brained” concept from that “guy in Tehachapi” into a real flight test program. Aeronautical concepts are often easy to come up with compared to really executing the operational flight test project, where many operational and practical technical issues have to be overcome. It's well-known the first flight failed due to active control surface problems with the first-stage Pegasus booster vehicle. Often aeronautical science can only be learned or validated from risky actual flight test. The next two flights to Mach 7 and Mach 10 between 2000 and 2004 were fully successful, demonstrating the positive scramjet thrust and airframe integration technologies.
A typical and interesting aspect of the Hyper-X project was the broad range of engineering disciplines that were required to work closely together to make the X-43 configuration and flight test program possible and as successful as it was. It was basically an aerodynamic and propulsion technology program requiring engineering specialists from both those areas for design and analysis but the unique configuration and complex flight test launch brought together all kinds of other engineering specialties as well. Flight launch and control of the integrated configuration as well as the mini- X-43 put great demands on flight control systems and guidance engineering specialties. The depressed trajectory configuration flight, hypersonic stage separation, and X-43 flight challenged the science of flight mechanics and dynamic stability and control. Structural loads and flutter dynamics played a major role in configuration carriage, drop and flight at high dynamic pressures far above what was normal for the Pegasus rocket. And, of course, many other support engineering sciences played major, critical roles such as electrical systems and engineering, aerothermodynamics, materials science, mechanical systems and engineering, etc.
The student engineer should realize from this that today’s highly complex, advanced R and D programs often require a multi-discipline, integrated engineering team through the many phases of such an advanced project as Hyper-X. It pays well in your future professional career to assemble as broad a technical disciplinary background as you can possibly manage in your course of studies. Good planning, technical writing and speaking skills are also crucial to a well-rounded engineering professional.