NASA X-43
The NASA X-43 represented a ground-breaking unmanned hypersonic aircraft with various planned scale variations. Its primary purpose was to conduct comprehensive tests in hypersonic flight. This aircraft was vital to NASA’s Hyper-X program, which took shape in the late 1990s. Throughout its missions, it established several impressive airspeed records for jet aircraft. Notably, the X-43 is the swiftest jet-powered aircraft ever recorded, boasting an astonishing speed of approximately Mach 9.6.
The launch procedure involved attaching the X-43 to a winged booster rocket, forming what was referred to as a “stack.” This stack was released from a Boeing B-52 Stratofortress aircraft. Following this launch, the booster rocket, a modified first stage derived from the Pegasus rocket, propelled the stack to the required speed and altitude. Once these conditions were met, the booster rocket was jettisoned, allowing the X-43 to operate independently using its scramjet engine.
The initial aircraft in this series, the X-43A, was designed for a single-use mission, with three of them constructed. Unfortunately, the first X-43A was lost due to a malfunction during a flight in 2001. However, the other two completed successful missions in 2004, accomplishing remarkable speed records. During their flights, the scramjets were active for approximately 10 seconds, followed by a 10-minute glide and a controlled descent into the ocean. Subsequent plans for additional aircraft within the X-43 series were either put on hold or cancelled, ultimately being replaced by the U.S. Air Force-managed X-51 program.
DESIGN AND DEVELOPMENT
The X-43 played a significant role in NASA’s Hyper-X program, which involved collaboration between the American space agency and various contractors, including Boeing, Micro Craft Inc., Orbital Sciences Corporation, and General Applied Science Laboratory (GASL). Micro Craft Inc. was responsible for constructing the X-43A, while GASL was tasked with building its engine.
A key objective of NASA’s Aeronautics Enterprise was to develop and showcase technologies for air-breathing hypersonic flight. This pursuit gained momentum after the National Aerospace Plane (NASP) program was cancelled in November 1994, leaving the United States without a comprehensive hypersonic technology development initiative. In response, NASA introduced the Hyper-X program in the late 1990s, aligning with the “better, faster, cheaper” approach. The Hyper-X program leveraged research and technology from the NASP program, propelling advancements in hypersonic air-breathing propulsion.
The Hyper-X Phase I initiative was executed under the purview of NASA’s Aeronautics and Space Technology Enterprise, with collaborative efforts between the Langley Research Center in Hampton, Virginia, and the Dryden Flight Research Centre in Edwards, California. Langley took the lead in hypersonic technology development, while Dryden focused on flight research.
The X-43A was a compact unmanned test aircraft, measuring slightly over 3.7 meters (12 feet) in length. It featured a lifting body design, where the aircraft’s body generated a significant amount of lift during flight instead of relying on traditional wings. The total weight of the X-43A was approximately 1,400 kilograms (3,000 pounds). Notably, this aircraft was engineered for complete controllability during high-speed flight, even gliding without propulsion. However, it wasn’t designed for landing and recovery; test vehicles intentionally crashed into the Pacific Ocean after their missions.
Flying at Mach speeds generates substantial heat due to the compression shock waves associated with supersonic aerodynamic drag. At these high Mach speeds, the heat generated could be so intense that it could cause metal parts of the aircraft’s structure to melt. To counteract this, the X-43A employed a system that circulated water behind the engine cowl and along the sidewall leading edges to cool these critical surfaces. This water circulation was initiated around Mach 3 during tests to manage the extreme heat generated during flight.
VARIANTS OF X-43
Following the X-43 tests 2004, NASA Dryden engineers expressed their anticipation that their efforts would eventually lead to developing a two-stage-to-orbit crewed vehicle within roughly two decades. However, they held significant doubts regarding the feasibility of creating a single-stage-to-orbit crewed vehicle akin to the National Aerospace Plane (NASP) in the foreseeable future.
Additional X-43 vehicles were initially planned, but as of June 2013, most of these plans were either suspended or cancelled. These vehicles were expected to maintain the fundamental body design of the X-43A, albeit with moderate to substantial increases in size.
X-43B: The X-43B was a full-scale vehicle featuring a turbine-based combined cycle (TBCC) or rocket-based (RBCC) ISTAR engine. It would rely on jet turbines or rockets for initial supersonic propulsion. At Mach 2.5, a ramjet engine would take over, with a subsequent conversion to a scramjet configuration at around Mach 5.
X-43C: The X-43C was designed to be larger than the X-43A and intended to explore the viability of hydrocarbon fuel, potentially using the HyTech engine. While most scramjet designs employed hydrogen as fuel, HyTech would utilize more conventional kerosene-type hydrocarbon fuels, which are more practical for operational vehicles. The project aimed to build a full-scale engine that could use its power for cooling. The engine’s cooling system would also serve as a chemical reactor, breaking down long-chain hydrocarbons into shorter chains for a rapid burn. However, the X-43C project was indefinitely suspended in March 2004.
X-43D: The X-43D would have closely resembled the X-43A but aimed to expand the speed envelope to Mach 15. As of September 2007, only a feasibility study had been conducted by experts from Boeing and NASA’s Langley Research Center. The objective of the X-43D was to gather valuable data on high Mach flight environments and engine operability, which is challenging to obtain on the ground.
These projects represented ambitious efforts to advance hypersonic flight technology. Still, they faced various challenges and, in many cases, were not pursued to completion due to budget constraints and shifting priorities within NASA.
OPERATIONAL TESTS OF X-43
The inaugural test of NASA’s X-43A, conducted on June 2, 2001, failed when the Pegasus booster lost control 13 seconds after its release from the B-52 carrier aircraft. The rocket encountered a control oscillation as it approached transonic speeds, ultimately causing the starboard elevator to malfunction. This deviation from the planned trajectory prompted safety measures, leading to the rocket’s destruction. Subsequent investigation revealed that imprecise data about the rocket’s capabilities and flight environment significantly contributed to the accident. The inaccurate data modelling for this test resulted in an inadequate control system for the Pegasus rocket, although the failure could not be attributed to a single factor.
In the second test, carried out in March 2004, the Pegasus booster performed successfully, releasing the test vehicle at an altitude of approximately 29,000 meters (95,000 feet). After separation, the engine’s air intake opened, igniting the engine and propelling the aircraft to Mach 6.83 (7,456 km/h or 4,633 mph). Fuel flowed to the engine for 11 seconds, during which the aircraft covered more than 24 kilometres (15 miles). Following Pegasus booster separation, the vehicle experienced a minor reduction in speed, but the scramjet engine continued to accelerate it during its ascent. After burnout, the aircraft remained manoeuvrable for several minutes, eventually descending into the ocean. This successful flight established the X-43A as the fastest air-breathing aircraft in the world.
NASA conducted a third X-43A test on November 16, 2004. The Pegasus rocket booster separated from the B-52 carrier at 40,000 feet, and the solid rocket propelled the combination to Mach 10 at 110,000 feet. The X-43A disengaged at Mach 9.8, and its engine ignited at Mach 9.65 for 10–12 seconds, producing thrust roughly equivalent to drag. Subsequently, the aircraft glided for 14 minutes before descending into the Pacific Ocean. Dynamic pressure during the flight peaked at 1,050 pounds per square foot (0.50 bar). The X-43A achieved a speed of Mach 9.68 (6,755 mph or 10,870 km/h) at 109,440 feet (33,357 meters), further testing the vehicle’s ability to withstand the associated heat loads.
