International Journal of Creative Research and Studies Volume-4 Issue-10, October 2020 INTERNATIONAL JOURNAL OF CREATIVE RESEARCH AND STUDIES www.ijcrs.org ISSN-0249-4655 A Review on Hypersonic Propulsion Technology: From History to Present Scenario with a Brief Overview of Hypersonic Propulsion Programs in India Ayushi Mehrotra Aerospace Engineer (MS) Department of Aerospace Engineering Auburn University, Auburn, Alabama, USA ABSTRACT Hypersonics is the regime of flight at which the velocity of flying object exceeds Mach 5. Dealing with the hypersonic flow requires a strong knowledge of high speed aerodynamics, as the regime is characterized by high amount of aerodynamic heating, shock waves and its interaction with the airframe components of a flying vehicle. Hypersonic wind tunnels and experimental rocket boosted NASA’s X-43A have been instrumental in predicting the physics involved in hypersonics. Air-breathing engines like Ramjet, have excellently demonstrated flight at supersonic velocities up to Mach 4, but it fails to operate when the requirement is to fly higher than Mach 5. This drawback was best overcome by Scramjet engines. In 2004, the experimental aircraft X-43A, that has a scramjet engine, was able to reach a velocity of Mach 9.65, with the help of an assisted rocket launch. Hypersonics is a promising propulsion technology especially for high speed applications like trans-atmospheric vehicles and space exploration. They can easily replace rockets as they are more fuel efficient, have much higher specific impulse and provide a faster means of travel. This can effectively benefit fields like space exploration, where distances between bodies are huge; it can also benefit military research and future means of aviation. In this paper, the author has attempted to present the evolution of Hypersonic Technology with time, since 1950s till up till now. The scope and future challenges involved to harness this technology with reference to India, to its maximum have also been discussed. Keywords: hypersonic, supersonic, scramjet, space exploration, Mach, Aerodynamics, Propulsion www.ijcrs.org Page | 1 International Journal of Creative Research and Studies ISSN-0249-4655 1. INTRODUCTION This paper studies in detail the various advancements in the field of Scramjet design and propulsion technology; from its inception in the early 1950s to the advancements up till date. It makes a brief foray into Hypersonics and its physics and then explores the realm where Scramjets dominate the field of study. Hypersonic can be described as the regime of flight where aerodynamic heating takes place. Mach 5 and higher is considered to be the regime of hypersonic flight. Important results in hypersonics have mostly been experimental. Supersonic wind tunnels and other related devices have produced flows with speeds up to orbital velocities. Hypersonics is important because it has provided us with optimal solutions relating to thermal protection during atmospheric entry. Due to this, ballistic missile nose cones have been developed which have been vital during missions to the Moon and planets like Jupiter. The second most important application of hypersonics has been in propulsion science. It has led to the development of high speed propulsion and has pursued to develop the scramjet as an advanced ramjet. Scramjets are built to achieve near orbital velocities. A good example of advanced Scramjet engine includes the flight of NASA’s X-43A in November, 2004 at Mach 9.65 by using a rocket. Supersonic flight is achieved when an aircraft touches Mach 1, which continues up to a range of Mach 4. Air-breathing engines like Pratt and Whitney’s J-58, a hybrid turbo- ramjet, have demonstrated excellent flight at supersonic regimes. Hypersonic velocities are achieved with a flight regime ranging from Mach 5 and above. Ramjets become highly inefficient at this range, mostly because of aerodynamic heating. A new engine, the Scramjet is ideally used for hypersonic regimes. Scramjet stands for Supersonic Combustion Ramjet. Unlike the ramjet, the combustion inside a scramjet is supersonic throughout. Scramjet engine technology is a promising technology of the future especially for very high-speed applications like space exploration, trans-atmospheric vehicles etc. which require high fuel efficiency along with speed and design accuracy. Scramjet engines also have a flourishing military applications as ballistic missiles, rockets etc. usually belong to the hypersonic regime. Scramjet technology promises high-speed, efficient propulsion system design which may replace rocket propulsion for better advances in space exploration. 2. SIGNIFICANT HYPERSONIC PROPULSION PROGRAMS THROUGHOUT HISTORY 2.1 The X-15 The X-15 belonged to the X-plane series operated by the United States Air Force (USAF) and the National Aeronautics and Space Administration (NASA). It was a hypersonic, rocket-powered aircraft. It has been regarded as the most important research plane in history. It was the highest and fastest flying manned aircraft. This aircraft was operational for a period of over ten years and had set the world record for speed and altitude at 4,520 mph (6.7 Mach) and 354,200 feet respectively. It was conceptualized in order to examine all aspects of piloted hypersonic flight. [1] Fig.1: The design of the X-15 [38] www.ijcrs.org Page | 2 International Journal of Creative Research and Studies Volume-4 Issue-10, October 2020 The X-15 had set an altitude record in the 1960s. It was able to reach the edge of outer space and was able to collect valuable data which later resulted in the development of the manned and space shuttle programs. William J. Knight was the US Air Force pilot that set the X-15’s official world record for the highest speed ever recorded for a manned, powered aircraft in October 1967 at Mach 6.7 at 102,100 feet (32,120 m) at a speed of 4520 miles per hour(7274 km/hour, 2021 m/sec). This record is still unbeaten as of February, 2018. [2] The X-15 was designed to be carried aloft and drop-launched from under the wing of a NASA B-52. The aircraft was released at an altitude of about 8.5 miles (13.7 km) at a speed of about 500 miles/hour. (805 km/hour) The rocket engine of the X-15 provided thrust for the first 80 to 120 seconds of flight. [3] The X-15 was primarily developed to provide information and data on aerodynamics, flight controls, structures etc. with reference to in flight conditions. Also, the physiological effects of high speed and high altitude flights were observed. The X-15 was flowed for a period lasting 10 years, June 1959 to October 1968. It took a total of 199 flights. It was instrumental in the development of Apollo, Gemini and Mercury manned space programs. 2.2 The SCRAM Program SCRAM stands for Supersonic Combustion RAmjet Missile. This project was a classified project taken up by the Johns Hopkins Applied Physics Laboratory (APL) from 1962 to 1978. It was declassified in 1993. The objective was to design a family of missiles that could fit in the Talos MK-12 launcher system or the Terrier MK-10 Launcher. A variety of Mach numbers, pressures and altitudes were tested for the testing of the engine modules at a direct connect, free-jet facility. The Mach numbers tested included Mach 4 (24,000 feet), Mach 5.3 (46,000 feet), Mach 7.8 (67,000 feet) and Mach 10 (88,000 feet). The experimental results showed that external burning could be feasible means of generating lift and minimizing drag, the efficiency was unsatisfactorily low if there was a net thrust required.{4} Stable combustion in supersonic flow resulted in the feasibility of an internally burning supersonic combustion ramjet (scramjet). The analytical and other experimental studies concluded that a scramjet would produce net thrust and would be more efficient than a supersonic combustion ramjet at Mach numbers above 6 up to 8. [5] As a result of these tests, preliminary conceptual designs of scramjets- powered missiles were started in 1961. A conventional, asymmetric external-internal contraction inlet was designed. But because of the weight and complexity of the variable geometry, it was necessary to assure inlet starting which suggested that alternative fixed- geometry inlet would be desirable for expendable lighter weight missiles.[6] These missile designs that included such streamlined inlets were called the SCRAM. These inlets were self –starting, and hence they did not require variable geometry. Fig.2: The SCRAM Missile [39] www.ijcrs.org Page | 3 International Journal of Creative Research and Studies ISSN-0249-4655 2.3 The National Aerospace Plane The NSAP, National Aerospace Plane program was announced in 1986 in the United States by the then president Ronald Reagan. Its objective was to develop two X-30 aircraft which would be capable of Single Stage to Orbit (SSTO) as well as horizontal takeoff and landing from conventional runways. The fuel to be used was hydrogen based and the aircraft was supposed to be hydrogen-fueled air-breathing space plane, which would have a low speed accelerator system to propel the aircraft up to Mach 3, from where the main dual-mode scramjet engine (Ramjet/Scramjet) would take over. A rocket would then take over the propulsion system at the edge of the atmosphere and provide the final energy for the orbit insertion. It was based on a classified DARPA (Defense Advanced Research Projects Agency) research program called Copper Canyon. The speed limit set for this program was Mach 25. However, it became clear that Mach 17 would be the limit due to weight penalty and complexity of the skin heat exchanger and other propulsion systems. The program was cancelled due to lack of funds and supporting technology. [7] Fig.