India successfully tested an indigenously-developed Hypersonic Technology Demonstrator Vehicle (HSTDV) powered by a scramjet engine on September 7, 2020. The HSTDV will help propel forward existing technological capabilities and serve as a crucial component of building next-generation hypersonic cruise missiles. The HSTDV test, conducted from the Dr Abdul Kalam Island off the Odisha coast at 11:03 am to demonstrate the autonomous flight of a scramjet integrated vehicle, put India in the inner-circle of the group of countries equipped with this technology till date – the USA, Russia and China. This launch was carried out using the Agni engine booster in the vehicle.
HSTDV USED BY INDIA FOR FIRST HYPERSONIC MISSILE LAUNCH
WHAT IS HYPERSONIC FLIGHT?
Hypersonic flight is flight through the atmosphere below about 90 km at speeds above Mach 5, a speed where dissociation of air begins to become significant and high heat loads exist. The first manufactured object to achieve hypersonic flight was the two-stage Bumper rocket, consisting of a WAC Corporal second stage set on top of a V-2 first stage. In February 1949, at White Sands, the rocket reached a speed of 8,288.12 km/h (5,150 mph), or approximately Mach 6.7. The vehicle, however, burned on atmospheric re-entry, and only charred vehicular remains were recovered.
To understand the preliminary science behind this technology, we need to understand that hypersonic flow is a high energy flow. When this flow enters a boundary layer, there are high viscous effects due to the friction between air and the high-speed object. In this case, the high kinetic energy is converted in part to internal energy and gas energy is proportional to the internal energy. Therefore, hypersonic boundary layers are high temperature regions due to the viscous dissipation of the flow’s kinetic energy.
The HSTDV is an unmanned scramjet demonstration aircraft for hypersonic speed flight. Apart from being used as a vehicle for hypersonic and long-range cruise missiles, the HSTDV is a dual-use technology that will have multiple civilian applications, including the launch of small satellites at low cost. Hypersonic missiles travel at speeds faster than 3,800 miles per hour or 6,115 km per hour, much faster than other ballistic and cruise missiles. They can deliver conventional or nuclear payloads within minutes. They are highly manoeuvrable and do not follow a predictable arc as they travel. They are said to combine the speed of ballistic missiles with the manoeuvring capabilities of cruise missiles. The speed makes them hard to track compared to traditional missile tech.
WHAT IS A SCRAMJET ENGINE?
A scramjet (supersonic combustion ramjet) is a variant of a ramjet air-breathing jet engine in which combustion takes place in supersonic airflow. As in ramjets, a scramjet relies on high vehicle speed to compress the incoming air forcefully before combustion (hence the term “ramjet”). A ramjet operates by combustion of fuel in a stream of air compressed by the forward speed of the aircraft itself, as opposed to a normal jet engine, in which the compressor section (the fan blades) compresses the air. The air flow through a ramjet engine is subsonic, or less than the speed of sound. Ramjet-propelled vehicles operate from about Mach 3 to Mach 6.
SCRAMJET ENGINE
In the 1950s and 1960s, a variety of experimental scramjet engines were built and ground tested in the US and the UK. In 1958, an analytical paper discussed the merits and disadvantages of supersonic combustion ramjets. In 1964, Drs. Frederick S. Billig and Gordon L. Dugger submitted a patent application for a supersonic combustion ramjet based on Billig’s Ph.D. thesis. This patent was issued in 1981 following the removal of an order of secrecy. In 1981, tests were made in Australia under the guidance of Professor Ray Stalker in the T3 ground test facility. The first successful flight test of a scramjet was performed by the Soviet Union in 1991. It was an axisymmetric hydrogen-fueled dual-mode scramjet developed by Central Institute of Aviation Motors (CIAM), Moscow in the late 1970s. The scramjet flight was flown captive-carry atop the SA-5 surface-to-air missile that included an experimental flight support unit known as the “Hypersonic Flying Laboratory” (HFL), “Kholod”.
In the 2000s, significant progress was made in the development of hypersonic technology, particularly in the field of scramjet engines. The HyShot project demonstrated scramjet combustion on July 30, 2002. The scramjet engine worked effectively and demonstrated supersonic combustion in action. However, the engine was not designed to provide thrust to propel a craft. A joint British and Australian team from UK defense company Qinetiq and the University of Queensland were the first group to demonstrate a scramjet working in an atmospheric test. On 22 and 23 March 2010, Australian and American defense scientists successfully tested a (HIFiRE) hypersonic rocket. It reached an atmospheric velocity of “more than 5,000 kilometres per hour” (Mach 4) after taking off from the Woomera Test Range in outback South Australia.
This technology has both advantages and disadvantages. Its pros are that it reduces the need for carrying an oxidizer which reduces weight. Its cons are that unlike jet or rocket propulsion systems facilities which can be tested on the ground, testing scramjet designs uses extremely expensive hypersonic test chambers or expensive launch vehicles, both of which lead to high instrumentation costs. Tests using launched test vehicles very typically end with destruction of the test item and instrumentation.
THE TECHNOLOGY BEHIND MISSILES
A missile, also known as a guided missile, is a guided airborne ranged weapon capable of self-propelled flight usually by a jet engine or rocket motor. Missiles vary from small tactical weapons that are effective out to only a few hundred feet to much larger strategic weapons that have ranges of several thousand miles. Almost all missiles contain some form of guidance and control mechanism. An unguided military missile, as well as any launch vehicle used to sound the upper atmosphere or place a satellite in space, is usually referred to as a rocket. A propeller-driven underwater missile is called a torpedo, and a guided missile powered along a low, level flight path by an air-breathing jet engine is called a cruise missile.
The propulsion system in a missile is required to achieve terminal conditions like range, speed and warhead carrying capability. The missile is propelled either by rockets or jet engines using solid or liquid fuel. Some missiles use hybrid technology for propelling it to its intended point. the function of the guidance system is to maintain the missile in its desired flight path by using altitude control mechanism. This is done by controlling the pitch, roll and yaw of the weapon. The guidance system operates as an autopilot, damping out fluctuations that tend to reflect the missile from its intended flight path.
The aerodynamic features of a missile, also called controlling surfaces, are used to control the missile’s flight. The fins, wings and tail are the three major aerodynamic control surfaces used to steer the missile. The missiles course can be altered by moving these controlling surfaces. A ballistic missile follows a ballistic trajectory to deliver one or more warheads on a predetermined target. These weapons are guided only during relatively brief periods, as most of the flight is unpowered.
TRAJECTORY OF AN ICBM
An intercontinental ballistic missile trajectory consists of three parts: the powered flight portion; the free-flight portion, which constitutes most of the flight time; and the re-entry phase, where the missile re-enters the Earth’s atmosphere. Ballistic missiles can be launched from fixed sites or mobile launchers. The powered flight portion can last from a few tenths of seconds to several minutes and can consist of multiple rocket stages. When the fuel is exhausted, no more thrust is provided and the missile enters free flight. In order to cover large distances, ballistic missiles are usually launched into a high sub-orbital spaceflight; for intercontinental missiles, the highest altitude (apogee) reached during free-flight is about 2,000 kilometers. Reentry vehicles reenter the Earth’s atmosphere at very high velocities, on the order of 6–8 kilometers per second (22,000–29,000 km/h; 13,000–18,000 mph) at ICBM ranges.
WHAT DOES THIS NEW TECHNOLOGY MEAN FOR INDIA?
On Twitter, the DRDO celebrated the achievement, describing the test as “a giant leap in indigenous defense technologies.” The organization also noted that the mission “demonstrated capabilities for highly complex technology that will serve as the building block for NextGen Hypersonic vehicles.” The HSTDV will pave the way toward a practical weapon in the next five years. Other nations to have tested the technology required for a hypersonic cruise missile are the United States, China, and Russia.
Alongside the HSTDV, India is also continuing to work with Russia on the scramjet-powered Brahmos-2 hypersonic cruise missile, with a preliminary agreement signed back in 2012 and involving both the DRDO and Russia’s NPO Mashinostroyenia. Plans call for the Brahmos-2 to be made available in versions launched from surface, aerial and naval platforms. The Brahmos-2 may also leverage technology from the NPO Mashinostroyenia 3M22 Zircon hypersonic ballistic cruise missile, for which there are plans to arm a range of Russian Navy warships and submarines.
By owning this important piece of technology, with applications in both defense and civilian spheres of application, India will now be in the same league as hypersonic technology equipped world powers like USA, Russia and China. Development in hypersonic technology will put our aerial defense and satellite communication capabilities at par with super powers. This is an important milestone in the development of Indian technology and will open a variety of avenues for various further advancements.
