The Scramjet Engine:
The scramjet engine, which on Monday powered the HSTDV to Mach 6 – six times the speed of sound – is an improvement over the ramjet engine. It operates efficiently at hypersonic speeds and allows supersonic combustion. In contrast, ramjets operate well at supersonic speeds of around Mach 3 but their efficiency drops at hypersonic speeds.
While this is an important achievement for DRDO, which has been talking about the technology since the early 2000s, the Indian Space Research Organisation (Isro) had tested its scramjet engine as early as 2016.
The military importance of this is that the scramjet engine, which has dual-use (military and civilian) will serve as a critical building block for the next-generation hypersonic cruise missiles, which will be designed to fly at speeds more than five times that of sound.
When ready for test and subsequent use, the hypersonic missiles will considerably augment India’s arsenal, putting it along a handful of countries that have such weapons.
Besides the velocity of over five times the speed of sound (Mach 5), the manoeuvring capability of hypersonic missiles makes them very effective offensive weapons capable of defeating enemy missile defence and tracking systems.
A hypersonic missile’s potency is the speed at which it travels, enabling it to have a quick reaction time considered invaluable for both defence and offence.
But India is still far behind countries like the US, China and Russia. China last year flaunted its DF-17 missile with a hypersonic glide vehicle at its national military parade.
India has been working on making BrahMos – a supersonic cruise missile – hypersonic, and the scramjet will help in that endeavour too. Developed jointly with Russia, the BrahMos now flies at Mach 2.8 speed.
Low-cost Sat Launches
Further, on the civilian side, the HSTDV can propel satellites at a low cost. However, its ability to do so will be restricted. Experts believe that such a vehicle, using scramjet, can only push satellites into LEO (low-earth orbit), as the air-breathing engines will not find oxygen at higher altitudes.
According to Isro, at present, satellites are launched by multi-staged satellite launch vehicles that can be used only once (expendable). These launch vehicles carry oxidiser along with the fuel for combustion to produce thrust. Launch vehicles designed for one-time use are expensive and their efficiency is low because they can carry only 2-4% of their lift-off mass to orbit.
Nearly 70% of the propellant (fuel-oxidiser combination) carried by today’s launch vehicles consists of oxidisers. Therefore, the next-generation launch vehicles must use a propulsion system which can utilise the atmospheric oxygen during their flight through the atmosphere which will considerably reduce the total propellant required to place a satellite in orbit.
Also, if those vehicles are made reusable, the cost of launching satellites will further come down significantly. Thus, the future reusable launch vehicle concept along with air-breathing propulsion is an exciting candidate offering routine access to space at a far lower cost.
A hypersonic vehicle/missile also has the potential to augment India’s Anti-Satellite (A-Sat) capabilities. The country, on March 27, 2019 successfully conducted an A-Sat missile test in an operation codenamed ‘Mission Shakti’, making it only the fourth country after the US, China and Russia to demonstrate such a capability.
The interceptor missile was a three-stage missile with two solid rocket boosters. The A-Sat not only adds to India’s strategic strength of protecting space assets, but is also a game changer that will add to abilities in tackling high-altitude incoming missiles.
India has a long BMD programme with multiple missiles already in its arsenal. But as of today those missiles cannot intercept a target that is at such altitude. The A-Sat, experts feel, can help our forces tackle incoming missiles at a greater height, which serves as a huge advantage.