Today, the cost of launching a satellite is prohibitively high. The chief reason is that present-day launch vehicles are designed for a one-time use and the efficiency of the launch vehicle is expressed in terms of how much it can carry for with a particular amount of fuel. In simpler terms, a launch vehicle weighing 400t will deliver a payload of only 2t. It may be noted that, nearly 85 per cent of the rocket mass is propellant (fuel + oxidiser) and nearly 75 per cent of the propellant is consumed during the atmospheric flight phase of the rocket (50 km above us) and the percentage of oxidiser in propellant is about 80-85 per cent. This means nearly 48 per cent of lift-off mass of the launch vehicle will be consumed during the atmospheric flight phase.
If the need to carry an oxidiser for the atmospheric flight phase is taken away, there will be considerable reduction in the lift-off mass of the launch vehicle. It will also cut costs.
Scramjet — the concept of air-breathing propulsion using atmospheric oxygen as an oxidiser, is not new. They are challenges, yes. Maintaining combustion at those speeds is like lighting a candle in a hurricane. The fuel must be injected, mixed, ignited, and burned within milliseconds. Worldwide efforts are on to achieve flight using a scramjet engine.
But research on these engines have been on since World War II. Much study has been done in Russia, USA, China, India, the UK, Australia and Brazil. They have been many collaborative efforts as well. In fact, a Soviet engine was made back in 1991 but the programme simply collapsed.
In India, development efforts on scramjet technology started in the mid-nineties with the objective to flight demonstrate the engine and develop all associated technologies. The ground testing of a scramjet engine was conducted back in 2006 at Mach 6, which validated the design.
But incredible efforts went into what took off on August 28, at 6am. At an altitude of 20 km, India’s scramjet engines reached ignition. Basically, the engines auto ignited and the flame was sustained for about six seconds at exactly Mach 6. Flight data confirms not only the ignition but the achievement of a positive thrust.
It may be noted that Isro had already carried out a flight test of the RLV-TD in May and both the scramjet engine flight test and the RLV-TD flight test are baby steps towards realising a full-scale space plane.
But more importantly, the successful tests of both the scramjet engine as well as the RLV-TD is an indication that Isro is on the right path, into a new orbit.
