Indian scientists have practically demonstrated, in laboratory conditions, a theory that by reducing friction, manned space missions could cut fuel consumption by 50%. That could also improve longevity of reusable space vehicles and long-range missiles.
K. Satheesh and G. Jagadeesh of the Indian Institute of Science, Bangalore, have, for the first time ever, experimentally demonstrated a long-nagging theory in aerodynamics called concentrated energy deposition, which potentially reduces frictional forces encountered by space vehicles when travelling at hypersonic speeds, or speeds greater than four times that of sound.
In the experiment, which was designed to simulate atmospheric conditions during a space vehicle ascent, these frictional forces—called drag—were reduced by almost 50%, according to their paper published in the peer-reviewed Physics of Fluids, an American Institute of Physics research journal.
“The future of defence research and space missions is all in hypersonics,” said A. Sivathanu Pillai, CEO and managing director of BrahMos Aerospace, an Indo-Russian joint venture formed to design, develop, produce and market BrahMos, a supersonic cruise missile. Lauding their research, Pillai said for manned space missions, it’s important to develop reusable launch vehicles—ones that can go out of the atmosphere, deposit the payload and return safely.
At hypersonic speeds, significant changes are effected on the atmospheric pressure surrounding the missile, most prominent being the creation of shock layers that mainly contribute to the high temperatures generated. These temperatures could go up to thousands of degrees and designing vehicles that can withstand this heat without compromising on vehicle speed, and fuel—and constructional—cost are the heart of hypersonic research, he added.
“We have demonstrated what has been the subject of theoretical research for years,” said Jagadeesh, “but till now no experimental measurement conclusively shows that concentrated energy deposition reduces the wave drag around blunt bodies flying at a hypersonic Mach (the measure of the speed of sound) number.”
For the experiment, the scientists created a hypersonic shock tunnel, which consists of a stainless steel tube of 50 mm diameter connected to a conical nozzle of 300 mm diameter. This apparatus is then kept in an argon, a gas, environment. The concentrated energy in question is provided for by high-voltage electric supply—10 kilovolts and 10 amperes. The tube-nozzle combination replicates a cruising missile at hypersonic conditions, thanks to the electricity and the argon gas which create conditions mimicking airflow and atmospheric conditions at that time.
Thus the atmospheric conditions are like an aura or halo, around a cruising body. Applying jolts of electricity around certain parts of the body, and measuring these effects on the drag reduction, is what the experiment is all about. “This is only the first step The next steps we are working on will be what would be the ideal gases to use to suitably and economically reduce drag effects. But that’s a long way into the future,” said Jagadeesh.
Developing hypersonic vehicles has been a focus of defence research in India, with the Defence Research and Development Laboratory, the missile research arm of the Defence Research and Development Organisation, leading the quest.
In 2005, it had started out on a project called the Hypersonic Technology Demonstrator Vehicle (HTDV) that aims to create hypersonic cruise vehicles, which can deliver payloads at Mach 6.5-7.
However, R. Palaninathan, a professor at Indian Institute of Technology Madras and who is involved with the HTDV project, sounded a note of caution. “I have not gone through the paper,” he said, “but given that it was still a laboratory simulation, we must wait for live, scaled-up demonstrations to see if it works.”
Hypersonics, as an area of research, has few experts in India, due to the extremely expensive facilities required to test its results. “Right now we have to depend on simulations and experiments to understand this field,” said Krishnendu Sinha, assistant professor, Department of Aerospace Engineering, IIT Bombay, adding, “It will be a while before all that we have learnt are actually used in our programmes (defence, space).”