The HSTDV is an unmanned scramjet demonstration aircraft for hypersonic speed flight. It is being developed as a carrier vehicle for hypersonic and long-range cruise missiles, and will have multiple civilian applications including the launching of small satellites at low cost. The HSTDV program is run by the Indian Defence Research and Development Organisation.
Introduction
India is pushing ahead with the development of ground and flight test hardware as part of an ambitious plan for a hypersonic cruise missile. The DefenseResearch and Development Laboratory's Hypersonic Technology Demonstrator Vehicle is intended to attain autonomous scramjet flight for 20 seconds, using a solid rocket launch booster. The research will also inform India's interest in reusable launch vehicles. The eventual target is to reach Mach 6 at an altitude of 32.5 km. Initial flight testing is aimed at validating the aerodynamics of the air vehicle, as well as its thermal properties and scramjet engine performance. A mock-up of the HSTDV was shown at the Aero India exhibition in Bangalore in February, and S. Panneerselvam, the DRDL's project director, says engineers aim to begin flight testing a full-scale air-breathing model powered by a 1,300-lb.-thrust scramjet engine in near future.
Design and development
The design for airframe attachment with the engine was completed in the year 2004. In May 2008, Dr. Saraswat said: Israel has provided some assistance on the HSTDV program, including wind tunnel testing, as has Cranfield University of the U.K. An unnamed third country is helping as well. According to a report, Russia has provided critical help in the project. India's main defense-industrial partner is Russia, which has carried out considerable research into hypersonic propulsion. The 1-metric-ton, 5.6-meter -long air vehicle under construction features a flattened octagonal cross section with mid-body stub-wings and raked tail fins and a 3.7-meter rectangular section air intake. The scramjet engine is located under the mid-body, with the aftbody serving as part of the exhaust nozzle. Development work on the engine is also in progress. Two parallel fences in the forebody are meant to reduce spillage and increase thrust. Part span flaps are provided at the trailing edge of the wings for roll control. A deflectable nozzle cowl at the combustor end can deflect up to 25° to ensure satisfactory performance during power-off and power-on phases. Surfaces of the airframe's bottom, wings and tail are made of titanium alloy, while aluminum alloy comprises the top surface. The inner surface of the double-wall engine is niobium alloy and the outer surface is nimonic alloy. In the June 12, 2019 test, the cruise vehicle was mounted on an Agni-Isolid rocket motor to take it to the required altitude. After the required altitude was reached and the Mach was achieved, the cruise vehicle was ejected out of the launch vehicle. Mid-air the Scramjet engine was auto-ignited, and propelled the cruise vehicle at Mach 6. Due to technology denial of material for the scramjet engine, a new program was initiated and the materials were developed in-house. This led to self-sufficiency in the area and the scramjet engine was ground tested successfully for 20s instead of the initial 3s.
A 1:16 scale model of the vehicle was tested at a hypersonic wind tunnel operated by Israel Aerospace Industries. The isolated intake has been tested at a trisonic wind tunnel at India's National Aerospace Laboratory in Bangalore. During the lab testing the scramjet engine was tested twice for 20s. A total of five to six tests are required before the test flight. The test flight was expected to take place by the end of 2010. In November 2010, DRDO officials told press that they were in the process of opening four state-of-the-art facilities inside as well as in the vicinity of Hyderabad at a cost of more than over the next five years. Reportedly, they will invest 3 to 4 billion for setting up a much-needed hypersonic wind tunnel at Hyderabad's Missile Complex. The facility facilitate testing of various parameters of the Hypersonic Technology Development Vehicle, including engine performance. "It is pivotal to test the in the range of up to Mach 12. This will be a unique installation in India," Saraswat told AW&ST on 22 November 2010. As of December 2011, the scientists had proved technologies for aerodynamics, aero-thermodynamics, engine and hot structures through design and ground testing. "Ahead of the launch, we will have to now focus on the mechanical and electrical integration, control and guidance system along with their packaging, checkout system, HILS and launch readiness," sources said.
Flight testing
In 2016, it was announced that the vehicle will be tested by December 2016. In early 2019, the vehicle was cleared for tests and was expected to be tested in same year. On June 12, 2019, it was tested from Abdul Kalam Island by the Defence Research and Development Organisation. With the scramjet engine, it can cruise at Mach 6. It was test-fired from launch pad number-4 of Integrated Test Range at Abdul Kalam Island in Balasore district at 11:27 AM. According to some unconfirmed reports, the test was a partial success since, allegedly, the Agni-I ballistic carrier vehicle on which the HSTDV was to receive its altitude boost didn't complete the mission. This was supposedly due to ‘weight issues’. The rumours however, were unconfirmed. According to the official statement by the Ministry of Defence, “the missile was successfully launched” and the data collected will be analysed to “validate critical technologies”.
