IAF Signals Hypersonic Ambitions With IISc-Led Propulsion Challenge

A Gemini rendition of the launch of a S-200 with a DMRJ powered curise missile

The Indian Air Force on January 29, 2026 signed a Memorandum of Agreement (MoA)  with the Foundation for Science Innovation and Development (FSID), IISc Bengaluru to indigenously develop an advanced high-speed air-breathing propulsion system.

Announcing the MoA, the IAF's official X handle stated that the MoA "underscores IAF’s commitment towards Atmanirbharta by development of high-speed flight systems with dual-use capabilities."

Copies of documents and diagrams posted on social media and associated with the MoA indicate that the proposed “advanced high-speed air-breathing propulsion system” is a dual-mode ramjet/scramjet engine (DMRJ), intended for use in propelling missiles or combat aircraft.

DRDO has already developed ramjet and scramjet engines for missiles. The former operate efficiently at high supersonic speeds and the latter operate efficiently through hypersonic speeds. 

DMRJ Engines Explained

In a ramjet engine the air entering the engine is slowed to subsonic speed and consequently compressed before combustion. In a scramjet engine, the air is similarly slowed down and compressed but remains supersonic throughout the combustor. 

Ramjet engines operate efficiently roughly from Mach 3 to Mach 6. Scramjet engines are needed for speeds beyond Mach 6–7

DMRJ, which combines ramjet and scramjet propulsion, can operate efficiently across a very wide supersonic to hypersonic speed envelope by switching how combustion occurs inside the engine.

DMRJ Development Status

The DMRJ concept has been tested but never operationalised.

Russia reportedly tested a hydrogen-fueled dual-mode scramjet  developed by the Central Institute of Aviation Motors (CIAM) in the 1990s under (Kholod Project). 

It modified a 5V28 missile from the S-200 long-range air defence system, replacing the warhead and guidance system with a DMRJ and its liquid hydrogen fuel tank.

To test a DMRJ, it first has to be accelerated to high supersonic speeds that can facilitate ramjet light-up. The S-200 is a heavy missile with a launch weight exceeding 7,000 kg and substantial payload capacity. The S-200’s solid boosters and liquid-fueled sustainer were well suited to accelerating the payload to hypersonic velocities. This modified S-200 served as a cost-effective, readily available booster, leveraging existing infrastructure.

Boosted to high speeds by the missile’s liquid rocket motor, the DMRJ successfully transitioned from ramjet propulsion to scramjet propulsion, achieving speeds over Mach 6.4, with scramjet mode sustained for 77 seconds across seven flight tests (1991–1998).

Russia used the data gathered from these tests to develop the 3M22 Zircon, which can achieve speeds near Mach 8. However, the Zircon uses a scramjet engine not a DMRJ. It is boosted to hypersonic speed directly by its solid-propellant rocket booster. 

Similarly, DRDO’s Hypersonic Technology Demonstrator Vehicle (HSTDV) and its follow-up system under development, the Extended Trajectory–Long Distance Hypersonic Cruise Missile (ET-LDHCM), both use scramjet propulsion, not DMRJ.

DMRJ Limitation

A notable limitation of a DMRJ is its inability to operate from zero airspeed. It needs to be accelerated to a high airspeed that can generate air compression due to airflow path constriction. To overcome this limitation, a dual-mode ramjet (DMRJ) can be paired with a rocket booster when used in a hypersonic cruise missile. 

For use in a combat aircraft, the DMRJ is paired with a turbine engine in what is called a Turbine-Based Combined Cycle (TBCC) architecture.

In a TBCC-powered combat aircraft, at speeds below ~Mach 2.5 to 5, a turbofan or turbojet provides thrust. The turbine is then shut down and bypassed, and the DMRJ takes over propulsion.

Combining a turbine with a DMRJ allows a combat aircraft to take off conventionally using a turbine engine and then accelerate all the way to hypersonic speeds.

Using TBCC propulsion, a combat aircraft can take off and loiter at subsonic cruise. When desired, it can accelerate to supersonic speeds using its turbine engine and then switch to DMRJ propulsion for sustained hypersonic cruise. Such a flight profile is impossible with a pure DMRJ + rocket booster combination.

TBCC Challenges

Ramjets, scramjets, and DMRJs are conceptually and mechanically relatively simple to build, as they involve no moving parts. However, the materials and techniques required to sustain supersonic and hypersonic combustion do pose significant challenges.

While a DMRJ can be combined with a turbine engine in a TBCC configuration, the engineering challenges are extremely complex, and the concept remains experimental.

The air flowing into a turbine engine has to be subsonic and at relatively low temperatures, whereas the airflow in a DMRJ has to be supersonic and at very high temperatures.

As such, the two engines share the inlet and nozzle, but not the combustor.

Smoothly switching from turbine to ramjet and then to scramjet operation is a particularly major challenge. Any pressure mismatch can cause the engine to fail to start or experience flameout.

Conclusion

As already noted, the engineering challenges of building a reliable ramjet that can transition to scramjet mode within the form factor of a compact missile fare immense.

While standalone scramjet and ramjet missiles exist or are being developed, true DMRJ designs remain in research and flight test demonstration programs rather than fielded systems

As already noted, there are no operational missiles powered by DMRJ propulsion, let alone the even more complex TBCC architecture.

Viewed in this light, the IAF’s MoA with IISc is clearly aimed at funding long-term research. This investment is unlikely to yield operational benefits for the IAF for at least a decade.

IISc has actively participated in the HSTDV programme, which successfully met its stated objectives. It therefore possesses the experience and technical depth required to undertake the development of DMRJ propulsion, and eventually progress to TBCC systems.

Supporting long-term technology development is, without doubt, a sound approach for the IAF.

However, there also appears to be a subtle but important message in the IAF’s tie-up with IISc:

While the IAF is willing to invest in future technologies, its immediate operational requirements cannot wait. These must be met through fast-paced procurement, preferably from domestic OEMs, but where necessary through foreign partnerships that guarantee continuity of support and supply.