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.

Copyright © Vijainder K Thakur. First published on Thumkar.

DRDO Cracks Scramjet Propulsion for Sustained Hypersonic Flight — BrahMos-2 Moves from Concept to Reality

 

@Grok generated visualisation of the Brahmos-2 hypersonic missile in flight

The Defence Research and Development Laboratory (DRDL) successfully conducted an extensive, long-duration ground test of its Actively Cooled, Full-Scale Scramjet Combustor, achieving a run time of over 12 minutes at its state-of-the-art Scramjet Connect Pipe Test (SCPT) Facility on January 9, 2026.

Earlier, on April 25, 2025, DRDL had successfully ground-tested a subscale actively cooled scramjet combustor for more than 1,000 seconds at the same facility.

The maiden ground test of the full-scale combustor, lasting 120 seconds, took place on January 21, 2025.

With these successful tests, the scramjet combustor is now poised for full-scale, flight-worthy testing.

So what exactly is an “Actively Cooled Scramjet Full-Scale Combustor,” and why is this technology significant? The following sections explain.

The Need for a Hypersonic Cruise Missile

An actively cooled scramjet combustor is the most critical component of a scramjet engine.

A scramjet engine differs fundamentally from a ramjet engine—such as those powering the Akash and BrahMos missiles. In a ramjet, airflow inside the combustion chamber is subsonic, whereas in a scramjet, the airflow remains supersonic throughout the combustion process.

A scramjet engine is an absolute prerequisite for sustained, level hypersonic flight within the atmosphere. The only alternative method of achieving atmospheric hypersonic flight is through boost-glide vehicles.

Boost-glide flight involves lofting a hypersonic glide vehicle (HGV) to altitudes of approximately 40–100 km using a booster rocket. The HGV then dives steeply toward Earth, achieving hypersonic speed due to gravity, before transitioning into a flatter glide trajectory, trading altitude to counter atmospheric drag. Importantly, the HGV is unpowered during this phase. (DRDO is also developing an HGV under the BM-04 project.)

HGVs have inherent operational limitations. Because they are lofted to high altitudes—or even beyond the atmosphere—by a booster, they are easily detected by radar and infrared sensors. Once detected, they can be readily tracked. During the boost and early glide phases, HGVs are particularly vulnerable to adversary air and missile defenses.

In contrast, hypersonic cruise missiles need not be lofted to extreme altitudes. For maximum range, they can climb to 20–30 km to minimize drag and then cruise at hypersonic speed. When operating at shorter ranges, they can fly at much lower altitudes, significantly reducing the probability of radar detection and tracking.

Understanding the DRDL Breakthrough

DRDL has taken the lead in developing long-duration, scramjet-powered hypersonic propulsion technology.

This effort is highly likely based on technology matured under the Hypersonic Technology Demonstrator Vehicle (HSTDV) programme.

The HSTDV programme demonstrated a scramjet-powered flight lasting 20 seconds. The current objective is to develop an engine capable of sustained hypersonic flight, enabled by an actively cooled scramjet combustor.

Twelve minute ground test of DRDL's Actively Cooled, Full-Scale Scramjet Combustor at its state-of-the-art Scramjet Connect Pipe Test (SCPT) Facility on January 9, 2026.

Scramjet Propulsion Challenges

One of the most formidable challenges in scramjet development is igniting the engine in supersonic airflow and maintaining stable combustion. Igniting a scramjet is often likened to lighting a matchstick in a hurricane.

The DRDL-developed scramjet combustor incorporates an innovative flame-stabilisation technique that sustains continuous combustion at airflow speeds exceeding 1.5 km/s.

Before arriving at the current engine configuration, DRDO evaluated several novel ignition and flame-holding techniques using advanced computational fluid dynamics (CFD) simulations and extensive ground testing.

Active Cooling

Long-duration scramjet operation necessitates active cooling, which allows engines to operate longer and at higher speeds without structural failure.

In active cooling, a coolant—often the fuel itself, such as an endothermic hydrocarbon fuel—is circulated through channels embedded in the combustor walls before being injected for combustion. The coolant absorbs heat from the structure, preventing overheating.

After absorbing heat, the now preheated fuel burns more efficiently, making the process thermally regenerative.

The indigenous development of endothermic scramjet fuel, jointly by DRDL and Indian industry, was a major breakthrough contributing to the success of the programme.

According to DRDO, these endothermic fuels undergo chemical reactions when heated, absorbing large quantities of heat. This not only cools the engine structure but also conditions the fuel for improved combustion efficiency.

Other Hypersonic Flight Challenges

Scramjet propulsion is only one of several challenges associated with hypersonic cruise missile development. Others include maintaining structural integrity and flight control at hypersonic speeds.

At Mach 5 and above, atmospheric drag generates intense frictional heating. The missile airframe must withstand extreme temperatures without structural degradation. Additionally, frictional heating can cause the missile to become enveloped in a plasma sheath, which can disrupt radio communications and guidance signals.

It is likely that DRDL addressed many of these challenges during the HSTDV programme. However, given that HSTDV demonstrated hypersonic flight for only 20 seconds, further work is likely required to validate long-duration performance.

ET-LDHCM

In July 2025, ET had reported that India is developing a new hypersonic missile that can travel at eight times the speed of sound and strike targets as far as 1,500 kilometres away. The Extended Trajectory Long Duration Hypersonic Cruise Missile (ET-LDHCM) is being developed under DRDO's Project Vishnu.

Conclusion

At present, Russia’s Tsirkon (3M22 Zircon) is the only operational hypersonic cruise missile. The missile has been used extensively against Ukrainian targets.

Tsirkon reportedly cruises at speeds of up to Mach 9, with a range of 400–450 km at low altitudes and up to 1,000 km when cruising at 20–40 km or along a semi-ballistic trajectory.

Ukrainian forces acknowledge that Tsirkon is extremely difficult to intercept. While occasional shootdown claims have been made, none have been supported by incontrovertible evidence.

China completed development of its YJ-20 hypersonic cruise missile with scramjet propulsion in 2025. With capabilities broadly comparable to Tsirkon, the missile is expected to enter operational service in 2026.

DRDO’s sustained progress in hypersonic propulsion suggests that India could field an operational hypersonic cruise missile within the next five years. It's moot whether the missile will ultimately be called ET-LDHCM, Brahmos-2 or something else. 

Copyright © Vijainder K Thakur. First published on Thumkar.