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.
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
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.
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