The hard part of hypersonics is not going fast. It is going fast often enough to learn anything.

Flight tests above Mach 5 are rare, enormously expensive and frequently one-shot. A programme might get a handful of attempts across a decade, and if two of them fail early you have spent years and hundreds of millions of dollars to learn almost nothing.

The Pentagon has been trying to break that bottleneck, and on 4 September GE Aerospace confirmed it has won the next phase of the effort: an air-launched test vehicle called Derecho, designed to cruise at Mach 5 and above, and designed above all to be flown repeatedly.

What a dual-mode ramjet actually does

This is the technically interesting part, and it is worth being precise about it.

A ramjet has no compressor. It relies on its own forward speed to ram air into the inlet and compress it, which means it produces no thrust standing still and needs a boost to get going. Inside a conventional ramjet the airflow is slowed to subsonic speed before combustion. That works well up to roughly Mach 5, above which slowing the air that much produces temperatures the structure cannot survive.

A scramjet — supersonic combustion ramjet — keeps the airflow supersonic through the combustor instead. That is much harder, because you are trying to inject fuel, mix it and burn it in air moving through the engine in a few milliseconds.

A dual-mode ramjet does both. It runs as a conventional ramjet at the lower end and transitions to supersonic combustion higher up, which widens the usable speed band of a single engine considerably. And because it is air-breathing, it takes its oxygen from the atmosphere rather than carrying an oxidiser, so more of the vehicle’s mass can be fuel or payload.

Booster plus cruiser

Derecho uses what the industry calls an all-up-round architecture. A high-thrust rocket booster accelerates the stack to the speed at which the air-breathing engine can work. The cruiser then takes over on the dual-mode ramjet and sustains hypersonic flight, carrying whatever the test campaign needs to evaluate: heat-resistant materials, sensors, flight control systems, structures.

The whole thing is air-launched, which matters more than it sounds. Dropping a test vehicle from an aircraft rather than launching it from a pad removes range scheduling, reduces cost per shot, and lets you put the vehicle where the weather and the instrumentation are good. It is the same logic that put the X-51A Waverider under the wing of a B-52.

Why the Defense Innovation Unit is running it

HyCAT is a DIU programme rather than a traditional service acquisition, and that is deliberate. DIU exists to pull commercial-sector speed into defence work, favouring agile prototyping and shorter contract cycles over decade-long development programmes.

The name says the goal out loud: high-cadence. Not one heroic flight, but a testbed that can be flown often enough that engineers get a dataset instead of an anecdote. Derecho is intended as a modular platform, so different payloads and subsystems can ride on successive flights.

This phase covers full vehicle integration plus component-level qualification testing of critical subsystems, building on concept and subsystem design work that started in 2023. GE has not disclosed what it is worth.

An explainer on the difference between ramjets and scramjets, the two modes a dual-mode ramjet has to bridge.

The thing to watch

Reported plans put the first flight test in 2028, which would be GE Aerospace’s first in-flight demonstration of its ramjet technology. The company has run the engine on the ground; flying it is a different order of problem.

If Derecho works as intended, the significant outcome is not a speed record. It is that American hypersonic programmes stop being limited by how rarely they can fly. Every serious aerospace advance — the transonic barrier, supersonic cruise, stealth — came from being able to test repeatedly and fail cheaply. Hypersonics has not had that yet.

Sources: GE Aerospace statement; US Defense Innovation Unit; Aviation Week; Breaking Defense; Defense Daily; AeroTime.