China successfully tests “most powerful” Mach 30 wind tunnel

In mid-July the government of the People’s Republic of China released a video showing what it claims is the world’s most powerful wind tunnel being used to conduct a scale separation test of what The Drive reports could be an air-launched space plan design from a mothership aircraft.

Video of the oblique detonation wave aired on Chinese media. Source: Twitter via The Drive

The video was broadcast on the state-run China Central Television’s Channel 13, which is the country’s largest 24-hour television news network. Clips of the video appeared on social media soon thereafter. The video highlighted three interesting developments related to the PRC’s approach to and prioritization of hypersonic vehicles—not just hypersonic weapons but also aircraft that can lower the cost and increase the frequency and flexibility of space launches.

Facility: The first development of interest is the validation that the JF-22 hypervelocity tunnel is, in fact, operational. The facility has been under development since 2018 and has garnered considerable attention in domestic press and among the “China Watching” community. While the Institute of Mechanics of the Chinese Academy of Science (CAS) did announce last month that the JF-22 facility had passed an “acceptance check” in which 16 experts from diverse institutes and organizations approved the facility for use, this was the first known test using the JF-22.

An image of the JF-22 wind tunnel. Source: JF-22 handout as published on The Drive

At just under 548 feet and with a test cabin of 13 feet in diameter, the tunnel is longer and more advanced than the JF-12 wind tunnel with which it is collocated, and which has been an important component of China’s hypersonic development to date. Chinese officials have stressed that the JF-22 uses a novel approach that involves using chemical expositions to crate hypersonic conditions while facilities in other states rely on mechanical compressors to produce high-speed airflow. The reported advantages help to simulate flights at higher altitudes and speeds (up to Mach 30) where fuel is burned much faster.

Shcramjet: The videos also contains footage of the high-speed oblique detonation wave engine, known as a shcramjet (an acronym for shock induced combustion ramjet and also referred to as Oblique Detonation Wave Engine (ODWE). Shcramjet engines should not be confused with scramjet engines, which provide another mechanism for achieving and sustaining hypersonic speeds.

While scramjet concepts rely on the diffusive burning of injected fuel, shcramjets seek to avoid a long combustion chamber by injecting the fuel in the inlet of the vehicle and burning the fuel/air mixture through a shock wave. This reduces the weight of the engine and, as a result, reduces the overall weight the hypersonic vehicle and takes advantage of the typically long inlets found at hypersonic velocities. Shcramjets, then, are more efficient than scramjet engines and are also believed to have a better overall propulsive performance than the scramjet at higher Mach numbers, especially above Mach 10.

Air-Launched Orbital Aircraft Concept: The wind tunnel and use of shcramjet technologies are likely to support China’s space ambitions generally and efforts to develop a two-stage mothership space launch concept and capability.

Indeed, the video showed a scaled down delta-winged and dart-shaped platform that, according to The Drive, “looks similar, in very broad strokes, to air-launched spaceplane and mothership concepts that Chinese aerospace companies and academic institutions have shown publicly in the past.”

The two-stage concept involves a mothership—usually a reusable space plane capable of landing on conventional runways—carrying a spacecraft to a very high altitude at which point the spacecraft is launched into space using its own propulsion. These motherships can use advanced high-speed air breathing engines such as shcramjets to increase the speed of launch. Two-stage launches increase the flexibility of launch as it does not require a large static infrastructure or time to prepare for launch. The concept can also reduce costs of space launch by as much as 90%, according to The EurAsian Times.