“The projectile did not follow the expected trajectory and the maximum range and altitude did not meet the design values,” said the Naval Engineering University team led by Lu Junyong in a peer-reviewed paper published by the academic journal Transactions of China Electrotechnical Society.
After scrutinising data transmitted back to the ground by the smart bomb, Lu’s team discovered that the projectile was rotating too fast during its ascent, resulting in an undesired tilt.
According to the mechanical sensor data provided in the paper, the projectile accelerated at roughly 35 times the force of gravity for around 5 seconds after launch, confirming the researchers’ claim that it exceeded hypervelocity, or Mach 5.
No details were given on the time and location of the test, although it must have occurred before August 2023 when the paper was submitted to the journal.
The designed speed and range of the hypersonic gliding guided bomb were also not disclosed, although naval scientists have published several papers in recent years outlining ambitions to eventually achieve 200km (124 miles) at Mach 7.
Some military scientists believe rail gun technology has the potential to revolutionise warfare, in a shake-up similar to the replacement of fossil fuel cars by electric vehicles. But the challenges are considerable.
Despite decades of effort and substantial investment, the US Navy announced its withdrawal from the field in 2021. In China, however, scientists and engineers have received consistent support, yielding a series of notable breakthroughs.
Chinese policymakers anticipate that the rail gun project’s progress will also spur the development of cutting-edge civilian technologies, such as hyper-speed railways and cost-effective space launches.
The technology harnesses potent electromagnetic forces to propel heavyweight projectiles along a rail, at speeds and ranges that are difficult to match with explosive-driven projectiles, promising significant reductions in the weapon’s operating costs.
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When the US disbanded its rail gun project, Lu’s team was busy with large-scale launch verification tests that revealed a hidden challenge known as “rotational speed latching” which can potentially send the projectile severely off course.
The effect is irregular and difficult to predict, the researchers said. “Even with the same type of projectile and under the same test conditions, rotational speed latching may still occur intermittently.”
The ghostlike problem did not appear during exhaustive wind tunnel tests and computer simulations, but the operation of the electromagnetic gun appears to be more complex than existing physical theories suggest, they said.
While rotation stabilises a shell’s trajectory, its frequency should decrease rapidly as flight speed increases. If it does not, the warhead can tilt upwards which introduces additional drag, affecting flight speed and potentially direction.
Conventional artillery relies on spiral grooves within the barrel to control this rotation. However, rail gun technology requires a different approach. The projectile spends considerably longer in the electromagnetic barrel and must not touch the gun walls.
Friction between the electric armature propelling the projectile and the rails generates high temperatures and pressures. The bomb can also produce lightning-like arcs as it exits the muzzle.
The researchers said these disturbances may cause the projectile to swing or rock, potentially resonating with its rotation frequency and preventing it from decreasing, resulting in latching.
Further analysis revealed that the phenomenon’s random occurrence is related to external protrusions, such as the gliding wings and tail rudders on the surface of the guided bomb.
Under the immense force of launch, these protrusions can undergo slight deformations, the research team found. In the hypersonic realm, such minor flaws can unexpectedly upset aerodynamic stability.
In their search for possible solutions, the scientists needed to replicate the failure on a computer. But the launch process of an electromagnetic gun involves complex multi-body physics problems in extreme environments, which are difficult to fully describe or solve using existing physical laws and mathematical tools.
Fortunately, Chinese scientists have amassed a wealth of raw data from their experiments and, with the help of AI algorithms, Lu’s team recreated the test in a computer simulation. They also used the tool to predict otherwise uncertain outcomes.
After analysing the probability of speed latching occurring under different conditions, the team proposed a series of solutions, including further increasing the initial rotation speed and adjusting the angle of the projectile’s tail rudder to suppress resonance.
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Lu is a core member of the National Key Laboratory of Electromagnetic Energy Technology, founded by PLA Navy Rear Admiral Ma Weiming in Wuhan, Hubei province to develop disruptive ship and weapon propulsion technologies.
Ma’s team is striving to create a nuclear-powered “super battleship”, capable of unleashing a vast array of long-range guided projectiles to dismantle an entire conventional aircraft carrier formation.
Previous setbacks include a laboratory explosion during a test in 2012. According to official media reports, Lu was first into the burning room – risking his life to put out the resulting fire and save critical equipment and data.
The Chinese military has already applied some new technologies developed by the project, including the electromagnetic catapult system for the conventionally powered Fujian aircraft carrier, similar to that used by the nuclear-powered USS Gerald R. Ford.
The Fujian’s phased array radars and other power-hungry electronic assets significantly outnumber the Ford’s, putting unprecedented pressure on the US military, particularly in situational awareness and electromagnetic suppression.
These advancements can be partially attributed to the rail gun project’s breakthroughs in energy storage, power management, wear-resistant coatings, high-precision sensors, and chips resilient to overloads and electromagnetic pulses, according to some military experts.