Chinese researchers have developed a new gravity-based detector that could be used to find submarines and render the proposed AUKUS submarine redundant.

Chinese technological advance is very likely to put another downer on the AUKUS submarine program. As I have previously detailed in Pearls and Irritations, the Chinese have been researching how to detect submarines using high-energy microwave synthesis technology. Now, as reported in _Interesting Engineering_, they are working on how to pinpoint ‘monsters of the deep’ by means of a gravity-based detector.

Led by Zhang Yingzi, a team from North University of China is building on previous breakthroughs made at the Chinese Academy of Sciences. The current research places China at the forefront of developing this technology.

What makes this gravity-based detector such a breakthrough is that unlike traditional submarine detection methods – sonar, radar or magnetic – which can be partially thwarted using the right countermeasures, this method cannot be deceived. A heavy object like a submarine cannot be hidden in terms of its gravitational effects. Mass cannot be turned off, reduced or absorbed. 

The method works using a highly sophisticated magnetometer called a superconducting quantum interference device (SQUID), a device that may be able, by picking up tiny changes in gravity, to find submarines.

Magnetometers are not new. You no doubt will have walked through one at airport security or seen one being used by someone combing a beach in search of lost coins or jewellery. A SQUID magnetometer operates at a whole other level: it is an extremely sensitive instrument able to measure miniscule changes in gravitation.

SQUID magnetometers have been used in neurology and cardiology to detect minute magnetic fluctuations. Super sensitive, they can measure magnetic fields 100 billion times weaker than that required to move a compass needle.

The device is effectively a frictionless floating mass that moves when gravity changes even very slightly. The device works by suspending a small object in mid-air and eliminating (as much as possible) any effects of friction upon it. Reliant on superconductivity, it needs to be cooled to temperatures near absolute zero. 

Prior to the work of Zhang’s team, the technology’s cost had been exorbitant because each device needed to contain at least six ultra-sensitive superconducting magnetic gradiometers, all equipped with a pair of superconducting coils. It was thought this was necessary to accurately detect submarines hundreds of metres below the surface and to estimate their location, speed and other physical characteristics. What Zhang’s team did was to design a probe that uses a single superconducting magnetic gradiometer to achieve a tenfold increase in sensitivity compared to those in use by anti-submarine forces across the globe.

Such ultra-sensitive movement detection is perfect for gravity detection, thus giving the technology its military use. When gravity changes even marginally (that is when an object moves nearby), this causes the device to move ever so slightly, measuring differences in gravity across space. The minuteness of variation is impressive. Assuming a ‘background’ gravity of say 9.800000000, when a submarine passes by the device, the reading will change to something like 9.800000002. This is a very tiny difference but enough for the detector to notice something is going on. 

The device has already been tested outside highly controlled laboratory settings, which is important because these detectors are very sensitive to interference, such as footsteps, passing vehicles, wind, waves and earth tremors. If the technology can be proven in these kinds of ‘signal dirty’ environments, then it is likely to work well on ships, aircraft, and drones.

While still not sensitive enough to be used for things like submarine detection, but once fully developed, the device is expected to be able to detect things like the current 18,750-ton US Ohio-class submarines. The Virginia class submarine, the first step in the AUKUS program, weighs 7,900 tons, and the proposed successor AUKUS-class submarine, which will weigh about 10,000 tons, are both significantly smaller than the massive Ohio class. However, one can assume that Chinese technology will advance to the point of using the same, even more highly calibrated technology, to make their detection possible. 

Given that the estimated timeline sees Australia acquiring Virginia class submarines not until the mid-2030s, with the AUKUS class acquisition date anyone’s guess, it can be assumed that any US, British or Australian submarines will by then be easily detectable. One hates to think of $368 billion (and counting) wasted on a project that, by the time it is delivered, technology will have made redundant. But when one is speaking of possibly as long as 30 years that very likely will be the case.