British scientists have developed technology that could allow submarines to determine their exact location without needing to surface.
Researchers at Imperial College London are working on a portable “quantum” accelerometer, which they claim would be far more accurate than current technology, by engineering smaller and better-controlled lasers.
This could allow accelerometers to help map the exact movements of a submarine or other vehicle as it moves around the globe, enabling the crew to determine their current position with an error range of just 1m.
Submarines currently need to surface to access satellite navigation – which is also vulnerable to interruption by outside signals – and cannot use radar or sonar without risking detection, so underwater navigation is usually based on calculated estimates.
But current accelerometers, which measure the force applied to a physical component, are not accurate enough to provide a precise navigation record because they tend to drift and need recalibration. For submarine navigation, this can produce errors of up to a kilometre when the boats finally surface.
The quantum accelerometer provides a much more accurate reading by measuring the force applied to individual atoms. A laser cools the atoms to near absolute zero, effectively freezing them in position and allowing another laser to measure any changes in the atoms caused by acceleration.
‘An atom is the same as every other atom of that type and it is also the same in a year from now, whereas if you have a piece of material [in an accelerometer], that material has stress in it and will change its properties over time,’ research leader Prof Ed Hinds told The Engineer.
‘So the zero of [a conventional] accelerometer will change over time. With an atom-interferometry accelerometer that doesn’t happen so you have a tremendous improvement in both the calibration accuracy and zero drift.’
The key engineering challenge is in miniaturising the quantum accelerometer’s components, including its lasers, optics, and control system. A crucial part of this is developing manufacturing techniques to produce control chips with very precise structures using the same techniques as processor fabrication.
‘The chip we make will be on a substrate – of silicon, gallium arsenide or one of the standard materials – and use the same kinds of methods such as lithography to make the structures,’ said Hinds. ‘But the structures will be totally different and therefore the recipes, until we develop them, don’t yet exist.’
Another key element will be producing a very small vacuum chamber with perfect optical properties – from glass rather than the typical steel – that doesn’t require mechanical pumping and is very good at preventing atoms from escaping.
The research is one of 13 projects funded by the government’s Defence Science and Technology Laboratory (DSTL) aiming to make greater use of quantum technology in navigation, sensing, communications and computing applications.
The current iteration of the accelerometer is housed in a box around 1m in length, but further work could make it portable enough to carry around, opening up other applications where GPS cannot currently work, such as indoor navigation.
‘Your GPS will never tell you what floor of a multi-storey car park you’re on’ said Bob Cockshott of the National Physical Laboratory where the technology was presented last week.
‘For navigation within buildings, shopping malls, airports and particularly within tunnels, there’s demand for that to happen,’ he said. ‘But the exciting applications are probably the ones we haven’t thought of.’