"Titanium avocado" could provide GPS-grade navigation sans satellites

Sandia National Laboratories is developing an avocado-sized vacuum chamber made out of titanium and sapphire that could one day use quantum mechanical sensors to provide GPS-grade navigation without the need for satellites.

In only a few short decades, GPS has gone from a military technology to finding so many everyday applications that modern society is now dependent on it. However, GPS is not always available in places like high polar latitudes or in deep mountain valleys, and it can be jammed or spoofed.

The vulnerability of GPS and similar systems lies in their dependence on constellations of satellites that orbit the Earth. These satellites emit time-stamped signals that are synced to atomic clocks. Using these signals, a GPS receiver in something as small as a wristwatch can use the Doppler effect on the satellite signals as they pass overhead to make an extremely precise fix on the receiver's position and velocity. If these signals are interrupted or corrupted, the system fails.

An alternative is a technology that was originally developed for military rockets during the Second World War and is commonly used on submarines while submerged to find their way. Called inertial guidance, it's a completely self-contained system that uses gyroscopes and accelerometers to calculate where the navigation device is in relation to a fixed known position.

It does this by measuring every rotation and movement of the device along all three axes. If these measurements are accurate enough, the results can rival those of GPS.

The problem is that, like GPS, inertial guidance systems must be very precise and have the same atomic-clock-level of timekeeping. This is possible with existing systems that use mechanical gyros or shine lasers through clouds of rubidium gas to measure quantum effects, but these rely on heavy and expensive vacuum systems that scrub out any molecules of air that might disrupt the measurements.

The Sandia team's approach is to take bespoke, robust quantum sensors and set them in a chamber with a volume of only a cubic centimeter (0.06 cubic inches). This chamber is made out of titanium with sapphire windows – materials that are very good at preventing even gases like helium from leaking in, unlike stainless steel and Pyrex glass.

The chamber can maintain a relatively hard vacuum for a long time, but instead of using complex and heavy pumps to produce this vacuum, the team fell back on an old electronics technology called getters. If you've ever looked at an old radio valve you may have seen a silvery or sooty smudge inside the top part of the tube. This is caused by a getter, which is a chemical plug formed around a filament. When a valve was manufactured, the vacuum inside wasn't hard enough, so a current was passed through the plug. This started a chemical reaction that absorbed any stray air molecules.

In the case of the Sandia chamber, the getters are about the size of a pencil eraser and are set in two narrow tubes that stick out of the chamber. It isn't certain how long the chamber will hold a vacuum, so the team is aiming at keeping one sealed and operational for five years. While waiting, the researchers will turn their attention to making the device less cumbersome and easier to manufacture.

The research was published in AVS Quantum Science.

Source: Sandia National Laboratories