“Titanium avocado” could offer satellite-free navigation in GPS quality


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

In just a few decades, GPS has evolved from a military technology to so many everyday uses that modern society today relies on it. However, GPS is not always available in places like high polar latitudes or in deep mountain valleys and can be blocked or faked.

The vulnerability of GPS and similar systems lies in their dependence on constellations of satellites orbiting the earth. These satellites send out time-stamped signals that are synchronized with atomic clocks. With these signals, a GPS receiver in a device as small as a wristwatch can use the Doppler effect on satellite signals as they pass overhead to determine the position and speed of the receiver with extreme precision. If these signals are broken or damaged, the system will fail.

An alternative is a technology originally developed for military missiles during World War II that is often used on submarines underwater to find their way. Inertial guidance is a completely self-contained system that uses gyroscopes and accelerometers to calculate where the navigation device is in relation to a fixed known position.

The new self-contained system could provide GPS-quality navigation fixes

Sandia National Laboratories

To do this, it measures 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 inertial guidance systems like GPS have to be very precise and have the same time measurement at atomic clock level. This is possible with existing systems that use mechanical gyroscopes or beam lasers through clouds of rubidium gas to measure quantum effects, but these rely on heavy and expensive vacuum systems that wash out any air molecules that could interfere with the measurements.

The Sandia team’s approach is to put bespoke, rugged quantum sensors in a chamber with a volume of just one cubic centimeter (0.06 cubic inches). This chamber is made of titanium with sapphire windows – materials that, in contrast to stainless steel and Pyrex glass, prevent even gases such as helium from entering.

The chamber can hold a relatively harsh vacuum for a long time, but instead of using complex and heavy pumps to create that vacuum, the team resorted to an ancient electronics technology called getters. If you’ve ever looked at an old radio valve, you might have seen a silvery or sooty stain on the top of the tube. This is caused by a getter, which is a chemical plug that is formed around a filament. When a valve was made, the vacuum inside was not strong enough to pass a current through the plug. This triggered a chemical reaction that absorbed any scattered air molecules.

In the Sandia chamber, the getters are about the size of an eraser and are inserted into two narrow tubes that protrude from the chamber. It is not certain how long the chamber will hold a vacuum, so the team aims to keep one sealed and operational for five years. While waiting, researchers will focus on making the device less cumbersome and simpler.

The study was published in AVS quantum science.

Source: Sandia National Laboratories

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