Secret X37-B spaceplane tests quantum alternative to GPS

The US Air Force’s secret X-37B spacecraft is to make its eighth space flight on August 21, 2025, to test quantum communication systems as an alternative to GPS.

Most of the tests, conducted using this orbiter, are classified. However, one of these tests is a test of the quantum communication system as an alternative to GPS.

The GPS satellite navigation system is used almost everywhere, in smartphones, transportation, and logistics. However, GPS does not work equally well everywhere. In space, especially beyond Earth’s orbit, GPS signals become unreliable or simply disappear. The same is true underwater, where submarines have no access to GPS at all.

Even on Earth, GPS signals can be jammed, distorted, or blocked. Traditional inertial navigation systems (INS), which use accelerometers and gyroscopes to measure a vehicle’s acceleration and rotation, provide independent navigation, because they can estimate a location by tracking its movement over time.

However, over time, without visual cues, small errors will accumulate and such inertial navigation systems will lose their orientation. As small measurement errors accumulate, they gradually go off course and require correction using GPS or other external signals. 

At very low temperatures, atoms obey the rules of quantum mechanics and behave like waves. They can exist in a state of superposition, which is the key property, that formed the basis of quantum inertial sensors. 

The quantum inertial sensor on board the X-37B uses an atomic interferometry technique in which atoms are cooled to a temperature close to absolute zero, so that they behave like waves. With the help of precisely tuned lasers, each atom is divided into a so-called superposition state, similar to a Schrödinger cat, so that it simultaneously moves along two trajectories, which are then recombined. 

Since in quantum physics an atom behaves like a wave, these two trajectories interfere with each other, creating a pattern similar to the overlapping circles on water. This pattern encodes detailed information about how the atom’s environment affected its trajectory. In particular, small changes in motion, such as sensor rotation or acceleration, leave noticeable traces on these atomic “waves.”

Compared to classical inertial navigation systems, quantum sensors have much higher sensitivity. Since atoms are identical and do not change, unlike mechanical or electronic components, they are much less prone to drift or displacement. The result is long-lasting and highly accurate navigation without the need for external sources.

The upcoming launch of the X-37B will be the first test of a quantum inertial navigation system in space. Previous missions, in particular, NASA’s Cold Atom Laboratories and the German Space Agency’s MAIUS-1 launched atomic interferometers into orbit or suborbital flights and successfully demonstrated the physics behind atomic interferometry in space. 

The X-37B experimental spacecraft is designed as a compact, high-performance and reliable inertial navigation module for real-life long-duration missions. It takes atomic interferometry from the realm of pure science to the realm of practical applications in the aerospace industry.