The US military’s spaceflight X-37B orbit test vehicle is scheduled to begin its eighth flight into space on August 21, 2025. Much of what the X-37B does in space is a secret. But it acts partly as a cutting-edge experimental platform.
One of these experiments is quantum inertial sensors, a potential alternative to GPS, which uses quantum science as a navigation tool.
Satellite-based systems such as GPS are ubiquitous in our daily lives, from smartphone maps to aviation and logistics. However, GPS is not available anywhere. This technology could revolutionize how spacecraft, planes, ships and submarines sail in environments where GPS is not available or infringed.
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In space, GPS signals are unreliable or simply disappear, especially beyond the Earth’s orbit. The same applies underwater, and the submarine has no access to GPS at all. And even on Earth, GPS signals can be clogged (blocked), spoofed (I think the GPS receiver is somewhere else) or disabled. For example, during a conflict.
This creates a critical challenge for navigation without GPS. In such a scenario, it is essential to have a navigation system that functions independent of external signals.
Traditional inertial navigation systems (INS), which use accelerators and gyroscopes to measure vehicle acceleration and rotation, provide independent navigation as they allow position estimates by tracking how the vehicle moves over time. Think of sitting in the car with your eyes closed. You can still feel the rotation, stop, acceleration, your brain integrates to guess where you are over time.
Related: 10 Things We Know About the Secret X-37B Space Plane
Ultimately, without visual clues, small errors accumulate and positioning is completely lost. The same applies to classic inertial navigation systems. As small measurement errors accumulate, they gradually drift off the course, requiring corrections from GPS or other external signals.
Where Quantum is useful
When you think of quantum physics, what might come to mind is a strange world where particles behave like waves and Schrödinger’s cat is dead and alive. These thought experiments really explain how small particles, like atoms, behave.
At very low temperatures, atoms follow the rules of quantum mechanics. They behave like waves and can exist in multiple states simultaneously.
The quantum inertial sensor mounted on the X‑ 37B uses a technique called atomic interferometry. The atoms behave like waves as they cool to absolute zero temperatures. Using finely tuned lasers, each atom is split into what is called a superposition state, similar to the Schrodinger cat, and travels along two paths at the same time, then recombined.
Because atoms behave like waves in quantum mechanics, these two paths interfere with each other, creating a pattern similar to the overlapping ripple of water. Encoded in this pattern is detailed information about how the environment of the atoms influenced its journey. In particular, the smallest shifts in motion, such as sensor rotation and acceleration, leave detectable marks on the “waves” of these atoms.
Compared to classic inertial navigation systems, quantum sensors offer orders of magnitude more sensitivity. Atoms are identical and unlike mechanical components and electronics, they do not change, resulting in much less tendency to drift and bias. The result is long-term and highly accurate navigation without the need for external references.
This is the first time that this level of quantum inertial navigation has been tested in space for the upcoming X‑ 37B mission. Previous missions such as NASA’s Cold Atom Laboratory and German Space Agency’s MAIUS-1 have successfully demonstrated the physics behind the voyage’s atomic interferometers in orbit and suborbital flights, but not specifically for the purpose of voyage.
In contrast, the X‑37B experiment is designed as a compact, high performance, resilient inertial navigation unit for long-term real-world missions. It moves atomic interferometry from the pure science realm to practical applications for aerospace. This is a huge leap.
This has important implications for both military and civilian spaceflight. For US space forces, it represents a step towards greater operational resilience, especially in scenarios where GPS may be denied. In future space exploration, such as the Moon, Mars, and even deep space where autonomy is important, quantum navigation systems can not only serve as reliable backups, but also as the main system when signals from Earth are unavailable.
Quantum navigation is just part of the wider current wave of quantum technology moving from lab research to real-world applications. Quantum computing and quantum communication often steal headlines, but systems such as quantum clocks and quantum sensors can be the first to use across a wide range of areas.
Countries, including the US, China and the UK, have invested heavily in quantum inertia, with recent tests of airborne and submarines showing strong promise. In 2024, Boeing and Assen conducted the world’s first quantum inertia navigation test on crew aircraft.
This demonstrated continuous GPS-free navigation for approximately 4 hours. That same year, the UK conducted the first publicly recognized quantum navigation flight tests on commercial aircraft.
This summer, the X‑ 37B mission brings these advances to space. Due to its military nature, this test may remain quiet and unknown. But if it succeeds, you can remember the moment Space Navigation moves quantum dramatically.
This edited article will be republished from the conversation under a Creative Commons license. Please read the original article.
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