Thursday night's SpaceX launch of the US Space Force's classified space plane, the X-37B, will be carrying an experiment we've mentioned briefly but they've said nothing about anything else on the USSF-36 mission.
About all I can recall of those posts is that they're investigating "next generation" or replacement technologies for GPS (the Global Positioning System) and while it will probably end up in many other systems other countries launch if it's successful, GPS is the US version.
In space, especially beyond Earth’s orbit, GPS signals become unreliable or simply vanish. The same applies underwater, where submarines cannot access GPS at all. And even on Earth, GPS signals can be jammed (blocked), spoofed (making a GPS receiver think it is in a different location) or disabled – for instance, during a conflict.
Before GPS, there were inertial navigation systems (INS), systems that relied on accelerometers and gyroscopes. The first systems measured changes in the vehicle's speed based on the changes in acceleration, while the second measured rotation. INS provided independent navigation, by tracking how the vehicle moved over time. Think of sitting in a car with your eyes closed: you can still feel turns, stops and accelerations, which your brain combines to guess where you are over time.
Eventually though, without visual cues, small errors will accumulate and you will entirely lose your positioning. The same goes with classical inertial navigation systems: as small measurement errors accumulate, they gradually drift off course, and need corrections from GPS or other external signals.
About here, an "I'm so old ..." story fits in. When I was getting my BS, the various physics classes I took mentioned quantum effects now and then, but were pretty much classical physics with no quantum concepts. I read a bunch of "Quantum Physics for Morons" books (the ones with absolutely no math) but have done very few of the practical problems. If you're like me, you probably think of the strange stuff, like a world where particles behave like waves and vice versa; a world where Schrödinger’s cat is both dead and alive. That kind of stuff.
At very low temperatures, atoms obey the rules of quantum mechanics: they behave like waves and can exist in multiple states simultaneously – two properties that lie at the heart of quantum inertial sensors.
The quantum inertial sensor aboard the X‑37B uses a technique called atom interferometry, where atoms are cooled to the temperature of near absolute zero, so they behave like waves. Using fine-tuned lasers, each atom is split into what’s called a superposition state, similar to Schrödinger’s cat, so that it simultaneously travels along two paths, which are then recombined.
Since the atom behaves like a wave in quantum mechanics, these two paths interfere with each other, creating a pattern similar to overlapping ripples on water. Encoded in this pattern is detailed information about how the atom’s environment has affected its journey. In particular, the tiniest shifts in motion, like sensor rotations or accelerations, leave detectable marks on these atomic “waves”.
Compared to classical inertial navigation systems, quantum sensors offer orders of magnitude greater sensitivity. Because atoms are identical and do not change, unlike mechanical components or electronics, they are far less prone to drift or bias. The result is long duration and high accuracy navigation without the need for external references.
While the coming mission will be the first time this level of quantum inertial navigation is tested in space, concepts that lead to this level have been launched already. Missions such as NASA's Cold Atom Laboratory and German Space Agency's MAIUS-1, have flown atom interferometers in orbit or suborbital flights and successfully demonstrated the physics behind atom interferometry in space, though not specifically for navigation purposes. It has been tested in the lower altitudes and slower speeds of commercial aviation, though. In 2024, Boeing and AOSense conducted the world’s first in-flight quantum inertial navigation test aboard a crewed aircraft.
By contrast, the X‑37B experiment is designed as a compact, high-performance, resilient inertial navigation unit for real world, long-duration missions. It moves atom interferometry out of the realms of pure science and into a practical application for aerospace. This is a big leap.
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This has important implications for both military and civilian spaceflight. For the US Space Force, it represents a step towards greater operational resilience, particularly in scenarios where GPS might be denied. For future space exploration, such as to the Moon, Mars or even deep space, where autonomy is key, a quantum navigation system could serve not only as a reliable backup but even as a primary system when signals from Earth are unavailable.
The X-37B inside its SpaceX Falcon 9 payload fairing before the launch of its eighth mission. (Image credit: U.S. Space Force)
It still peeves me off that there is no manned version of this obviously great space plane.
ReplyDeleteInstead Boeing provided us the Stayliner.
One more time:
DeleteThe Astronaut Office made it VERY clear they would not accept any vehicle for human space flight that uses WINGS!
That might have changed by now, but back when the current vehicles were being designed, THAT was the absolute rule.
Back in the late 60's and early 70's I was part of an air crew, which supply food, mail, materials to the string of islands in the marrians, yap, angar, siapan, can't remember the rest, Johnson island also, These island had LORAN-C stations maintained by the Coast Guard. That is where I learned.about beetle nuts.
ReplyDeleteThe near absolute zero temperature requirement is going to be problematic to wide adoption.
ReplyDelete