Semi-related, X-37B is heading up next month, and unlike so many missions they're saying a little bit what this one is for. It'll attempt to do some laser communications demonstrations. And... it has a "quantum inertial sensor", as a would-be GPS alternative. https://www.airandspaceforces.com/x-37-eighth-mission-laser-...
The article says it uses magnetic and gravitational field sensing. I don't know how surprised I'd be to hear magnetic field sensing would work: I'd sort of assume there'd be some significant variance day-by-day week-by-week. But getting up there and seeing what you get is probably the way to find out?
rich_sasha · 44m ago
Whay do you do once you measured the gravitational fluctuations so precisely? Is there some kind of map of fluctuations you compare to? Arent these almost the same on adjacent points? Or is it a function of local terrain topography (mountains, lakes etc?)
i_am_proteus · 41m ago
Indeed.
>The system deduces the strength of Earth’s gravity in every given point of the journey from the motion of the atoms illuminated by laser beams inside a vacuum chamber and compares that data with gravity maps compiled from satellite measurements.
arethuza · 19m ago
Is that like TERCOM but using strength of gravity rather than terrain height?
i_am_proteus · 10m ago
Precisely.
tamimio · 1d ago
> “You can’t spoof gravity without literally moving a mountain,” said Biercuk.
What about weather conditions? Clouds, heavy rain, hurricanes, etc.
rcxdude · 1d ago
Relevant if you're trying to do extremely fine gravity measurements, but for navigation (and with the performance of these sensors), it's not going register much, the natural contours of earth's gravity over longer distances are large compared to these effects.
XorNot · 36m ago
Though the more interesting part is that with such sensitivity you would likely be able to infer nearby masses moving around - shipsnor stealth planes for example.
https://www.nist.gov/publications/time-transfer-performance-...
https://www.jeffgeerling.com/blog/2025/bps-gps-alternative-n...
The article says it uses magnetic and gravitational field sensing. I don't know how surprised I'd be to hear magnetic field sensing would work: I'd sort of assume there'd be some significant variance day-by-day week-by-week. But getting up there and seeing what you get is probably the way to find out?
>The system deduces the strength of Earth’s gravity in every given point of the journey from the motion of the atoms illuminated by laser beams inside a vacuum chamber and compares that data with gravity maps compiled from satellite measurements.
What about weather conditions? Clouds, heavy rain, hurricanes, etc.