https://www.army.mil/article/88361/Miniaturized_atomic_clock...
Also related, NASA has a spaceborne atomic clock in testing that, if it works, will make space navigation much more efficient: https://www.nasa.gov/mission_pages/tdm/clock/index.html
Hrm, it would definitely stop a spoofer from misleading you about what time it is.
If you care about your position: given the fact that GPS satellites are so far away and the signal is so weak, I don't see how it provides any defense against jamming specifically. If you can't hear the satellites, you can't hear them.
Regarding spoofing, it really only defends against spoofed signals emanating from other satellites. This is a big concern for the military. For everybody else "spoofing" means spoofed signals from other land-based or atmospheric transmitters, which once again are close enough to easily drown out the true signal completely.
TL;DR: useful if threat model includes attacker-controlled satellites.
In terms of spoofing, one method is to emit signals from ground based transmitters that match the signal from the actual satellite, but with offset times, and at higher power levels than the actual satellite[1]. This gives the receiver a false location.[2] If you have a source of time-truth, you can reject these signals.
In terms of jamming, you'll note that it allows rapid resynchronization after jamming. During jamming, you don't know where you are. After jamming, without a highly precise clock, you need to solve for the actual time by integrating signals from >=4 satellites. With a highly precise clock, this step is removed.
[0] There are confounding factors, like refraction in the ionosphere, but a rough approximation is that the signal is travelling at c
[1] Higher power is trivial because the signals from the satellites are very weak
[2] This is a classic example: https://en.wikipedia.org/wiki/Iran%E2%80%93U.S._RQ-170_incid...
TL;DR: useful for existing ground/air based threats.
Jamming nowadays does not work by simply throwing off random numbers. This is trivially defeated by gyroscope. It works by feeding time data that initially is exactly the same as the satellite, and slowly changes that as if it was in some other plausible direction, ultimately giving total control.
Against primitive forms of jamming, sure this might work. Against modern spoofing attacks, no there is no fix. Overall, what worked works and what doesn't work won't.
No. If you have both a source of time-truth and a source of location-truth you can reject these signals.
But if you had a source of location-truth you wouldn't need GPS.
GPS spoofers start off feeding you exactly the same data as the GPS satellites, then start diverging exactly as if you were slowly turning in a different direction.
Ergo, this will not work at all.
Any introduction of a false timing signal whose time offset from the true signal is greater than the local clock's uncertainty can be flagged as false. Higher-accuracy local clocks reduce the amount of error that can be introduced without detection.
CSACs don't solve the issue, but they do allow for detection of more spoofing signals, and they reduce the amount of error that any successful spoofing signal can introduce.
Any introduction of a false timing signal whose time offset from the existing measurements is greater than the local clock's uncertainty can be flagged as false.
If your previous reported satellite time is Sp, previous local time is Lp, local time uncertainty is U, current local time is Lc = Lp + Ld±U, and current reported satellite time is Sc = Sp + Sd, then, roughly speaking,
if Sd > (Ld + U) or Sd < (Ld - U), the reported signal is a spoof.
So the original spoof signal as well as any subsequent spoof signals are subject to the stricter constraints offered by your higher-accuracy local time source.
Edit: At second glance, it seems liks they are actually using Cesium now (some other demonstrators use Rubidium). The principle is the same, but the hyperfine splitting is 9.192631770 GHz (by definition) and the laser wavelength is 894 nm.
I thought Rubidium fountains were easier to minaturise. I can't see where I can find out how the device is made - there's not much detail.
Ah - you're right, it's Caesium. https://ww1.microchip.com/downloads/en/DeviceDoc/A3405FE2-C1...
I used to run an NTP server, in the pool. But it was stratum 2; it would stroke my ego to run a stratum 1 server. But 3.5 kilodollars: I'll wait.
Fountains need to have a minimum size in order to achieve a sufficient flight time when throwing the atoms up on a ballistic trajectory. Obviously, they also have to be very carefully aligned with respect to gravity.
One of those arcseconds passes by approximately 15 times a second, so using an atomic clock for that is way overkill - any time source more accurate than 1/15 of a second is unnecessary.
The main problem is that once you have aligned your telescope, now what you are trying to do is measure the direction of gravity, compared to the direction you're pointing the telescope, and that's a lot harder. Partly because that's a mechanical angle measurement (you need a pendulum that can freely swing and rest with minimal friction pointing directly in the direction of gravity, and then you need to measure angle). But then also, you need to take account of the fact that the gravitational field on the Earth is lumpy. If you're sitting next to a mountain, the gravitational field will be deflected slightly from pointing directly downwards - and in fact that was used a while back to measure the density of the Earth.
But theoretically, if you can solve the angle measurement bit, you could determine your location on Earth with an error of around 30m.
I'm not sure if this clock would be good enough for GPS. It's 3 orders of magnitude less accurate than a cesium clock. But with so many StarLink sats overhead, and synchronizing with more accurate ground clocks, might make up for that.
This thing is sufficiently small, low-power, and low-cost to use in something like StarLink sats, and it's accuracy is advertised as "±5.0E-11 accuracy at shipment", compared to about ~3e-15 or so for cesium clocks. With 30k+ StarLink sats in orbit one might be able to see enough sats overhead to provide comparable accuracy on the ground as GPS (but I've not done the math).
IMO it was a bit of gimmick. Apart from being a little too chunky for a wristwatch, just because it's an "atomic clock" doesn't mean it's "atomic powered". IIRC the CSAC uses about 1/8 W which is really pushing it for a low-power device like a watch. It might lose "one second per millennium" as advertised but good luck keeping it continuously operating anywhere near a thousand years.
Unlike Rubidium references, the light is supplied by a solid state laser, eliminating another huge power sink.
I expect these devices have a practically infinite life. What an amazing set of innovations.
https://www.microchip.com/en-us/products/clock-and-timing/at...
https://www.nist.gov/system/files/documents/2017/05/09/VCAT-...
Many teams around the world are actively developing improvements on this technology.
https://www.nist.gov/news-events/news/2019/05/nist-team-demo...
Perhaps it would be possible to have a pair of identical crystals tied together but electrically opposite in phase so that external vibrations tended to cancel. (Like a differential signaling pair in a cable)
