DARPA's ROCKn Program Aims To Make Optical Atomic Clocks Portable (newatlas.com) 55
DARPA has announced a new initiative called the Robust Optical Clock Network (ROCkN) program, which will look to develop a practical, super-accurate optical atomic clock that is robust and small enough to fit inside a military aircraft, warship, or field vehicle. New Atlas reports: Ignoring a lot of technical details, a conventional atomic clock works by using a beam of microwaves to measure the frequency of the target atoms, but by replacing the microwaves with light, the accuracy is boosted by a factor of 100. In fact, such optical clocks are so accurate that the most advanced wouldn't gain or lose a second through the entire lifespan of the universe. Such optical atomic clocks have been built, but they're still huge, delicate, room-filling machines that aren't practical for military application. The goal of DARPA's ROCKn program is to study the basic physics of the principle behind the optical clock and find a way to make optical atomic clocks with low size, weight, and power (SWaP). Not only that, they will be more precise and accurate than current state-of-the-art atomic clocks.
To do this, ROCKn will first look to produce a robust, high-precision small portable optical clock that can maintain picosecond accuracy for 100 seconds at a time. This clock would be small enough to install in a fighter jet or satellite and tough enough to withstand the temperatures, acceleration, and vibrational noise of such an environment. The second stage will aim to create a larger transportable version that can be used in a Navy ship or field unit that is accurate to a nanosecond for up to 30 days without an outside GPS signal.
To do this, ROCKn will first look to produce a robust, high-precision small portable optical clock that can maintain picosecond accuracy for 100 seconds at a time. This clock would be small enough to install in a fighter jet or satellite and tough enough to withstand the temperatures, acceleration, and vibrational noise of such an environment. The second stage will aim to create a larger transportable version that can be used in a Navy ship or field unit that is accurate to a nanosecond for up to 30 days without an outside GPS signal.
Critical timing (Score:5, Interesting)
If the portable clock in the fighter or ship were synchronized with the GPS signals they are receiving, it would seem to also make it much harder for the enemy to spoof the GPS signals and lead the system astray. It might also help keep critical timing of operations of Selective Availability was ever turned back on.
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It must be hard to synchronized precisely with GPS when moving at several thousand miles per hour in a jet fighter and even maybe slower airplanes . Please see my other post just below yours and feel free to elaborate. At last news for nerds on Slashdot :)
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Modern jet fighters max-out at 960 miles/hour. Even the Lockheed SR-71 Blackbird did only 2,200 miles/hour. IIRC, relativistic effects can't even be measured under about 29,000 miles/hour.
IIRC, once a jet fighter is synchronized, it switches to dead-reckoning. So ECM won't disable its navigation and air-land targeting.
Re:Critical timing (Score:5, Informative)
Relativistic effects can be measured even within conventional aircraft. The effect is small and hard to measure, and it helps if the journey is long (to accumulate the effect to something measurable). You have to take into account both special (i.e., velocity-related) and general (i.e., gravitational and acceleration) effects into account. But it was first accomplished in the 1970s [wikipedia.org].
The cruising speed of commercial planes produces a (special relativistic) time dilation effect of about 0.5 parts per trillion. So if a clock on the ground measures 1 second, the traveling clock would measure 1.0000000000005 seconds. (Again, ignoring general relativistic effects.) That's a tiny effect, but accumulated over hours (10^4 seconds), it becomes measurable using clocks that have parts-per-billion (i.e., nanosecond) accuracy, which is downright easy these days.
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>Modern jet fighters max-out at 960 miles/hour.
Not true. Lots of modern fighters can reach much higher speeds at altitude.
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Modern jet fighters max-out at 960 miles/hour.
[citation needed]
I can't think of a single "modern jet fighter" that is not faster than that.
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How about the FA-18?
Max speed is 1189 m/h, or 1915 km/h for those of us who live in "modern" times, since the FA-18 only came out recently in 1978.
The last time I checked, 1189 MPH was faster than 960 MPH?
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"It must be hard to synchronized precisely with GPS when moving at several thousand miles per hour in a jet fighter and even maybe slower airplanes ."
Meanwhile, the GPS satellites move at 9,000 miles per hour.
Your ground-based receiver will happily listen to satellites moving "towards", "away" and "sideway", a 18,000 miles per second variation in speed.
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The level of accuracy they are going for suggests that they are looking for very small errors, like centimetre level. I'm not sure it's even feasible when you consider random propagation delays.
For missiles they will use some other terminal guidance system (e.g. IR or radar) and the kinds of small atomic clocks we have had for a while now are good enough to detect when GPS is metres off, so I'm thinking there must be some other application for these.
Maybe transferring tracking data about hypesonic weapons?
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Maybe they're for those new-fangled 500 Hz gaming monitors [slashdot.org] ... :-)
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The only reasons I can think of are to be immune from GPS spoofing (You expect me to believe those signals? They're off by a whole nanosecond!) and to build your own dynamic positioning network by comparing timestamps of all your various vehicles as perceived by each other (I'm 1234.567m from you, and 2345.678m from him, and how far are you from each other?).
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I like your idea, and believe they're going to build a terrestrial positioning network based on time of flight and known reference points. Any materiel parked long enough gets its position narrowed down to the point where it is a reference point itself. Then they can stop using GPS for these purposes, and leave it as primarily a civilian-use network. Time is also relevant to crypto, perhaps they have in mind an ultra-secure wireless net.
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TFA really doesn't explain why it is they want such accurate timing.
The only reasons I can think of are to be immune from GPS spoofing (You expect me to believe those signals? They're off by a whole nanosecond!) and to build your own dynamic positioning network by comparing timestamps of all your various vehicles as perceived by each other (I'm 1234.567m from you, and 2345.678m from him, and how far are you from each other?).
Or time based gravitometers?
Buy one from NASA? (Score:2)
I wonder if they have considered just buying one from NASA.
https://www.nasa.gov/feature/j... [nasa.gov]
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That's a microwave frequency clock. DARPA apparently want's the same thing but at visible frequencies.
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The level of accuracy they are going for suggests
that they are looking for very small errors, like centimetre
level. I'm not sure it's even feasible when you consider
random propagation delays.
Notice the article never says why they want
better-than-regular-atomic-clock accuracy.
Re:Critical timing (Score:5, Informative)
Military receivers mostly use the encrypted P(Y) code or newer M-code (M for military), rather than the spoofable civilian signals.
Selective Availability is almost certainly [gps.gov] not coming back -- the newest GPS satellites do not include it. They do, however, include spot beam [geospatialworld.net] capability that lets them bump their M-code power up by 20 dB for areas where adversaries are jamming or spoofing other signals. (... assuming they ever fix their delays [breakingdefense.com]. Hopefully they don't really need M-code before mid-2025 [uscg.gov].)
I recall a guy on ntp forums (Score:4, Interesting)
I recall a guy on ntp forums which owned two atomic clocks and he put one of them in the trunk of his car while going for a summer road trip for a vacation driving across US at mostly 60 mph. He left the other atomic clock in his house.
While in his house, both clocks kept the same time as expected. When he got back home, he could measure the time dilation on the clock he took in the road trip.
For starters, the clock that experience acceleration/deceleration is always the one getting slower over time.
So I hope the military planned acceleration sensors to calculate and compensate for clocks they want to put in airplanes, especially jet fighters. Otherwise, those clocks will definitely drift and be out of sync with stationary military hardware.
Of course, maybe adjusting them after every flight might be sufficient. In the car driving guy story, I guess the difference was only a few micro-seconds, not even millis, I don't recall exactly but he could measure it.
I am almost sure someone could find that story and the exact numbers if an Internet search was made about that story.
Re:I recall a guy on ntp forums (Score:5, Informative)
Re:I recall a guy on ntp forums (Score:4, Insightful)
Anyone capable of designing or building a portable atomic or optical clock will be well aware of what relativity and gravity does to timekeeping and will take that into account.
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Maybe the fact that the trunk of his car reached temperatures of 50+ Celsius (let's say 140 Fahrenheit) helped?
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The relativistic effects are quite noticeable at the nanosecond level in aircraft or spacecraft. It's a good thing that we have computers that can deal with that complexity.
Hmm.. (Score:2)
Does anything outside of this one second I'm in even exist. Did I exist a second ago? But more importantly, why does the me of this second care so damn much about what happens to the me of the next second?
Puff puff.
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No children, huh?
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Instructions unclear. (Score:2)
The project is called the Robust Optical Clock Network (ROCkN). I see zero information about how the "network" part of this is supposed to happen, specifically, how they plan to lockstep all these vehicle mounted clocks that are accurate to within one second of the heat death of the universe. Information seems scant via searches as well.
Can anyone elaborate?
How do they know how accurate atomic clocks are? (Score:3)
Serious question - if the clock who's accuracy you're measuring is the most accurate clock on the planet, how do you measure its accuracy? Conversely why not define seconds based on that type of clock so it'll always be accurate?
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And indeed, this makes timekeeping difficult in general -- no two atomic clocks, no matter how precise and accurate, tick the same way, because of even minor variations in local gravity, latitude, etc. Even, like, UTC is measured in terms of a calculation based on hundreds of atomic clocks all around the world.
(also random trivia: partially because of the above, the UTC that we all sync our clocks to isn't actually UTC, it's an _approximation_ of UTC (which is why in some situations, you need to specify whi
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Serious question - if the clock who's accuracy you're measuring is the most accurate clock on the planet, how do you measure its accuracy?
Build two and measure their deviation.
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That only tells you that one or both of them are wrong.
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Build a hundred and measure their error distribution. There's a fairly sophisticated field of applied mathematics that deals with exactly this kind of problem, called statistics.
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That only tells you that one or both of them are wrong.
Isn't that precisely what you were after? If you need to gauge how wrong they are then build multiple and then analyse them statistically.
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But, someone with a network of clocks knows that it's their average.
You can look at relative errors between the clocks in the network to estimate individual clock accuracy
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Prior art for portable atomic clocks (Score:2)
HP 19" atomic clock with wrist straps [leapsecond.com].
Relativity made obvious (Score:2)
Such portable atomic clocks should allow anyone to check relativity. Say if you have a pair of such clocks, one on each wrist, and move rapidly one arm they will instantly differ by many picoseconds. To make good use of such movable clocks (for example in fighter jets) one will need to take into account all the path in the gravity field and the speed of the jet, otherwise the indicated time will look garbage.
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Unfortunately, it won't convince the flat-earthers and science deniers. They'll just come up with more outlandish and fanciful explanations, then claim their just doing their own research.
Rubidium standard? (Score:3)
What problem is this solving where a rubidium standard which is already packaged in something the size of a child's closed fist not accurate enough for this purpose?
Is this just miniaturization for miniaturization's sake or is there a practical application to making such highly accurate timepieces portable given we already have portable timepieces so accurate they can be used to calculate your position to within a couple of meters all the way from medium earth orbit?
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Because rubidium is still an order of magnitude worse than the best clocks we have now.
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That wasn't the question. The question is what *problem* are they trying to solve. I.e. what application do you have that requires a clock an order of magnitude more accurate than rubidium standards and also require it to be portable?
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That wasn't the question. The question is what *problem* are they trying to solve. I.e. what application do you have that requires a clock an order of magnitude more accurate than rubidium standards and also require it to be portable?
Because people, even when moving about, continue to wonder:
Does anybody really know what time it is? Does anybody really care?
Well apparently the military does.
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The R in DARPA stands for research. Not everything they do has immediate applications. A more accurate portable atomic clock would make GPS more accurate though, and would be useful for multi-satellite physics experiments like gravity probe B, orbital interferometric telescopes, possibly gravity wave observatories....
I'm not really sure why you'd want to put one in a jeep or a fighter jet, but DARPA probably has reasons that at least sound good to generals.
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I know they are less accurate, the question was why? If the answer is penis waving or bragging rights it may be quite the waste of resources. We have some minor needs for clocks more accurate than rubidium standards, but where is that need for a portable application?
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They want position sensing without GPS, and without being just 'within a couple of meters' (being off by 'a meter or more' is listed as a problem). https://www.darpa.mil/news-eve... [darpa.mil]
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Except by localizing clocks you don't suffer the problem of your clock being somewhere in space generating the inaccuracy. If you are going to carry a reference clock with you and you know the location of said reference clock then you already get about 1cm accuracy using rubidium standard via D-GPS, and those D-GPS units are already portable...
2nd Amend. slippery slope to (Score:1)
..."every person has a right to carry nukes"?
Not that accurate in the long term (Score:2)