4 ms·

What are the legacy GPS system stats? Its kinda important to compare before deciding the Russians hacked them. Its surprisingly difficult to find real, detail

by VLM 10y ago

What are the legacy GPS system stats? Its kinda important to compare before deciding the Russians hacked them. Its surprisingly difficult to find real, detailed data about the GPS system. The block II first production run of GPS sats that were launched around 1990 and decommissioned in at most 17 years had a design life of a pitiful 7 years and used dual Rb clock and Cs clocks. I'm not sure the modern block details are declassified. Anyway the failure rate for Galileo seems consistent with a "less than a decade design life" I'm not sure block IIIa is even finished designing yet. People have this peculiar idea that "the gps satellite" was launched one time in the 80s and its been running ever since... not so, gosh there must have been a hundred or so launched over the last couple decades. I have some limited experience with Rb-standards and on the ground in telco land you'll get an amazing song and dance from the mfgr about how in theory they should run for eternity but being a vacuum tube (actually conceptually closer to a fluorescent light) they do wear out and end up on ebay after a decade or so for ham radio microwave and EME operators to do peculiar things with them cheaply. Not good enough to run a data center is still stable enough to help bounce signals off the moon. I have no experience with hydrogen standards they don't even appear on ebay in my price range. Again perhaps its normal for them to wear out, etc. So Rb standards "should" die off on a regular basis. Possibly the biggest classified secret of the entire GPS project MIGHT be you have to massively overspec your clocks or you get an economic kill shot of spending a billion bucks (rubles, euros) on something that only runs six months LOL shoudda just licensed our technology that learned the lessons the hard way in developmental block I satellites in the mid 80s.

stefantalpalaru 10y ago
> before deciding the Russians hacked them Actually, the first suspect is the US: https://en.wikipedia.org/wiki/Galileo_(satellite_navigation)#Tension_with_the_United_States https://en.wikipedia.org/wiki/Galileo_(satellite_navigation)...
- dogma1138 10y ago
  The frequencies have changed after everyone realized it was a pretty darn dumb proposal to begin with. Also I like how everything is now being blamed on hacking, a freaking atomic clock that was launched on top of rocket into space fails and it's Russian hackers.
  - toomuchtodo 10y ago
    > and it's Russian hackers. Seems to be the goto scapegoat for catastrophic failures, technical or otherwise.
    - cynoclast 10y ago
      Russian hackers made my coffee pot overflow this morning.
  - ChuckMcM 10y ago
    I'm sure that actual Russian hackers would like to be perceived as people who can hack an atomic clock in space with no connection to earth :-) Such a feat would demonstrate some fairly elite skills would it not?
  - maxxxxx 10y ago
    When someone comes up with some conspiracy theory or someone suspecting my code to do something really weird I always try to imagine what it would take to actually pull it off. Let's say hackers really did this, how could you do the same if you really wanted to? Often it turns out you simply couldn't do it even if you wanted to.
  - throwaway5752 10y ago
    "Also I like how everything is now being blamed on hacking, a freaking atomic clock that was launched on top of rocket into space fails and it's Russian hackers." The only mention I see anywhere of blaming hackers (Russian or otherwise) is VLM 3 comments up from you. It's certainly not in the linked article. Am I missing something?
analog31 10y ago
Not good enough to run a data center is still stable enough to help bounce signals off the moon. Out of curiosity, why does a data center need a Rb clock?
- electrum 10y ago
  Very accurate time is important for some applications: https://www.wired.com/2012/09/google-spanner/ https://www.wired.com/2012/09/google-spanner/
  - ajross 10y ago
    Not at this level. The Rb resonance in question is ~6.8 GHz, which means that counting it (which is functionally all atomic clock is really doing) will give you accuracy higher by definition than the cycle time of the CPU running your timing-sensitive application. GPS needs that because at the speed of light in vacuum that corresponds to ~2cm of wavelength, which is only 2 orders of magnitude from the design accuracy of the whole system.
    - cnvogel 10y ago
      Cycle-to-cycle accuracy of an atomic clock (then called a timing and frequency standard) is never dominated by the resonance frequency, and you never extract the timing information from the radio-frequency that interacts with the physics directly. The reference frequency used externally for timing is the reference oscillator which typically was 5 or 10 MHz, but nowadays tends to be 100 MHz as HF electronics became better. For an older Caesium clock, a block diagram is explained on this page: http://www.leapsecond.com/museum/hp5062c/theory.htm http://www.leapsecond.com/museum/hp5062c/theory.htm {a Rb clock is very similar electronically, only you are not looking at count-rates of Cs atoms flying through your spin filter but you are observing the optical attenuation of a rubidium gas, both vary with radio-frequency waves being injected into the package. Also Cs is a primary standard and Rb is very stable - but adjustable and susceptible to extarnal magnetic fields.} From the reference frequency, a series of synthesizers / multipliers generate the radio frequency that is relevant to the physics process. And this frequency is then modulated slightly (137 Hz label in Figure 5) so that correlation in the physics process from being too high, or too low in resonance frequency, can be observed (Figure 9, you vary between f2 and f1 137 times per second). A good GPS steered quartz oscillator will use around 100s of loop time-constant, the time constant for the control loop in a caesium clock will be much higher.

by VLM 10y ago

stefantalpalaru 10y ago

> before deciding the Russians hacked them Actually, the first suspect is the US: https://en.wikipedia.org/wiki/Galileo_(satellite_navigation)#Tension_with_the_United_States https://en.wikipedia.org/wiki/Galileo_(satellite_navigation)...

dogma1138 10y ago
The frequencies have changed after everyone realized it was a pretty darn dumb proposal to begin with. Also I like how everything is now being blamed on hacking, a freaking atomic clock that was launched on top of rocket into space fails and it's Russian hackers.
- toomuchtodo 10y ago
  > and it's Russian hackers. Seems to be the goto scapegoat for catastrophic failures, technical or otherwise.
  - cynoclast 10y ago
    Russian hackers made my coffee pot overflow this morning.
- ChuckMcM 10y ago
  I'm sure that actual Russian hackers would like to be perceived as people who can hack an atomic clock in space with no connection to earth :-) Such a feat would demonstrate some fairly elite skills would it not?
- maxxxxx 10y ago
  When someone comes up with some conspiracy theory or someone suspecting my code to do something really weird I always try to imagine what it would take to actually pull it off. Let's say hackers really did this, how could you do the same if you really wanted to? Often it turns out you simply couldn't do it even if you wanted to.
- throwaway5752 10y ago
  "Also I like how everything is now being blamed on hacking, a freaking atomic clock that was launched on top of rocket into space fails and it's Russian hackers." The only mention I see anywhere of blaming hackers (Russian or otherwise) is VLM 3 comments up from you. It's certainly not in the linked article. Am I missing something?

analog31 10y ago

Not good enough to run a data center is still stable enough to help bounce signals off the moon. Out of curiosity, why does a data center need a Rb clock?

electrum 10y ago
Very accurate time is important for some applications: https://www.wired.com/2012/09/google-spanner/ https://www.wired.com/2012/09/google-spanner/
- ajross 10y ago
  Not at this level. The Rb resonance in question is ~6.8 GHz, which means that counting it (which is functionally all atomic clock is really doing) will give you accuracy higher by definition than the cycle time of the CPU running your timing-sensitive application. GPS needs that because at the speed of light in vacuum that corresponds to ~2cm of wavelength, which is only 2 orders of magnitude from the design accuracy of the whole system.
  - cnvogel 10y ago
    Cycle-to-cycle accuracy of an atomic clock (then called a timing and frequency standard) is never dominated by the resonance frequency, and you never extract the timing information from the radio-frequency that interacts with the physics directly. The reference frequency used externally for timing is the reference oscillator which typically was 5 or 10 MHz, but nowadays tends to be 100 MHz as HF electronics became better. For an older Caesium clock, a block diagram is explained on this page: http://www.leapsecond.com/museum/hp5062c/theory.htm http://www.leapsecond.com/museum/hp5062c/theory.htm {a Rb clock is very similar electronically, only you are not looking at count-rates of Cs atoms flying through your spin filter but you are observing the optical attenuation of a rubidium gas, both vary with radio-frequency waves being injected into the package. Also Cs is a primary standard and Rb is very stable - but adjustable and susceptible to extarnal magnetic fields.} From the reference frequency, a series of synthesizers / multipliers generate the radio frequency that is relevant to the physics process. And this frequency is then modulated slightly (137 Hz label in Figure 5) so that correlation in the physics process from being too high, or too low in resonance frequency, can be observed (Figure 9, you vary between f2 and f1 137 times per second). A good GPS steered quartz oscillator will use around 100s of loop time-constant, the time constant for the control loop in a caesium clock will be much higher.