Got the time? - Galileo style - Page 1
Forum section: electronics / general

author: Unknown
author_rank: Unknown
timestamp: December 14, 2011, 11:54:12 pm
content: I did not see this on TV or heard it on the radio or read it on a newspaper, so here goes.On the 21st of October this year the European Space Agency launched two Russian Soyuz rockets from the Guiana spaceport in France. The rockets are carrying the first 2 of 30 satellites that together will constitute the Galileo system, Europe's version of the American GPS. On board the satellites, passive hydrogen MASERs are used as the clock sources. These clocks, the most accurate ever launched in space, will drift by 1 second in 3 million years. 1 second in 3 million years. 3 million years.http://www.esa.int/esaNA/galileo.html

author: EEVblog
author_rank: Unknown
timestamp: December 15, 2011, 02:12:41 am
content: No trimpot to tweak it spot on?Dave.

author: Unknown
author_rank: Unknown
timestamp: December 15, 2011, 02:14:35 am
content: Quote from: EEVblog on December 15, 2011, 02:12:41 amAnd half a drop of Locktite before liftoff.

author: BravoV
author_rank: Super Contributor
timestamp: December 15, 2011, 03:17:19 am
content: The question is, does it have the "undocumented" turn off switch that US military can toggle.

author: amspire
author_rank: Super Contributor
timestamp: December 15, 2011, 03:38:51 am
content: If it is going to be a whole second out in 3 million years, that will be totally useless for navigation in the year 3002011.

author: McMonster
author_rank: Frequent Contributor
timestamp: December 15, 2011, 01:03:59 pm
content: Quote from: EEVblog on December 15, 2011, 02:12:41 amJust the coarse, 23578358-turn pot for rough adjustments.

author: Mechatrommer
author_rank: Super Contributor
timestamp: December 15, 2011, 02:11:04 pm
content: Quote from: amspire on December 15, 2011, 03:38:51 amthey should prepare another Y2K bug when the time comes, like i care? they should! during that time they should pretty well prepared!

author: SoftwareSamurai
author_rank: Regular Contributor
timestamp: December 15, 2011, 03:00:23 pm
content: What is the leakage rate of H in the containers/clocks?(i.e. Eventually it will run out of H, right?)

author: Short Circuit
author_rank: Frequent Contributor
timestamp: December 15, 2011, 05:04:45 pm
content: Quote from: BravoV on December 15, 2011, 03:17:19 amIt shouldn't, that was the whole idea for this system in the first place.Anyway, the clocks have to be so accurate. Otherwise these satellites would be unusable by the time the system really goes operational.The project became more about politics than tech, so delayed, postponed, budget problems, more delays, etc. Commercial managementcan such the life out of a project delays, but never as bad as politicians

author: BravoV
author_rank: Super Contributor
timestamp: December 16, 2011, 03:23:37 am
content: Quote from: Short Circuit on December 15, 2011, 05:04:45 pmI'm aware of the reason for this project was created from the 1st place, but you should aware too on how uncle sam reacted when it was introduced for the 1st time few years ago.Putting that "switch" should be pretty easy especially few members of the consortium are uncle sam's puppies that we all know very loyal to their master.Heck, some of them are even happily sent their countrymen to die at some "funny" wars when master asked for it, so its no brainer that putting this switch is not a big deal at all.

author: 12AX7
author_rank: Newbie
timestamp: December 16, 2011, 04:38:46 pm
content: And twice a year they have to fly somebody up there to "spring ahead, fall backwards"...

author: ivan747
author_rank: Super Contributor
timestamp: December 16, 2011, 05:12:03 pm
content: Quote from: BravoV on December 15, 2011, 03:17:19 amIt's called signal jamming. The US opposed to the projet because the intended operating frequencies were too close to the military GPS ones. In case of an attack using Galileo as a guidance system, they would jam it, but if the frequencies were close, so they would be jamming their own service too, so they forced the EU to used another frequency.Galileo was supposed to be more accurate than GPS, more available, completely open for civilian use, immune to political decisions -no one could turn it off without taking away the military GPS band, so the US government though they must have control over it by means of jamming.http://en.wikipedia.org/wiki/Galileo_(satellite_navigation)#Tension_with_the_United_StatesThe US government even took a whole frequency band for their military system (L2). Look at the crowded L1 band. That's the some of the civilian frequencies for satellite navigation systems.

author: gregariz
author_rank: Frequent Contributor
timestamp: December 16, 2011, 05:50:48 pm
content: Quote from: ivan747 on December 16, 2011, 05:12:03 pmI think you'll find that the GPS modernization project will have allowed the government receivers to remain up while jamming both civilian and the old military GPS. However when the government now degrades all of the gps and remains up they will probably knock out galileo completely. To move galileo on top of GPS was a smart move from the perspective of allowing your OEM's to simply decode all systems at once using the same receivers however wasnt so smart from the perspective of denial of service. Then there is the cost issue. With glonass and gps operating at more or less full strength, is it rational to ask the european tax payer to fund another system?

author: ejeffrey
author_rank: Super Contributor
timestamp: December 16, 2011, 07:55:28 pm
content: Quote from: EEVblog on December 15, 2011, 02:12:41 amObviously in jest, but it is no joke. Atomic clocks actually need a considerable tuning range. The MASER itself runs at fixed frequency but it is only used to discipline a quartz clock. The frequency ratio of the quartz clock is slightly tunable. While the atomic clock runs at its design frequency (ticks per second) without fail, there is a problem: the second is annoyingly variable. Due to its orbital velocity and altitude, special and general relativity cause atomic clocks in orbit to operate at different frequencies relative to clocks on the ground. These effects are not small: gravity makes the clock in orbit run about 0.5 ppb faster than one on the ground, while the orbital velocity makes it run about 0.2 ppb slower. This is enormous compared to the 10 parts per _quadrillion_ quoted stability of the clocks used here. The net result is that they have to keep tweaking the clock rate to keep spot-on UTC.For those of you who like measurement porn, a bit over a year ago some scientists at NIST in colorado made a pair of atomic clocks so precise that they could see the difference when the jacked one up by 30 cm.

author: ivan747
author_rank: Super Contributor
timestamp: December 16, 2011, 09:11:59 pm
content: Quote from: ejeffrey on December 16, 2011, 07:55:28 pmEinstein's relativity theory was right, after all

author: Mint.
author_rank: Frequent Contributor
timestamp: December 17, 2011, 08:35:06 pm
content: Quote from: amspire on December 15, 2011, 03:38:51 amHah, bump!