Quoth The Maven


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Quoth The Maven, Yet another Blosxom blog.



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Sat, 15 Jan 2005

Earth Space
These days, just about everyone knows about GPS technology; the constellation of U.S. military satellites used for a wide range of navigational purposes. But, like all technology, it is aging and has it's limits.
In 1999, the Euorpean Union started a project called Galileo that will introduce an additional constellation of 30 satellites that will compliment the existing 30 GPS satellites. However, Gallileo will be fundamentally different from GPS, in three important areas:

  1. more accurate (up to 1m)
  2. civillian controlled (not U.S. military)
  3. complimentary with GPS (both can be used simultaneously)
Additionally, it is designed to provide better coverage in cities or buildings where the current GPS service fails.
After much negotiation, the EU and the US have finally come to an agreement. I think the sticking point was Article 11 - National Security Compatiblity and Spectrum Use. The US is planning to deploy a new signal, known as M-code, in 2012. It would allow the US military to jam just civilian use of their GPS satellites. Thus preventing any bad guys (and any civilian good guys, for that matter) from using them while the US military still can.
A few Galileo test satellites will begin launching in late 2005. And the full constellation is scheduled to be deployed in 2007 and ready for commercial exploitation in 2008.

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Earth Time
Also known as TAI (International Atomic Time [in French]), is occasionally adjusted by a leap second in order to compensate for wobbles in the rotation of our planet. The International Earth Rotation Service is responsible for deciding how much adjustment is necessary every six months. The announcement is called Bulletin C and was just released for the upcoming Summer (Northern Hemisphere) 2005 window. 

No adjustment necessary.
This particular Bulletin C #29 is interesting because of the 26 December 2004 earthquake/tsunami that caused Earth to wobble about an inch off its axis. However, no compensation is needed because regular tidal effects of the moon still cause far greater fluctuations.
We have had no leap seconds introduced since January 1999. This adjusted TAI time totals 32 leap seconds since the inception of the IERS. But more importantly 22 leap seconds since the begining of the Unix time epoch.
If you look at this chart, you can predict that if the astronomical time (UT1/UTC/GMT) trend continues, we will bee needing another leap second very soon now.

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