 Check out the bookstore at IRBS.com |
|
|
|
|||||
|
||||||
From: ron 'coyote' lussier (no email)
Date: Fri Sep 26 2003 - 11:55:20 EDT
On Friday, September 26, 2003, at 06:23 AM, Jim Townsend wrote:
> My theory is that if the DOD found it necessary to "turn off" the GPS
> system it would be to prevent "guidance systems" from operating.
> (missles, rockets etc.) The system could be switched on for a couple
> of minutes for "position takers" and still be left off for too long
> for "guidance demanding" equipment.
Actually, the DOD still retains the right to turn on Selective
Availability (SA). SA was turned off by President Clinton on May 1,
2000 (http://www.navcen.uscg.gov/gps/selective_availability.htm). SA
'randomizes' the last few bits of the location signal, dropping the
accuracy from a few meters to about 50 meters.
If the U.S. were to go to a war situation and the president decided
that GPS was giving advantage to the enemy, then the solution would
probably be to turn SA back on. If this were done, then navigators
would still be able to use GPS to get at least the accuracy of
sextant-based positioning. Like the latter, GPS would *not* be useful
for getting through a gap in a coral reef, or into a harbor. (And we
probably shouldn't be using GPS for that anyhow.)
It is extremely unlikely that the entire GPS system would fail. To do
so would require a catastrophic event, such as a high-altitude nuclear
explosion or an invasion of extraterrestrials. The loss of any one or
two satellites (or even 5) would still leave the system operational,
albeit less accurate.
Lastly, the E.U. is moving towards developing their own redundant GPS
satellite network, titled 'Galileo'. More details can be found here:
http://europa.eu.int/comm/dgs/energy_transport/galileo/index_en.htm
coyote
---
ron lussier / lenscraft fine art photography
67 crescent avenue
AIM sausalito / ca 94965
http://www.lenscraft.com/ +1 415.331.3687
------------------------ Yahoo! Groups Sponsor ---------------------~-->
Buy Ink Cartridges or Refill Kits for your HP, Epson, Canon or Lexmark
Printer at MyInks.com. Free s/h on orders $50 or more to the US & Canada.
http://www.c1tracking.com/l.asp?cid=5511
http://us.click.yahoo.com/mOAaAA/3exGAA/qnsNAA/A1TolB/TM
---------------------------------------------------------------------~->
To unsubscribe from this group, send an email to:
Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
|