GPS : 18KM OPERATIONAL LIMIT???
I have been digging a little into some technical aspects of GPS technology these days. At one point (and since my working hypothesis is that GPS works thanks to the aluminum/barium salts sprayed by airplanes at, say, no more than 15 - 20 km of altitude) I asked myself: do GPS devices carried in high-altitude balloons work at even higher altitudes - as they obviously should ? (GPS satellites are said to orbit at about 20.200km)
(Current world record for unmanned balloons: 53km
Sanriku Balloon Center at Ofunato City, in Japan on May 23, 2002)
http://global.jaxa.jp/article/interview/vol42/p2_e.html
Before proceeding, I just wish to remind the reader about the very basics / essentials of how we are told that GPS technology works - in layman's terms. Let me just use a segment of this article published on The Economist:
Now, here is what we can read on the GPS Wikipedia page, in a paragraph titled "Restrictions for civilian use" (of GPS receivers):
"In essence, GPS works by measuring the time it takes a radio signal from a satellite to reach a receiver on the ground. Each satellite continuously broadcasts a signal that gives its position and the time. A GPS receiver compares its own time with the satellite's time, and uses the difference between the two to calculate the distance. Taking measurements from four satellites allows the receiver to pinpoint latitude, longitude and altitude, and to correct for errors in its clock, which is not nearly so precise (or costly) as the clocks in the satellites. The problem is simply one of solid geometry: finding the point of intersection of four spheres, each centred on one of the satellites." - Read more at: http://www.economist.com/node/1020779
Restrictions for civilian use:
The U.S. government controls the export of some civilian receivers. All GPS receivers capable of functioning above 18 kilometers (11 mi) altitude and 515 meters per second (1,001 kn) or designed, modified for use with unmanned air vehicles like e.g. ballistic or cruise missile systems are classified as munitions (weapons) for which State Department export licenses are required.
Basically, what they are saying is that any airborne GPS receiver flying HIGHER than 18km (11m) or moving FASTER than 515m/s (or 1,001knots) needs special permission by the US State Dept. One has to wonder how & why they chose these peculiar numbers ... but let's get on.
So I wondered: what about civilian / amateur air balloons? Will their GPS receivers just stop functioning above 18km (or 60.000ft) of altitude? Nah, I thought to myself...that cannot possibly be the case. It was therefore quite a 'shock' to me to learn that this has, apparently, indeed been the case - and has been a topic hotly discussed on Air Balloon Forums for many years. Here's a website (last updated in 2009) which was trying to keep track of the rare few GPS devices which, reportedly, had managed to surpass the 18km altitude limit :
Here are a couple Q&A forums which discuss the nagging issue (you will have to check them out - so as to fully grasp the issue) :GPS RECEIVERS vs 60KFT - by Ralph Wallio http://showcase.netins.net/web/wallio/G ... s60kft.htm
"The 60kft limit (aka 18km) is one of the three vehicle dynamics limitations placed on GPS receivers for we civilian unwashed, altitude, vehicle velocity and acceleration. GPS receiver manufacturers are allowed some leeway to juggle the values of these limits to serve their markets so details vary between manufacturers, between models from the same manufacturer and even between software versions in the same model. The 60kft (18km) upper limit of controlled airspace is the altitude limit most often used."
http://diydrones.com/forum/topics/gps-m ... h-altitude
http://electronics.stackexchange.com/qu ... er-balloon
Ok, so today it seems that there now exist some GPS devices which will keep functioning above the bizarre 18km limit.
The UK High Altitude Society now says that there are ... three of them (one wonders what clearance you'd need to get one):
But here is my point: WHY would the DoD / US Department EVER have needed to set an altitude limit for manufacturers of GPS receivers? Were they afraid of terrorists using Hot Air Balloons to strike American cities?At present there are 3 GPS Modules that are regularly used by UKHAS balloon flights. These modules use an AND statement rather than OR for their COCOM limits. This allows them to be used in high altitude balloon flights as they continue to function above 18km (60,000ft) as long as it doesn't exceed 515 m/s (which our balloon/payloads hopefully don't!).
http://ukhas.org.uk/guides:gps_modules?s
Or is it because - perhaps - GPS doesn't work too well at altitudes above 18km ? And if so, could this mean that GPS signals are bounced off the aluminum / barium clouds sprayed by those pesky "chemtrail"-spraying airplanes?