REGISTER | LOGIN
Home    Bloggers    Blogs    Article Archives    Messages    About Us   
Tw  |  Fb  |  In  |  Rss
John Teel

Thank you Albert Einstein for GPS

John Teel
RichQ
RichQ
6/3/2015 2:34:49 PM
User Rank
Newbie
Re: Minor correction
I started my engineering career at JHU/APL, the creators of Transit. I remember doing a comparative study of navigation systems there, back when there were only a few GPS satellites in orbit and Transit was still in use. An amusing tidbit I learned then: when Transit first became operational the Navy compared the positional fixes from conventional surveying against the Transit results and determined they were pretty good when it came to most continental positions. Islands, however, were not as good. Hawaii was about a mile off and Sydney was so far off a nuclear missile strike would completely miss, so its true position was made classified information for the next decade. So I was told, anyway.

50%
50%
teelengineering
teelengineering
6/3/2015 2:17:18 PM
User Rank
Newbie
Re: Minor correction
Thanks for the comment Rich.  I knew the early Transit system lacked precise atomic clocks but didn't realize they instead used Doppler shift.  Thanks for sharing.

50%
50%
RichQ
RichQ
6/3/2015 1:55:00 PM
User Rank
Newbie
Minor correction
The mention of GPS being developed in the 60's is a bit off. Those first navigation satellites were the Transit series, and they worked on a slightly different principle. The receiving station used the doppler shift of the received signal to determine the range to the satellite rather than the signal's propagation delay, because in those day they couldn't outfit the satellites with precise, synchronized clocks. But they could build sufficiently precise frequency sources. They also used a lower orbit, about 600 miles.

The GPS satellites we use today were first launched in 1978 but the 24-satellite constellation wasn't fully populated until 1995, according to the offical Air Force GPS site - af.mil/AboutUs/FactSheets/Display/tabid/224/Article/104610/global-positioning-system.aspx

 

50%
50%
netrick
netrick
5/31/2015 11:08:16 AM
User Rank
Newbie
Re: It's the simple things in life...
Thank first Pierre-Louis Moreau de Maupertuis and his colleagues: La Condamine, Celsius,

Clairaut, etc...who made exact measurements of the earth's shape in ...1735-40 in

Lappland and Ecuador. 

Originally, GPS was called "Transit" and it was used to reset the position of the inertial

platforms in the "Polaris" nuclear subs, and correct the drift of their integrating loops.

The Transit satellites looking like little windmills were more "polar" than the present

GPS ( 65 °). A Transit receiver system consisted in : 

* One upside-down double conoic antenna ( 5 feet high )

* One low noise cooled preamp box ( alike half a desk ) 

* One power-supplies cabinet

* One "Digitizing" cabinet where each ADC was a full 19 inch rack

* One control panel cabinet with a lot of manual switches and "Nixie" tubes

* One computer cabinet, with a "militarized" DEC PDP-11

* One data storage cabinet with IBM style drums

I/O was done with a militarized TTY ( about 200 pounds ) connected with 

ASCII-2 / RS-232.

* A synchronization with Omega hyperbolic positioning system was also provided.

I was working for ITT and we received the rights to sell the system for civilian

applications in 1968. But only in NATO countries. Customers were oil companies

for positioning of off-shore platforms, super-tankers ( after Torrey-Cannyon

disaster ), coast-guards, meteo frigates, etc...

Competitor was Magnavox with a lower performance system.

Standard unit price was ...1.8 million $ ....of that time !!!!!

 

 

50%
50%
teelengineering
teelengineering
5/29/2015 1:39:52 PM
User Rank
Newbie
Re: Thanks...
Thanks for the comments David.  I too love seeing examples of physics in our every day lives.  GPS has been one of my favorite examples for a long time so it was fun writing this article.  Relativity isn't exactly a theory of our everyday world so seeing how it affects a technology we all use everyday is quite unique.

50%
50%
David Ashton
David Ashton
5/29/2015 6:08:11 AM
User Rank
Artist
Thanks...
John, thanks, a very interesting article.  While I don't have anything like your understanding of relativity, I know a bit about it (I cut my teeth on an excellent explanation in one of the old Time-Life science books :-).  I have a habit of looking for commonplace demonstrations of Physics - for example the doppler effect when a train goes past you, or how your hands under a hot-air dryer suddenly get a lot hotter once all the water has evaporated.  But I had never thought of any comonplace applications that demonstrate relativity.  I guess you can't see the proof of this (you can't switch the relativity compensation off!) but it's interesting to know it is there.

50%
50%
teelengineering
teelengineering
5/27/2015 5:08:16 PM
User Rank
Newbie
Re: It's the simple things in life...
Thanks for the positive feedback!  Having some understanding of relativity really gives you a new perspective on our universe.


Yeah, one beauty of special relativity is that mathematically its very simple once you make the right assumptions (that light speed in constant, not time or distance).  General relativity on the otherhand is mathematically very complicated.  At one point I spent months teaching myself the math behind general relativity (tensor analysis) and you can definitely see why it took Einstein a decade to formulate the math behind it.  Very complex mathematically and it requires math that most engineers have never seen.  When he released this theory I think only a couple of people in the world really understood the math behind it.

 

50%
50%
eafpres1
eafpres1
5/27/2015 3:47:58 PM
User Rank
Blogger
It's the simple things in life...
Hi John.  I enjoyed the article.  If I take the inhabitants of the US as a target, and define a "understanding cross section", calculating the cross section for understanding both how important is GPS and that Relativity Theory is essential for a practical system, I get a number very close to zero.

Relativity has always fascinated me.  An interesting thing about the Lorentz transform is that you can derive it using a simple geometric argument and the assumption that c (speed of light) is a true constant in a given medium.  

50%
50%
More Blogs from John Teel
Radio-controlled toys helped drive me toward a career in electronics engineering.
flash poll
educational resources
 
follow Planet Analog on Twitter
Planet Analog Twitter Feed
like us on facebook
our partners
Planet Analog
About Us     Contact Us     Help     Register     Twitter     Facebook     RSS