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Electronic navigation: The path from the past

Jan 14, 2013

It seems like yesterday when the electronic/computer world was preoccupied with Y2K and worried about the collapse of our digital world when the calendar ushered in the new millennia on Jan. 1, 2000! Well, we made it through the Y2K crisis and we made it through the Mayan end of the world so I think a little history is in order so we don't take our vessels’ potpourri of electronic devices/systems for granted. Let’s start out 2013 by considering the early history of satellite navigation, how it has affected voyaging, and where we are today.

In a galaxy not so far away and not so long ago, there were no manmade artificial satellites, no communications satellites, and no navigational satellites. This changed in October 1957, however, when the former Soviet Union launched Sputnik-1. The world’s first artificial satellite was a 184-pound, 23-inch diameter shiny metal sphere that broadcast a 20-MHz and 40-MHz radio signal from its low Earth orbit. Sputnik’s signal lasted for 22 days until its internal batteries ran out on Oct. 26, 1957. Sputnik continued orbiting Earth until finally burning up upon its atmospheric re-entry on Jan. 4, 1958.

The Sputnik-1 launch immediately precipitated the Space Race and the evolution of ever more useful artificial satellites. Since necessity is the mother of invention and Sputnik was transmitting radio signals, it only took scientists at Johns Hopkins University a few days to figure out a way to fix the exact orbital position of Sputnik. By knowing their exact position on Earth and using the Doppler shift (frequency change of signal coming and going) of the satellite’s radio signals they were able to deduce its position in orbit. Another scientist from the Johns Hopkins Applied Physics Laboratory thought about the inverse of this procedure: if you know where the satellite was then you could use this same Doppler shift to pinpoint your location on Earth. Satellite navigation was born!

By 1958 development started on the TRANSIT-1B experimental satellite, which was launched in April 1960. The Navy’s TRANSIT NAVSAT system was born and would become operational for fleet use in 1964 but remain a military secret until 1967. This first satellite navigation system was an amazing, all-weather system that provided a positional accuracy of 100 meters. The ship’s navigation setup consisted of an antenna with built-in preamp, receiver/demodulator, digital section, control group, and 5-MHz oscillator most of which was installed in a metal box about three feet square. When I was a young Navy sea pup/electrician’s mate working aboard my first ship, USS McMorris, DE 1036, I would often find myself up on the bridge staring in amazement at the AN/SRN-9 NAVSAT box and asking the on duty quartermaster questions about it. I was absolutely amazed at the time and thought of it as almost magical, which later on in my electronics career I found out wasn’t so far off from the truth, which is why technicians refer to advanced electronics as FM (freakin’ magic)!

The actual satellite was a technological marvel at the time and only weighed 130 pounds. In TRANSIT’s final iteration there were eight to 10 satellites in low Earth polar orbit, but only five were being used, the others being hot spares. As the five satellites orbited from pole to pole they transmitted two carrier frequencies of 150 MHz and 400 MHz. These frequencies were modulated with data regarding the satellite’s exact position in its orbit. The shipboard receiver was able to deduce the vessel’s location from demodulating and processing these signals. With one satellite it was possible to fix the following parameters: ship’s latitude, ship’s longitude, and exact GMT. It must be emphasized that for every pound in orbit it took literally tons of ground based equipment and hundreds of individuals to keep this system going and accurate.

The TRANSIT system served the country and mariners well until 1991 when it was finally turned off, but not to worry because by then we had GPS with accuracies to within three to 10 feet and receivers down to the size of a wristwatch. What used to take highly accurate chronographs and optical instruments to shoot the sun and stars and involved manual processing to get a position to within miles can now be done by glancing at your wrist. Modern ship electronics is getting more like magic every day…don’t forget that, and don’t take your systems for granted!

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Feb 18, 2014 05:32 pm
 Posted by  Anonymous

i operated that system in 1971 aboard the mac. sure beat relying on loran or asmuths.

Feb 18, 2014 06:24 pm
 Posted by  Anonymous

azimuth...been a long time.

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