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A Brief History of Navigation
by Steven Craig
A Brief History of Navigation
From early in human history, people have always faced the problem of getting someplace. Often, they also desired to return to where they started. This rather inofficious start brought us to need reliable methods to determine starting location, destination, and locations in-between. Navigation was born, and the need for it has never diminished.
Early navigation was performed rather haphazardly, observing local landmarks, following the same route, which inadvertently created paths that could be followed. After a fashion, more serious efforts were made in response to a growing need for reliability. Sticks stuck in the ground at periodic intervals, piles of rocks, totem poles would eventually lead to marks on objects that would lead to signs. To use these devices, you would have to see them, so night travel was all but ruled out. Bad weather made it difficult if not impossible as well. So one did not travel in stormy weather.
And it was a very big world out there, and such efforts were entirely local to a group, a tribe, eventually a village.
One day, someone noticed the sun. And the shadow it made. And they noticed that the sun would basically be in the same spot at the same time each day. If one were to use the sun as a kind of marker in the sky, one might be able to move about on the earth from place to place without rock piles and totems.
But a more serious observer noticed that the sun changed a little day by day, week by week, month by month. Often, the sun was totally obscured by cloud and storm. And rather useless at night.
Still, others for reasons of religious or agricultural purposes, began to notice that, while the sun changed position, it seem to do so rather reliably to a certain pattern associated to the seasons. There might be something there. But it would take a while.
Its 1540. It had been some 50 years since Columbus sailed west from Spain thinking he would bump into China in a few weeks (you remember Columbus, having sailed for nearly 4 months, he bumped into a little island, and proclaimed that this must be India, because it sure doesnt look like China
), that something remarkable happened. Something secret. Portugal had developed a large trading fleet and was making a great deal of money
if the fleet could get back home to Lisbon. All too often, the fleet would not make it to where it was suppose to go, or ended up returning to other places instead, or not making it at all. Something had to be done. And it was. The Portuguese navigators developed using latitudes to determine direction to a destination. Latitudes were the parallel east/west lines on a map. And these guys drew a lot of maps. They noticed that hometown Lisbon was at 39 degrees north latitude. If they could determine when a ship was at 39 degrees north latitude, all they needed to do was turn right and sail a straight course and Lisbon was bound to show up. And it did. They would use the sun to determine the latitude every day or so. All the sun had to do was be exactly 39 degrees north of a known angle in the sky .. the location of the ecliptic or the path of the sun through the sky.
There were just a few thousand things to work out mathematically. For the sun was only at this magic spot twice a year. But someone bright noticed that the sun would move a little north or south of this magic spot predictably and at the same time on the same day of the year. Every year. The best minds were put to work on solving the problem, and created a sun table, listing the angle of the sun in the sky on an hourly basis for every day of the year. This gave us hourly sun sightings. And it could be used at sea or on land travels. And it was always correct.
The sun tables were top secret. The Portuguese did not want anyone else to find out about their solar ephemeris and use what they developed at great cost to Portugals dis-advantage.
For 80 years, other nations tried to obtain this information. Captains in the Portuguese navy were expected to keep this book from all comers. It was demanded that this book be destroyed in the event of the ship being captured or sunk. And many a captain went down with his ship clutching his sun tables to ensure just that. (Bet you always wanted to know why they did that, right?).
But about 1620, the English did capture a book and a navigator who know how to use it and the jig, at least for the Portuguese, was up.
There was still a missing piece in the puzzle. From the sun tables, you could tell how far north/south you were, and thus determine a pretty good location on your map
north south, but half of every problem was just were east/west were you?
Some thought that if they kept a good record of their speed, they could tell how far east/west they were. A rope was tried for a while. Knots were tied into it at regular intervals and it wold be tossed overboard and the ship would sail along it and the knots counted to determine speed. (Yup, knots). But sea currents, storms, darkness
all made this very impracticable to use.
It was a ticking clock that brought the answer. First, a large prize was offered by the English to whoever could make a clock reliably work in a storm-tossed sea onboard a ship. There was a theory that time would be the answer to determining longitude. Clocks worked with pendulums, and wave motion distorted that motion. The clock would have to be stabilized. Gyroscopes of a sort, and lots of springs and some banging on brass and the 3 axis stabilized ships clock was created. Now, for the first time, you could take a accurate clock along with you where ever you navigated. Now, those sun tables came back into play. Time was not the same time everywhere on the planet, if you judged time by the location of the sun at noon. For noon changed position depending on where you were
and if you looked at things a little differently, noon was at a different time in different locations. If you had a reasonability accurate time piece, you could tell the difference in time when traveling from one location to another. When you took your noon sun siting, the time would actually be a little different from the previous days fix. Either a few seconds/minutes longer or shorter depending of direction of travel. With a little math, one could determine from this difference in time, an angle. (To help out, someone started making maps divided accurately into degrees, minutes, and seconds
). Again, with a little math, the determined angle could be used to produce a distance traveled from siting to siting, and a better fix on longitude was possible. If you had a really good mathematician for a navigator, you could move about the whole world now and have a pretty good idea where your were at all times (as long as the clock worked). Ships started carrying more than one clock as insurance that they could get around without hassle. All that you needed to support this was a fixed time location. Lacking one, the English provided the Royal Observatory at Greenwich to maintain the time standard reference for world navigation Thus, Greenwich Mean Time (GMT) was born.
And the world navigated, and all was good and smooth and lovely on the high seas and on the caravan route.
Then, in 1903, it got complicated again. Things started flying around in the air. After crashing into a few hills and mountains, the flyers quickly discovered that they needed to know their altitude as well. Altimeters were developed that would read out height
based on atmospheric pressure. The higher you went, the less atmosphere there was above you, thus the less pressure. But, wouldnt you know, the presence of a storm, or really excellent clear weather could change the atmospheric pressure, changing the readout of the device by thousands of feet. Planes kept crashing into mountains.
It was surely an accident of providence that radio was being developed at about the same time as the airplane. Again, some bright boy determined that if you were to fly your plane along as retrieve the latest barometric pressure from someone on the ground, you could adjust (calibrate) your altimeter and avoid that mountain out in front of you. Radio updates worked both ways, in that while you got the latest weather report from the ground, they determined were you were and how your progress was and report that to your family, friends, or the people you worked for.
Radio worked so well, another bright boy determined that it could be used for navigation. All you needed was a computer. And World War II brought us the computer. Planes were buzzing around from place to place, ships were sailing about from place to place (and it helped to stay together), armies were marching about from place to place, and everyone needed to get where they were supposed to be. Navigation and the tools used were just barely good enough to do this most of the time. But when you got where you were going, you had to do something. In war, that meant hitting your target.
The navy had these great ships and on them very large and powerful guns that could hurl a ton of high explosive over 20 miles. That was so far, you could not see the target. You had to determine both your location and the target location, and both may be moving. You had to compute all these motions, determine range, weather conditions, and then, point your gun at a precise angle with three directions of accuracy and fire the gun at precisely the right time with the right amount of gunpowder to send the projectile to the desired location. Initially, it was a waste of time, as 98% of all shots were more than a thousand yards off target. Unless you could compute all these factors quickly enough and with enough accuracy, you were unlikely to hit anything you wanted, and likely to hit everything you did not, like your one troop
.
Thus, the US Navy worked on and developed an electronic computer solely for the purpose of gun laying
determining all the variables in a calculation to aim a gun, and hit within 100 yards of a target. With some number of shots, it was mathematically likely you would get a direct hit in a few minutes.
This computer went on to become more general purpose, made smaller, faster, easier to use and you are likely wearing one today on your wrist.
At the end of World War II, the Germans developed the first operational rocket weapon. The V-2 rocket could carry one ton warhead of high explosive 250 miles from the point of launch
well over the horizon. Thousands of the things rained down on targets in England and western Europe up until the end of the war. The rocket traveled at great speed, over 4,000MPH, and could not be stopped by any technology of the day (SCUDs are the grand children of the V-2). There was only one real problem with using the V-2 as a true weapon. It could not be aimed with any precision. If it hit within ten miles of a desired target, that was pretty darn good. The war ended fortunately before they developed any navigational method to improve accuracy. Further, almost all the rocket scientists were gobbled up by either America or Russia, so they continued their work after the war.
Which almost brings us to GPS, but not quite. First, we must look thermonuclear war in the face.
In 1957, the Russians launched a simple satellite into earth orbit. When I was a child, I heard it pass overhead on my fathers radio
. Bleep bleep bleep
nothing fancy, but there was something there
a tone change as it moved about its orbit over the short time it was overhead, and then silence after it dropped below the horizon. What was known as the Doppler effect I thought was curious.
Others did not see curiosity but fear. A rocket that could launch a satellite into earth orbit could drop a H-bomb on any spot in America. Hundreds, even thousands of bombs, on every spot in America. War came to America at the beginning of World War II when the Japanese Imperial Navy took more than 10 days to sail only halfway to America to bomb the American Fleet based at Pearl Harbor. The aircraft that the Japanese Navy launched to bomb the fleet traveled at 140MPH and took over 2 hours to fly from their aircraft carriers to bomb the base. 17 ships were bombed, and 2500 Americans were killed.
Now, Russian rockets could carry H-Bombs to American cities at 17,000MPH, taking perhaps as long as 30 minutes from launch to target, and kill 140,000,000 Americans before an hour had passed.
Americas answer was to ensure that no matter what the Russians did in a first attack, enough American weapons wold survive to lay waste to the Russians as well. Mutual Assured Destruction was the policy. We just called it MAD.
The secure launch points that the Russians could not bomb were to be a fleet of nuclear submarines carrying the nuclear response. They would go out into the ocean, and lurk quietly until called upon to launch a response to an attack. There was only one little problem
accuracy.
First of all, where were they located when the call came. How far to target, and just where was the target (thats a different story). Coming up to the surface and taking a sun fix would be difficult and potentially embarrassing if a Russian was nearby. And it was dark a lot, and the weather at sea was often horrible, and a lot of submarines operated under the polar ice cap where it was night half the time and the weather was even worst. What was to be done
The US Navy had one invaluable resource, the Applied Physics Laboratory. The bright boys and one bright girl in its fledging space department had a theory. They did not know it then, but they saved the world from thermonuclear annihilation and gave the world globally accessible, extremely reliable navigation
But first, they had to re-discover the world.
A Doppler Lighthouse
It was a simply stated problem. Enable a ship (in this case, a submarine) far out at sea to determine its location rather precisely at any time in any weather condition. No currently existing tool could perform the job. Further, the solution had to be found quickly to support a growing navy fleet. And it had to be found before the world disappeared beneath a mushroom cloud.
The year was 1960. The Applied Physics Laboratory (APL) and the Naval Research Laboratory (NRL) took on the task, and proposed something remarkable. If you did enough math quick enough, you could navigate any vehicle anywhere on the earth using a radio signal from space.
There was a lot to work out, but there was also a lot to draw on. Brand new technology that we still had trouble even getting off a launch pad was to be made operational in just a few short years. Despite the howls and laughter, the work began.
A satellite was to be the totem. It would be launched by a rocket. It would use a clock, a precise atomic clock to generate time. Instead of the sun, the ephemeris would be for this satellite. A table of time to look for the satellite would be prepared for users on the ground. It would use radio signals to get the useful navigation data to the ground. A computer would keep track of the received data, and the time received and as the satellite position changed, work out precise angles and ranges from the satellite to the ground location. The computer would take advantage of the Doppler effect of a moving radio transmitter to determine range. Ground and satellite clocks would be calibrated and synchronized to a time standard, the GMT. Given all this working correctly, the receiver on the ground could determine its longitude, latitude, and elevation theoretically to a number of inches. A Doppler lighthouse would shine brightly over every spot on the globe, and a ground user would be able to perform something never before possible
precise navigation.
In those early days, things never worked. Answers to problems always had to be developed right on the spot. Launchers failed on the launch pad. Satellites failed to achieve orbit. Even if the things got up there, it was not a given that the desired orbit was achieved. It was to be a close run thing that it even worked at all.
An array of ground tracking stations were deployed to positions all over the world to track the satellite, and provide data on its operation as well as input data to compute its orbit by a giant computer at APL. If the orbit could be determined with enough accuracy, an ephemeris could be worked out to predict were the satellite would be over time and allow the remote users to obtain accurate location fixes.
A satellite series was developed call TRANSIT. Early launch attempts failed. Equipment failed. Program cancellation was just around the corner. Thus came the launch of TRANSIT-4A. The launcher was to place the satellite into polar orbit. This would allow the earth to rotate beneath the satellite and thus allow the satellite to be seen over every spot on the surface at least twice a day. If this worked out, a series of satellites would be launched to provide greater and more frequent earth coverage.
On the day of the launch, the rocket was to proceed south from the Cape over the Atlantic and put the satellite into its desired orbit about 600 miles above the earth. At liftoff, the satellite transmitter was turned on and the rocket proceeded up, and then veered off to the north. The upper stage failed to ignite and the works crashed back to earth somewhere in the North Sea. Failure.
But there was a tracking station near Greenwich, England. The crew had the set turned on, tempting fate as it was an all vacuum tube design. The satellite was not due over their location for hours but as serendipity would have it, as the vehicle was headed to its splash into the north sea, it was visible over the station for 37 seconds. For those 37 seconds, the punched paper tape recorder clanked away, recording raw Doppler signal data from the doomed satellite. The crew almost threw the paper tape away believing it local radio interference, but a frantic call from the Cape alerted all stations to turn on equipment and record anything as the satellite was lost and its fate uncertain.
The paper tape was some 18 inches long. It was sent to APL, and processed and processed and processed through evolving algorithms to determine that range could be obtained from Doppler transmissions. And it came to pass that the scientists at APL stood before the Navy and held this worn paper tape in the air above their heads and said Eureka! Satellite navigation had been born.
TRANSIT-4B was launched successfully, and everything worked. Everything until it got blown out of the sky so to speak.. After a few months on orbit to the delight of the Navy, it suddenly stopped working while over the central Pacific Ocean. It was never heard from again. Everyone scratched their heads. At about the same time, odd news reports began to arrive from Pearl harbor, something about electric overloads and massive equipment failures. In a deep dark secret program, the Air Force was performing nuclear tests from a facility on Johnson Island 800 miles south of Pearl Harbor. Using Thor rockets, they were launching live nuclear weapons into space, and detonating them. In a matter of bad timing, TRANSIT-4B was flying by, as were two other satellites. Electro-Magnetic Pulse can sure ruin your day.
In the years that followed, all sorts of problems needed to be understood, and solutions worked out. The earth as it turned out, was not uniform in shape. Its gravitational field was not consistent world wide. The empty space was full of molecules from the exosphere or from the sun that impacted the orbit of the satellite. The ionosphere was there bending radio signals from the satellite in all directions. Data from the satellite had to be recovered in a timely fashion, sent to APL on a daily basis so that new orbit ephemeris could be worked out. Spacecraft memory was truly expensive, and only 18 hours of ephemeris data could be placed onboard. The accuracy of that ephemeris was impacted by processing time, solar storms, radio interference on the ground, other spacecraft using the same frequencies, and unforeseen physics.
But it worked. It worked so well, that every other competing form of navigation paled in accuracy and reliability. Some military services wanted to put flashing lights on satellites and use ground photographic systems to obtain position. Others wanted to orbit giant mirrors, and shoot laser beams at them, and obtain position data from light propagation delay timing devices. Short based radio such as LORAN could not compete.
Eventually, 5 TRANSIT satellites were on orbit, providing navigational data to the ground. Each was visible over the earth for up to 18 minutes. Generally there was a gap of time before another was visible, but that was ok. The fleet was supported, and nuclear war was averted for the time.
But even more remarkable, a new industry was about to be born. Point Positioning. That is, using a portable receiver to receive navigational signals from the TRANSITs and refine the position relative to current maps. It would be discovered that maps were up to 60 miles off in some locations of the world, that elevations were hundreds of feet off, and even more to the point, you could survey where you were very precisely.
There were only a few significant problems. Tracking equipment was literally a tractor trailer of equipment, weighing several tons, took a large crew to operate, and took a long time to complete gathering enough data to do the job. Up to a month would be required, a month to gather data, and process the data on huge and expensive computers. But the money was provided, and dozens of tracking systems were build, and flown all over the world to remote locations to re-map the world.
In the 1970s, several things happened. Chips for one. Computer chips made the possibility of truly portable tracking equipment that could process its own position data in more or less real time. The other was a need for real time, all the time navigation. The NRL developed the TIMATION satellite series of navigation research satellites. Flung into high earth orbit (11,000 miles), these things would be visible over the earth for hours. The theory went, if you had enough of these, you would have total coverage planet wide. If you had a few more, you could track more than one satellite at a time, and the receiver could resolve location errors through integration. All you had to do was build a receiver that could track a number of satellites at the same time, and process their data fast enough to give truly precise location data into the hands of a person anywhere on the globe.
Light bulbs went on in Washington. A Global Positioning System was being born. GPS was about to fly.
There were of course, just a few things to do first.
06/14/2008 Posted on 06/14/2008
Copyright © 2024 Steven Craig
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