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GPS: How Satellites Revolutionized Our Mastery of Geography

A long time ago, to be a sailor or a pilot you needed an array of skills, and one of the most important skills was that of navigation. Pilots throughout both world wars were equipped with a compass and map and were quite skilled at using their speed and direction to find their way home. But in the cold war era of ballistic missiles, supersonic jets, and aircraft carriers, this rudimentary method simply wasn’t going to cut it. This brought about the Global Positioning System, or GPS. The GPS, originally intended for military use, has now become an everyday essential, used for things like Google Maps tracking an Amazon Package, and much more. Join us today as we explore the history, development, and the surprising variety of ways GPS is used around the world today.

History

In 1957, the Soviet Union stunned the world by placing the first satellite in space. This satellite, Sputnik 1, was monitored by scientists all over the globe. Most notably, two physicists from the Applied Physics lab at John Hopkin’s University were listening in to its radio signals. These men quickly realized that by analyzing the wavelength of transmissions received, they could use the Doppler Effect to locate the position of the satellite. The Doppler Effect, which has been known since the 19th century, essentially describes the change in wavelength relative to an observer moving towards or away from the source.

Basically, as a source moves toward the observer, waves will appear slightly blue-shifted, or shorter in wavelength. As the source moves away from an observer, the light waves are perceived as slightly red- shifted, or longer in wavelength. It’s the reason the sound a freight train makes changes as it speeds towards you, past you, and then away from you, you are experiencing the Doppler Effect with sound waves.

So, by using the observed changes in transmission wavelength from Sputnik 1, and with a little help from a computer that was the size of a room, the scientists were able to track Sputnik 1 throughout its orbit around the earth, with an error margin of a few hundred meters. With this accomplished, around a year later the physicists successfully reversed the process and were able to roughly calculate their own position based off of where the satellite was in its orbit, and satellite navigation was born.

The US Military wasted no time funding this new development. The Navy had recently developed a submarine class designed to fire ballistic missiles, and accurate satellite navigation was crucial for this. In 1960, the Transit system was tested. Transit was a group of 10 satellites – 5 active satellites and 5 more ready as back up, each travelling at 17,000 miles per hour, or 27,000 kilometers per hour. It was overall a huge success, and remained functinal for nearly 40 years. It was even the system used in the late 80s to determine a more correct height of Mt. Everest, the world’s tallest mountain.

These satellites were also used to verify Einstein’s general theory of relativity, part of which states that objects in different gravitational fields will experience time at different rates. The prediction was that clocks nearer to the earth would run about 7 microseconds faster than clocks in orbit, and this time dilation was observed when highly accurate atomic clocks were first placed on the satellites. This difference, without correction, would lead to the navigational reading being incorrect at a growing rate

of 10 kilometers, or 6 miles, every day, quickly rendering it too inaccurate to be useful. Fortunately, this small difference was expected and likewise accounted for.

But as great as the Transit system was, it had its faults. Firstly, users were only able to calculate their location once every hour or so. The earth blocks the radio signals sent from the satellites, and so with only 5 in orbit, you often had to wait for one to pass into range. This was far too slow for the Air Force to utilize. Another issue was the lack of computerization at the time. Transit was mainly designed to track nuclear submarines, but at the time there wasn’t a computer small enough to fit through the submarine hatch, so a new one had to be invented. It also could only give location estimates with an error margin of around 100 meters, and well, you want all the accuracy you can get when launching nuclear warheads. Also of concern to the American military was the plans for a Soviet navigational system, later known as GLONASS.

GLONAS illustration
GLONASS illustration

With this in mind, in 1973 military officials at the Pentagon discussed an improved version of Transit, called Navstar-GPS, later known simply as GPS. 10 Navstar satellites were put in orbit by the year 1985, (though one of them had to be rebuilt after an explosion during lift-off). These GPS satellites were a massive improvement from the Transit satellites before them – For example, with 10 active in orbit, you could now receive transmissions far more often, and newer receivers had been designed to correct for several factors that had plagued Transit, including gravity fluctuations and atmospheric interference.

These satellites were crucial for the military, but up until the 80s, civilian access to them was still restricted. That all changed in 1983, when Korean Airlines flight 007, carrying nearly 300 passengers, accidentally drifted into restricted Soviet airspace due to a navigational error, and was immediately shot down. This prompted US President Ronald Regan to announce public access to GPS satellites for public safety, industry, and navigation. By 1989, nine more satellites had been added to the orbital system, giving nearly constant access to anyone with a GPS receiver from nearly anywhere on the globe.

Following the announcement, businesses quickly found many uses for GPS, but they were still limited to an intentionally weakened signal, as the strong wavelength was reserved strictly for the military. This was known as selective availability. At this time the GPS headquarters that monitored the satellites was moved to Colorado Springs, Colorado, and was overseen by the Air force space command.

Throughout the 90s, GPS was steadily improved, with more satellites being launched nearly every year, reaching its full operational status in 1995 with 24 active satellites. Soon after, in the year 2000, President Bill Clinton approved the removal of selective availability, meaning that the full strength of GPS was now available to the public. With no more restrictions on the signal strength and speed of their receivers, and with the exponential growth of computer speed, GPS technology worked its way into virtually every industry.

Uses

Throughout its operational history, GPS has been used for hundreds of purposes.

Intercontinental Ballistic Missiles, or ICBMs, could now fly across the entire planet and hit a target only a few meters wide. Submarines no longer relied on maps, compasses, and a stopwatch to navigate the depths of the oceans, and airplanes could now be accurately tracked throughout their flight anywhere on earth. These and other military applications were first seen in combat during the Gulf War, proving

Test launch of an LGM-25C Titan II ICBM from an underground silo at Vandenberg AFB, United States, 1975
Test launch of an LGM-25C Titan II ICBM from an underground silo at Vandenberg AFB, United States, 1975

what an advantage satellite navigation could be. Indeed, this is why it was first funded by Congress, who at this point had invested over 5 billion dollars, or almost 10 billion in today’s money.

But throughout the 90s and early 2000s, people in various fields started to find other uses for GPS. The most widely used form is navigation, though an app like Google or Apple maps. A receiver in your phone is pinpointed by three or four satellites overhead, giving a location with an accuracy of a couple meters. In some places, industrial receivers compatible with a stronger signal can actually have an accuracy below 2 centimeters, or just under an inch.

These navigation tools are not only useful for finding KFC when traveling though, they are also essential for agriculture. Autonomous farming machines use GPS to operate in precisely the right places in vast fields, and the GPS timestamps help farmers know exactly when to return to a certain area. They also allow suppliers to track shipping containers and delivery routes to maximize efficiency and monitor for safety. Banks also use GPS to track ATM transactions and ensure the safety of cash transfers.

Loggers even use GPS to know where they should be cutting down trees, and to know where the edge of private property is. In a similar fashion, property disputes can and have been resolved when officials accurately map each owner’s land with satellite-based coordinates.

With the help of satellite tracking tags, marine biologists can use GPS to follow migration patterns and monitor the population of dolphins, whales, and other animals. Over 50 large sharks have been tagged by the organization OCEARCH, and if they get too close to shore an alert is sent to nearby lifeguards, who can safely get the swimmers back onto the beach. These tags also revealed some new behavior, like sharks moving into warmer waters in the Gulf of Mexico that were previously thought to be shark-free. You can even go to the OCEARCH website and see for yourself, and watch as the tiger sharks, great whites, and a shortfin mako shark named Buc-ee are tracked in real time.

Scientists are also working on using GPS to measure earthquakes. For example, after the 2011 earthquake that ravaged Japan, a size 9.1 on the Richter Scale, scientists were able to see that parts of the seafloor had moved as much as 200 feet, or about 60 meters! But hopefully in the future, GPS will help geologists warn the public ahead of time – when a fault line in the earth shifts or the ground has a slight shake, even if it’s imperceptible to humans, GPS can detect a change in the distance between two receivers, even a change as small as a half an inch, or about a centimeter. This could potentially indicate imminent geologic activity, such as an earthquake or a volcanic eruption. But this technology is still being developed – currently, within about 10 seconds of an earthquake starting, scientists can use GPS to determine what strength it will reach.

Other applications for studying the earth include measuring water levels in lakes and rivers, monitoring snow levels using signals that are reflected off of snow and ice, and detecting particle and chemical changes in the atmosphere. These changes, strangely enough, can even be a result of a tsunami, allowing it to be tracked as it moves across the ocean.

Future

At the moment, the United States has 31 GPS satellites in orbit, with 24 of them active most of the time. This group, also known as a constellation,is not the only accessible system orbiting earth.

Other constellations currently in use include the Russian GLONASS, the Chinese BeiDou, and the European Space Agency’s Galileo. While the GPS does have full global coverage, other countries are

incentivized to launch their own systems in case there is ever a conflict with the United States, like in the case of the Indian Military in 1999, who were denied GPS access by the US government while fighting Pakistan in the Kargil War.

To remain competitive with other constellations, improvements planned for GPS in the near future include upgrading the full constellation to send L5 transmissions, which are more powerful and are used for fast measurements in the Air force. Currently 16 satellites have this capability, and the US plans to have that number to 24 by the year 2027.

As well as new military signals, newer satellites are also being designed with L1C frequencies. This frequency was designed with intended compatibility with the Galileo and BeiDou constellations, and will hopefully become an international standard, which would not only improve navigational accuracy worldwide, but also encourage cooperation between nations such as the US, Russia, and China.

With these improvements planned, and likely others down the line, it’ll be interesting to see what new uses we find for this life-changing technology.

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