"We used nine hours of running time,” Herget boasted at the time, “and completed more computations than had ever before been done at one time in the history of astronomy." Shortly after the NORC machine had been installed at the Dahlgren location, an astronomer named Paul Herget used it to calculate the orbits of multiple planets, including the most precise measurement of Earth’s recent orbit ever recorded. But early experiments with the machine demonstrated that it could be used for space-related projects as well. The Navy’s primary interest in this “supercomputer” derived from its ability to do complex ballistic computations that could project the exact trajectory of missiles, factoring in numerous variables-wind, air pressure, temperature, and more. The Navy dubbed it NORC, short for Naval Ordnance Research Calculator. In the summer of 1955, IBM delivered to the Naval Proving Ground in Dahlgren, Virginia, a custom-built, room-sized, vacuum-tube-based machine that was, by many accounts, the most powerful computer the world had ever seen. When you are measuring microseconds to determine your exact location using GPS, those gravitational variations can make a massive difference-the difference between landing your plane on the runway and crashing it into the airport parking garage.īy this point, it was the mid-1950s, and a new employment position was beginning to appear in government agencies and military institutions around the country, a job that would go on to become one of the most highly-coveted careers in the 21st century: computer programmer. But Einstein proved that time was distorted by gravity-the technical term for it is “time dilation”-and Earth’s gravitational fields are wildly inconsistent, depending on where you happen to be on the planet.
In a world of Newtonian physics, this would all work perfectly. (A satellite farther away from you will have an earlier transmission time, a satellite closer to you will have a later transmission time.) Because the satellites have predictable orbits, a GPS receiver can determine its location if it can get an accurate reading of its distance from four satellites. (Each satellite contains a fantastically precise atomic clock.) Because radio waves take time to travel over long distances, a receiver on the ground can calculate its distance from each satellite by calculating the difference between the transmission time of the signal and its reception. When your phone picks up signals from GPS satellites, the information it’s receiving is a time-stamp marking of the exact moment each satellite sent out its signal. The ironic thing about GPS is that it is a technology designed to locate your position spatially that is enabled largely by an ultra-precise measurement of time. Impressed with the demo, the grad students’ supervisor suggested that the approach could be reversed: if you knew the exact location of at least three satellites in orbit above you, by triangulating their various signals you could theoretically determine your location on the ground-or, if you happened to be on one of the new Polaris nuclear submarines the military was building, you could use it to determine your location in the middle of the ocean. After the Soviets launched Sputnik, the first man-made satellite to orbit Earth, in October of 1957, a pair of graduate students at the Applied Physics Laboratory in Maryland devised an ingenious system for tracking Sputnik’s location by analyzing slight variations in the microwave signals the satellite was transmitting, in effect using an antenna’s known location on Earth to calculate the satellite’s unknown location in orbit. Like many of the core technologies that define the digital age, GPS was an offshoot of American Cold War competition with the Soviet Union and the threat of nuclear annihilation.
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