Skip to Content
Uncategorized

Space Tracker

The earliest satellite watchers’ ideas led to GPS.
December 1, 2004

Over the past decade or so, the Global Positioning System has grown from a military navigation tool to a near ubiquitous tracking system. Biologists use it to follow migrating animals, while motorists depend on it to avoid getting lost on highways. But while the system’s wide availability has sparked an explosion in innovative applications, satellite navigation itself can be traced back to the first satellite in orbit: Sputnik.

On October 4, 1957, the Soviet Union launched its famous orbiter, beating the United States into space and shocking the world with its technological prowess. For 23 days, Sputnik circled the globe emitting a radio signal, a constant beep that could be heard by anyone tuned to its frequency.

A few days after Sputnik’s launch, physicists William Guier and George Weiffenbach at the Johns Hopkins Applied Physics Laboratory set up a receiver to listen for its signal. Because of the Doppler effect, the tone they heard varied slightly in frequency as the satellite passed overhead. The men realized they could use this shift to calculate Sputnik’s position relative to their receiver and soon were able to accurately predict Sputnik’s path.

A few months later, Guier and Weiffenbach were called before their boss, Frank McClure, who asked them to reverse the Sputnik tracking problem: use a known orbit and the same Doppler shift to calculate the position of a ground receiver. McClure envisioned a handful of satellites that continually broadcast their coordinates to submarines at sea, whose onboard computers would determine the vessels’ locations every few hours, whenever a satellite passed above. After Guier and Weiffenbach confirmed that the idea was feasible, McClure and another Hopkins scientist, Richard Kershner, outlined what would be known as the Transit Navigational System.

In 1960, the first Transit satellite entered orbit. In 1967, the government opened the system to civilian ships and surveyors, who soon constituted the majority of users. The Transit program was gradually replaced by GPS – a different tracking method that employs many more satellites and does not require any waiting time to pinpoint position. The Transit system was retired in 1996, after more than 30 years of successful service.

Keep Reading

Most Popular

Workers disinfect the street outside Shijiazhuang Railway Station
Workers disinfect the street outside Shijiazhuang Railway Station

Why China is still obsessed with disinfecting everything

Most public health bodies dealing with covid have long since moved on from the idea of surface transmission. China’s didn’t—and that helps it control the narrative about the disease’s origins and danger.

individual aging affects covid outcomes concept
individual aging affects covid outcomes concept

Anti-aging drugs are being tested as a way to treat covid

Drugs that rejuvenate our immune systems and make us biologically younger could help protect us from the disease’s worst effects.

Europe's AI Act concept
Europe's AI Act concept

A quick guide to the most important AI law you’ve never heard of

The European Union is planning new legislation aimed at curbing the worst harms associated with artificial intelligence.

Stay connected

Illustration by Rose WongIllustration by Rose Wong

Get the latest updates from
MIT Technology Review

Discover special offers, top stories, upcoming events, and more.

Thank you for submitting your email!

Explore more newsletters

It looks like something went wrong.

We’re having trouble saving your preferences. Try refreshing this page and updating them one more time. If you continue to get this message, reach out to us at customer-service@technologyreview.com with a list of newsletters you’d like to receive.