Episode Details

Daniel uses GPS every day. He has never paid for it. And he just realized that someone must be paying for all those satellites.

Someone is. The US government spends around two million dollars a day maintaining the GPS system. And you use it for free. Every time you ask your phone for directions, check your location, or track a delivery -- you are using a network of about thirty satellites orbiting twenty thousand kilometers above Earth, owned and operated by the US military, and broadcasting continuously without ever charging you a cent.

Here is how it actually works.

Each GPS satellite broadcasts two pieces of information -- who it is, and exactly what time it is. Your phone picks up signals from several satellites at once. Because each signal takes a slightly different amount of time to reach your phone depending on distance, your phone can calculate exactly where it must be for all those timing differences to make sense. It is geometry, solved in real time. And your phone never sends anything back to the satellites. It only receives. Which is why GPS works even when you have no cell service. As Daniel puts it -- it is basically a radio station. Except it is about thirty satellites and it tells you where you are.

GPS was developed in the 1970s for military use -- guiding missiles, navigating ships and troops. Civilians were not originally part of the plan. Then in 1983, a Korean Air passenger plane strayed off course and was shot down over Soviet airspace. All 269 people on board were killed. That tragedy helped convince the US government that civilians should eventually have access to GPS too. President Reagan announced it would be made available for peaceful civilian use once the system was fully operational.

But there was a catch.

For years, the military deliberately made the civilian version less accurate. They inserted tiny errors into the satellite timing signals -- a system called Selective Availability -- so civilian GPS was accurate to only about a hundred meters. Military GPS was far more precise. The idea was to give civilians navigation help without giving potential adversaries the same accuracy as US weapons.

Then in 2000, President Clinton turned it off. He flipped a switch. Overnight, civilian GPS went from roughly a hundred meters of accuracy to about twenty meters. Every GPS device in the world became dramatically more accurate without anyone buying anything new.

Two decisions, decades apart, that together gave the whole world free and increasingly precise navigation.

Daniel's closing line -- about writing a thank-you card -- is the last exchange worth staying for.

What you will find in this episode:

• How GPS actually works -- and why your phone never sends anything back to the satellites
• Why the US military built it and why civilians were eventually included
• The 1983 tragedy that helped change US policy on civilian GPS access
• What Selective Availability was -- and why GPS was deliberately less accurate for years
• How one decision in 2000 made every GPS device in the world ten times more accurate overnight
• Daniel's thank-you card idea

Short, surprising, and the kind of episode that makes every navigation app feel like a small miracle.

Listen, wonder, and learn.

Find us @smilewithDaniel everywhere.