Today’s Factismal: The joint USA-Canada ISIS Satellite launched January 30, 1969.
Let’s suppose that you live in Oklahoma and want to talk to a friend who lives in Canada. In the days before the internet, you had four choices: You could travel to Canada to talk to your friend, but that would take weeks and cost a lot of money. You could send your friend a letter, but that would take weeks even if it was fairly inexpensive. You could call your friend on the phone, but that was very expensive even if it was fast. Or you could radio your friend, using the ionosphere to send the signals over the horizon to Canada. And, because it was cheap, fast, and tricky, that’s what geeks would do.
Using the ionosphere to skip signals over the horizon and around the globe has been popular since radio was born. And it was the experience of the early radio “hams” that helped scientists predict the existence of a layer of ionized gas in the atmosphere that they called the ionosphere (“sphere of ions” in science-ese). The gas acted like a mirror, reflecting radio signals over the horizon, just as a periscope reflects light around a corner. And thanks to the ionosphere, ham radio operators and others could send their signals more than 2,000 miles across the globe, instead of being limited to the sixty miles or so that direct line of sight provides. (This is also why you can sometimes receive an AM radio signal from very far away.)
But the ionosphere is more than just a plaything for radio enthusiasts. It is also part of the Earth’s magnetosphere; the magnetic field that protects life on Earth from the deadly ionizing rays of the Sun. Without the ionosphere, solar flares would scorch the Earth and coronal mass ejections would blast the surface with radiation. But thanks in part to the ionosphere, these events get turned into harmless auroral displays; bright bands of fire, dancing in the night sky. And the Sun pushes the ionosphere closer to the Earth on the day side and pulls it further away on the night side, affecting communications and ion distribution. Because it interacts with the Sun, the ionosphere is not a fixed layer with a constant geometry. Instead, it is a constantly-moving, ever-changing layer of churning electrons, protons, and ionized plasma.
There have been a number of satellites that have investigated the ionosphere, either by recording electrical activity from above or by dipping samplers into it. One of the most successful of these was the ISIS 1 satellite. A joint project of NASA and the Canadian Space Agency, ISIS 1 measured the density of electrons in the ionosphere and the relative contributions from the Sun and from cosmic rays. The success of this program led to more joint satellites and eventually to the development of the CANADARM, a remote waldo that is installed on the International Space Station.
If you’d like to experiment with the ionosphere yourself, then join NASA’s INSPIRE (Interactive NASA Space Physics Ionosphere Radio Experiments) Project: