The International Space Station, or ISS, orbits our planet once every 90 minutes at the lofty height of 400 kilometers (about 248 miles) above the surface of our planet. This altitude puts it pretty well above the vast majority of the atmosphere, but it doesn’t place it outside the reaches of the magnetic field which surrounds our Earth.
The magnetic field of our planet — otherwise known as the magnetosphere — extends out to about 65,000 kilometers (40,000 mi) above the surface of the planet. However, that “about” part is pretty critical — the magnetosphere isn’t a fixed boundary, which always remains at exactly 40,000 miles from the surface. This surface is a little more flexible, and if you’ve ever held two opposing magnet ends against each other, you’ve felt this exact flexibility. The resistance between two magnets isn’t a wall, where suddenly you can’t move them any closer to each other. The pressure there is a little more like pressing on a slightly under-inflated balloon.
In the case of the Earth’s magnetic field, the pressure on our magnetic field comes from the Sun. The Sun is constantly battering everything surrounding it with a solar wind, made up of charged particles. If you’re a planet without a protective magnetic field, this solar wind will slam into your atmosphere, and can destroy it over time. This is roughly what we believe happened to Mars’ atmosphere. The Earth has a very fortunate protective shield, but this constant pressure on the Sun’s side of our planet means that this magnetic protection is pressed back, closer to the planet. That 40,000 mile number I gave is this: the typical, Sun-compressed, Sun-facing side of our magnetosphere. The nighttime side of our planet, facing away from the Sun, has a long magnetic tail drifting out beyond it, extending several times farther out than the Sun-side.
If the Sun has a particularly strong outburst – a coronal mass ejection or any kind of solar flare — the pressure on our magnetic field gets much stronger, but nothing the Sun typically does will press the magnetic field down close enough to the Earth’s atmosphere so that the ISS would exit the magnetic field. Some of our highest orbiting satellites do exit the magnetic field of the Earth, as of course all craft going to other planets must also do. However, these satellites and spacecraft must be constructed to protect their inner workings from the charged particles in the solar wind. Satellites are effectively very elaborate electronics, and electronics do not like being exposed to charged particles. It shorts their circuits.
All this really means that the ISS is in a much safer region of space than it could be – not that it’s totally safe. Our magnetic field is not a perfect blocker of high energy particles, and so things like gamma rays, cosmic rays, and other damaging radiation can still appear in higher quantities than they would if the astronauts were still safely on the ground. Our atmosphere is pretty good at blocking a lot of these high energy particles, so on the ground you’d never get exposed to them. But the ISS is above the atmosphere, and doesn’t have this extra layer of shielding, so there are radiation monitors on the space station to keep track of how much of a radiation dose they’re getting. If a solar flare is on its way, the astronauts usually have a few days’ warning, and can take shelter in more strongly shielded section of the ISS if they need to. (Not all solar storm are aimed in their direction, and not all storms are strong enough to require this precaution.)
So yes, the ISS is firmly embedded in the Earth’s magnetosphere, making it — for a space based outpost — a relatively safe haven for our astronauts.
Sign up for the mailing list for updates & news straight to your inbox!