CÓMO ORBITA LA ISS LA TIERRA

The ISS orbit, in real numbers

The International Space Station doesn't "fly" in the traditional sense — it's in permanent free fall around Earth, moving so fast that it never actually reaches the ground. To understand its flight path you need four numbers: speed, altitude, orbital period, and inclination. They're all connected, and together they define the exact route you see traced on our real-time map and 3D globe.

Speed, altitude, and orbital period

The ISS orbits at roughly 27,600 km/h (17,150 mph), fast enough to complete one full lap of the planet every 90-93 minutes. That works out to about 16 complete orbits per day — the crew sees a sunrise and sunset roughly every ninety minutes, about 16 times per Earth day.

Its average altitude sits around 400 km (250 miles) above the surface, though that's not a fixed figure: it drifts naturally between roughly 400 and 420 km depending on how long it's been since the last orbital reboost (more on that below). At that altitude the station is still technically inside Earth's exosphere, with enough residual atmosphere to create a small but constant drag.

That specific combination of speed and altitude isn't arbitrary — it's exactly the velocity required for the curve of the ISS's fall to match the curve of the Earth beneath it. Any faster and it would drift to a higher orbit; any slower and it would sink into denser atmosphere and re-enter.

Why is the current position of the ISS orbit inclined 51.6 degrees?

The ISS doesn't orbit along the equator — its path is tilted 51.6° relative to it. That number isn't random. Much of the station's assembly and resupply has come from the Baikonur Cosmodrome in Kazakhstan, located at 45.9° north latitude. For safety reasons, rockets launched from there can't fly over other countries' territory during the early stages of ascent, which forces a launch azimuth that produces a minimum achievable orbital inclination of 51.6°.

That inclination has one very visible consequence: it defines the band of latitudes the station can ever fly over. The ISS regularly passes over everything between 51.6° north and 51.6° south — a strip that covers nearly the entire world population, but excludes the far north of Scandinavia, Alaska, or Antarctica.

Why does the flight path of the ISS look like a wave on the map?

If you've ever watched the 2D map on this site, you'll have noticed the ISS's flight path isn't a straight line or a simple curve — it looks like a sine wave, rising and falling between 51.6° north and south as it sweeps eastward.

That shape comes from two independent motions combining. The ISS's orbital plane stays nearly fixed relative to the stars while the station moves within it; meanwhile, Earth rotates underneath at its own pace (about 1,670 km/h at the equator). When that fixed orbital plane is projected onto a flat map of a rotating surface, each pass appears shifted westward relative to the one before. String several orbits together and the result is exactly that wave pattern — the ISS's "ground track."

The effect is even easier to see on our 3D globe, where you can watch the fixed orbital plane in space while the planet spins beneath it in real time.

What is an orbital reboost, and why is it needed?

Even at 400 km, the air isn't a perfect vacuum. That residual atmosphere creates a small but constant drag on the ISS's structure, acting like a gentle, continuous brake. As a result, the station gradually loses altitude — anywhere from a few hundred meters to about two kilometers per month, depending on solar activity (a more active Sun heats and expands the upper atmosphere, increasing the drag).

To counter that, ground teams periodically perform an orbital reboost: the engines of a docked spacecraft (a Russian Progress, a Cygnus, or the Zvezda module's own thrusters) fire for several minutes to push the station back up to its target altitude. These maneuvers also double as debris-avoidance moves when needed, which is why the ISS's exact altitude shifts slightly from one week to the next.

Frequently asked questions

Why doesn't the ISS fall out of the sky?

It technically does fall — it's in constant free fall. But its horizontal speed of 27,600 km/h is so high that the curve of its fall matches the curve of the Earth's surface beneath it, so it never actually gets closer to the ground. That, precisely, is what being in orbit means.

Why does the flight path on the map look like a wave?

Because the orbital plane stays fixed in space while Earth rotates underneath it. Each lap is projected slightly further west than the one before, and stringing several orbits together on a flat map produces that sine-wave shape.

Is the orbit always exactly the same?

No. Altitude drifts naturally due to residual atmospheric drag and is corrected periodically with orbital reboosts from docked spacecraft. The 51.6° inclination, on the other hand, stays essentially constant.

How fast is it compared to a plane?

At 27,600 km/h, the ISS flies more than 30 times faster than a commercial airliner cruising at around 900 km/h. At that speed it covers a full marathon's distance in under 5 seconds.