What is the International Space Station?

The International Space Station is the largest structure humans have ever put in orbit. It is about the size of a football pitch, weighs around four hundred and twenty tonnes, and circles the Earth roughly four hundred kilometres above your head. It has been continuously inhabited since November 2000 — meaning there has been at least one person living off the planet, without a single day’s break, for over two decades.

A laboratory, not a spaceship

It helps to think of the Station as a laboratory rather than a vehicle. It does not go anywhere in the way a rocket does; it falls around the Earth in a fixed orbit, again and again, ninety-two minutes per lap. Inside that falling laboratory, crews run experiments that only work in the near-total weightlessness of free fall — growing protein crystals, studying how the human body wastes away without gravity, testing materials and life-support systems for journeys further out.

The science is the point. Almost everything aboard exists to keep a small team of people alive and working in a place that is fundamentally trying to kill them.

Who built it

The Station is a partnership between five space agencies: NASA (United States), Roscosmos (Russia), ESA (Europe), JAXA (Japan) and CSA (Canada). Construction began in 1998 and continued, module by module, for more than a decade — each piece launched separately and bolted on in orbit. No single country could have built it alone, and that was rather the point of the name.

Who is up there now

The Station is run in numbered Expeditions, each lasting around six months, with crews of usually seven. They arrive aboard SpaceX Dragon or Russian Soyuz capsules, overlap with the outgoing crew for a handover, and then take over. You can see who is on board right now, which agencies they fly for, and what each of them does.

A typical day mixes scientific work with the unglamorous business of keeping house — exercise to fight muscle and bone loss, maintenance, repairs, and the constant management of air, water and power.

How fast and how high

A few numbers worth holding on to:

• Altitude: roughly four hundred kilometres, kept up by occasional engine boosts as the thin upper atmosphere slowly drags it down.
• Speed: about twenty-eight thousand kilometres an hour — fast enough to cross a continent in minutes.
• Orbit: ninety-two minutes per lap, which works out to sixteen sunrises and sixteen sunsets every single day.
• Inclination: tilted 51.6 degrees to the equator, which is why it passes over most of the world’s population and why you can see it from so many places.

Watching it for yourself

All of this is happening overhead right now. The same Station that hosts the experiments is the steady bright dot you can watch cross the evening sky — see our guide on how to spot it with the naked eye, or jump straight to the live tracker and cameras to see where it is this minute.