The International Space Station circles Earth every 90 minutes, at roughly 28,000 km/h (5 miles per second) — so fast its crew sees 16 sunrises and 16 sunsets in a single day. NASA confirmed on October 2 that its Crew-12 team is heading home after finishing its science mission on board, which makes this a good moment to actually unpack that number instead of just repeating it.
Who just left, and what they were doing up there
Crew-12 launched to the station on February 13, 2026, carrying NASA astronauts Jessica Meir and Jack Hathaway, ESA astronaut Sophie Adenot, and Roscosmos cosmonaut Andrey Fedyaev. Over the following months they ran a packed science program, according to NASA's own mission update: growing protein crystals meant to improve cancer treatments (ADSEP-PIL-15), testing a metal 3D printer that works in microgravity, running ultra-cold atom experiments in the Cold Atom Lab, and growing bone and cartilage tissue samples for regenerative medicine research — work that depends entirely on the weightlessness only a continuous low orbit can provide.
The number that matters: 90 minutes, 16 times a day
Here's the part that's easy to say and hard to picture: while Crew-12 was running those experiments, they were never actually still. NASA's own station facts page puts it plainly — the ISS makes 16 full orbits of Earth every 24 hours, one every 90 minutes, at an altitude NASA lists at 370–460 km, tilted 51.6° from the equator so it passes over about 90% of the world's population. The station has kept this up, nonstop, since its first crew arrived on November 2, 2000 — close to 26 years of continuous human presence circling the planet without a single day off the clock.
Why Mercury, the fastest planet, still takes 88 days
Here's where the comparison gets interesting. Mercury is the fastest-moving planet in the Solar System — NASA's own fact sheet puts its speed at nearly 47 km/s, almost six times faster than the ISS. And yet Mercury takes 88 Earth days to complete one trip around the Sun, not 90 minutes.
The difference isn't speed. It's distance. The ISS is skimming Earth from only a few hundred kilometers up, so even a "modest" 28,000 km/h is enough to loop the whole planet in an hour and a half. Mercury is racing around the Sun from about 58 million kilometers out — a vastly longer track — so even its blistering speed stretches into nearly three months per lap. An orbit's length isn't just about how fast something moves; it's the relationship between that speed and how far it has to travel to get back where it started.
See the difference, not just read about it
That relationship — speed versus distance versus orbital period — is exactly what's hard to grasp from a number on a page and easy to see in motion. In Solar System Live, you can watch Mercury's tight, fast lap around the Sun next to Earth's much longer one, in real time, and get a feel for why "fast" doesn't automatically mean "quick lap." The ISS itself orbits too close and too low to show up on a Solar System scale, but the same physics that just carried Crew-12 home 16 times a day is what keeps every planet in the simulator moving on its own clock.
What to do next
Open the simulator, find Mercury, and watch one of its orbits play out next to Earth's — then picture Crew-12 completing that same lap distance in under two hours, over and over, for months, right above your head.