The International Space Station Orbits Earth Every 90 Minutes

To keep the International Space Station from falling back to Earth, it must travel at an immense speed. This concept, known as orbital velocity, is a delicate balance between the station's forward momentum and the constant pull of Earth's gravity. At its altitude of roughly 408 kilometers, the station must fly at nearly 28,000 kilometers per hour. This speed is so great that as the station is pulled downward, the Earth's surface curves away from it at the same rate. In essence, the ISS is in a perpetual state of falling around our planet, never getting any closer to the ground.

This incredible velocity has a profound effect on the daily lives of the astronauts on board. Completing a full circuit of the globe every 90 minutes means the crew experiences a sunrise or a sunset approximately every 45 minutes. To manage this disorienting cycle, the station runs on Coordinated Universal Time (UTC), and astronauts follow a strict 24-hour schedule for work, meals, and sleep, often using window shutters to simulate a normal night. This rapid orbit provides them with a breathtaking and constantly changing perspective, allowing them to watch weather patterns form, witness the glow of cities at night, and see entire continents glide by in the time it takes to watch a TV show.