The International Space Station (ISS) is a continuously inhabited artificial satellite dedicated to scientific research and international collaboration. Circling Earth hundreds of kilometers above, it serves as a unique platform where astronauts conduct experiments and observe our planet. A common point of fascination is the incredible speed at which the ISS travels to maintain its position in orbit.
The Orbital Balancing Act
Maintaining an object in Earth’s orbit is a delicate interplay between Earth’s gravity and its forward motion. Gravity constantly pulls the ISS towards the surface, similar to how an apple falls from a tree. However, instead of falling directly down, the ISS moves sideways at such a high velocity that it continuously “falls around” the Earth. This phenomenon, known as orbital mechanics, requires a precise balance.
If the ISS moves too slowly, Earth’s gravity pulls it into the atmosphere; too fast, and it escapes Earth’s gravitational embrace. The specific altitude of the ISS dictates the exact speed required to achieve this equilibrium, ensuring it remains safely in its designated path around the planet.
The ISS’s Incredible Speed
The International Space Station travels at approximately 17,500 miles per hour (28,000 kilometers per hour). This velocity allows the station to complete one full orbit of Earth in roughly 90 to 93 minutes. For perspective, the ISS could traverse the distance from Atlanta to London in just 14 minutes.
This rapid orbital pace means the ISS experiences multiple cycles of daylight and darkness. Astronauts witness approximately 16 sunrises and 16 sunsets every 24 hours, with a sunrise or sunset occurring roughly every 45 minutes. This constant transition is a direct consequence of the station’s high orbital velocity.
Staying in Orbit
Even at its altitude of around 400 kilometers (250 miles) in low Earth orbit, the ISS experiences atmospheric drag. While the atmosphere at this height is extremely thin, it still contains enough trace gas molecules to create a small amount of drag on the station. This atmospheric drag causes its orbit to gradually decay, meaning it slowly loses altitude, about 100 meters (328 feet) daily.
To counteract this orbital decay and maintain altitude, the ISS undergoes periodic “reboosts.” These maneuvers involve firing the station’s thrusters or those of visiting spacecraft, primarily Russian Progress cargo vehicles. European Automated Transfer Vehicles (ATVs) have also provided reboost capabilities. These controlled burns increase the station’s velocity, pushing it back to a higher orbit. SpaceX’s Cargo Dragon spacecraft has also begun to offer reboost capabilities.
Life at Orbital Velocity
Despite the speed at which the International Space Station travels, astronauts do not feel any sensation of motion. This experience can be counterintuitive, as on Earth, such speeds would generate immense forces and discomfort. The reason for this lack of sensation is that the astronauts, along with everything inside the ISS, are in a continuous state of freefall around Earth.
This constant freefall creates the sensation of weightlessness, or microgravity, inside the station. There are no jolts, no feeling of acceleration, and no “wind” as the station moves through the vacuum of space. Astronauts perceive no relative movement or sensation of speed, similar to how a person would feel if they were inside a falling elevator (without the impact).