The International Space Station (ISS) serves as an orbiting laboratory hundreds of kilometers above Earth. Its presence in space often sparks curiosity, particularly regarding the incredible speed at which it travels. The station continuously orbits our planet, performing scientific research.
The Speed of the International Space Station
The International Space Station maintains an average altitude of approximately 400 kilometers (250 miles) above Earth’s surface. At this height, it travels at about 28,000 kilometers per hour (17,500 miles per hour). To put this velocity into perspective, the ISS moves at roughly 8 kilometers (5 miles) per second. This speed is significantly faster than a jet plane and allows the station to traverse the entire United States in just a few minutes.
The ISS completes one full orbit around Earth in approximately 90 to 93 minutes. Astronauts aboard the station witness about 15.5 to 16 sunrises and sunsets every 24 hours. The station covers a vast distance daily, equivalent to traveling to the Moon and back.
Why the ISS Travels at This Speed
The speed of the International Space Station is a direct consequence of orbital mechanics. The ISS orbits due to a balance between Earth’s gravitational pull and the station’s forward momentum. Earth’s gravity constantly pulls the station towards the planet’s center, similar to how it pulls objects on the surface. However, the station’s high horizontal speed causes it to continuously “miss” the Earth as it falls.
This phenomenon is often described as being in a continuous state of “freefall” around the Earth. While gravity at the ISS’s altitude is slightly weaker than on Earth’s surface, it is still present. The station’s velocity ensures its curved path due to gravity matches the curvature of the Earth, preventing it from either falling back into the atmosphere or escaping Earth’s orbit.
How the ISS Maintains Its Speed
Despite orbiting in the vacuum of space, the International Space Station is not entirely free from external forces. It experiences a small amount of atmospheric drag from residual air molecules present even at its high altitude. This drag causes the station to gradually lose speed and, consequently, its altitude. On average, the ISS can lose about 100 meters (330 feet) of altitude per day due to this drag.
To counteract this orbital decay and maintain its altitude, the ISS undergoes periodic maneuvers called “reboosts.” During a reboost, thrusters are fired, typically from docked spacecraft. The station’s own thrusters can also perform these boosts. Reboosts occur about once a month, though the exact frequency can vary depending on solar activity, which influences the density of the upper atmosphere and the amount of drag experienced.