The International Space Station (ISS) orbits the Earth at an average speed of approximately 28,000 kilometers per hour (17,500 miles per hour). This high speed is necessary to counteract the Earth's gravitational pull and maintain a stable orbit around the planet.
Astronauts can walk and move inside the space station despite its high speed because they are in a state of freefall. The ISS and everything inside it, including the astronauts, are constantly falling towards the Earth under the influence of gravity. However, because of their high horizontal velocity, they keep missing the Earth and remain in orbit. This continuous freefall creates a microgravity environment inside the station, allowing astronauts to move around as if they were floating.
The relative velocity of the ISS does present challenges for docking spacecraft. When a spacecraft approaches the ISS for docking, it needs to match the station's velocity and position itself correctly. This requires careful planning, precise calculations, and the use of thrusters for maneuvering. Spacecraft, such as the Russian Soyuz or the SpaceX Dragon, have sophisticated guidance, navigation, and control systems to perform the necessary orbital maneuvers and approach the ISS safely.
To dock with the ISS, the incoming spacecraft needs to align its trajectory and speed with the station's orbit. Once the spacecraft is in close proximity to the ISS, robotic systems, such as the Canadarm2, may be used to capture and attach the incoming vehicle to a docking port on the station. The process requires coordination and precise control to ensure a successful and safe docking.
While the high speed of the ISS does add complexity to the docking process, it has been successfully accomplished numerous times by various spacecraft over the years. The crew on board the ISS and the teams on the ground work closely together to monitor and execute docking procedures, ensuring that the spacecraft aligns properly with the station's movement before establishing a secure connection.