The International Space Station (ISS) maintains a continuous human presence in Low Earth Orbit. While it appears to glide silently across the night sky, this calm masks the blistering speed required to maintain its orbit. Understanding the velocity of the ISS reveals the delicate balance of physics that keeps the station flying approximately 250 miles above our planet.
The Exact Speed of the ISS
The International Space Station travels at approximately 17,500 miles per hour (28,000 kilometers per hour). This tremendous speed is a strict requirement of orbital mechanics at its altitude. A commercial jet airliner typically cruises at around 575 miles per hour, making the ISS over 30 times faster. If the station flew from New York to Los Angeles, it would cover that distance in less than 10 minutes. This constant, rapid movement makes the ISS the fastest human-made object in continuous orbit around Earth.
The Mechanics of Orbital Velocity
The ISS must travel at this specific velocity to achieve a continuous state of freefall, known as orbit. This balances the constant pull of Earth’s gravity with the station’s forward momentum. Isaac Newton’s laws describe this as an object thrown so hard horizontally that the curve of its fall perfectly matches the curve of the Earth.
If the station traveled slower, gravity would cause it to spiral inward and re-enter the atmosphere. If it were faster, it would escape Earth’s orbit entirely. The ISS orbits in Low Earth Orbit (LEO), typically at an altitude between 256 and 262 miles (413 to 422 kilometers).
The velocity required is determined by the station’s distance from the center of the Earth. Objects orbiting closer must travel faster to counteract stronger gravitational pull. At its current altitude, 17,500 miles per hour creates the centripetal force needed for a stable, slightly elliptical path. Minimal atmospheric drag causes slight orbital decay, necessitating periodic reboosts by visiting spacecraft to maintain the required speed and height.
Translating Speed into Earth Time
The orbital velocity of the ISS affects the passage of time experienced by the crew. The station completes one full revolution around the Earth in approximately 90 to 93 minutes. This means astronauts orbit the planet about 15.5 times every 24-hour Earth day.
This rapid cycle results in an altered day-night rhythm for the crew, who witness 15 or 16 sunrises and sunsets daily. During each 90-minute orbit, the station spends roughly 45 minutes in sunlight and 45 minutes passing through Earth’s shadow. This constant cycling requires the crew to adhere to a strict UTC-based time schedule and use specialized lighting to regulate their internal body clocks.