Image Courtesy: SpaceX

The International Space Station (ISS) loses roughly 100 meters of altitude every day as it battles the faint traces of Earth’s atmosphere. Without regular boosts, the orbiting laboratory would gradually spiral back to Earth, eventually burning up during reentry. Instead, a docked Russian spacecraft periodically fires its engines to push the station back into a higher orbit.

Although the ISS circles Earth at an average altitude of about 400 kilometers, space at that height is not completely empty. Sparse molecules of oxygen and nitrogen create a small but persistent atmospheric drag that steadily slows the station as it races around the planet at nearly 28,000 kilometers per hour. This drag causes the ISS to lose altitude every day, with the exact rate varying depending on solar activity.

During periods of high solar activity, ultraviolet radiation heats and expands Earth’s upper atmosphere, increasing its density at the station’s altitude. That thicker atmosphere creates more drag, forcing the ISS to perform orbital “reboosts” more frequently than during quieter phases of the Sun’s cycle.

The station has no engines of its own for this task. Instead, Russian Progress cargo spacecraft, docked to the Zvezda service module, fire their thrusters for several minutes to raise the ISS back into its operational orbit. These maneuvers are typically carried out about once a month, although the schedule also depends on planned spacecraft arrivals and debris avoidance operations.

NASA has demonstrated limited reboost capability using Northrop Grumman’s Cygnus cargo spacecraft, but Progress remains the primary vehicle responsible for maintaining the station’s altitude. This reliance also highlights the importance of the Russian-built Zvezda module, which provides the structural support needed to transfer engine thrust through the station.

Without these routine boosts, atmospheric drag would eventually accelerate the ISS’s descent. Once the station reached lower altitudes, the increasing drag would cause it to lose orbit much more rapidly before breaking apart during reentry.

NASA currently plans to retire the ISS in the early 2030s using a dedicated SpaceX-built U.S. Deorbit Vehicle. Rather than allowing the station to fall uncontrollably, the spacecraft will guide it into a controlled reentry over the remote South Pacific, ending more than three decades of continuous human presence aboard the orbiting laboratory.