Why Does the ISS Need Periodic Boosts while Satellites Do Not?

The International Space Station (ISS) is a unique satellite that operates at a significantly lower altitude compared to most other satellites. This difference in orbit requires periodic boosts for the ISS to maintain its operational altitude, a requirement that does not apply to many other satellites. Let's dive into the reasons behind this necessity.

1. Understanding the Issue

The reason why the ISS needs periodic boosts is straightforward: air resistance (or drag). Even though the ISS operates in the thinnest layers of Earth's atmosphere, its relatively low altitude of around 400 kilometers (248 miles) still poses a significant challenge. Imagine the solar panels on the ISS as large sails; they effectively catch the stray molecules in this thin atmosphere, causing the spacecraft to slow down over time and lose altitude.

2. The Role of Atmosphere

Atmospheric drag is crucial in understanding why the ISS needs regular boosts but other satellites often do not. Unlike the ISS, many satellites operate at much higher altitudes where the atmosphere is negligible, almost completely eliminating the drag effect. For instance, GPS satellites orbit at altitudes between 19,000 to 36,000 kilometers (12,000 to 22,000 miles), well above the significant atmospheric layers that affect lower orbits.

3. The Phenomenon of Orbital Decay

The constant gravitational pull from the Earth, combined with the atmospheric drag, causes the ISS to experience something called orbital decay. In simpler terms, the ISS gradually moves closer to Earth due to this drag, which necessitates periodic pushes to maintain its altitude. These boosts can be provided by visiting spacecraft (like the SpaceX Dragon or the Russian Progress resupply vehicles) or by the ISS's own thrusters.

4. The Purpose of Mission Duration

The ISS is designed as a long-term habitat for astronauts and hosts extensive scientific research. This means that it must maintain a stable orbit indefinitely to ensure the safety and operational readiness of the station. Therefore, regular boosts are essential for the ISS to stay at its optimal operational altitude.

In contrast, many satellites, particularly those designed for specific tasks with finite lifespans, are equipped with propulsion systems for station-keeping or maneuvering. However, these satellites generally do not require periodic boosts as frequently as the ISS does. They are built to operate efficiently over extended periods with fewer adjustments.

5. Design and Construction Differences

The operational design of the ISS makes it more susceptible to orbital decay than most satellites. This is primarily due to its size and complex structure, which include large solar panels and other external components. These designs add to the overall surface area, making the ISS more prone to atmospheric drag.

6. Conclusion

In summary, the International Space Station needs periodic boosts primarily due to atmospheric drag at its operational altitude. Many other satellites, operating at higher altitudes, do not face the same challenges and can maintain their orbits for longer durations without such frequent interventions. This differs significantly from the ISS, which is a complex structure operated at a lower altitude where atmospheric effects are more pronounced.