Why is the ISS at an altitude of 400 km?
The International Space Station is the most important space laboratory today. It must be kept at an altitude of 400 km. And, of course, such an attitude was chosen for a reason.
As we increase the orbit higher and higher, the distance needed for rockets to get to the station increases, so the cost per launch increases as well.
Placing the station in a lower orbit isn't an option -- the atmospheric drag increases causing tremendous maintenance costs.
Even at an altitude of 400 km, the ISS is dropping at a rate of 2 km per year, so to keep it in a stable orbit, translational burns are used.
In practice, everything is not so precise. Keeping the station in orbit is the constant work of hundreds of engineers and scientists on the ground. The ISS orbit may be dropped from 400 to 320 km. Sometimes the control may decide to raise the station to 427 km if any difficulty in maintaining orbit is expected.
Image Credits: NASA, ISS, Paolo Nespoli
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