I have an app that shows live feeds, positioning, and other current information about the ISS (International Space Station). I noticed that its speed seems to vary. How can that be? Doesn’t the speed need to be constant for it to stay in orbit?
In: Physics
If the speed is being reported relative to the earth’s spinning surface, then it will vary even if the ISS is traveling at constant speed relative to the earth’s center. The ISS’s orbit is angled about 50 degrees from the equator, so when it is directly over the equator, the earth will be spinning faster than when it is over the higher latitudes. The north-south component of its orbit will also be fastest over the equator.
In addition, objects only maintain a constant speed in a perfectly circular orbit. The ISS’s orbit is nearly circular but does vary by 2 km (408 vs. 410 km) over the course of each orbit.
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