So Wikipedia says that the orbit period at 2000km (upper limit of LEO) is about 127 minutes, but when I calculate...

$$T=\sqrt{\frac{4 \pi^2r^3}{\mu}}=\sqrt{\frac{4 \pi^2(2000 \text{ km})^3}{398600 \text{ km}^3/\text{s}^2}}=890 \text{ s}$$

I get 14.8 minutes. Can someone tell me what I'm doing wrong?

  • 1
    $\begingroup$ Here's the notation we use. $\endgroup$
    – HDE 226868
    Apr 9, 2015 at 1:12
  • $\begingroup$ You got the answer, now here's a shortcut. Just replace the 2000 km with any altitude above Earth to get its orbital period. If you want in minutes, just add in minutes to the end of the formula. Or any other time unit you want that Google recognizes. ;) $\endgroup$
    – TildalWave
    Apr 9, 2015 at 10:44

1 Answer 1


You're using the orbit's altitude as the orbital radius. Add the radius of Earth to the orbit altitude to get the actual radius.

Note that an Earth orbit at 2000km radius would be subject to significant lithospheric drag.

  • 3
    $\begingroup$ lithospheric drag ... lol! $\endgroup$
    – user8406
    Apr 10, 2015 at 2:17
  • $\begingroup$ quite a sleeper here! maybe we need a Wiki to start curating these. $\endgroup$
    – uhoh
    Apr 24, 2017 at 2:14

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