## 159. Math Puzzle $8 / 78$

A spacecraft is flying in a circular orbit over the equator around the Earth. For a complete Earth orbit, it must travel a distance of $42600 \mathrm{~km}$.

How high above the Earth's surface is the spacecraft flying?

Hint: Necessary information about the Earth can be found in the data tables.
The spacecraft flies $405 \mathrm{~km}$ above the Earth's surface. The radius of the circular orbit could be determined according to the formula $u=2 \pi r$ or rearranged

$$
r=\frac{u}{2 \pi}=\frac{42600 \mathrm{~km}}{2 \pi}=6783 \mathrm{~km}
$$

From this, only the radius of the Earth at the equator (6378km) had to be subtracted.