Quick questions on Orbital motion and satellites explained: HSC Physics Module 5

Low Earth Orbit (LEO). Altitude 200 to 2000 km. Periods 90 to 130 minutes. Used by the ISS, Earth-observation satellites, and Starlink. High orbital speed (about 7 to 8 km/s).

In low orbits (below about $400$ km), residual atmosphere creates drag, slowly reducing orbital energy. Satellites must boost periodically (the ISS does this every few months) or eventually re-enter.

Because $v = \sqrt{GM} \times (1/\sqrt{r})$, plotting orbital speed $v$ against $1/\sqrt{r}$ for several satellites (of any mass, since $m$ cancels) gives a straight line through the origin, with gradient $\sqrt{GM}$. This is a common way exam graphs test whether you can linearise a square-root relationship rather than just substitute into $v = \sqrt{GM/r}$ directly.

Altitude 200 to 2000 km. Periods 90 to 130 minutes. Used by the ISS, Earth-observation satellites, and Starlink. High orbital speed (about 7 to 8 km/s).

Altitude about 35 800 km (radius $4.22 \times 10^7$ m). Period exactly one sidereal day (about 23 h 56 min). The satellite sits over a fixed equatorial point.

Altitude 2 000 to 35 800 km. Used by GPS satellites (about 20 200 km altitude, 12-hour period).