Question

Why are satellites placed into orbit at least 150 km above Earth’s surface?

to avoid air resistance
to match Earth’s curvature
to create inertia
to increase friction

Answer 1

to avoid air resistance

Explanation: below ~100–150 km the atmosphere is still dense enough to produce significant aerodynamic drag. That drag would slow the spacecraft, lower its orbit, and cause rapid re‑entry. Placing satellites ≳150 km keeps them in a region with negligible air resistance so they can remain in orbit.