What speed must the ISS maintain at its 400 km altitude to balance gravity?

Answer

Roughly 7.66 kilometers per second (about 17,150 miles per hour)

To balance its momentum against Earth's gravity and stay aloft at 400 km, the ISS must maintain speeds of roughly 7.66 kilometers per second.

What speed must the ISS maintain at its 400 km altitude to balance gravity?
SpaceorbitISSKármán line