Question

How does the ISS stay in orbit?

Explain using relevant physics concepts why the ISS astronauts practice underwater for their task of assembling the ISS in a low Earth orbit (LEO)? How similar do you think is moving under water to moving in the ISS? What are some important differences?

Answer 1

International space station (ISS) experiences two forces while in the orbit

1. Gravitational pull from the earth. The direction of this force is towards the earth
2. The centrifugal force which is experienced by an object when it is in a circular motion. This force is away from the center of the rotation.

ISS is continuously rotating around the earth. It is in such a orbit that the gravitational force is equal to the centrifugal force. It does not fall to the earth because of its motion.

The gravitational force decreases if the object is away from the earth. In the orbit of ISS, the acceleration due to gravity is almost zero. To experience the zero gravity, moving under water is an easy alternative. Under water, one of the force is gravitational force and the upward force is provided by the buoyancy of water. Effectively, the object will fell and effective zero gravity.

Under water, the pressure will be very high. However at ISS, the pressure will be very low because of the low density of air.