You often see in movies that the spacecraft look weightless while orbiting the earth. It looks like there is no gravitational force of earth in the space and anyone can float in the space. The real fact is that there is also a very strong gravitational force of earth in the space. Now the question arises how spacecraft's remaining floating and orbiting the earth. Let’s find one by one.
To understand the weightlessness we can take the example of coming down by a lift. You feel weightlessness in the lift when coming downward. In reality, you never lose a single gram of weight. What happens in the lift? Does lift has the absence of gravity?
The real science behind this is the lack of opposite contact force. A contact force is generating from the contact of two objects. For example, the fiction of foot with earth is a contact force. When we jump the contact force of foot and earth upwards against the downward gravitational force and we feel the weight of our body. In the lift, we cannot feel our body weight because the contact force is an act in the same direction as the gravitational force of earth is working.
The same case happens to the spacecraft. They don’t have any other external force other than the gravitational force so look weightless. Weightlessness is a sensation not reality.
Let’s find out how these orbiting earth if gravitational force is also there acting on the center of mass of spacecraft. How these maintain a constant circular orbiting path continuously to orbit the earth? Because of the presence of their immense orbital velocity. What is orbital velocity? Orbital velocity is a speed where the gravitation force of an object creates a circular path. For earth, the speed of it is more than 28160 km/ hours where the gravity creates an orbital path.
So the lack of contact force against the action-at-a-distance (gravity) is the reason for the weightlessness of the spacecraft orbiting the earth.