Final answer:
Astronauts appear weightless in space due to a continuous state of free-fall, where they are falling toward Earth but the planet's curvature falls away at the same rate, creating an illusion of zero gravity inside the spacecraft.
Step-by-step explanation:
Astronauts appear weightless in space despite being within Earth's gravitational field because they are in a state of continuous free-fall towards Earth. The gravitational force is not absent; in fact, astronauts still experience about 88% of Earth's gravitational pull. However, because the space station and everything in it, including the astronauts, are falling at the same acceleration due to gravity, all objects appear to float relative to each other, creating the illusion of zero gravity. This phenomenon is similar to the experience of free-fall when an elevator cable breaks or during parabolic flight maneuvers in aircraft designed for astronaut training.
To simulate this condition on Earth, astronauts train in aircraft that dive at the acceleration due to gravity, mimicking the weightlessness they will experience in orbit. While in orbit, the astronauts' spacecraft travels at a high velocity parallel to the surface of Earth, ensuring that as they fall towards the planet, Earth's curvature continues to 'fall away' from them, effectively keeping them in orbit.