An astronaut inside an orbiting satellite experiences apparent weightlessness. Which one of the following best explains this observation?
(a) The gravitational field of Earth at the satellite’s location is practically zero.
(b) The astronaut’s mass becomes zero in the micro-gravity environment of space.
(c) The astronaut and the satellite are both in free fall, accelerating equally under gravity.
(d) A centrifugal force in the rotating reference frame exactly cancels Earth’s gravity at the satellite’s orbit.