At the height of the ISS, Earth’s gravitational field is still very strong — around 90% of its value at the Earth’s surface. Gravity is constantly pulling the astronauts towards the centre of the Earth. So why don’t they fall straight down? The key idea is that the ISS is moving sideways at very high speed (about 7.7 km/s). As it falls towards Earth under gravity, the curved surface of the Earth falls away beneath it. The result is continuous free fall around the Earth, not down to it i.e. the answer is C.
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