Complex sentence: The Earth's gravity is only slightly weaker at the altitude of the ISS than at the surface, but objects in orbit are in a continuous state of freefall, resulting in an apparent state of weightlessness.
Split into simpler sentences: The Earth's gravity is only slightly weaker at the altitude of the ISS than at the surface. However, objects in orbit are in a continuous state of freefall, resulting in an apparent state of weightlessness.