The International Space Station (ISS) orbits the Earth at an altitude of around 410 km. The ISS
does not fall towards the Earth, and the astronauts & objects are floating weightlessly. On Earth’s
surface, objects fall with a gravitational acceleration of approximately 9.81 m/s2
.
(a) Show that the following equation gives the percentage P of how much the grav. acceleration
decreases between Earth’s surface (R: Earth’s radius, 6371 km) and an object at altitude z:
P(z) = 1 −

1
1 + z
R
2
(b) What is P(z) for the altitude of the ISS, and why are objects weightless nevertheless?
(c) At what distance does the grav. acceleration become only 1% of that on Earth’s surface