The ISS orbits the earth at an altitude of 400 km which puts it in the low earth orbit category (160km-2000km). This is pretty high but it still experiences about 89% of the gravity you feel on earth, astronauts and the orbiting objects are actually in a constant free fall at this altitude. This means that in order to stay in orbit it has to have a very fast orbital speed approximately 27,600 km/h or about 7.7km/s. How fast is that? The ISS orbits the earth about 16 times a day or once every 92 minutes. You can track the ISS and possibly see it if you are lucky enough to be below its orbital path from SPOT THE ISS. The ISS also has an amazing view of the earth from this altitude, in fact as you view this video from the ISS perspective you can see approximately 2300 km to the horizon. That means you can see New York while over Dallas or Saint Petersburg from London. Think about that the next time you are in plane or better yet calculate yourself how far you can see with the equation below.

FORMULAS:

**Distance to horizon = √(H² + 2RH)**

H = height (convert to km)

R = Radius of earth (approximately 6400 km)

Gravity @ various altitudes:

**g1/g2 = (r2/r1)² **

reduced to **g1 ÷ (r2/r1)²= g2** (gravity @ altitude in m/s²)

g1 = 9.8 m/s² (Constant earth surface gravity)

g2 = gravity @ altitude in m/s²

r1 = 6400km (Radius of earth )

r2 = r1+ altitude

To calculate the percentage difference in gravity simply divide (g2/9.8)