The International Space Station (ISS) orbits the Earth at 250 miles above sea level in the part of space known as Low Earth Orbit (LEO). In order to maintain its orbit it travels around the planet at 17,500 MPH. How does it go that fast? Imagine if you’re standing on the ground and you throw a ball in the air. It follows a parabolic trajectory and Earth’s gravity pulls it down by 9.8M/s. However, if you stood on a high enough hill and threw the ball fast enough it would go into orbit. That’s what rockets do.

Launch vehicles like the Space Shuttle, which was the primary launch vehicle used to build ISS, use huge amounts of chemical energy to accelerate out of the atmosphere and deliver payloads into orbit. ISS is not totally free of Earth’s influence though because there is a small amount of atmospheric drag exerted on it, so it periodically needs to be “boosted” to a higher orbit. The energy for such a maneuver is typically provided by a visiting Russian Progress freighter’s engines. ISS and everyone on board are traveling at the same rate of speed, and the boost adds just a little bit more velocity and altitude. When the boost occurs the station accelerates but the astronauts do not. This video shows the effect in action, sped up 8x.