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When you think of satellites, you probably think of those big finned boxes bouncing cellular signals out in orbit. They’re certainly not the kind of thing you would consider a “vehicle,” but it is a fact that all satellites in orbit are actively moving around the Earth. Just because satellites aren’t built for someone to sit in and steer, that doesn’t mean they’re just floating stationary in space.

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In fact, satellites of all kinds, both autonomous relays and manned constructs like the International Space Station, are moving remarkably fast, far faster than anything you’d find here on the surface of the Earth. This isn’t because satellites are equipped with powerful thrusters like those found on rocket ships, though the mighty power of those rockets do have a lot to do with how quickly satellites travel through the darkness. Satellites can travel upwards of 17,500 miles per hour, but the actual speed depends heavily on the speed of the craft that brought it into space, as well as how close it is to the Earth’s surface.

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The important thing to remember is that satellites aren’t rockets; they don’t have thrusters, or if they do, they’re not nearly as powerful as the ones you’d see on a rocket. Rather, it’s those very rockets that determine a good bulk of a satellite’s travel speed. To actually get a satellite into orbit, it needs to be mounted onto a rocket, and they are shot into orbit at speeds of around 17,800 miles per hour. Once the rocket reaches orbit, it spits the satellite out, which carries the momentum of the initial launch along with it, give or take a few hundred miles per hour.

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A big factor that determines how much of that inertia the satellite maintains is which of the three primary orbital altitudes it’s launched to. For example, if it’s still relatively close to the Earth’s surface, around 200 to 1,200 miles above the surface, that’s known as a low-Earth orbit. It’ll travel around the same speed as the initial launch, approximately 17,500 miles per hour. According to the Japan Aerospace Exploration Agency, that’s about 90 times the average speed of a bullet train.

However, if a satellite is in geosynchronous orbit, it’s substantially further from Earth, about 22,000 miles above the surface. Satellites launched into this kind of orbit may have additional thrusters onboard, which are fired to subtly shift their arc. This is all with the intent of matching the speed of the Earth’s rotation, roughly 7,000 miles per hour. A slight variation of this is the geostationary orbit, where the satellite is parked directly over Earth’s equator.

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Different satellites and constructs will orbit the Earth at different speeds and altitudes depending on their job. For example, Tracking and Data Relay satellites, used by NASA to receive info from its other missions, sit in geosynchronous orbit at around 7,000 miles per hour so operators always know exactly where they are. The Geostationary Operational Environmental Satellites are also in this kind of orbit because they’re designed to receive and send environmental data like weather reports. It needs to be in line with Earth’s orbit so it can always get and deliver the necessary information in 24-hour intervals.

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Constructs like the International Space Station, meanwhile, don’t really need to be in perfect step with Earth’s rotation, so instead they move at 17,500 miles per hour in low-Earth orbit. The Hubble Space Telescope is also in low Earth orbit at that same speed, as it doesn’t need to be directly above us to be accessed.