Where We Keep Our Most Important Stuff in Space

The place we call space officially starts about 60 miles (100 kilometers) above the surface, a delineation known as the Kármán line. But that’s not a feasible altitude for orbit, owing to atmospheric drag. To reach orbit, an object must ascend to altitudes starting at around 100 miles (160 km) above the surface. This is the lowest possible boundary of low Earth orbit, or LEO, which extends to a maximum altitude of about 1,200 miles (2,000 km), NASA says.

Satellites must maintain an orbital speed of around 4.9 miles per second (7.8 km per second) to remain in low Earth orbit. At this speed, it takes a satellite roughly 90 minutes to complete a full circle of Earth. The Hubble Space Telescope, which orbits in LEO at an altitude of approximately 332 miles (543 km) and travels at speeds reaching 17,400 miles per hour (28,000 km/hr), completes nearly 15 revolutions of Earth each day.

LEO is a workhorse orbit within which the vast majority of our satellites are located. As of April 30, 2022, some 4,700 operational satellites are in LEO, according to the UCS Satellite Database (the true number is now much higher, given the rapid pace at which SpaceX is launching its Starlink satellites). Low Earth orbit is useful because it’s so close, allowing, for example, low-cost launches to space, Earth-observing satellites to take high-resolution images of the surface, low-power amplifiers for data transmission, and quick and easy access to space stations (fun fact: no human has traveled beyond LEO since the Apollo era). What’s more, the plane of low Earth orbits can be tilted, providing many available orbital paths for satellites.

That said, the speed poses a problem for communication and navigation satellites, as it’s challenging for ground stations to track objects whipping around in LEO. Satellite constellations are an effective but costly work-around, as multiple satellites work together to create a virtual net around the planet. Starlink is a good example—a megaconstellation currently consisting of 3,182 operating satellites that provide internet coverage around the world. The Iridium satellite constellation also works from LEO, providing voice and data coverage to satellite phones and other receivers across the globe.

Another downside of LEO is that it’s increasingly home to a lot of space junk, stuff like defunct satellites, spent upper stages, launch adapters, slag particles, copper wires, and even flecks of paint. Frighteningly, large swaths of LEO could eventually become inaccessible if nothing is done to curb the amount of debris in LEO.

The place we call space officially starts about 60 miles (100 kilometers) above the surface, a delineation known as the Kármán line. But that’s not a feasible altitude for orbit, owing to atmospheric drag. To reach orbit, an object must ascend to altitudes starting at around 100 miles (160 km) above the surface. This is the lowest possible boundary of low Earth orbit, or LEO, which extends to a maximum altitude of about 1,200 miles (2,000 km), NASA says.

Satellites must maintain an orbital speed of around 4.9 miles per second (7.8 km per second) to remain in low Earth orbit. At this speed, it takes a satellite roughly 90 minutes to complete a full circle of Earth. The Hubble Space Telescope, which orbits in LEO at an altitude of approximately 332 miles (543 km) and travels at speeds reaching 17,400 miles per hour (28,000 km/hr), completes nearly 15 revolutions of Earth each day.

LEO is a workhorse orbit within which the vast majority of our satellites are located. As of April 30, 2022, some 4,700 operational satellites are in LEO, according to the UCS Satellite Database (the true number is now much higher, given the rapid pace at which SpaceX is launching its Starlink satellites). Low Earth orbit is useful because it’s so close, allowing, for example, low-cost launches to space, Earth-observing satellites to take high-resolution images of the surface, low-power amplifiers for data transmission, and quick and easy access to space stations (fun fact: no human has traveled beyond LEO since the Apollo era). What’s more, the plane of low Earth orbits can be tilted, providing many available orbital paths for satellites.

That said, the speed poses a problem for communication and navigation satellites, as it’s challenging for ground stations to track objects whipping around in LEO. Satellite constellations are an effective but costly work-around, as multiple satellites work together to create a virtual net around the planet. Starlink is a good example—a megaconstellation currently consisting of 3,182 operating satellites that provide internet coverage around the world. The Iridium satellite constellation also works from LEO, providing voice and data coverage to satellite phones and other receivers across the globe.

Another downside of LEO is that it’s increasingly home to a lot of space junk, stuff like defunct satellites, spent upper stages, launch adapters, slag particles, copper wires, and even flecks of paint. Frighteningly, large swaths of LEO could eventually become inaccessible if nothing is done to curb the amount of debris in LEO.