Where we keep our most important stuff in space
The place we call space officially begins about 100 kilometers above the surface, a boundary known as the Kármán line. But this is not a feasible altitude for orbit, due to atmospheric drag. To reach orbit, an object must rise to altitudes about 160 km above the surface. This is the lowest possible limit of low Earth orbit, or LEO, which extends to a maximum altitude of about 1,200 miles (2,000 km), NASA said.
Satellites must maintain an orbital speed of about 4.9 miles per second (7.8 km per second) to stay in low Earth orbit. At this speed, it takes about 90 minutes for a satellite to complete a full circle around the Earth. The Hubble Space Telescope, which orbits in LEO at an altitude of about 332 miles (543 km) and travels at speeds reaching 17,400 miles per hour (28,000 km/h), completes nearly 15 revolutions of the Earth each day.
LEO is a workhorse orbit in 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 actual number is now much higher, given the rapid pace at which SpaceX is launching its Starlink satellites). Low Earth orbit is useful because it is so close, allowing, for example, inexpensive launches into space, Earth observation satellites to take high resolution images of the surface, low amplifiers power for data transmission and quick and easy access to space stations (fun fact: no human has traveled beyond LEO since the Apollo era). Additionally, the plane of low Earth orbits can be tilted, providing many available orbital paths for satellites.
That said, speed is a problem for communications and navigation satellites, as it is difficult for ground stations to track moving objects in LEO. Satellite constellations are an effective but expensive solution, as multiple satellites work together to create a virtual network around the planet. Starlink is a good example, a megaconstellation currently composed of 3,182 satellites in operation that provide Internet coverage worldwide. The Constellation of Iridium satellites also works from LEO, providing voice and data coverage to satellite phones and other receivers around the world.
Another disadvantage of LEO is that it houses more and more space debris, stuff like defunct satellites, worn upper stages, launch adapters, slag particles, copper wires, and even paint stains. Scary, large swaths of LEO could eventually become inaccessible if nothing is done to limit the amount of debris in LEO.