In its most basic sense, LEO is exactly what it sounds like: an orbit around Earth at an altitude near the bottom of the spectrum of possible orbits. This equates to about 1,200 miles (2,000 kilometers) or less. Low Earth orbit is home to most satellites, as well as the International Space Station (ISS).
To stay in this orbit, the satellite must travel at a speed of about 17,500 miles per hour (7.8 kilometers per second), which takes about 90 minutes to complete a worldwide orbit.
The orbit is possible because of the force of gravity – the same force that holds us on the surface of the planet. Just as we would float in space if gravity were not present, satellites would fly tangently if the force were not present to keep them moving around the Earth.
This is actually the case in the case of a spacecraft traveling very fast – faster than Earth’s flying speed of 25,000 miles per hour (11.2 km/s). On the other hand, if an object is moving slower, such as the New Shepard suborbital Blue Origin rocket, it will fall back to Earth just as you would when you jump through the air.
This may seem confusing if you’ve ever seen a space launch, because rockets usually go straight vertically when they explode. But that’s because they need to rise above the atmosphere – or most of it – as quickly as possible to escape the gravitational force. But once they are above the atmosphere they switch to horizontal movement. When a satellite reaches orbital speed, it is officially in orbit.
The speed of 17,500 mph (7.8 km/s) is the speed at which the force of gravity prevents an object from flying in the shadow. As a result, objects moving at that speed will spin and revolve around the earth. This is the horizontal velocity parallel to the planet’s surface.
satellites in low earth orbit
The orbital speed of 7.8 km/s (17,500 mph) refers to the LEO system just above Earth’s atmosphere. At higher altitudes, the speed required to keep the satellite in orbit changes. In fact, this actually decreases with increasing altitude.
However, this does not mean that rockets need to spend less energy to put satellites into higher orbits. This is because it takes a large amount of energy just to reach this higher altitude. This extra effort to reach higher altitudes is one reason why most satellites are placed in low Earth orbit, along with other considerations such as the high resolution rendering that Earth observation satellites can get from closer distances.
However, there is one particular high-altitude orbit that is worth the extra effort to get there – the geosynchronous orbit (GEO). LEO satellites complete about 16 orbits each day, or for every complete rotation of the Earth itself. However, geosynchronous orbits are at an altitude of about 22,000 miles (36,000 km), where the orbital speed slows down, so that one orbit corresponds exactly to one rotation of the Earth.
This means that a satellite at this altitude is effectively hovering above a single point on the Earth’s surface, which makes it very useful for satellite television and other communications systems. The orbit of a satellite usually follows an elliptical path called an ellipse, its length and width known as the major and minor axes.
When these two axes are the same size, the orbit is a complete circle, which is a special case of an ellipse. Most satellites have semicircular orbits, but in some cases the ellipse can be more elongated, with the principal axis being longer than the minor axis. The orbit of Molnia, for example, used for communications at northern latitudes, has a low point of about 495 km, but a high point of about 25,000 miles (40,000 km).
LEO is the most common type of orbit, but not the only one; Here are a few others.
News summary:
- Lower earth orbit
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