![]() ![]() Rhett Allain, " What's So Special About Low Earth Orbit? (opens in new tab)", Wired, September 2015.Australian Space Academy, " Specifying Satellite Orbits (opens in new tab)", accessed May 2022.ESA, " Types of orbits (opens in new tab)", March 2020.ESA, " Low Earth orbit (opens in new tab)", March 2020.Additional resourcesįor more information about low Earth orbit and satellite design check out " Low Earth Orbit Satellite Design (Space Technology Library Book 36) (opens in new tab)" by George Sebestyen, et al, and NASA's webpage on " Low-Earth Orbit Economy". LEO is the most common type of orbit, but not the only one here's some others. ![]() The Molniya orbit, for example, used for communications in northerly latitudes, has a low point of around 308 miles (495 km) but a high point around 25,000 miles (40,000 km). Most satellites have near-circular orbits, but in a few cases the ellipse can be much more elongated, with a major axis much longer than the minor axis. When these two axes are equal in size, the orbit is a perfect circle, which is just a special case of an ellipse. Satellite orbits usually follow an oval-type path called an ellipse, the length and width of which are known as the major and minor axes. ![]() This means that a satellite at that altitude effectively hovers over a single spot on the Earth’s surface, which makes it especially useful for satellite TV and other communications systems. ![]() However GEO is at an altitude of around 22,000 miles (36,000 km), at which point the orbital speed has slowed, so a single orbit corresponds to precisely one rotation of the Earth. There is, however, one particular high-altitude orbit that’s worth the extra effort to get to - and that’s Geosynchronous orbit (GEO).Ī satellite in LEO completes around 16 orbits every day, or for every complete rotation of the Earth itself. Orion spacecraft: NASA's next-gen capsule to take astronauts beyond Earth orbit Artificial gravity: Definition, future tech and research What's the difference between orbital and suborbital spaceflight? This extra effort in getting to higher altitudes is one of the reasons most satellites are placed in LEO, together with other considerations such as the higher resolution views that Earth-observing satellites can get from closer range. This is because it takes a huge amount of energy just to reach that higher altitude. However, this does not mean that a rocket needs to expend less energy in order to put a satellite into a higher orbit. In fact, this actually decreases with the increase in altitude. At higher altitudes, the speed required to keep a satellite in orbit changes. The orbital speed of 7.8 km/s (17,500 mph), refers to the LEO regime just above the Earth’s atmosphere. When a satellite reaches orbital speed, it is officially in orbit. But once they are above the atmosphere they switch to horizontal motion. But that’s because they need to get up above the atmosphere - or the greatest part of it - as quickly as possible to avoid drag forces. This may seem confusing if you’ve ever watched a space launch, because rockets generally go straight up vertically when they blast off. This is a horizontal speed, parallel to the surface of the planet. The result is that an object moving at this speed will simply go round and round the Earth. The speed of 17,500 mph (7.8 km/s) is the speed at which the force of gravity prevents an object from flying off at a tangent. ![]()
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