Low Earth Orbit
Estimated number of objects in low Earth orbit. Credit: NASA

Guide to Space

Low Earth Orbit

2 Apr , 2011 by

Low Earth Orbit is an orbit that extends from the Earth’s surface at sea level to an altitude of 2,000 km. What is interesting about the majority of Low Earth Orbit is that most of it lies within the Earth’s atmosphere. For this reason most spacecraft and artificial satellites have rapidly decaying orbits due to the drag created by air molecules in the thermosphere, the last layer of the Earth’s atmosphere, before the exosphere.

Low Earth Orbit is a region that includes Earth at Sea Level and up to 2000 kilometers above sea level. This region is close enough for a panoramic view of the Earth but just far enough that most space craft can stay in orbit without being pulled down to the surface by Earth’s gravitational field. However satellites at this altitude have to move at extraordinary speeds to partially escape the pull of Earth’s gravity. A satellite in low Earth orbit travels at a mean velocity of 26,000 to 27,000 km per hour or 17,000 miles per hour

Low Earth Orbit has been used for both military and aeronautical purposes. Military rocketry and missiles have long taken advantage of this orbit to launch missiles and rockets over long distances. A missile launched in low earth orbit follows three stages. First it would launch into a suborbital path using its engine. The second stage would be where the thrust and momentum created would allow the missile to reach cruising speeds. In final stage the influence of gravity brings it back to Earth towards it target. In space flight the majority of human spaceflight occurs here. Right now the cost of human spaceflight are astronomical so most space agencies are funded by governments and need to work within set budgets for missions. This is why Low Earth Orbit is still the destination of choice for missions.

Other than lunar flights Low Earth Orbit defines the boundary of all human space exploration. This shows the major technical and financial obstacles that need to be overcome in order to make even nearby interplanetary travel possible. However there is promise in the technologies used to send satellites into Geostationary Orbit and beyond. In the meanwhile there are a lot major achievements in low earth orbit such as the international space station and the ongoing development of commercial space flight and space stations. The first commercial space flight companies are rapidly finding ways to make spaceflight cheaper and more accessible.

We have written many articles about low Earth orbit for Universe Today. Here’s an article about the Earth’s orbit, and here’s an article about the orbit velocity.

If you’d like more info on low Earth orbit, check out the types of orbit from the European Space Agency website. Also, here’s a link to NASA’s article about Low Earth Orbit.

We’ve also recorded an entire episode of Astronomy Cast all about Getting Around the Solar System. Listen here, Episode 84: Getting Around the Solar System.


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