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Space debris in Low Earth orbit. Credit: ESA
Low orbit is the general region at the top of a planet’s atmosphere but still within the influence of its gravitational field. When most people in aeronautics refer to low orbit they are referring to low Earth orbit, the region below 2500 km above the Earth’s surface.
This region is very important when talking about spaceflight in general. The space shuttle, for example, is actually a low orbit space vehicle. It can’t be used to go anywhere outside this region of space and is normally used to carry payloads and conduct experiment in the region of space near the Earth. It’s also the region where many of the artificial satellites hold their orbit. Any higher and they leave the influence of Earth’s gravity. It’s also the area of space where important structure like the International Space Station are. Another characteristic is that most objects in this region are still subject to atmospheric drag. This explains why the orbit of man made objects decays over time. The friction slowly reduces the orbit speed of artificial satellites until they are no longer fast enough to resist the pull of gravity.
Despite its importance to many aspects of spaceflight, low orbit also present some unique challenges. One of them we created ourselves. We now know that the space between planets isn’t empty. As a matter of fact, this region of space has numerous objects, such as meteoroids, that vary in size from a grain to the size of a bowling ball. Some of these debris collide with satellites and other space vehicles and break off pieces. Over time, this has left a cloud of man made debris that now populates the entire low Earth orbit region. This is a problem because many of these pieces of space junk now move at incredibly high speeds that can make them deadlier than bullets or debris thrown by tornadoes and hurricane force winds. This presents a potentially dangerous hazard for manned space missions. According to NASA, there are now around 8,500 pieces of space debris that are identified as being larger than 10cm. That is not including the estimated millions of pieces of debris that are smaller than this.
Another problem that may loom in the future is that we may run out of space. Low Earth orbit is vast, but finite, and current satellites can only keep orbit within Low Earth Orbit. Already there have been a couple of reports of satellites colliding. Hopefully in the future advances in aeronautics will find solutions to these problems. This just underscore the importance of low orbit to the future of spaceflight.
If you enjoyed this Universe Today article there are others you might enjoy. Here is an article on space debris. Another is an interesting article on the collision of two satellites.
Here are some resources that I found helpful. This article on NASA website had some helpful info. Also this was an another article on space debris.
You will also like this episode of Astronomy Cast.
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