Such orbits — about 35, km above the ground — are especially useful for communications satellites, since ground stations can maintain contact without the need for active tracking. This means that, in addition to the active GEO satellites, the region is also host to thousands of objects larger than 10 cm, and at least tens of thousands larger than 1 cm.
Assessing the hazard is more challenging for GEO than it is for LEO for various reasons: the number of orbiting objects is harder to establish with confidence; orbits tend to be largely synchronous; and the population of active satellites is distributed unevenly around the equator. Still, researchers have produced a range of estimates for the danger, with those at the bottom end going so far as to suggest that the risk of collision is so low that even the routine use of graveyard orbits for retired GEO satellites is unnecessary.
The methods used by Oltrogge and colleagues involved statistical extrapolation from catalogues of known debris, records of close approaches, and simulations of the passage of satellites through known and estimated RSO populations. The analyses included orbital drift induced by the gravitational effects of the Sun and Moon, and also took account of the elongated shape and alignment of the typical GEO satellite.
The researchers found that the average time between satellite—debris collisions is just four years for the population of RSOs 1 cm across, but this was not the only alarming result. Such impacts are energetic enough to cause catastrophic damage to satellites, which are not designed with mechanical robustness in mind.
Collisions with objects 20 cm in size were inferred to occur every 50 years on average, and events like this can produce clouds of high-velocity fragments that spread throughout the GEO region, potentially triggering a cascade of secondary impacts. But if we should expect collisions among GEO satellites to be commonplace, one might wonder why we hear so little about them.
For the 21st century and beyond, satellites will play an important role in some of the fundamental challenges. Not to mention, the physics of satellite orbits are remarkable. And they have many practical purposes for science and innovation. If you want to build on your expertise in satellite orbits, here a few more resources to expand your knowledge. I feel Pradeep Datta answer is incorrect as well. From an observers eye, there is NO possible way anyone could see a satellite the size of a small sedan.
If the object is in a geosynchronouss orbit that is inclined with respect to the Equator, then the object will move in a figure eight pattern aka an analemma during the course of a sidereal day. This is not correct. The orbit may have an inclination to the equator or even eccentricity. Similarly, it is considered good practice to move almost-dead satellites into a "graveyard" orbit above geosynchronous orbit before they run out of fuel, to clear the way for the next generation.
The satellites must also be located far enough away from each other so their communications don't interfere with each other, which could mean a separation of anything between 1 and 3 degrees.
As technology has improved, it's possible to pack more satellites into a smaller spot. Join our Space Forums to keep talking space on the latest missions, night sky and more!
And if you have a news tip, correction or comment, let us know at: community space. Elizabeth Howell is a contributing writer for Space. She is the author or co-author of several books on space exploration. Elizabeth holds a Ph. These rockets will be more flexible and will extend what Europe is capable of getting into orbit, and will be able to deliver payloads to several different orbits in a single flight — like a bus with multiple stops. Upon launch, a satellite or spacecraft is most often placed in one of several particular orbits around Earth — or it might be sent on an interplanetary journey, meaning that it does not orbit Earth anymore, but instead orbits the Sun until its arrival at its final destination, like Mars or Jupiter.
There are many factors that decide which orbit would be best for a satellite to use, depending on what the satellite is designed to achieve. GEO is used by satellites that need to stay constantly above one particular place over Earth, such as telecommunication satellites. This way, an antenna on Earth can be fixed to always stay pointed towards that satellite without moving. It can also be used by weather monitoring satellites, because they can continually observe specific areas to see how weather trends emerge there.
Satellites in GEO cover a large range of Earth so as few as three equally-spaced satellites can provide near global coverage. This is because when a satellite is this far from Earth, it can cover large sections at once. This is akin to being able to see more of a map from a metre away compared with if you were a centimetre from it.
So to see all of Earth at once from GEO far fewer satellites are needed than at a lower altitude. This means Europe can always stay connected and online. By comparison, most commercial aeroplanes do not fly at altitudes much greater than approximately 14 km, so even the lowest LEO is more than ten times higher than that. This means there are more available routes for satellites in LEO, which is one of the reasons why LEO is a very commonly used orbit.
It is the orbit most commonly used for satellite imaging, as being near the surface allows it to take images of higher resolution. It is also the orbit used for the International Space Station ISS , as it is easier for astronauts to travel to and from it at a shorter distance. Satellites in this orbit travel at a speed of around 7.
However, individual LEO satellites are less useful for tasks such as telecommunication, because they move so fast across the sky and therefore require a lot of effort to track from ground stations. Instead, communications satellites in LEO often work as part of a large combination or constellation, of multiple satellites to give constant coverage.
This lets them cover large areas of Earth simultaneously by working together. It is similar to LEO in that it also does not need to take specific paths around Earth, and it is used by a variety of satellites with many different applications. It is very commonly used by navigation satellites, like the European Galileo system pictured. Galileo powers navigation communications across Europe, and is used for many types of navigation, from tracking large jumbo jets to getting directions to your smartphone.
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