The fact that the planets were all formed together this way is why all the planets have orbits around the Sun in the same direction, in roughly the same plane. When rockets launch our satellites, they put them into orbit in space.
There, gravity keeps the satellite on its required orbit — in the same way that gravity keeps the Moon in orbit around Earth.
Whilst it is your throw that gives the ball its initial speed, it is gravity alone that keeps the ball moving towards the ground once you let go.
As shown in the figure, the difference is that throwing something will make it fall on a curved path towards the ground — but a really powerful throw will mean that the ground starts to curve away before your object reaches the ground. You have reached orbit. In space, there is no air and therefore no air friction, so gravity lets the satellite orbit around Earth with almost no further assistance.
Putting satellites into orbit enables us to use technologies for telecommunication, navigation, weather forecast, and astronomy observations. On each mission, a rocket places one or more satellites onto their individual orbits.
The choice of which launch vehicle is used depends primarily on the mass of the payload, but also on how far from Earth it needs to go. Depending on which orbit Ariane 5 is going to, it is able to launch between approximately 10 to 20 tonnes into space — that is 10 —20 kg, which is about the weight of a city bus. Vega is smaller than Ariane 5, capable of launching roughly 1. Both Ariane 5 and Vega can deploy multiple satellites at a time. 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. Medium Earth Orbit MEO Although over 90 percent of all satellites are situated in LEO below 2, kilometers and GEO near 36, kilometers , the space between the two most popular orbital regimes can be an ideal environment for a smaller subset of satellite systems.
The inner belt extends from roughly km to 5, km at the equator and the outer belt extends from 12, km to 22, km. Satellites in these regions can be outfitted with shielding to lower the risk of damage during their operational lifetime.
Although many of the orbits previously discussed assume a circular or nearly circular path around the Earth, some satellites are situated such that they orbit the Earth in an oblong elliptical path, called highly elliptical orbit , or HEO. One example of a highly elliptical orbit is a Molniya orbit. Molniya orbits have an inclination of For the majority of their periods, satellites in Molniya orbit are primarily observing the northern hemisphere of the Earth.
Since both the United States and Russia are in the northern hemisphere, Molniya orbits were ideal for reconnaissance in the Cold War Era. The period of a satellite, or how long it takes to orbit the Earth one time, is dependent on its orbital altitude.
Satellites in MEO take about 12 hours to do the same. Satellites orbiting at 35, km have a period precisely equal to one day. Satellites in this orbit, known as geosynchronous Earth orbit , or GEO, observe the Earth as if it were not rotating.
While about 55 percent of all operational satellites are in LEO, another 35 percent are in GEO, making it the second most popular orbital regime. If it is close to one, the ellipse is long and slender. The four seasons are determined by the fact that the Earth is tilted In short, when the northern hemisphere is tilted away from the Sun, it experiences winter while the southern hemisphere experiences summer. Six months later, when the northern hemisphere is tilted towards the Sun, the seasonal order is reversed.
In the northern hemisphere, winter solstice occurs around December 21st, summer solstice is near June 21st, spring equinox is around March 20th and autumnal equinox is about September 23rd. The axial tilt in the southern hemisphere is exactly the opposite of the direction in the northern hemisphere. Thus the seasonal effects in the south are reversed. L1, L2, and L3 sit along a straight line that goes through the Earth and Sun. L1 sits between them, L3 is on the opposite side of the Sun from the Earth, and L2 is on the opposite side of the Earth from L1.
These three Lagrange points are unstable, which means that a satellite placed at any one of them will move off course if disturbed in the slightest. The L4 and L5 points lie at the tips of the two equilateral triangles where the Sun and Earth constitute the two lower points. These two Lagrange Points are stable, hence why they are popular destinations for satellites and space telescopes.
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