How satellite is kept moving in its orbit around the Earth and what is the lifespan of a satellite in space?
Satellites are kept moving in their orbit around the Earth primarily due to two forces: gravity and their own momentum. Gravity, exerted by the Earth, pulls the satellite towards it. At the same time, the satellite's forward momentum tries to keep it moving in a straight line away from the Earth. The balance between these two forces keeps the satellite in a stable orbit. Essentially, the satellite is constantly falling towards the Earth but also moving forward quickly enough that it keeps missing the Earth.
The lifespan of a satellite in space can vary significantly depending on several factors such as its orbit, the type of mission, and how well it's built to withstand the harsh conditions of space.
Generally, satellites have design lifespans ranging from 5 to 15 years, though some, especially those in higher orbits or with more robust designs, can last much longer. For instance, communication satellites in geostationary orbit typically have expected lifespans of about 15 years. After a satellite has reached the end of its operational life, it may be moved to a "graveyard" orbit or, if in low Earth orbit, it will eventually re-enter the Earth's atmosphere and burn up.
Gravity is a force of attraction between masses. It provides the centripetal force needed to keep a satellite in orbit around a planet, or a planet in orbit around a star such as the Sun. The motion of the moon around the earth is due to the centripetal force. A satellite maintains its orbit by balancing two factors: its velocity (the speed it takes to travel in a straight line) and the gravitational pull that Earth has on it. A satellite orbiting closer to the Earth requires more velocity to resist the stronger gravitational pull. A satellite's circular orbit is maintained by balancing two factors: its velocity (the speed required to proceed in a straight line) and Earth's gravitational attraction. To counteract the larger gravitational attraction, a satellite circling closer to the Earth must have a higher velocity. The gravitational force due to the earth keeps the satellite in the orbit around the earth. It is the centripetal force which is gravitational force keeping body in orbit. A satellite rotates around the earth by using earth's gravitational force as centripetal force. Also as there is no air in space, it does not have to work against air resistance. Hence it doesn't lose any energy while rotating. So it does not require fuel to rotate around the earth. Satellites orbit the Earth at tremendous speeds while they continuously fall. The most important factor affecting their flight is the presence or lack of obstacles. As long as there is nothing to obstruct them, they can keep moving. Small satellites (10–100 kg) usually have a lifetime less than 5 years. Larger satellites in the Low-Earth orbit (LEO ~ 160–2000km) have a lifetime of 5–10 years while geosynchronous satellites (GEO ~36000km) operate for 15 years or more. Satellites in low orbits at an altitude of a few hundred kilometers from the ground will enter the atmosphere and burn up in several years to several decades. On the other hand, satellites in high orbits over 1,000 km will continue to revolve for more than 100 years.
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