What is Sattelite: Definition and 11 Discussions

In the context of spaceflight, a satellite is an object that has been intentionally placed into orbit. These objects are called artificial satellites to distinguish them from natural satellites such as Earth's Moon.
On 4 October 1957, the Soviet Union launched the world's first artificial satellite, Sputnik 1. Since then, about 8,900 satellites from more than 40 countries have been launched. According to a 2018 estimate, about 5,000 remained in orbit. Of those, about 1,900 were operational, while the rest had exceeded their useful lives and become space debris. Approximately 63% of operational satellites are in low Earth orbit, 6% are in medium-Earth orbit (at 20,000 km), 29% are in geostationary orbit (at 36,000 km) and the remaining 2% are in various elliptical orbits. In terms of countries with the most satellites, the United States has the most with 1,897 satellites, China is second with 412, and Russia third with 176.
A few large space stations, including the International Space Station, have been launched in parts and assembled in orbit. Over a dozen space probes have been placed into orbit around other bodies and become artificial satellites of the Moon, Mercury, Venus, Mars, Jupiter, Saturn, a few asteroids, a comet and the Sun.
Satellites are used for many purposes. Among several other applications, they can be used to make star maps and maps of planetary surfaces, and also take pictures of planets they are launched into. Common types include military and civilian Earth observation satellites, communications satellites, navigation satellites, weather satellites, and space telescopes. Space stations and human spacecraft in orbit are also satellites.
Satellites can operate by themselves or as part of a larger system, a satellite formation or satellite constellation.
Satellite orbits vary greatly, depending on the purpose of the satellite, and are classified in a number of ways. Well-known (overlapping) classes include low Earth orbit, polar orbit, and geostationary orbit.
A launch vehicle is a rocket that places a satellite into orbit. Usually, it lifts off from a launch pad on land. Some are launched at sea from a submarine or a mobile maritime platform, or aboard a plane (see air launch to orbit).
Satellites are usually semi-independent computer-controlled systems. Satellite subsystems attend many tasks, such as power generation, thermal control, telemetry, attitude control, scientific instrumentation, communication, etc.

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  1. Z

    Is My Idea for a Small Ion-Engine Satellite Feasible and Original?

    Would it be possible to build an approximately 10x10x10 cm ion-engine to put on a cube sattelite? I am a university student, so we have a lot of tools, but not a lot of money. What do I need to consider and how much would it cost?
  2. U

    What's different between a receiver & transmitter antennas?

    Hello, I'm currently working on satellite model for high-school compatition, and I'm not sure if there's a visual difference between a reciver & transmiter antenas (on satellites)... Also, is it possible to satellite to recive a radio wave information from another satellite Thank you
  3. U

    Does pulsed plasma thruster fits my satellite?

    Hi, I don't know if it's the right place for this question, but- I need to create a satellite model, that after being in space, will come close to the atmosphere, and then go back up again. In its way up it need to use a pulsed thruster. (This needs to happen multiple times...) Does a pulsed...
  4. Q

    Possibility of multiple moons in Earth-Moon system

    I am interested in theoretical (what if) possibility of our Earth having more than one moon, I wonder if they can be arranged at the same orbital resonance as the Galilean moons 1:2:4 If yes, would such system be stable? If yes, should our Moon be the first, second or third satellite out of the...
  5. Z

    Cost of setting up a sattelite?

    Homework Statement A scientist wants to put an 100kg experimental package in orbit around the Earth. The cost of deployment depends on the amount of extra energy it takes to get it into the required position i.e. how much more energy is used than just sending the rocket up there. a)...
  6. M

    Sattelite orbiting mars, work done to change distance.

    Homework Statement A 2700 kg spacecraft is in a circular orbit 1000 km above the surface of Mars. How much work must the spacecraft engines perform to move the spacecraft to a circular orbit that is 4000 km above the surface? mars: Mass=6.4185*10^23 KG, radius=3397000 m Homework...
  7. B

    Zero accerlation for spacewalking astronaut and sattelite?

    [b]1. An 8- kg spacewalking astronaut pushes off a 640 kg satellite, exerting 100N force for the 0.5s it takes to straighten his arms. How far apart are they after 1 minute? Homework Equations [b]3. So, I calculated the the accelration of the spaceman and the satelite during...
  8. B

    Geosynchronus Sattelite Question

    Homework Statement A satellite that stays over the same spot on a planet as it rotates is called a geostationary satellite. (Geostationary satellites must be positioned somewhere over the equator of the planet.) What is the average orbital radius of a geostationary satellite for a planet with...
  9. S

    Can overhead tranmission lines be located via sattelite imagery?

    Not really sure if this is the place for this, but can overhead tranmission lines be located via sattelite imagery?
  10. L

    Discovering the Mystery of Satellite Shadows: A Beginner's Guide

    Another noob qeustion that I do not have the knowledge to figure out. It's is possible to see the shadow of a sattilte?
  11. J

    Space shuttle releases a sattelite into a circular orbit

    The space shuttle releases a sattelite into a circular orbit 680 km above the Earth. How fast must the shuttle be moving (relative to the Earth's center) when the release occurs? I know that G (m*m(earth)/r^2) = m (v^2/r)...with r = r(earth) + h. In this equation, r=6380+680=7060 km. There...