‘Science and Technology for WBCS Mains Part-I PDF’
- A satellite is an artificial object which has been intentionally placed into orbit.
- Satellites fly high in the sky, so they can see large areas of Earth at one time. Satellites also have a clear view of space. That’s because they fly above Earth’s clouds and air.
- An orbit is a path. It’s the way something goes around an object in space. The moon goes in orbit around Earth.
- An orbit is a curved path, like a circle or an oval. (The technical word is “ellipse.”) A comet’s orbit is very long and thin. The moon’s orbit is almost circular.
- For the planets, the orbits are almost round. The orbits of comets have a different shape.
- Satellites that orbit the Earth are not always the same distance from the Earth. Sometimes they are closer, and at other times they are farther away.
- The closest point a satellite comes to the Earth is called its perigee. The farthest point is the apogee.
- The time it takes a satellite to make one full orbit is called its period. The inclination is the angle the orbital plane makes when compared with the Earth’s equator.
- A moving object will continue moving unless something pushes or pulls on it. This statement is called Newton’s first law of motion.
- Without gravity, a satellite would fly off into space. With gravity, a satellite is constantly pulled back toward Earth. This tug-of-war keeps the satellite in orbit.
- Escape velocity is the speed an object must go to break free from a planet’s gravity and enter into orbit.
- Escape velocity depends on the mass of the planet. Each planet has a different escape velocity. The object’s distance from the planet’s center is also important.
- The escape velocity from the Earth is about 11.3 kilometers (7 miles) per second.
TYPES OF SATELLITE ORBITS
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.
LOW-EARTH ORBIT (LEO)
- Low-Earth Orbit (LEO) is restricted to the first 100 to 200 miles of space.
- LEO is the easiest orbit to get to and stay in.
- This is where the Shuttle and ISS(International Space Station) conduct their operations.
- One complete orbit in LEO takes about 90 minutes.
- Any satellite with an orbital path going over or near the poles maintains a polar orbit.
- Polar orbits are usually in low-Earth orbit.
- They remain in place while the Earth passes under. This means that eventually, the entire Earth’s surface passes under a satellite in polar orbit.
- Polar orbits are often used for earth-mapping, earth observation, capturing the earth as time passes from one point, reconnaissance satellites, as well as for some weather satellites.
- A geostationary orbit often referred to as a geosynchronous equatorial orbit (GEO) or geostationary, is a circular geosynchronous orbit 35,786 km (22,236 mi) above Earth’s equator and following the direction of Earth’s rotation.
- An object in such an orbit appears motionless, at a fixed position in the sky, to ground observers.
- Communications satellites and weather satellites are often placed in geostationary orbits.
- A geostationary orbit is a particular type of geosynchronous orbit, which has an orbital period equal to Earth’s rotational period, or one sidereal day (23 hours, 56 minutes, 4 seconds).
SUN-SYNCHRONOUS ORBITSPOLAR ORBITS
- A Sun-synchronous orbit (SSO, also called a heliosynchronous orbit ) is a nearly polar orbit around a planet, in which the satellite passes over any given point of the planet’s surface at the same local mean solar time.
- Satellites are used for many purposes. 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.
- The first artificial satellite was Sputnik 1, launched by the Soviet Union on 4 October 1957
- Sputnik 2 was launched on 3 November 1957 and carried the first living passenger into orbit, a dog named Laika.
Science and Technology for WBCS Mains Part-I PDF
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