- T = time period of revolution of the planet,
- a = semi-major axis of the elliptical orbit.
Definitions [2]
Define time period of a satellite.
Time taken by the satellite to complete one revolution round the Earth is called time period.
Time period, T = `"Distance covered"/"Orbital velocity"`
T = `"2πr"/"v"`
Definition: Artificial Satellite
If a manmade object revolves around the earth or any other planet in a fixed orbit it is called an artificial satellite.
Formulae [2]
Formula: Escape Velocity
vesc = \[\sqrt{\frac{2\mathrm{~GM}}{\mathrm{R}}}\]
where
- G = Gravitational constant
- M = mass of the planet
- R = Radius of the planet
Formula: Kepler's Law
Kepler’s Third Law relates the time period T of a planet’s revolution to the semi-major axis a of its elliptical orbit:
T2 ∝ a3
where,
Key Points
Key Points: Artificial Satellites
- Natural satellites are natural (like the Moon); artificial satellites are manmade and orbit planets.
- Sputnik was the first artificial satellite, launched by the USSR in 1957.
- Satellites use solar panels for energy and send/receive signals.
- Types of satellites: weather, communication, broadcast, navigation, military, and Earth observation.
- India uses INSAT, GSAT, IRNSS, and IRS satellites, launched by GSLV and PSLV rockets.
Key Points: Orbits of Artificial Satellites
- Satellites are placed into orbit using launchers and require a specific tangential speed (the critical velocity).
- Low Earth Orbits (180–2000 km) are used for space stations and weather studies.
- Medium Earth Orbits (2000–35780 km) are used for GPS and polar satellites.
- High Earth Orbits (≥35780 km) include geostationary satellites used for TV, phone, and weather.
- The higher the orbit, the lower the speed needed; satellite speed doesn’t depend on its mass.
