• Question: How so we ensure that satellites continue to orbit the earth? (Ones that Are supposed to orbit the earth)

    Asked by Zobo64 to Colin, John, Kevin, Shikha, Triona on 12 Nov 2014.
    • Photo: Kevin Motherway

      Kevin Motherway answered on 12 Nov 2014:

      When something is in orbit it is actually falling back to earth very very slowly (maybe over thousand of year for geostationary satellites at 35,000 km height). The Space Station which is about 330km up falls about 4 km closer to the earth every 2 months or so and the have to re-boost its orbit by firing up the engines on a soyuz or progress spacehip docked to it. All satellites have thursters to do the same, but eventually they run out of fuel and will either be commanded to re-enter for a safe splashdown or will tumble out of the sky and hopefully all burn up. Huge chunks of Skylab fell in western Australia and the local government sent NASA a litter fine. It still hasn’t been paid!

    • Photo: Shikha Sharma

      Shikha Sharma answered on 15 Nov 2014:

      Hi Zobo64,
      We can get the answer if we think logically. Let’s say we want to put a satellite at a certain distance/altitude ‘X’ from earth surface. And we want the satellite to orbit around the earth forever maintaining the same ‘X’ distance from earth surface. There are 2 things which will play major in this. (a) The velocity of the satellite at which it is going away from the earth and (b) amount of gravitation pull earth putting on the satellite. If velocity of satellite is very high, greater than the escape velocity (the velocity, if applied to a body, the body will just be able to move away earth forever nullifying the gravitational pull of the earth), the satellite will move away from earth forever. On other hand if velocity of satellite is low then gravitational force of the earth will dominate, pull down the satellite and eventually the satellite will collide on earth surface. It is exactly the same as if someone throws a stone in sky,
      Hence, it is obvious that we need to create a balance the velocity of satellite and gravitational pull of earth on the satellite at altitude “X” so that neither of these dominates each other. Since we can’t earth gravitational force we must adjust the velocity of satellite at altitude ‘X’ so that balance can be created and satellite remains orbiting around earth at distance ‘X’ forever. Scientist use mathematical formula to calculate the velocity of satellite very preciously. The higher the altitude of the satellite the lesser the velocity is required to be given to satellite.

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