Why satellite need no feul after being in orbit?
Answers
The fuel was already spent in launching the satellite into orbit; once there, the satellite retains its orbital velocity essentially “forever,” because of the total lack of friction in space.
Well, near-total, anyway. At the altitudes considered to be “low-Earth-orbits,” there IS still some wispy, incredibly thin traces of the atmosphere still left. It’s enough so that over months or years, the orbit can decay and, unless the satellite is reboosted back to its desired orbital velocity, it will eventually come down (and generally burn itself out on reentry).
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The satellite is pulled by gravity towards the earth. It’s moving fast though and as it falls towards the earth’s surface, the earth’s surface curves away below it. The only thing that happens is that it’s direction is changed. If it was moving faster it would move into a higher orbit or escape the earth’s gravity altogether. If it as moving slower it would fall, as it did so it would pick up more speed and move to a lower orbit or fall to the ground.