How is the velocity of a satellite controlled when moving in elliptical orbit?

Question

The velocity of a satellite at perigee (10.15 km/s) decreases to a min.
1.6 km/s at apogee during its journey along an elliptical orbit. Is this velocity reduction done forcefully using computer measuring the height of satellite at every moment or it happens naturally by gravitational force and momentum ?

Answer 1

The satellite is in a constant state of free-fall, controlled by the planet's gravity. No satellite carries enough fuel to accelerate and decelerate that much even for one orbit.

Example: Throw a ball in the air, almost vertically. It starts fast, is slowed near the top of it's arc (when all its speed it horizontal) and then speeds up again at the bottom of its fall. Similarly, the satellite accelerates from its apogee until it is going fastest at closest approach (perigee) and slows again until it reaches apogee again.

Satellites do have small thrusters to change their orbits slightly. But such "repositioning" or increasing a decaying orbit can only be done a finite number of times.

Answer 2

In addition to Kepler's Laws as the others have suggested, another way to get an understanding is the conservation of mechanical energy.

As the satellite moves through its orbit it trades potential energy for kinetic energy. That is one explanation as to why it is moving fastest at the perigee and slowest at apogee. The total mechanical energy remains constant.

Conservation of angular momentum also provides some insight, but maybe not as clearly. The total angular momentum is also constant and is equal to the vector cross product of the position vector and the velocity vector. So as the magnitude of the position (the altitude) increases that of the velocity decreases, and vice versa. This also explains why the satellite stays in its orbital plane, though that may even be less clear.

Answer 3

Kepler's Laws of planetary motion are quite interesting... check them out (particularly his 2nd law for your question).

The velocity is usually not controlled in a satellite, it is left alone once it is in orbit. Since an orbiting object has to sweep equal areas in equal time (by Kepler's 2nd law), the object must move faster near perigee since the area slices are smaller than those when near apogee. See the animation at the linked site.

Answer 4

its physics...

by keplar's 2nd law of satellite motion
" the body revolvin around d parent body spans equal areas, for the same intervals of time, anywhre in its orbit"

hence for this 2 b true...its speed is max at perigee and min at apogee

make a diagram...n then c..u'l b able 2 undrstand better

Answer 5

Yes, all due to the laws of physics!

Answer 6

the last one.