Help with orbital decay! (1 Viewer)

[The Savior]

There is a bit of a confliction between the jacaranda and physics in focus textbooks on orbital decay. Jacaranda talks about orbital velocity increasing at lower altitudes, because Ep is transformed into Ek, thus by Ek=1/2mv2, higher Ek results in greater orbital velocity. However, physics in focus says orbital velocity decreases at lower altitudes because Fc=mv2/r, which means if velocity is decreased then orbital radius has to decrease as well. umm a bit confusing? Any help is much appreciated!

 

[Fizzy_Cyst]

Ewwwwwww @ PIF explanation.

From what is said here it seems like they are assuming Fc to be constant, which is of course untrue (assuming a stable circular orbit) as Fc is provided by Fg, which is inversely proportional to r^2.

If a satellite is travelling at any speed other than its orbital speed we cannot use Fc to describe the force(s) acting on it as it is not experiencing a centripetal force as it will not be undergoing circular motion.

 

[The Savior]

So orbital decay is a result of atmospheric drag, which causes a loss of energy that shifts the satellite into a lower orbit. At the same time, the lower orbit requires a greater orbital velocity according to the formula: v=√(GM/r). This means that the satellite is essentially moving faster as its orbit decays, but the atmospheric drag also increases due to the increasing density of the atmosphere. Eventually, the drag force is so great that it will actually decelerate the satellite.

 

[anomalousdecay]

So orbital decay is a result of atmospheric drag, which causes a loss of energy that shifts the satellite into a lower orbit. At the same time, the lower orbit requires a greater orbital velocity according to the formula: v=√(GM/r). This means that the satellite is essentially moving faster as its orbit decays, but the atmospheric drag also increases due to the increasing density of the atmosphere. Eventually, the drag force is so great that it will actually decelerate the satellite.

Yep pretty much.

Just be careful with wording (I'm talking about the last sentence). Drag always occurs as long as there are atmospheric particles around. It is just that as the altitude of orbit is lower, there is much more drag. It doesn't "eventually" become large "enough" to decelerate the satellite. It is just an ongoing thing and it has more and more of an effect on the satellite as the lower the altitude of the orbit gets.