A Conversation for Man-made Satellites

losing speed

Post 1

wastrel_minstrel

"If the satellite slows down, then gravity pulls it closer to the earth (experiment with this principle with your ball and rope) and if it speeds up, then it moves farther away"

I'm fairly sure that this isn't the case. I think that something in a orbit losing energy will move closer to the earth but actually speed up.

Low orbits are faster than higher orbits even though they have a lower kinetic energy.


losing speed

Post 2

wastrel_minstrel

Ok, I'm thinking about this properly now.

I'm probably wrong ..


losing speed

Post 3

wastrel_minstrel

Ok, apologies for the triple post.

I've had a think about this now, provided a good distraction from work.

By equating the potential energy and and kinetic energy of a body in a stable orbit it's possible to find that the orbital speed is inversely proportional to the distance from the centre of the planet. As height decreases, speed increases.

It's easy to imagine this if you consider the orbital height becoming very large; at great distances a body does not have to travel very fast to escape from the gravitational pull of a planet. At low altitudes the orbital speed would have to be very high as the gravity is much stronger.

I am wrong, but it's an interesting diversion to say that if a satellite loses energy due to atmospheric friction it will move into a lower altitude orbit and hence move faster.

I suppose this poses problems for satellites. Does anyone know the height of a geostationary orbit and whether this is outside the atmosphere?

Interesting article.


losing speed

Post 4

stellarinfo

You are right in your conclusion.
For example the International Space Station has been
experience atmospheric drag during the 9 years or so
of its existence. It is now moving faster than ever before.


losing speed

Post 5

Gnomon [194] gone to Greece - back in 2 weeks

The explanation of orbits in this was completely wrong. I've rewritten it.


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