satellites / earth's mass?

Question

Some one on here gave this answer :
every time we launch a satellite into orbit the mass of the Earth decreases.

Is that true? if so how ?
what would make it lose mass?

sounds fishy to me so I thought I'd check it out.

Answer 1

It is fishy.

There is the obvious, that the satellite weighs SOMETHING so if you throw 1000 kg off the Earth, the Earth will weigh 5,973,600,000,000,000,000,000,000 -1000 kg, a difference beyond the precision of our ability to measure. Essentially there is no change. Further, if the satellite is still closer to the earth than the observer the observer still feels the gravity of the combined mass of both the earth and the satellite in question. For instance, you could turn the entire mass of the earth into launched satellites in low earth orbit and the moon would hardly notice a difference (some small difference in mass distribution would make a miniscule difference.)

So, it is technically right, but in a meaningless way, sort of like making the claim that you lose weight everytime you exhale.

Answer 2

That's actually true!
The metals, etc. in the satellite came out of the earth. So the earth would get lighter by the mass of the satellite, assuming the exhaust gases from the satellite's rockets wafted back to earth.
However, obviously the effect on the earth's mass is miniscule.
I'd have to think about it, but I'm not sure it would have even the most miniscule effect on the orbit of anything else, for two reasons. One, the mass of that satellite is still orbiting earth, so maybe at least some of it seems to be emanating from the Earth's center. Secondly, the orbiting satellite will have a miniscule effect on the Earth's moment of inertia, and due to conservation of angular momentum it may have miniscule effects on other satellite orbits. You'd have to ask a NASA expert on orbits to get a detailed scoop on that one.

Answer 3

Yes it is true that the Earth is less massive, by the amount of the satellite. On the other hand, the Earth gains tons and tons every day, because of meteorites coming in.

For something as big as the Earth, neither effect makes any practical difference.

Answer 4

Since the satellite is made on earth of earth stuff (metals, ceramics, fibres, and chemicals), the moment you put it into orbit you are reducing the total mass of the earth by the mass of that stuff.

Answer 5

well the earth loses the mass of the satellite, and anything else that ends up in space and doesnt fall back to earth

Answer 6

Bravo morningfoxworth,
I would add that since the satelites have not escaped the earths gravity, but remain in orbit, they do not change the mass of the "earth system".

Answer 7

Hey, if you use matter from the Earth to manufacture into a satellite, and then send it away from Earth -- little by little you decrease the earth's mass.

This is elementary stuff.