Is there a relation between the mass of a satellite and its orbital altitude? I mean, will a heavy satellite orbit at a higher or lower altitude than a lighter one, considering everything else being equal?

  • $\begingroup$ I tried to make sense of the question with my edit, please review. One part that's still unclear, despite me adding the everything else being equal part is if you want us to also discuss orbital decay and various perturbations (Yarkovsky/YORP, tidal effects, atmospheric drag since you tagged your question with low-earth-orbit,...) or should we restrict our answers to a two-body problem alone? $\endgroup$ – TildalWave Jul 19 '15 at 17:49
  • $\begingroup$ Does an object inside the ISS try to take up a completely different orbit as soon as someone releases it? $\endgroup$ – DJohnM Jul 19 '15 at 23:07
  • $\begingroup$ @DJohnM: Technically, it would, if it was not in line with ISS center of mass - if it was closer to zenith or nadir of ISS, it would be in elliptical orbit. Except. to prevent forming dangerous CO2 pockets, ISS constantly circulates its air, and that would simply pull the object to the nearest air intake vent grate, ending its satellite career prematurely. $\endgroup$ – SF. Jan 29 '17 at 23:37

While this question betrays a serious lack of understanding of physics, it's also a common lack of understanding, so I think it is in a way a good question.

We are used to helium balloons floating up into the air, wood floating on the surface of water, and cannon balls sinking to the bottom of the sea.

Intuitively, when we think of things "floating" in space we try to do it with the analogy of buoyancy because that's what we are used to, but the physics of buoyancy simply do not apply in a vacuum where there is no air or water pressure to "bouy" an object up.

When an object is in space, it is actually in perpetual freefall, nothing is holding it up against the force of gravity and it is constantly falling towards Earth with no resistance whatsoever, the force of gravity is unopposed. Because there is no resistance, the material properties of the object simply do not matter, explanations of this often involve a feather compared with something heavy.

Yet how can something be constantly falling but never reach the ground? The reason is because it is also travelling sideways at very high speeds, this causes it to take a curved trajectory that misses the earth. See Newton's cannonball for a visual example of how this kind of trajectory works.

  • $\begingroup$ Very applicable - m.youtube.com/watch?v=2p_8gx-XHJo - "you also have to go really fast to the side so that when you fall back toward earth you miss and go around instead; that's how you stay in space." $\endgroup$ – iAdjunct Dec 10 '16 at 3:04

Yes and no.

No: The equations that govern the orbit of a satellite don't say anything about weight, so if you launch a heavy satellite and a light one to the same orbit, they'll stay together.

Yes: In the equations that govern the launch of a satellite, weight is a variable. When you launch two identical rockets, one with a heavy payload and one with a light payload, the light payload will end up in a higher orbit.

  • 6
    $\begingroup$ I realize that this is nitpicking as far as artificial satellites with negligible mass compared to the primary body they orbit are concerned, but the first paragraph is incorrect. Mass of two orbiting bodies and their distance to each other will define position of their common barycenter, orbital focus that they both orbit. This matters even for artificial satellites when in orbit around a small mass body, and is the effect that NASA wants to try during the proposed asteroid redirect mission (ARM), with the orbiter as a gravity tractor. $\endgroup$ – TildalWave Jul 19 '15 at 17:40

The mass of the satellite definitely affects where it stays in the orbit (leo, meo or geo). Gravitational force between two objects is directly proportional to the product of their masses and indirectly proportional to the square of the distance between them. If a balloon is launched about 2km away from the Earth, it stays up. With its mass and at that distance, the gravitational force on it could be zero. Same cannot be said of a metal ball of higher mass. Objects with higher mass will require longer distance for the force of gravity to be ineffective.


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