# Objects orbiting in vacuum, in ISS, question:

sonhouse
Science 24 Jul '17 00:00
1. sonhouse
Fast and Curious
24 Jul '17 00:00
So space bends making it look like an attracting force, so is it possible to have two objects like 2 one Kg masses, spherical shape, maybe make of lead for compactness, could they orbit one another and if so, what velocity would it take to make it so? And in the absence of air molecules wouldn't they co-orbit each other till time runs out?
2. 24 Jul '17 05:36
Originally posted by @sonhouse
So space bends making it look like an attracting force, so is it possible to have two objects like 2 one Kg masses, spherical shape, maybe make of lead for compactness, could they orbit one another and if so, what velocity would it take to make it so? And in the absence of air molecules wouldn't they co-orbit each other till time runs out?
Two objects, without disturbance of anything else, put in an circular orbit, then yes, they will orbit until time ends.

Sloooowly...
3. 24 Jul '17 08:11
Originally posted by @sonhouse
So space bends making it look like an attracting force, so is it possible to have two objects like 2 one Kg masses, spherical shape, maybe make of lead for compactness, could they orbit one another and if so, what velocity would it take to make it so?
As FabianFnas says, they would have to orbit very slowly to avoid reaching escape velocity which would be very low.

And in the absence of air molecules wouldn't they co-orbit each other till time runs out?
There are other forces involved that would likely affect the system. If they were inside the ISS then the gravity of the ISS would probably overwhelm the two masses, so the system wouldn't work anyway. But if they were free floating, then we have the solar wind, the earths gravitational field, then perturbations by the moons gravity etc. Even without the moon, the earths gravity on one side of each mass is slightly different from the gravity on the other side, and there are slight differences between the two masses as they orbit each other. If they are not perfectly symmetrical, this will result in rotations being set up that will affect the system.
4. 24 Jul '17 09:28
Originally posted by @fabianfnas
Two objects, without disturbance of anything else, put in an circular orbit, then yes, they will orbit until time ends.

Sloooowly...
Inside the ISS? I missed that bit of information.

Inside the ISS there are always disturbances. By most by ISS itself.
I will turn around my answer completely.

This orbit will decay quite quickly, long before the time ends.
5. sonhouse
Fast and Curious
24 Jul '17 10:08
Originally posted by @fabianfnas
Inside the ISS? I missed that bit of information.

Inside the ISS there are always disturbances. By most by ISS itself.
I will turn around my answer completely.

This orbit will decay quite quickly, long before the time ends.
Yes, that would happen in an air atmosphere but I specified it being in a vacuum chamber or outside the ISS. I calculated (if correct) the orbital velocity would indeed be very low, 50 microns per second or so average velocity. 1 kg of lead has a radius of about 2.37 cm so supposing a 3 cm orbit radius, say 18 cm circumferance, 180 mm or 180,000 microns so it would orbit about once an hour! So don't hold your breath🙂 But it seems reasonable to suppose if someone wanted to do that as a real experiment it would work!
I guess I shouldn't be surprised.
6. 24 Jul '17 10:40
Originally posted by @sonhouse
Yes, that would happen in an air atmosphere but I specified it being in a vacuum chamber .....
The problem is the vacuum chamber is NOT mass-less, so its gravity would interfere.
7. sonhouse
Fast and Curious
24 Jul '17 11:081 edit
The problem is the vacuum chamber is NOT mass-less, so its gravity would interfere.
Yes, that's why I thought it would be better outside ISS. Even there gravity is no zero. You would not find true zero anywhere in the galaxy. Maybe nowhere in the universe but close enough for this experiment just outside ISS.

Just thinking, wouldn't the mass around the experiment, assuming inside a vacuum chamber in ISS be the gravity equivalent of a faraday shield? It seems to me it would help zero out effects if the two masses were in the center of the chamber and masses averaged out in the perifery.
8. 24 Jul '17 11:16
Originally posted by @sonhouse
Yes, that's why I thought it would be better outside ISS. Even there gravity is no zero. You would not find true zero anywhere in the galaxy. Maybe nowhere in the universe but close enough for this experiment just outside ISS.
You don't need zero gravity, but you can't have local massive objects or the two masses will be attracted to them instead.

Just thinking, wouldn't the mass around the experiment, assuming inside a vacuum chamber in ISS be the gravity equivalent of a faraday shield?
If that worked, then you could fly when inside a house.

It seems to me it would help zero out effects if the two masses were in the center of the chamber and masses averaged out in the perifery.
Its complicated. But in general, no, the masses would end up going towards one surface and sticking to it.
9. 24 Jul '17 11:421 edit
Originally posted by @sonhouse
Yes, that would happen in an air atmosphere but I specified it being in a vacuum chamber or outside the ISS. I calculated (if correct) the orbital velocity would indeed be very low, 50 microns per second or so average velocity. 1 kg of lead has a radius of about 2.37 cm so supposing a 3 cm orbit radius, say 18 cm circumferance, 180 mm or 180,000 microns s ...[text shortened]... omeone wanted to do that as a real experiment it would work!
I guess I shouldn't be surprised.
Well, one disturbance would be the ISS itself. Think of the gravitation.
What would attract the most? Ten tonnes (?) of ISS or 1 kilogram of the other ball?

No, no stable orbits to be found there.
10. sonhouse
Fast and Curious
24 Jul '17 12:41
Originally posted by @fabianfnas
Well, one disturbance would be the ISS itself. Think of the gravitation.
What would attract the most? Ten tonnes (?) of ISS or 1 kilogram of the other ball?

No, no stable orbits to be found there.
Inverse square law would say put it a hundred meters away from ISS and the only thing left is Earth moon and sun to screw up the experiment🙂
11. 24 Jul '17 13:31
Originally posted by @sonhouse
Inverse square law would say put it a hundred meters away from ISS and the only thing left is Earth moon and sun to screw up the experiment🙂
You know the gravitational laws. Put in the parameters in the formula and you will have the answer how much ISS will affect your balls in relation to the Earth, the Moon and the Sun. I would think ISS wins this battle.

Then we have also solar wind, assymetric heat, and certainly other pertuberations too.
12. sonhouse
Fast and Curious
24 Jul '17 14:031 edit
Originally posted by @fabianfnas
You know the gravitational laws. Put in the parameters in the formula and you will have the answer how much ISS will affect your balls in relation to the Earth, the Moon and the Sun. I would think ISS wins this battle.

Then we have also solar wind, assymetric heat, and certainly other pertuberations too.
I think it is a bit more complex than you think. For instance, calculating the orbital velocity of the two spheres in isolation is not that hard, but if it is inside ISS, the gravity pull would be anti-grav, in that the walls would pull away and you might end up in the center if unperturbed. Even in orbit away from ISS there will be problems with atmosphere leftovers at that altitude to say nothing of Earth moon and sun effects. It sure wouldn't take much to upset the little orbits around each other since according to my so-called math 🙂 they would have an orbital period of about one hour, plenty of time for perturbutions to take effect. All in all, I think it would be a nice experiment. For instance, about the complex nature of mass around you, suppose you were in a chamber in the center of Earth, assuming you have ambient conditions, you would be in zero gravity more or less, with perturbutions from the sun but I think you would still be able to float around like you were on ISS.
13. 24 Jul '17 14:27
Originally posted by @sonhouse
I think it is a bit more complex than you think. For instance, calculating the orbital velocity of the two spheres in isolation is not that hard, but if it is inside ISS, the gravity pull would be anti-grav, in that the walls would pull away and you might end up in the center if unperturbed. Even in orbit away from ISS there will be problems with atmospher ...[text shortened]... urbutions from the sun but I think you would still be able to float around like you were on ISS.
With all due respect - I don't think this experiment will give us more information about gravitation and grav systems than we already know. It doesn't add anything to our previous knowledge. (If you think I am wrong, please, speculate.)

Moreover, it will be very hard (and expensive, and time consuming) to conduct this experiment out fully. What will be the orbital period? Years? Hundred of years?

As food for thoughts and an interesting discussion in the matter - but besides that..., I don't know.
14. 24 Jul '17 14:38
Originally posted by @sonhouse
All in all, I think it would be a nice experiment.
A very uninteresting one.

The LISA pathfinder mission had two masses in free fall and constantly measured the distance between them very accurately:
15. sonhouse
Fast and Curious
24 Jul '17 15:52
Originally posted by @fabianfnas
With all due respect - I don't think this experiment will give us more information about gravitation and grav systems than we already know. It doesn't add anything to our previous knowledge. (If you think I am wrong, please, speculate.)

Moreover, it will be very hard (and expensive, and time consuming) to conduct this experiment out fully. What will b ...[text shortened]... od for thoughts and an interesting discussion in the matter - but besides that..., I don't know.
I calculated the orbital period at around one hour. I didn't claim something new would be found about gravity, just a fun experiment.