Orbital math/tiny object orbits - questions

[Whatu]

In LEO nothing can orbit anything in any sort of stable manner. When you're inside the sphere of influence of a major body like earth, you won't be able to orbit anything except earth.

Take Phobos for example. Get in a delta glider and get a circular orbit around Phobos. Yes, you can obtain a nearly 0 eccentricity orbit, but watch the orbit map as time goes on... Because Phobos orbits inside of the Martian sphere of influence, you won't even make one orbit around Phobos before mars ruins it all... And here you're dealing with a much larger object than the shuttle, or a golf ball...

I agree, in a true 0 G environment (maybe between 2 galaxies), you could get a golf ball to orbit a bowling ball, but it would be at a ridiculously slow velocity, and the slightest force would result in escape velocity for the golf ball...

Hmm thanks for the explanation! Just to clear things up, i have one more question.

So being in the SOI of a major body, you can't orbit anything other than the major body itself, right?

If we take our reference body as the Sun, the Earth and also the Moon can't orbit anything than the Sun. But the Moon orbits Earth because it's inside Earth's SOI. And the Moon is also orbiting the Sun because the Earth's SOI is also orbiting the Sun.

Is this correct or am I just messing my head?

 

[Sword7]

Hello, folks...

Hmmm. Interesting. I checked Phobos and Deimos on Wikipedia. It said that velocity escape is 11.3 m/sec for Phobos and 5.6 m/sec for Deimos. Also surface gravity (Phobos) is around 8.4 to 1.9 mm/sec^2. For small asteroids, you can jump into orbit yourself.

Also, I heard that NASA plans to launch setallite to visit Apophis (much smaller asteroid - 700 to 1000 feet diameter) and will orbit it.

At true zero gravity env (between 2 galaxies), it is possible to orbit a space shuttle yourself. Or golf ball can orbit you as well.

For just curious, does anyone try to launch two large man-made satellites to orbit each other (away from Earth)? How about atoms or particles?

Thanks again,
Tim

 

[Zatnikitelman]

What about this, depleted uranium large bowling ball. With depleted uranium golfball. What's the numbers for those?

 

[ijuin]

What about this, depleted uranium large bowling ball. With depleted uranium golfball. What's the numbers for those?

Depleted Uranium is about three and a half times as dense as Earth, so the period of an object orbiting it will be correspondingly shorter. Since the minimum orbital time around a sphere is dependent only on its density and not its radius, in the absence of other gravity sources, an object could orbit it in a little under 30 minutes at close to its surface.

However, you WOULD have to be in an environment that lacks other gravity sources, as your "bowling ball's" gravitational acceleration is mere microns per second squared--as stated in earlier posts, a larger gravity source will tend to dominate. Maybe out in the Kuiper Belt you could do it.

Does anybody know if Orbiter simulates gravitational attraction exerted by vessels?

 

[tblaxland]

Another thing worth mentioning about trying to get small things to orbit each other in LEO is the effect that the direction of gravity won't be the same for the two objects. If the two objects are at the same height, but slightly apart, the two vectors from the two golf balls to the centre of the earth will not be parallel, but will point ever so slightly towards one another. This will have the effect of 'pulling' the two balls together ever so slightly. I can't remember off the top of my head what this effect is called

Tidal forces?

 

[Quick_Nick]

Does anybody know if Orbiter simulates gravitational attraction exerted by vessels?

I don't believe it does. But if you're only dealing with a bowling ball and a golf ball, basically spheres and with no thrust, you could possibly make a tiny planet and moon/vessel.

 

[James.Denholm]

Allow me to correct myself, an unpowered object cannot orbit it, ie: a golf ball....

So that's why I couldn't land my DGIV on Phobos... That was a bit pointless of Dan, putting a Prelude II base on Phobos when you can't land on the stupid thing anyway.

 

[thomasantony]

So that's why I couldn't land my DGIV on Phobos... That was a bit pointless of Dan, putting a Prelude II base on Phobos when you can't land on the stupid thing anyway.

Well you can actually land on it. Thats why there is a scenario to do just that. Only, its more like docking. Once you are close enough to the surface, orient yourself the correct way and use RCS to contriol your vertical speed and slowly put it down on the pad. It may even bounce once as the acceleration due to gravity is only around 0.0084-0.0019 m/s^2 .

I have done it a couple of times, so I know.
~
Thomas

 

[Zatnikitelman]

Actually, you can land on it. I've not made a soft landing, but I did "bump" phobos. I used another vessel placed on the surface as a docking target and used the docking hud and eventually met Phobos's surface. The slightest thruster burn will push the DG off however so good luck actually staying and doing any good.

 

[James.Denholm]

:chair:

 

[agentgonzo]

Tidal forces?

No, it's more specific than that. "Something" gravity I think it's called.

 

[Sword7]

Like I wrote above - the maximum possible orbital radius for the Shuttle is 120 cm.

If the Shuttle would weight 100 times more, the maximum possible radius would grow only by 100^1/3 = 4.6 - 5.5m radius.

Check http://www.asterism.org/tutorials/tut22-1.htm for more information. I found formula for hill sphere: Rh = a(m/3M)^1/3.

Yes, when further away from Earth or Sun, that is possible to orbit shuttle.

I have a question for you. Is it possible to orbit inside shuttle within its hill sphere with air or without air?

Oh, I now remember about Star Wars. There was giant ball-shaped spacecraft. That is possible to orbit it with small fighter or yourself.

Did you try them in Orbiter software yet?

Thanks again,
Tim

 

[reverend]

Hmm thanks for the explanation! Just to clear things up, i have one more question.

So being in the SOI of a major body, you can't orbit anything other than the major body itself, right?

If we take our reference body as the Sun, the Earth and also the Moon can't orbit anything than the Sun. But the Moon orbits Earth because it's inside Earth's SOI. And the Moon is also orbiting the Sun because the Earth's SOI is also orbiting the Sun.

Is this correct or am I just messing my head?

A couple things...

You can "orbit" phobos as in circling around it once, but you cannot "orbit" phobos when it's implied that it's a stable orbit, one that without constant thrusts to maintain the orbit, that would not decay for years.

The sun's SOI extends about twice the distance of neptune's orbit.

The moon orbits earth outside of earth's SOI, the moon has it's own SOI.

Phobos and Diemos orbit inside of mars SOI. You could say they don't have their own SOI. ( I think they do, it's just below the surface. )

Because the moon orbits earth within the sun's SOI, eventually, the moon's orbit will decay and it will either collide with earth, or spin off from earth to take an orbit around the sun, i think.

 

[ijuin]

The Moon IS spinning off from Earth--it was less than 20,000 km away when it first formed, and it is expected to take several billion years more to escape completely--longer than the Sun's life expectancy.
​

 

[James.Denholm]

*brain explodes*

 

[Scarecrow]

The Moon IS spinning off from Earth--it was less than 20,000 km away when it first formed, and it is expected to take several billion years more to escape completely--longer than the Sun's life expectancy.
​

What?:huh: The moon is gaining orbital energy?

 

[ijuin]

Yes--and this energy is stolen from Earth's rotation--the tidal interaction of Earth and Moon causes the Earth's rotation to slow down, while the Moon speeds up. In fact, the periodic addition of "leap seconds" at the end of most years these days is the result of the Earth's rotation slowing down, requiring us to add in the extra seconds to bring the clock back into agreement with the Earth.

 

[Whatu]

A couple things...

You can "orbit" phobos as in circling around it once, but you cannot "orbit" phobos when it's implied that it's a stable orbit, one that without constant thrusts to maintain the orbit, that would not decay for years.

The sun's SOI extends about twice the distance of neptune's orbit.

The moon orbits earth outside of earth's SOI, the moon has it's own SOI.

Phobos and Diemos orbit inside of mars SOI. You could say they don't have their own SOI. ( I think they do, it's just below the surface. )

Because the moon orbits earth within the sun's SOI, eventually, the moon's orbit will decay and it will either collide with earth, or spin off from earth to take an orbit around the sun, i think.

Interesting, thanks!

 

[ZCochrane]

This thread has reminded me to ask a (relatively) related question: I remember on the old forums there being a discussion of "moons orbiting moons" in the Sol.cfg file - - - I'm at work presently, but have modified a copy of my Sol.cfg file. Does anyone here remember/know the correct syntax for altering the Planet/Moon list such that I can have, say, a fictional body orbit the Moon? My guess is that it's something like this

Star1 = Sun
.
.
Planet3 = Earth
Earth:Moon1:Moon
Moon:Moon1:5786 Talos

... but I'm not certain it will work. Any ideas/confirmations?

Thanks a googleplex!

Warmly,
ZCochrane

 

[Lunar Pilot]

Orbiter Vessels

To agree with Quick_John (sorry if I murdered your name), I really don't think it does. To test it, I took a DG out to about, well really far, the sun didn't look any bigger than any of the other stars. Then I used the docking fuction in the Scenarior Editor and docked a completed version of Station V from 2001 to it. I didn't measure a thing. Although, if I could get a rough estimation of the mass of Station V, I might be able to calculate exactly how much gravity it has. hint, hint.