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My kerbin have a third moon !


Elowiny

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And as a funny sidenote, Earth "currently" has a second moon, since at least 775 years and for around the next 165 years "2014 OL339" - it's officially a quasi-satellite, but hard to say after how many years in an orbit it can be called stable ;)

I hadn't heard about 2014 OL339, thanks. Perhaps an even more relevant example of a non man-made object being captured by the Earth is 2006 RH120. It was most recently in Earth orbit between September 2006 and June 2007. According to Wikipedia, the object made four Earth orbits of about three months each before being ejected after the June 2007 perigee.

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I hadn't heard about 2014 OL339, thanks. Perhaps an even more relevant example of a non man-made object being captured by the Earth is 2006 RH120. It was most recently in Earth orbit between September 2006 and June 2007. According to Wikipedia, the object made four Earth orbits of about three months each before being ejected after the June 2007 perigee.

Sounds like my place satellite contract yesterday :D Target orbit was only half a million meters further out then mun, and somehow my first try of using muns gravity to raise PE ended in coming three times in a row out of muns SOI and getting captured again shortly after leaving it.

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Whoa, I was in orbiting in General, but now am lurking in Science Labs... I think I've just experienced a moderator assisted capture! :cool:

Yup, that's how you secretly learn stuf. You're just playing around and one day you realize that you know orbital mechanics.

Than you talk about your playing on the forum, and suddenly you realyze you know the theory behind it.

It's scary

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This could happen in KSP theoretically. If an asteroid aerobraked at Kerbin, then was accelerated by either the Mun or Minmus, it could raise the periapsis out of Kerbin's atmosphere and put it in an orbit

I don't think that could happen in the game though given aerobraking isn't simulated while on rails (unless you were following it with a ship within 2.5km, which would be fun but might be challenging during the aerocapture). Also, I haven't yet seen any asteroids that dip into Kerbin's atmosphere, I've had a few on a collision course and some with a pretty close periapsis, but none lower then 200km altitude. I imagine it's possible though.

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  • 2 weeks later...
  • 2 years later...

Two simple reasons, this happens in Tutorials, Asteroid Rendezvous.

A Gravity Brake, leaded by Retrograde approach to Mün. Causing Loss of speed, to put in stable orbit, no effect by Minimus its minimal. Another but Prograde approach to Mün (Gravity Assist) lead to Escape Velocity. 

Try it yourself, its Safer but longer than AeroBrake or LithoBrake.

Put mün Transfer from Prograde orbit, you will either escape or get in circular or Less Eccentric orbit.

Use Retrograde orbit to end on Kerbin Directly. A Tylo Gravity Brake Is Lots Safer than a Laythe or Jool AeroBrake and a Gravity Assit may help to direct in Solar Orbit.

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On 17.12.2014 at 6:19 PM, Pope_Gregory_IX said:

I wish I understood this - once a satellite has been captured by a body and made a couple of orbits, how does that satellite then gain enough kinetic energy to reach escape velocity without input from some external energy source? With J002E3 is the additional energy just provided by crossing the moon's orbit?

Cheers,

Adam

If you are captured by the moon in ksp or real life it will have an orbit who crosses the moon orbit and the moon will disturb its orbit and eject it. 
In KSP this is simple to get an Moon capture the asteroid has to pass trough Moon SOI and the resulting orbit also has to pass trough it some times. 

Its probably more common than we realize as something pretty much in the plane of moon orbit will capture easy but also get ejected easy. 
In real world its no SOI so its more complex but the overall rule applies. 

In real world the Lagrangian points works for this too, This is probably how Mars got its two small moons. Passing trough the L1 or L2 will shift the orbit a bit and this can get you into orbit. 
Tidal forces will then circulate the orbit, this is very unlikely on earth because of our large and fat moon who mess up for the small guys. 
This however is pretty common for the gas giants who have lots of mostly smaller moons in weird orbits outside the major ones Triton is an exception and also captured. 

For earth to have an Minmus I guess it had to be captured before the impact who created the Moon. 
Impact is another way to do it, think its only earth moon who has done it for larger bodies but its probably common for asteroids. 

On 22.12.2014 at 11:05 PM, Branjoman said:

This could happen in KSP theoretically. If an asteroid aerobraked at Kerbin, then was accelerated by either the Mun or Minmus, it could raise the periapsis out of Kerbin's atmosphere and put it in an orbit

Aerobrake is extremely unlikely as the window is so tiny the next orbit will also have an lower Pe as all aerobrakes do unless Mun saves it who require an Mun intercept. 
In practice it would not work at all as only active objects aerobrakes, 
An well know exploit in KSP is that you can intercept an ship in an 80 Ap, 40 Pe orbit and refuel it as the orbit is stable if ship is not active while in atmosphere, this is not uncommon for upper stages. 

For real world asteroids its just as unlikely, something like Mars moons is larger than the dense part of the atmosphere and the moon will break up in atmosphere even if surviving the tidal forces. 

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On 12/22/2014 at 5:05 PM, Branjoman said:

This could happen in KSP theoretically. If an asteroid aerobraked at Kerbin, then was accelerated by either the Mun or Minmus, it could raise the periapsis out of Kerbin's atmosphere and put it in an orbit

The resulting orbit could not be long-term stable, however -- if it had a high enough apoapsis for Mun (or moreso Minmus) to pull periapsis up out of the atmosphere, the apoapsis would stay high enough to guarantee another encounter in the future (and if it's going out to Minmus orbit, there's also a likelihood of a Mun encounter along the way, if it's got low enough inclination for the Mun/Minmus encounter to result in stabilizing what ought to have been a decaying orbit).

Never mind that aerobraking in KSP is Heisenbergian (i.e. nothing happens if it's not observed) and that asteroids don't seem to get low enough to aerobrake without being on a hard-surface collision course; even if it happened, it couldn't produce a "new Mun" in KSP as the game exists now.

Now, asteroids making a close approach at relatively low velocity do often read as "orbiting Kerbin" for periods of up to several tens of Kerbin days.  The first two I tried to intercept showed that way, including an orbit plot that was elliptical, rather than parabolic or hyperbolic, despite also showing "Kerbin escape" after some period of time.  The one I finally went out into "orbiting the sun" territory to intercept and managed to bring back is really in orbit; it's got a period of about 4 days and never gets close enough to Mun to enter SOI.

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^ ^ ^

On 12/17/2014 at 9:45 AM, SlyReaper said:

In reality, it is possible for an asteroid or moonlet to be captured and end up in a stable orbit, but it's extremely rare. As far as I know, the only way for it to happen is for two small objects orbiting each other, they enter the sphere of influence of the larger body.

Yep. A very, VERY lucky aerobrake.

 

And alright, is there a visualization somewhere of the moon's orbit forming? I know there's the theory that it was formed from a collision with primordial Earth, but how did it ever achieve a stable orbit?

 

 

Edited by vger
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3 hours ago, vger said:

^ ^ ^

Yep. A very, VERY lucky aerobrake.

 

And alright, is there a visualization somewhere of the moon's orbit forming? I know there's the theory that it was formed from a collision with primordial Earth, but how did it ever achieve a stable orbit?

 

 

Just a guess, but if it was formed from remnants of Theia and ejecta from earth, the individual pieces would all have been on either hyperbolic or suborbital trajectories, but when they smashed together, they would change each others' paths into something that didn't hit the surface or escape the system.

Then once you have an elliptical orbit in a "dirty" region of space, it will tend to circularise, as the body is hitting things harder and more often at perigee when it is moving faster. As well as circularisation due to tidal effects.

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The reverse happened to me twice: once a contract told me to put a sattelite into a very similar orbit to the mun, it got kicked out a while later. As that happend the contract told me to change the orbit of the sattelite, "good luck with that now...".

The secont time was over at Jool, a sattelite got kicked out somehow(i blame Tylo), an after a 300 m/sek burn it was heading for Eeloo. (that was very lucky!) The problem was that without Eeloo the orbit was almost hyperbolic so it needed alot of dv to slow down. It had an ion engine, but not much solar power that far out, and it was very heavy sat(the biggest relay + ion engine = low twr). I succeded getting into orbit but not much more as I was out of fuel...

It is still called "Jool Relay", and now my tiny laythe science plane had no signal...

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3 hours ago, vger said:

snip

And alright, is there a visualization somewhere of the moon's orbit forming? I know there's the theory that it was formed from a collision with primordial Earth, but how did it ever achieve a stable orbit?

 

Maybe you find something to watch when searching for giant impact hypothesis. I have seen different ones simulations, the latest from just a few years ago when the impact angle was recalculated but i couldn't find it now. I think it was Science magazine ...

The stable orbit thing comes quite automatically. The two cores of the bodies (they just had differentiated) united. Part of the mantle material was ejected into orbit and most of it just fell back. The rest gathered around the wobbling new mess err mass and did what it could do best: formed a disc on a low orbit with a few bigger lumps that served as condensation cores. It started on a quite low orbit, tidal forces let it slowly drift higher.

Edit: Here you go, @vger not a cinema style motion picture but a nice visualisation.

Edited by Green Baron
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9 hours ago, peadar1987 said:

Just a guess, but if it was formed from remnants of Theia and ejecta from earth, the individual pieces would all have been on either hyperbolic or suborbital trajectories, but when they smashed together, they would change each others' paths into something that didn't hit the surface or escape the system.

Then once you have an elliptical orbit in a "dirty" region of space, it will tend to circularise, as the body is hitting things harder and more often at perigee when it is moving faster. As well as circularisation due to tidal effects.

Yes, its not aerobrake, Moon was created with an impact, guess this is main reason why asteroids has moons too. Perhaps also Kuiper belt objects even if suns gravity has an low gravity gradient out there and the speeds are pretty low. 
The small outer moons of the gas giants are captured asteroids then because they got captured by L1 or L2. 

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