Jool System - N-body Vall destruction

[Hypercosmic]

So, I think everybody knew about Vall's orbital instability in N-body space already, but my simulation in Universe Sandbox² revealed more than orbital instability of Vall.

 

PARAMETERS CONFIGURATION

MASS = original * 10²

SEMI-MAJOR AXIS = original * 10¹

START OF THE SIMULATION: 3.88 HOURS (due to time spent to make the game recognize the orbits, so I can edit the orbits.)

OBJECTS INCLUDED: JOOL, LAYTHE, VALL, TYLO

 

The result is pretty spectacular.

 

At first, Vall and Laythe interacts, pushing Vall outward and Laythe slightly inward. (This would cause Laythe to have even more volcanoes.) Then, in the final encounter, Vall is thrown outward.

In other n-body simulation, Vall would get slingshot by Tylo to eccentric orbit, but this?

 

http://imgur.com/a/xR9sN (Idk how to embed)

 

A spectacular COLLISION.

 

R.I.P Vall 14 days from the beginning of the simulation.

 

Note: I did not included any other objects in Kerbol system, so it is possible that Vall will survive the fate, but in any case Tylo's tidal force would shred Vall apart.

Edited September 28, 2016 by Hypercosmic

[RA3236]

You should also think of Bop and Pol, and I might look at this too  

EDIT: Also keep the SMA increase at the same multiplier as Mass (10^2) (The edit box is really horrible on mobile...) so that it is closer to what actually would happen, or alternatively make Jool its actual KSP parameters by turning off realistic radius and make the moons the mass and orbit they are meant to be (or in other words, all multipliers 10^0)

Edited September 28, 2016 by RA3236

[KerikBalm]

I agree, keep all multipliers at 1.

Since I don't have universe sandbox... I was wondering if you could run simulations of various versions of my "Rald" planet/moon, and tell me which ones seem to be stable...

I've got one version of about duna mass orbiting at keostationary orbit (I fear it would wreak havoc on Mun, or vice versa).

Another version orbits where Minmus used to be, with minmus as a subsatelite of it (I fear that minmus would not be stable, and that it still may screw up Mun).

Both of these would probably only need to be simulated with Kerbin, Mun, and Minmus

Another version is at Sun-Kerbin L4... I'm guessing it requires Kerbin, Jool, Duna, and Eve to simulate if it is stable (or approximations of Kerbin and duna, where a planet with the mass of kerbin+Mun+ Minmus is used instead of kerbin, and a planet with the mass of Duna+Ike is used instead of Duna. I'd guess that Jool's moons aren't big enough ot make a difference, and Gilly doesn't make a difference)

While Squad may not have cared about stability for the Jool system, I care about it for my planet addon

if you could help me determine which configurations are stable, that would be great.

Edited September 28, 2016 by KerikBalm

[Hypercosmic]

5 hours ago, RA3236 said:

You should also think of Bop and Pol, and I might look at this too  

EDIT: Also keep the SMA increase at the same multiplier as Mass (10^2) (The edit box is really horrible on mobile...) so that it is closer to what actually would happen, or alternatively make Jool its actual KSP parameters by turning off realistic radius and make the moons the mass and orbit they are meant to be (or in other words, all multipliers 10^0)

Note that SMa are increase to match real world scale (10 times). From US², each moons appeared on the sky of each other as they should in KSP, even it is actually bigger. When radius increased by 10 times, mass must be increased by 1,000 times, but I do only 100 times because KSP planets are too dense to be realistic (they are much smaller than Earth, so they are super dense to keep the gravity). Note that each moon's surface gravity is the same as in KSP!

3 hours ago, KerikBalm said:

I agree, keep all multipliers at 1.

Since I don't have universe sandbox... I was wondering if you could run simulations of various versions of my "Rald" planet/moon, and tell me which ones seem to be stable...

I've got one version of about duna mass orbiting at keostationary orbit (I fear it would wreak havoc on Mun, or vice versa).

Another version orbits where Minmus used to be, with minmus as a subsatelite of it (I fear that minmus would not be stable, and that it still may screw up Mun).

Both of these would probably only need to be simulated with Kerbin, Mun, and Minmus

Another version is at Sun-Kerbin L4... I'm guessing it requires Kerbin, Jool, Duna, and Eve to simulate if it is stable (or approximations of Kerbin and duna, where a planet with the mass of kerbin+Mun+ Minmus is used instead of kerbin, and a planet with the mass of Duna+Ike is used instead of Duna. I'd guess that Jool's moons aren't big enough ot make a difference, and Gilly doesn't make a difference)

While Squad may not have cared about stability for the Jool system, I care about it for my planet addon

if you could help me determine which configurations are stable, that would be great.

This time I'll test your mod, running Rald on KSP scale. (And also, real scale would be fun to make too.)

 

(Wait a minute, what are the parameters of Rald? (Mass, radius, orbital configuration...)

Edited September 28, 2016 by Hypercosmic

[Sharpy]

3 hours ago, KerikBalm said:

While Squad may not have cared about stability for the Jool system, I care about it for my planet addon

if you could help me determine which configurations are stable, that would be great.

 

Resonant orbits of non-even number resonance are quite stable. So, e.g. one or two Rald orbits per three Mun orbits, Orbit of Minmus around Raid would be worse, but resonance of n+1/2 with Mun would help (every other time Mun passes Rald, Minmus is on the opposite side as before, relative to Mun - say, Rald and Mun are in 1:3 resonance, Mun circling Kerbin three times before Rald completes its one orbit. Minmus could circle Rald 32.5 times without being very disturbed by Mun -  every time Mun and Rald line up, Minmus is after 10 full orbits, plus 0.5 (ending up on the opposite side of Rald as by the previous pass) plus 1/3 (as Rald circles Kerbin, it covers 1/3 the circumference of its orbit by each Mun pass; Minmus must be that 1/3 "ahead" of the previous orientation so the set Kerbin-Mun-Rald-Minmus remains unchanged [except for Minmus being on the opposite side].

It would still be destabilized by Kerbin, but make it either tidally locked, or the orbit resonant in integer-number ratio (1:1, 1:2, 1:3, 1:4...) with Rald's spin period, and quite eccentric, and you can explain it away by Rald's uneven mass distribution counter-acting Kerbin's destabilization through tidal forces stabilizing Minmus orbital speed. If you want better explanation, just ask.

Edited September 28, 2016 by Sharpy

[KerikBalm]

as you like, it could be fun to just have a thread for N body simulations.

As for the rescaling: yes 10x to SMAs does get them to about "real" values.

Yes KSP planets are unrealistically dense by about a factor of 10, so you could do the increase to the power of 2 instead of 3 (because volume is related to r^3), but that will change orbital periods. I wonder what it does to resonances though...

Mass directly scales acceleration at a given distance: A = v^2/r. You increase A bu 100x, and r by 10x, v thus increases by sqrt (10)

Orbital period proportions are determined by sqrt( SMA^3/ Mass)  so a 10x increase to SMA and a 100x increase to mass means that orbital period increases by sqrt 10 as well... all increases are proportional resonances should be maintained. It seems everything stays proportional as long as we treat things as point masses... So is that the only difference between your simulation and previous ones? Your simulation allows for collisions and the other ones treated them as dimensionless point masses (which would almost never collide)

[Hypercosmic]

I've built and ran the simulation for stock sized KSP.

Due to nature of US², adjusting eccentricity can change value of SMa and make the whole simulation less accurate, but anyways, the result is pretty much the same:

Vall slammed right into Tylo.

So, let's talk about Rald.

[KerikBalm]

7 minutes ago, Sharpy said:

Resonant orbits of non-even number resonance are quite stable. So, e.g. one or two Rald orbits per three Mun orbits,

Well, I didn't want to change Kerbin's properties, and with such a massive moon in so close, I'd think Kerbin would have to tidally lock to Rald - so Rald goes to keostationary orbit, no changing that. Rald orbit = 1 Kerbin day

I suppose I could then move the Mun to have an orbit with an exact integer value... if I move it out so its sidereal orbital period is 7 days instead of ~6.43 days, that should be stable? That wouldn't disrupt the system too much, and it would still be "basically" the stock system with a large habitable Keosynchronus moon.

Quote

Orbit of Minmus around Raid would be worse, but resonance of n+1/2 with Mun would help (every other time Mun passes Rald, Minmus is on the opposite side as before, relative to Mun -

I'm assuming you mean orbit of Minmus around kerbin with Rald as an inner moon... or do you mean the version where Rald moves to where minmus was I have too many versions of this... I'd like to figure out which would be "workable" so I can discard some variants as excessively unrealstic

Ok, so if Mun's modified orbit is 7 days, and stock Minmus orbits at 49.875 kerbin days... if I make it 49 (a multiple of 7) +3.5 (half 7) = 52.5 day orbital period, it should be relatively stable?

*oops reading below, it seems you're talking about minmus orbiting rald, with rald much farther out

Quote

say, Rald and Mun are in 1:3 resonance, Mun circling Kerbin three times before Rald completes its one orbit. Minmus could circle Rald 32.5 times without being very disturbed by Mun -  every time Mun and Rald line up, Minmus is after 10 full orbits, plus 0.5 (ending up on the opposite side of Rald as by the previous pass) plus 1/3 (as Rald circles Kerbin, it covers 1/3 the circumference of its orbit by each Mun pass; Minmus must be that 1/3 "ahead" of the previous orientation so the set Kerbin-Mun-Rald-Minmus remains unchanged [except for Minmus being on the opposite side].

It would still be destabilized by Kerbin, but make it either tidally locked, or the orbit resonant in integer-number ratio (1:1, 1:2, 1:3, 1:4...) with Rald's spin period, and quite eccentric, and you can explain it away by Rald's uneven mass distribution counter-acting Kerbin's destabilization through tidal forces stabilizing Minmus orbital speed. If you want better explanation, just ask.

Well, I did have Minmus tidally locked to Rald, and orbiting quite close. With Rald-Minmus' orbital period of about 50 kerbin days... Rald-Minmus and Mun are closest to a 7:1 resonance (49 and 7 day orbital periods). I'd have to move Rald closer to have a 21 day orbit... to get this 3:1 resonance.

Lets leave it at the 7:1 resonance... with rald-minmus' orbital period around kerbin being 49 days, mun orbits 7 days. What would a good orbital period be for Mimus? Have Minmus orbit rald 7.5 times per orbit of Mun, thus its orbital period is 7.5/7 = 1.07 days?

What about for the version where I make Rald more massive, and have Duna orbit Rald (tidally locked to each other, Duna's rotation periods stays the same, so ~3 kerbin days).

Can I just put Ike far enough out and not care about resonances? IIRC Mun and Minmus aren't in any resonances, but Minmus is relatively stable.

Is rald at Sun-Kerbin L4 stable, or is it really unstable being nearly 10% kerbin's mass? particularly with Eve close by (being proportionally much more massive than Venus) and knowing that "Theia" if it existed probably became unstable when its mass exceeded 10% of Earth's mass?

 

29 minutes ago, KerikBalm said:

Orbital period proportions are determined by sqrt( SMA^3/ Mass)  so a 10x increase to SMA and a 100x increase to mass means that orbital period increases by sqrt 10 as well... all increases are proportional resonances should be maintained. It seems everything stays proportional as long as we treat things as point masses... So is that the only difference between your simulation and previous ones? Your simulation allows for collisions and the other ones treated them as dimensionless point masses (which would almost never collide)

 

25 minutes ago, Hypercosmic said:

I've built and ran the simulation for stock sized KSP.

Due to nature of US², adjusting eccentricity can change value of SMa and make the whole simulation less accurate, but anyways, the result is pretty much the same:

Vall slammed right into Tylo.

So, let's talk about Rald.

Cool, my thought that things stay proportional and it wouldn't matter after all (despite earlier saying to keep all multipliers at 1x) ended up being right.

Talking about rald... it seems like Sharpy is giving me hope that I can make the inner moon version of Rald work... with Rald, Mun, and Minmus being in a 1:7:49 resonance. Later today I'll calculate the SMAs needed to get that resonance, and it would be cool if you could model that for me to confirm

 

[Hypercosmic]

23 minutes ago, KerikBalm said:

Well, I didn't want to change Kerbin's properties, and with such a massive moon in so close, I'd think Kerbin would have to tidally lock to Rald - so Rald goes to keostationary orbit, no changing that. Rald orbit = 1 Kerbin day

I suppose I could then move the Mun to have an orbit with an exact integer value... if I move it out so its sidereal orbital period is 7 days instead of ~6.43 days, that should be stable? That wouldn't disrupt the system too much, and it would still be "basically" the stock system with a large habitable Keosynchronus moon.

I'm assuming you mean orbit of Minmus around kerbin with Rald as an inner moon... or do you mean the version where Rald moves to where minmus was I have too many versions of this... I'd like to figure out which would be "workable" so I can discard some variants as excessively unrealstic

Ok, so if Mun's modified orbit is 7 days, and stock Minmus orbits at 49.875 kerbin days... if I make it 49 (a multiple of 7) +3.5 (half 7) = 52.5 day orbital period, it should be relatively stable?

*oops reading below, it seems you're talking about minmus orbiting rald, with rald much farther out

Well, I did have Minmus tidally locked to Rald, and orbiting quite close. With Rald-Minmus' orbital period of about 50 kerbin days... Rald-Minmus and Mun are closest to a 7:1 resonance (49 and 7 day orbital periods). I'd have to move Rald closer to have a 21 day orbit... to get this 3:1 resonance.

Lets leave it at the 7:1 resonance... with rald-minmus' orbital period around kerbin being 49 days, mun orbits 7 days. What would a good orbital period be for Mimus? Have Minmus orbit rald 7.5 times per orbit of Mun, thus its orbital period is 7.5/7 = 1.07 days?

What about for the version where I make Rald more massive, and have Duna orbit Rald (tidally locked to each other, Duna's rotation periods stays the same, so ~3 kerbin days).

Can I just put Ike far enough out and not care about resonances? IIRC Mun and Minmus aren't in any resonances, but Minmus is relatively stable.

Is rald at Sun-Kerbin L4 stable, or is it really unstable being nearly 10% kerbin's mass? particularly with Eve close by (being proportionally much more massive than Venus) and knowing that "Theia" if it existed probably became unstable when its mass exceeded 10% of Earth's mass?

 

 

Cool, my thought that things stay proportional and it wouldn't matter after all (despite earlier saying to keep all multipliers at 1x) ended up being right.

Talking about rald... it seems like Sharpy is giving me hope that I can make the inner moon version of Rald work... with Rald, Mun, and Minmus being in a 1:7:49 resonance. Later today I'll calculate the SMAs needed to get that resonance, and it would be cool if you could model that for me to confirm

 

From my simulator, and Rald's mass is 1/10 times Kerbin mass (real mass).

Result: Keep that tidal locking, in case of 24 hours orbit.

For an inconveniently close 6 hours orbit molten Rald and heats up Kerbin into uninhabitability.

 

Using stock mass, Kerbin and Rald orbits without heating problem (probably).

 

I suggest putting this away from Kerbin.

Note that in binary star system, circumbinary planets' SMa are at least 7 times the parent separation.

Edited September 28, 2016 by Hypercosmic

[KerikBalm]

Quote

Result: Keep that tidal locking, in case of 24 hours orbit.

I do keep tidal locking, but at 1 kerbin day, ie 6 hour orbit

Quote

an inconveniently close 6 hours orbit molten Rald and heats up Kerbin into uninhabitability.

I thought that there wouldn't be any heating if they were already tidally locked and the eccentricity was low... just a litte from the tug of Mun, is that enough or did you not have them tidally locked?

so for the inner moon, rald is too close to the roche limit?

I wonder how roche limit scales.... 10x SMA, and 100x mass, does it still shred?

[Sharpy]

36 minutes ago, KerikBalm said:

Well, I didn't want to change Kerbin's properties, and with such a massive moon in so close, I'd think Kerbin would have to tidally lock to Rald - so Rald goes to keostationary orbit, no changing that. Rald orbit = 1 Kerbin day

 

Kerbin remains the same. Rald would be quite stable as keostationary, but it would be destabilizing Mun and Minmus something awful. We're talking more about Rald on Minmus orbit scenario - or actually, on an orbit that is similar but not the same as Minmus.

 

Quote

I suppose I could then move the Mun to have an orbit with an exact integer value... if I move it out so its sidereal orbital period is 7 days instead of ~6.43 days, that should be stable? That wouldn't disrupt the system too much, and it would still be "basically" the stock system with a large habitable Keosynchronus moon.
 

There is no need for tidal lock or any synchronicity between Kerbin and anything that orbits it - though moving Mun to KEO would automatically explain its stability (tidally locked and stabilized by Kerbin's tidal forces). But let us leave Mun and Kerbin alone - we're only moving Rald and Minmus.

 

Quote

I'm assuming you mean orbit of Minmus around kerbin with Rald as an inner moon... or do you mean the version where Rald moves to where minmus was I have too many versions of this... I'd like to figure out which would be "workable" so I can discard some variants as excessively unrealstic

No, I'm assuming Minmus circling Rald, with Rald circling Kerbin. Rald is on an orbit that is similar, but not quite the same, as stock Minmus orbit.

 

Quote

Well, I did have Minmus tidally locked to Rald, and orbiting quite close. With Rald-Minmus' orbital period of about 50 kerbin days... Rald-Minmus and Mun are closest to a 7:1 resonance (49 and 7 day orbital periods).

 

Make Rald-Mun a perfect 7:1 and you have that pair not destabilizing each other.

Keep Minmus (circling Rald) 100% tidally locked to Rald (both spin and orbit - Rald-synchronous) and you have it not just stable, but being actively stabilized against destabilizing influences (albeit weakly so).

Have Minmus orbital period be n+0.5+1/7 of Mun and you have Mun's destabilization minimized.

 

Of course not in that order.

0. We're not touching Kerbin or Mun.

1. We're moving Rald to an orbit of 7*6.43 = 45.1 days, to be in 1:7 resonance with Mun.

2. We're moving Minmus to an orbit of 6.43*1.143 / (n+0.643) days with some reasonable n so that the final number comes somewhere close to 1.

 -- 0.143 is 1/7.

-- 6.43*1.143 is the frequency of Mun aligning with Rald - 1+1/7 times Mun orbital period (per one Mun period, Rald travels 1/7 the orbit ahead.)

-- 0.643 is 1/7 + 1/2. This is the adjustment of sidereal vs synodic day of Minmus vs Kerbin, plus landing on opposite side of Rald.

Let's pick n = 10. It's promising. 7.349 / 10.643 = 0.69 Kerbin day. That will be Minmus orbital period around Rald. Put it in an orbit to match. If it's too large (getting disturbingly close to Mun), increase n or increase Rald mass, but don't overdo it (that WILL destabilize Mun- tidal stabilization is weak!)

3. We're adjusting Rald's spin period to the same 0.69 Kerbin day, so that it looks like Minmus is tidally locked with it.

 

 

Edited September 28, 2016 by Sharpy

[KerikBalm]

17 minutes ago, Hypercosmic said:

From my simulator, and Rald's mass is 1/10 times Kerbin mass (real mass).

Result: Keep that tidal locking, in case of 24 hours orbit.

For an inconveniently close 6 hours orbit molten Rald and heats up Kerbin into uninhabitability.

Using stock mass, Kerbin and Rald orbits without heating problem (probably).

Well, I'm "fine" with it if the stock mass doesn't make a heating problem... if we scale it up to a "realistic" size, I think its also fair to say we also changed the rotation period of Kerbin to a more realistic 24 hours instead of 6... I wonder what a real life earth witha  6 hour day would do to the moon...

But since this also simulates habitable conditions... I wonder how the Rald-Duna version fares. Rald is a bit far out to have liquid water... but I'd think its borderline.... particularly if we have a 0.135 atm atmosphere of which half is CO2 for some greenhouse effect... but if the energy budget is coming up short, I wonder where I could put Ike, or how much eccentricity to give to Duna to get some tidal heating to make up the difference. (am I correct in assuming in just a tidally locked binary system with no eccentricity, that there is no heating?)

14 minutes ago, Sharpy said:

Kerbin remains the same. Rald would be quite stable as keostationary, but it would be destabilizing Mun and Minmus something awful.

That's what I thought. The inner-moon variant was for looks, and I found some other people liked it, but I've played mostly with the sun-kerbin L4, and the Rald-Duna variants. I thought Minmus would be far enough away that it would be stable though...

So its still not stable even if Rald and Mun are in a 1:7 resonance with each other? Rald is a 1 day orbit, and we move Mun to be in a 7 day orbit?

Can minmus survive a 49:1 resonance with Rald?

Quote

There is no need for tidal lock or any synchronicity between Kerbin and anything that orbits it

Doesn't that happen naturally if things orbit too close? I always hear about how a planet in the "habitable zone" of a red dwarf would quickly become tidally locked to its star because red dwarfs are so dim and a planet woould need to orbit very close.

Quote

Make Rald-Mun a perfect 7:1 and you have that pair not destabilizing each other.

0. We're not touching Kerbin or Mun.

Cool, but I still think we should allow for moving Mun... I'm liking the idea of a 7:1 resonance with Rald having a 49 kerbin day orbit (thus the mun woves a bit outward to hav a 7 day orbit)

Quote

1. We're moving Rald to an orbit of 7*6.43 = 45.1 days, to be in 1:7 resonance with Mun.

2. We're moving Minmus to an orbit of 6.43*1.143 / (n+0.643) days with some reasonable n so that the final number comes somewhere close to 1.

 -- 0.143 is 1/7.

-- 6.43*1.143 is the frequency of Mun aligning with Rald - 1+1/7 times Mun orbital period (per one Mun period, Rald travels 1/7 the orbit ahead.)

-- 0.643 is 1/7 + 1/2. This is the adjustment of sidereal vs synodic day of Minmus vs Kerbin, plus landing on opposite side of Rald.

Let's pick n = 10. It's promising. 7.349 / 10.643 = 0.69 Kerbin day. That will be Minmus orbital period around Rald. Put it in an orbit to match. If it's too large (getting disturbingly close to Mun), increase n.

3. We're adjusting Rald's spin period to the same 0.69 Kerbin day, so that it looks like Minmus is tidally locked with it.

Sounds good to me, but I might want to weak those numbers for a Mun at a 7 day orbit.

[Sharpy]

11 minutes ago, KerikBalm said:

So its still not stable even if Rald and Mun are in a 1:7 resonance with each other? Rald is a 1 day orbit, and we move Mun to be in a 7 day orbit?

Can minmus survive a 49:1 resonance with Rald?

This might work, with Rald not being very heavy.

Quote

Doesn't that happen naturally if things orbit too close? I always hear about how a planet in the "habitable zone" of a red dwarf would quickly become tidally locked to its star because red dwarfs are so dim and a planet woould need to orbit very close.

Tidal lock and orbital resonances happen all the time, and not even very close.

That whole bunch of dwarf planets found outside Neptune orbit? About all are in orbital resonance with Neptune. Mercury is spin-locked in 1:3 resonance with Sun. Most of moons of Jupiter and Pluto are in some kinds of resonances. If you look at orbital periods and spin periods of bodies in the solar system, you will spot a lot of such dependencies.

 

Tidal forces are acting friction-like, tending towards certain equilibria and keeping locked bodies in these equilibria. They aren't very strong forces, but given enough time they can affect very huge objects even over quite long distances.

 

Quote

Cool, but I still think we should allow for moving Mun... I'm liking the idea of a 7:1 resonance with Rald having a 49 kerbin day orbit (thus the mun woves a bit outward to hav a 7 day orbit)

That's okay, but unnecessary. AFAIK lock of orbit to spin of the central body in any ratio but 1:1 is not all that frequent.

[Hypercosmic]

1 minute ago, Sharpy said:

That whole bunch of dwarf planets found outside Neptune orbit? About all are in orbital resonance with Neptune. Mercury is spin-locked in 1:3 resonance with Sun. Most of moons of Jupiter and Pluto are in some kinds of resonances. If you look at orbital periods and spin periods of bodies in the solar system, you will spot a lot of such dependencies.

Mercury is in spin:orbit 3:2, making each solar day on Mercury two times the actual year.

 

Resonance can make very stable system or very unstable systems depended on how you place them. In case of Galilean moons, that's very stable. In case of Joolian moons, that's very unstable. Plutino's 2:3 orbital resonance with Neptune prevent them from colliding with the ice giant.

In the other note, I have something unrelated to some extent, but still quite related.

Try playing both at the same time.

[Sharpy]

18 minutes ago, Hypercosmic said:

Mercury is in spin:orbit 3:2, making each solar day on Mercury two times the actual year.

 

 

Thanks for the correction

 

Also: why are we observing so many stable resonances and so few unstable? Because the unstable ones have long caused a crash or an escape, while the stable ones... remain stable.

[KerikBalm]

26 minutes ago, Sharpy said:

This might work, with Rald not being very heavy.

Tidal lock and orbital resonances happen all the time, and not even very close.

#1) Define "not very heavy"? currently Rald is in the mass range of 0.09 to 0.1 Kerbin masses

#2) Tidal lock and orbital resonances are quite different. Its not surprising that something is in a resonance with Neptune. I would be quite surprised to find that something at Neptune's orbit or beyind was tidally locked with the sun (but its not surprising that pluto and charon tidally lock with each other, or that triton tidally locks to neptune)

[eddiew]

I approve of anything that persuades @KerikBalm that Rald should be allowed to stay in Kerbin's SoI  

[Sharpy]

4 minutes ago, KerikBalm said:

#1) Define "not very heavy"? currently Rald is in the mass range of 0.09 to 0.1 Kerbin masses

#2) Tidal lock and orbital resonances are quite different. Its not surprising that something is in a resonance with Neptune. I would be quite surprised to find that something at Neptune's orbit or beyind was tidally locked with the sun (but its not surprising that pluto and charon tidally lock with each other, or that triton tidally locks to neptune)

1. Should be okay. I was comparing gravity on the surface of Mars/Earth pair, and Duna/Kerbin, completely neglecting radius and somehow imagined Mars being 1/3 Earth... with Rald being "Terraformed Mars" that wouldn't be good. But 10% Kerbin is okay.

2. They are both caused by similar factors, and often accompanied. And the surprising thing about lock with Neptune is that objects in orbits reaching 4x as far as Neptune are still locked with it - I mean, at their apoapsis, they are nearly as close to Jupiter as to Neptune nearly half the time.

[Hypercosmic]

8 minutes ago, Sharpy said:

1. Should be okay. I was comparing gravity on the surface of Mars/Earth pair, and Duna/Kerbin, completely neglecting radius and somehow imagined Mars being 1/3 Earth... with Rald being "Terraformed Mars" that wouldn't be good. But 10% Kerbin is okay.

2. They are both caused by similar factors, and often accompanied. And the surprising thing about lock with Neptune is that objects in orbits reaching 4x as far as Neptune are still locked with it - I mean, at their apoapsis, they are nearly as close to Jupiter as to Neptune nearly half the time.

In case that you don't understand.

Tidal lock: When one side of an object is forced to face to the parent object forever, like the Moon to Earth. The special case would be a planet rotating in a simple ratio with its orbital period. (Parent - Orbiting, Rotational period - Orbital period) It's certainly not natural object if you find anything tidally locked to the sun at SMa of about >10 AU, because there is not enough time for it to lock yet. Example being Mercury (2:3 spin - orbit)

Resonance: Gravitational interactions that caused bodies' orbital period to lock in simple ratio. (Orbiting - Orbiting, Orbital period - Orbital period) It's easy to find stable resonance planets, because if it is stable, then it is VERY stable for long term. Those objects that are locked in 2:3 resonance with Neptune is called "Plutino" after Pluto, which is orbiting in a 2:3 resonance with Neptune.

[Sharpy]

@Hypercosmic - yes, I know it all. I also know the mechanism of tidal lock appearing quite thoroughly, and I'm preeetty sure I know the mechanism of orbital resonance appearing.

 

Also, nomenclature: body facing the central body with one side vs orbiting at a synchronous orbit as well - like Pluto-Charon pair? Or is it just "Pluto and Charon are mutually tidally locked"?

[KerikBalm]

22 minutes ago, Sharpy said:

1. Should be okay. I was comparing gravity on the surface of Mars/Earth pair, and Duna/Kerbin, completely neglecting radius and somehow imagined Mars being 1/3 Earth... with Rald being "Terraformed Mars" that wouldn't be good. But 10% Kerbin is okay.

Any math to support this? This is why I was hoping for an N-body simulation of it.

Comparing surface gravities makes me wonder if I should be trusting you

After all, Mars has a surface gravity of .376, but its only 0.107 Earth masses.

10% mass doesn't mean 10% surface gravity unless you "neglect radius". Mars is .533 Earth radii. 1/.533 ^2 = 3.52

3.52* 0.107 = 0.3766 ... just about what Mars' surface gravity is.

So I'm very interested in seeing if a Rald:Mun:Minmus 1:7:49 resonance would be stable.

If it is, I'll leave it in. I'd also like to see what Universe sandbox says about the presence of water on Rald out at the orbit of Duna with its atmosphere (principally: 50% CO2, 38.5% N2, 10% O2, 1.5% Ar)- woul I need to introduce tidal heating or not?

This is getting quite off topic maybe it should have been another thread.

 

As for the tidal locking, I've been making Rald and kerbin mutually locked when its an inner moon, but neither locked when its an outer moon. I made minmus and Rald mutually locked for the outer moon variant.

Duna-Rald are mutually locked. I forget if I made Ike locked, but in that case its clearly not a mutual lock

[Sharpy]

1 minute ago, KerikBalm said:

Any math to support this?

 

Nope, just Pluto not losing all its moons due to Charon.

 

1 minute ago, KerikBalm said:

Comparing surface gravities makes me wonder if I should be trusting you

After all, Mars has a surface gravity of .376, but its only 0.107 Earth masses.

Yup, my SNAFU. Additionally "supported" by my old calculation where I found for same density escape speed grows linearly with body radius. And completely forgetting volume and mass grows with third power of it.

 

[problemecium]

I'm sad that the album you linked does not include any images of the actual cataclysmic collision. In lieu of this, is it possible for you to provide the scenario file for us to play ourselves?