Outpost placement violating roche Limit

[TonyFlury]

I have noticed (2 examples in my systems ) that when the primary port is around a gas giant with rings, and an outpost is built, that the outpost is placed into a almost polar orbit around the planet, and that The orbit is inside the inner limit of the rings (ie between in the inner edge of the ring and the planet).

Since it is generally accepted I think that ring systems form due to a larger body straying inside the Roche Limit for the planet, it implies then that the outpost itself (which dwarfs any asteroid inside the rings) is also inside the Roche limit and would not likely to be structurally stable.

In my experience, most 'hand placed' outpost (ie pre Trailblazers) in orbit around gas giants with rings either orbit in the plane of the rings and on the outer edge of the ring, although i am aware of one that orbits inside the ring system and one that has an interesting orbit that intersects the plane of the rings.

Is the placement of an outpost inside the Roche limit another example of the Trailblazers placement algorithm getting the placement wrong ?

I don't know if this is just coincidence that it happens in the two systems where the primary port was around a ringed gas girant, or whether this is common.

I have no knowledge or what happens if the primary port is chosen to be a large model (ie a Corriolis or Ocelus) ... can someone comment ?

 

[Ian Doncaster]

Since it is generally accepted I think that ring systems form due to a larger body straying inside the Roche Limit for the planet, it implies then that the outpost itself (which dwarfs any asteroid inside the rings) is also inside the Roche limit and would not likely to be structurally stable.

The Roche Limit isn't a constant distance - it's the distance at which the gravitational gradient across the specific approaching body is sufficient to overcome its internal material resistance to being pulled apart by tidal forces.

An outpost made of reinforced steel and composites just a few kilometres across is going to have a gravitational gradient so small as to not be worth considering. Even an Orbis likely is going to take minimal stress. Sure, they're bigger than the surviving asteroids, but a lot of their size (and rounded edges, of course) will have been from being worn down from collisions between much larger fragments after the initial shattering, not because no larger rock would be tidally stable.

(The stations originally put in ridiculously tight orbits around neutron stars or white dwarfs? Yeah, those should have disintegrated. But outposts around conventional planets/giants should be perfectly safe even at atmospheric distances)

 

[morph113]

Yeah depending on the mass of the orbiting satellite, each would have a different roche limit for the body it orbits. You can actually do the calculation yourself, just need to know the mass of that gas giant (which is displayed ingame) and then for the outpost I guess we will have to do an estimation as I'm not sure we have any source on that. I just tried doing the math based on 1 Jupiter mass and then density of the Coriolis station based on a post in this forum from 2017 where someone calculated the mass and volume/density of a coriolis station. So it would have a roche limit for Jupiter of 557715.13 km or 557 Mm or less than 2 light seconds which is pretty damn close. Now an outpost would have significantly less mass/density than a Coriolis station so could orbit much closer to the gas giant even (based on the 1 Jupiter mass example). Basically almost touching the atmosphere of the gas giant. Just think of the ISS which orbits Earth at a very close distance where even some very thin atmosphere is left.

Btw. my math could be totally off here, had to do some googling so correct me if I'm wrong.

 

[Ian Doncaster]

The main thing to note is that the classical Roche limit calculations only really apply in the first place to objects which are themselves primarily being held together by gravitational attraction. That's not what's holding a space station together in the first place - it's bound by forces much stronger than gravity [1].

For an everyday example, using the equations from Wikipedia, a gravitationally-bound body with a density of 1 kg/l would enter its Roche limit for Earth at about 18 times the Earth's radius (or about 30% of the way to the moon). Humans have an approximate density of 1 kg/l and of course generally live much closer, at 1x Earth radius, yet are able to survive intact.


[1] Ultimately expressions of the electromagnetic force.

 

[Markov Chaney]

For a comparison, the Earth-Moon Roche limit is (only) about 20,000km (not even 0.1ls!)

The Roche equation is an approximation anyway, because the full version is hard to solve analytically, and solving things numerically was not quite as convenient before MATLAB existed ...

There's a fun short story by Larry Niven called "Neutron Star" which covers what might happen inside a ship when it's orbiting one. Just because the ship made of unobtanium is in a stable orbit that doesn't mean the pilot is safe...