Colony mass

[Erik L (OP)]

I was talking to a friend and we were discussing a settlement on Deimos. Deimos is small. 12km diameter and 1.48 x10^15 kg in mass. The question came up if a sizable settlement on the moon would disrupt its orbit enough to cause the orbit to decay. I know we've got rocket scientists and physics types on the board here. Anyone have an idea?

The settlement in question is 5 million people with 125,000 tons of initial infrastructure.

[xeryon]

I am not a rocket scientist or physics major but I too have been amused by the apparent lack of population limits on small bodies in the universe.  I have just started to build up a colony on a body that is very small (numbers are not in front of me) and was wondering if there was an actual cap that no one has mentioned in the forums.  Searching had revealed nothing so far. 
Likewise the size of the body really should have a weighted effect on terraforming as well, but that might be a topic for a different thread.

[Steve Walmsley]

I was talking to a friend and we were discussing a settlement on Deimos. Deimos is small. 12km diameter and 1.48 x10^15 kg in mass. The question came up if a sizable settlement on the moon would disrupt its orbit enough to cause the orbit to decay. I know we've got rocket scientists and physics types on the board here. Anyone have an idea?

The settlement in question is 5 million people with 125,000 tons of initial infrastructure.

The surface area of a body with a 12km diameter, such as Deimos, is 1800km2. Manhattan, with a population of 1.5m, is about 60km2. So while I could restrict the population of tiny bodies to perhaps 40-50m, the requirement for infrastructure on such a small body is already a significant restriction and it doubt it would hit the population limit . When you get to bodies which have perhaps 0.1g, the available space is vast, especially for a higher tech civilization than our own.

Steve

[Garfunkel]

If average weight of a human is 80kg (just pulled that out of thin air), then the combined weight of the colonists would be 400,000,000 kg ->

400,000 tons + infrastructure = 525,000 tons of additional mass. In my uneducated opinion, that addition wouldn't affect Deimos at all, as

Deimos current mass, in tons =  1,480,000,000,000
Deimos with additions, in tons = 1,480,000,525,000

Then you would probably have to add furniture, equipment, food stuffs, drinking and septic water and all that jazz, so maybe the weight of infra would double. Would be interesting if someone had the math to actually calculate this through, to find at which point the orbit starts to decay enough that it would plummet to Mars in human life time.

[Thiosk]

Ok, someone has universe sandbox.  Make a stable deimos and gradually increase its mass until it goes unstable.  Thats what the "game" is for, righT?

[xeryon]

Most system bodies already have unstable orbits.  Our own Luna is moving away from us on a measured interval.  Something like 2inches a circuit or some such.  Adding .1% mass to Demios would probably change it's trajectory on a universe time scale.  100,000 years from now it might break orbit or something but nothing we should notice.

[Geoffroypi]

With a gravitational simulation i've pushed deimos mass to 2.15 moon mass (a lot lot lot lot more than deimos initial mass) and still deimos orbit is relatively stable (SMa 30500 km(if you don't put all your installation at once)) also... phobos didnt like it and made a fresh crater on mars(so i guess mars did'nt like it too)). But still you must find a way  to put the equivalent of 3 moons of infrastructures on deimos  ^^.

The most challenging thing would be to put a space station on a STABLE orbit around ones of jupiter moons, or make safe spaceship travel ( with newtonian aurora)  in the jovian system. Peoples who played Orbiter knows what i'm talking about

I wonder if with newtonian aurora we will be able to do such experiments : make orbital manipulations , deviating asteroids toward peaceful worlds for example (mouhaha) . 

[Aldaris]

If I remember my physics correctly, if you combine the equations of centripudal force and gravitational force, the mass of the orbiting body features equally in both, and it ends up cancelling out. This is also why astronauts and space shuttles (with vastly different masses) can have identical orbital paths.

I'm no expert, but this should mean that unless you add so much mass that the volume of Deimos becomes big enough for Mars' tidal forces to start wreaking havoc, you'll be fine no matter what you do.

[Garfunkel]

I wonder if with newtonian aurora we will be able to do such experiments : make orbital manipulations , deviating asteroids toward peaceful worlds for example (mouhaha) . 

Wasn't that how the Bugs attacked Humanity in Starship Troopers? Been ages since I read it.

[Thiosk]

Yes it was.  The thing that always bothered me is that they did it from very far away.  I don't think they deflected the asteroid from their own star systems and got it to earth, but at the same time we never heard about bug starships that I can recall.

Harumph.  Annoying details.

[Erik L (OP)]

Weber used asteroids as kinetic weapons in his Dahak series. Even a moon

[Geoffroypi]

When i was talking about deviating asteroids , it was half a joke (and a winck to starship troopers)^^
I guess it would take a huge amount of energy to change its orbit and even more energy to add more velocity (because the interception with the target should be in high relative speed) we have seen in this topic that even the biggest battleship would have an insignificant mass compared to small body like deimos (or even phobos). Also, I think that would be too easy to redeviate or to simply destroy it (in the armaggedon fashion ^^) + i think the maneuver to deviate the astoeroids whould not be very descreet and very long , and the  engine used could be easily destroyed before it even started the burn.
What i'm thinking seriously is about peaceful (or not directly threatening) orbital manipulation. Let say there is a huge asteroid full of very valuable ressource. problem : Its inclinaison/eccentricity/average distance to x or y are too high.  maybe if the cost can be justified we could put special engine (ion) or solar sail to slightly ajust its orbit. of course it would be a very long terme project (like terraformation) and could be expensive.
 Another example : put a body exactly on a lagrange point to use it as a outpost.
* Many kuiperian body like sedna (due to a very high eccentricity) are traveling far away and might one day escape frome earth influence.could be a problem for the colony when he reaches the point of no return.

 i'm thinking about civilian orbital manipulations that , in my opinion would be fun