A guy in the answerhub told me I must use ultra small ships and planets to make an openworld space game (something like EVE) work.
I need somebody to approve this and is there another way 
Ship from EVE in unreal engine
1:1 Scale is basically impossible when you’re talking about a space game, there is no way you’re going to put an earth in there that is 1274200000 units in diameter into the engine, that would be true 1:1 scale.
I don’t want 1:1, but atleast 3-4 times bigger than EVE models.
Doesn’t low scale models limit your poly (you must use low poly models) ?
Doesn’t textures get limited, because they are based on pixels and you can’t make “smaller pixels” to have a clear texture ?
Couldnt you have the meshes scale down based on their position to a planet?
Size is about relativity. It is pointless to center your models relative to an entirely different game. Just pick a base “medium” ship and have all of the rest of your models relative to that. You can decide how large you really want the ship by placing a sphere in your map and say “this is a planet” and pick a size relative to the planet you want your ship to be.
There was a mod for UT3 and later a stand alone UDK game called Planetstorm if I remember right.
Here’s a link to the video: - YouTube
You should take a look how they did that. Simple yet effective.
Size of models does not impact texture quality or mesh. Visual quality will remain regardless the scale of your objects. Well, at least to some degree because your are limited by floating point precision. It’s unlikely but If you make your models extremely small or extremely big they will suffer from precision errors during rendering. What you should be aware of is the is the limitation of engine’s world size and object’s position in world space(world space position is a floating point vector). I’m not up to date with Unreal’s newest open world system but it appears to be quite powerful. It’s up to you to judge scale of your models. As guys mentioned, keep your models scale relatively consistent to each other and try to fit whole universe within UE world boundraries.
Btw, If you think about using VR, things get complicated because you will have to override interpupillary distance(IPD) and scale positional tracking vector accordingly to your universe scale.
Thank you guys 
I have one more question about the models.
I think of the game I am planning to be MMO openworld like Star Citizen.
I shouldn’t use high poly models right ?
How will it impact the machine (PC) performance if there are 100 players near you and the ships are high poly models ?
Depends on the capabilities of that machine, which you have no control over. What you do have control over is the LOD of your models, so providing alternate levels of detail for your models will make things work nice and neat if they are running on a machine that is 4 years old or 4 years in the future.