Regarding the Design of Orbspace for a 3D MMORPG, the whole of the Playable Space would be a Spherical Space with 4 Star Systems, realistically balanced with each other so the 16 Planets and 4 Stars, under the guidance of the Physics Engine of the Game, do not crash into each other in their Orbits or Operations. They are still close enough to each other to where they are all clearly visible to each other in the skies of each Planet. 

This is a Simulated Cosmos, though. The Virtualization of the Cosmological Bodies is merely a Database of Predictably Shifting Numberical Values to be used to give Accurate Data to various parts of the Game.

There is The Planetary Sky-view and the Space-Travel view. These 2 views are seperate Game Spaces with Loading Screens between them, just as the different Planets are all different Game Spaces from each other. Locations on a given Planet would even have individual Game Spaces in a Style that prevents Lag and Overburdening the GPU of the Player. 

The Player may Walk, Run, and Jump on the Planet Surface.

The Player may launch into Space from a Spaceship, from the Planet Surface into Space, which Transitions the Game Space from Planetary to Outer Space, and then back to Planetary upon proximity and intent to Land.

Space Travel without a Ship is a High-Level Ability achieved in the Elite Player Levels near the end of the Playable Quests and Storylines.

The Loading of the Entire Orbspace as a solid Game Space would take an immense amount of Processing Power for a CPU and GPU, and those Computer System Resources add up to Expenses that would go beyond the range of a Player’s Subscription Fee.

Likely the Player’s Subscription Fee would be paying for only a Small Portion of the Available System Resources allocated per Player, with the rest of the Money going to the Game Company that is Managing the Game.