It's not fair that you blame Blitz since these problems are mostly due to hardware. Realize a couple things, one being that 3D hardware is designed for the needs of most games and most games take place on a normal human scale (ie. a building or city or something, not an entire solar system.) Note that actual scientific simulations of the solar system only run on supercomputers and even then are nowhere near real-time speeds.
Meanwhile, to get around the limits of hardware, developers of large space sims (or whatever) cheat on scale a LOT. Planets are a lot closer together than they are in reality, ships move much faster than in reality, etc. Think "Master of Orion" where the entire galaxy can be traversed in just a few turns.
Note that these cheats on scale are a good idea anyway from a game design perspective. No player wants to sit around forever waiting for ships to get from planet to planet nor is it conducive to gameplay if the planets are so small on screen they don't even occupy a pixel (as would be the case if the solar system were at realistic scale and you displayed everything onscreen at once.) Even on a human scale things are normally compressed for the sake of gameplay. For example in most games players move much faster than normal humans can because it is boring if it takes too long to run from one end of the level to the other.
If your goal is to create a perfectly realistic simulation of the solar system then that's a pretty misguided goal. Realistic isn't fun but people often get the two concepts confused because they normally aren't contradictory either. In this case however they are; the reality of the vast emptiness of space isn't fun (except perhaps to a very small audience of astronomers) so realistic is not a good goal for your game. To put it in persepctive, note that a game about spaceships zipping between planets and managing a space empire is fundamentally unrealistic anyway; these things are not real but it more fun to pretend they are. Similarly, it is more fun to pretend planets are closer together than they actually are.
Meanwhile, to get around the limits of hardware, developers of large space sims (or whatever) cheat on scale a LOT. Planets are a lot closer together than they are in reality, ships move much faster than in reality, etc. Think "Master of Orion" where the entire galaxy can be traversed in just a few turns.
Note that these cheats on scale are a good idea anyway from a game design perspective. No player wants to sit around forever waiting for ships to get from planet to planet nor is it conducive to gameplay if the planets are so small on screen they don't even occupy a pixel (as would be the case if the solar system were at realistic scale and you displayed everything onscreen at once.) Even on a human scale things are normally compressed for the sake of gameplay. For example in most games players move much faster than normal humans can because it is boring if it takes too long to run from one end of the level to the other.
If your goal is to create a perfectly realistic simulation of the solar system then that's a pretty misguided goal. Realistic isn't fun but people often get the two concepts confused because they normally aren't contradictory either. In this case however they are; the reality of the vast emptiness of space isn't fun (except perhaps to a very small audience of astronomers) so realistic is not a good goal for your game. To put it in persepctive, note that a game about spaceships zipping between planets and managing a space empire is fundamentally unrealistic anyway; these things are not real but it more fun to pretend they are. Similarly, it is more fun to pretend planets are closer together than they actually are.