Many Factors can be included in this guide, such as g forces. If the space ship endures too many g forces, it may rip apart. Also another limiting factor might be the engines, as many engines on airplanes, cars and trucks are not usually meant to squeeze every single ounce of power out the design of the vehicle it is in. And also, another limiting factor might be atmospheric drag, as that is what causes a lot of drag, especially at high speeds. Also, if any developer is reading this: Please add Human or Alien cities on Habitable Plants, as it would make it a LOT more interesting, another thing i would want to see in this game is if you could add more space ships or even a space hub or a space station. I know you guys are in the Early Access version right now, but it would mean a lot to me if you just added just 1 of these features.