Space Travel
Big is as Big as Big can be Big

 In Future space travel, rocket engines and rocket vehicles will be "reusable" like all other forms of transportation. Railways, shipping lines, airlines etc don't use the word "reusable" because it's obvious. We don't talk about "reusable cars", "reusable buses", or "reusable airplanes". So it should and will be with space vehicles. So, far from being a small technical back-water, rocket engineering is still in its early days and has yet to see its heyday.

So we're looking forward to the era in which chemical rocket engines of many sizes and shapes are in everyday use - the "work-horses" of life in orbit. Without trying to predict the details such as what size and types of vehicles, what orbits, what types of engine and so on will be used, it is possible to foresee many of the broad outlines of the "rocket age". For example, rocket vehicles for launch, for in-orbit operations, and for longer trips such as to the Moon and back, will differ in many ways - though some may be multi-purpose, probably particularly at the early stages before the different markets are large enough to support more specialized vehicles. Specifically, vehicles used for launching from Earth to orbit and returning to Earth need to have aerodynamic and thermal protection which isn't needed for operations in space. Vehicles that operate only in space will have weird and wonderful shapes without concern for aerodynamics, but to have minimum mass among other constraints.