Space Travel

Space travel can be broadly categorized into orbital travel, interplanetary travel and interstellar travel. They differ significantly in terms of the drive technology used and the size of the vehicles. Additionally, there are differences between passenger and cargo transport.

Orbital Travel

In orbital travel, i.e. travel between the planet surface and space as well as maneuvers in the planet's orbit, is closest to how space travel used to look in its early days in the 20th century. Escaping the gravity well requires a high amount of thrust, but it doesn't have to be maintained for a long time, these spacecraft use chemical fuel. This usually takes the form of liquid hydrogen and oxygen, which are readily available through large scale electrolysis powered by nuclear reactors and burn cleanly. Orbital travel showcases the biggest differences between passenger and cargo transport. For passenger vessels, safety and comfort are paramount. Here single-stage-to-orbit spaceplanes (SSTOs for short) are used. After a century of perfecting the technology, a ride does not feel much different from one in a normal autogyro, except for the better view and the weightlessness. SSTOs of course rely on the presence of an atmosphere. In other places, ascent and descent are performed in a more traditional way. Luckily, bodies without an atmosphere are generally less massive, making it much easier to reach orbit. None of this is a concern in the transport of bulk cargo, where all that matters is the highest payload for the lowest cost. In this area, engineers have long ago stopped trying to cleverly sneak their way past the tyranny of the rocket equation and started to punch their way right through. With hydrolox fuel being basically free, all you need to do is build an enormous but simple rocket, which is exactly what the Leviathan is. There are also cargo spaceplanes, though they are only used for fragile or important cargo.

Interplanetary Travel

In interplanetary travel, slow and steady wins the race. Instead of having a big chemical burn and then just coasting along, it is quicker to maintain a smaller amount of thrust through the whole journey. This can be achieved with ion engines, which turn a little bit of gas and a whole lot of electricity into thrust. Nonetheless, an interplanetary journey takes a couple of days or weeks. An interplanetary ship therefore needs to house the crew and passengers for that amount of time. Passenger ships usually feature rotating habitation rings generating artificial gravity, cargo ships may have a smaller one or forgo it entirely. Because of the facilities necessary for longer journeys, interplanetary ships are much larger than their orbital counterparts and are typically assembled in orbit. They are incapable of taking of from or landing on planet surfaces, instead they rendezvous with orbital craft for passenger transfer or dock at hub stations, if such infrastructure is in place.

Interstellar Travel

Interstellar travel poses the same problems as interplanetary travel, except exaggerated to the extreme. In fact, early colony ships, such as the Nadezhda were basically scaled up interplanetary ships. However, with the advent of the medusa drive, high accelerations could be achieved for long durations, leading to the development Libra and Taurus class interstellar spacecraft. As an additional benefit the drive negates the need for rotating habitats, artificial gravity is instead generated by the constant 1g acceleration.