Fusion Engines

Traditional rocket engines rely on the controlled explosion of a chemical fuel, over a very short period of time. The maximum efficiency of these rockets is limited however, as illustrated by the rockets used to land on the Moon, our closest neighbor in space, weighing in at over a million kilograms.

Nuclear fusion reactors available to the modern Arskodian universe can give a spacecraft a delta v of thousands of kilometers per second, meaning even small craft can have significant range and mobility while being relatively safe to operate.

Early Fusion Rockets
Fusion reactors in the early 21st and 22nd centuries were incredibly huge and inefficient devices, taking up the volume of a building and weighing tens of thousands of tons. Rockets employing fusion engines were mostly heat radiatiors and radiation shields by mass simply to get rid of the massive neutron and x-ray byproducts of the fusion reactions. Accelerations of centimeters per second were considered impressive, and ships took months or even years to traverse interplanetary distances. No one dreamed of lifting off the surface of a planet in these ships, especially since they were flimsy, unaerodynamic things that couldn't maintain structural integrity inside a planetary gravity well.

Modern Fusion Rockets
Advancements in science over the past 700 years, both human and otherwise, have led to devices millions of times more compact and efficient than anything dreamed up in the early space age. The technology involved in reactors and rockets would be incomprehensible to 21st century scientists, what would be called Clarketech by science fiction writers. A reactor with an output of 80 gigajoules per second would fill a stadium with machinery and mass 100,000 tons in the 22nd century, but in the modern day, it fits in a suitcase. A rocket with that power would blast a city into a charred husk, yet with the advances in spacetime technology and mastery of fields and forces, the equivalent rocket today could land on top of a helipad in a crowded city safely.