Hydrogen Refueling Network
On the other hand most stellar systems offer virtually limitless resources of hydrogen already in orbit: the water ice in many asteroids, comets, moonlets and planetary rings. The latter source is by far the most convenient: the inner rings are generally only a few meters thick, made of small particles that are easy to process, and most of all on orbits that are generally very well located with respect to both interstellar and in-system jump points.
This explains why most refueling stations along the shipping lanes linking major civilization hubs are located in the rings orbiting ice giants.
In practice these stations extend on both sides of their host ring. Besides their intrinsically balanced design they feature ballast systems to dynamically maintain their center of mass by their ring scoop. Since they only orbit planets with long-stabilized rings, a limited armored deflector is sufficient to protect the station’s internals from residual higher energy particles.
After extraction the water ice undergoes an electrolytic process to obtain primarily hydrogen and oxygen. Hydrogen is then liquefied and stored in cryogenic tanks.
Besides water the rings very often contain significant traces of other substances that constitute the raw materials for on-board processing plants. The largest stations are built from the richest locations and include shipyards fitted with advanced in-orbit manufacturing facilities.
While fusion engines excel in deep space they struggle to provide the necessary thrust to weight ratio for ground to orbit ascents, especially in the dense atmospheres of inhabited terrestrial planets. Moreover the associated safety issues have yet to be completely solved. As a result the need for more convenient transportation methods has been a key issue since the very beginning of the interstellar age and has led to the development of large scale space structures.
The first of these systems is the space elevator. A cable and counterweight are built so that their global center of mass lies on a stationary orbit with respect to the planet’s surface. When the cable is long enough to reach and be anchored to the ground then loads can be lifted to orbit along its length. In practice a space station is connected to the structure at the stationary orbit altitude to serve as a transportation hub.
The cable is made of high-performance low-density high-tensile-strength carbon-based metamaterials to be able to withstand both its own and the traveling payload’s weights with the required safety margins. (Incidentally these are the very same materials used in spaceship engineering). Integrated magnetic tracks allow the “climber” (lift) to self propel and glide along the structure without any drag and at very high velocities. At favorable planets with short rotation periods and stationary altitudes < 20,000 km a transit time of 6 hours is typical.
Work in progress!