Advancements in propulsion systems were making it possible for some of the newer ships to bypass Yellow City on their way to Jupiter and beyond, but Ceres was still a major stopping point.

The same with the propulsion units.

Rocket propulsion elements.

Mark had to trace innumerable leads from the panel through the walls of the craft back to the wings, tail, and especially the propulsion compartment.

The material used was wood, the means of propulsion sails, with some thought of steam-engines and paddle-wheels; the means of offence were cast-iron guns large in number but small in size, the largest being 9 or 11 inches in diameter and throwing a shell of some 75 or 130 pounds weight, while the means of defence consisted solely in the "wooden walls," and modern ideas regarding armor had not even appeared above the horizon.

He had a digital copy of much of the layout of the asteroid, and information on the power plants, propulsion structures, and sheathing equipment.