Welcome to the Barn-Acc
The Marathon is one of three Gaia-Class colony ships constructed in Martian orbit, approximately 35 years ago. Gaia-Class ships are the largest machines ever built by humans. Each is several dozen miles in diameter. The Marathon's destination was an earth-like exoplanet about 12 lightyears away from Earth, named Earth-2. (The 2nd ship, the Far Horizon was sent in the opposite direction to Earth-3 about 15 lightyears away, while the 3rd ship, Prometheus, was damaged in orbit and has yet to be launched).
Each ship is constructed to hold 200,000 people, large wildlife reserves, and all the resources and machinery required to colonize an alien planet. Ringing each vast ship is a Gravity Wave Drive, a toroidal particle accelerator hundreds of miles in circumference.
The Gravity Wave Drive uses a burst of energy to expose the M-surface from which gravity emanates. This causes an intense gravetic "shockwave" at the bow of the ship which pulls the ship forward at a significant portion of lightspeed (between 0.28c and 0.4c depending on the Generation of the drive) towards a specific end target. The shockwave causes a "Wave Envelope" which exists around the ship. The Wave Envelope is a sub-section of space-time that experiences a gravetic pull orders of magnitude higher than that of "normal' gravity." The ship traveling inside the Wave Envelope, however, experiences a force of approximately 1G (higher near the bow, lower near the stern), pulling towards the source of the shockwave (near bow of the ship). Thus, for inhabitants of the Marathon all travel is "downward".
The BarnAcc is a haphazard stack of several thousand small ships piled on top of each other near the stern of the Marathon. These ships are of countless designs, and many are ad-hoc creations constructed from the cast-off parts of the giant Martian factories that built the Gaia-class colony ships.
The BarnAcc is only about 5 miles across. This tight formation is enforced by the physics of the Wave Drive. Ships beyond that boundary are not fully covered by the Wave Envelope, and thus are not completely protected with violent interact with normal space.
The Red C
The center of the BarnAcc is an bare expanse of the Marathon's hull 100 meters wide by 100 meters long. This open area is the rear docking-bay door of the Marathon. No ship is allowed to graft itself to that area bay doors, for fear that they would inhibit the opening of the docking-bay. The docking bay is "Docking Bay C", and is marked with an enormous red letter C. Thus, this area is known as "The Red C" and Barnacles pray for the day when it will be "parted" to let the Barnacles inside.
The BarnAcc has three distinct strata of ships, based on when they arrived. First Wave Barnacle ships are grafted directly to the hull of the Marathon, while Second and Third wave ships have been grafted to the ships of earlier waves. Ships have then been connected to each other by an organic network of jury-rigged connections, gangways, and airlocks. Ships in the First Wave stratum tend to be very well interconnected, as constructing connections across the hull of the Marathon was relatively simple. Second Wave ships tend to be connected downward into the First Wave, so travel between 2nd Wave ships tends to go through the First Wave. Third Wave ships were designed to be interconnected with each other (based on learnings from the Second Wave), and tend to have a flexible lattice of interconnection.
The Omphalos is the first ship to land on the hull of the Marathon, piloted there by Petros Zero. This ship, constructed from the enormous, discarded fuel tank of Earth-Mars transport ship, is much larger than most Barnacle vessels. Both its size, and its historic significance have made it the natural home of the BarnAcc council, its seat of government.