The Brobdingnag is seventeen hundred kilometers long in total
The Brobdingnag is a very large ship, a mobile planetoid and ISO. It originated from a group of modosophonts and transapients in the Mutual Progress Association who became interested (fascinated, obsessed) with a lo tek generation ship. They imagined a large, wandering planet-ship that would be visit many systems for trade and tourism. It would travel between stars while rejecting the transapient elegance of form that defined so many MPA megascale projects. It would be "a work of steel, and aluminum, and fusion, and modosophonts," and it would look like an Interplanetary Age vision of a generation ship. "All knobs and modules and radiators," to quote one of the human founders of the Brobdingnag project. Very little of the original vision for technology restrictions survived contact with either engineering calculations or the MPA archailects who joined the project. However, the final Brobdingnag ship did adopt a layout similar to the "Enzmann Starship," which was proposed in 4AT and utilized by famous ships like the Tau Ceti Colony ship Red.
Aesthetic choices aside, Brobdingnag was predicated around moving lots of bionts between stars at modest speeds. Ten to twenty percent of light-speed seemed a good balance between debris threats, aesthetics, and travel times. Further, it would have enormous resources to accept an expanding population and/or reconfigure the ship. It did not have a unifying habitat theme like the New Brooklyn Worldships or various proposed mobile megastructures (e.g., the diskworld which the Solar Dominion plans to send to the galactic core), so its form is not dominated by a single McKendree cylinder or Bishop ring.
Rather, the ship is dominated by several functional modules. The stern is a cluster of drive nozzles while the nose mounts an 800-kilometer diameter, spherical Mass Reserve. The engine are mounted in the 250-kilometer diameter, 800-kilometer long cylindrical fuselage behind the Mass Reserve. The great Fuselage is currently mostly hollow and undeveloped, awaiting for residents to fill it with habitats. Finally, a diffuse ring of free flying habitats and clusters orbit the mass reserve within the 1,000-kilometer circle of safety afforded by the active debris defenses. The Brobdingnag's acceleration burn was the final public demonstration of what was claimed to be (in 8873AT) the largest artificial reaction drive. Shadkov thrusters were dismissed by Brobdingnag's builders because they used "natural" stars.)
Brobdingnag was built from a Ceres-sized, ice-rich carbonaceous asteroid of 1.5x10^21 kilograms mass and useful metal content. Very little of that mass went to waste. Some of the mass went into building the ship's frame, systems, and habitats. About 2x10^20kg were consumed during the ship's initial acceleration as reaction mass. But 1x10^21 kilograms remain in the Mass Reserve and S5 displacement drivesvoid motes.
The Mass Reserve
The spherical Mass Reserve tank is a carbon nanotube pressure vessel 800 kilometers in diameter. It is filled with the cryogenically (20K) frozen remnants of the original asteroid. The entire asteroid was mined, reprocessed, and re-built into the current Mass Reserve, which is an artificial asteroid of carefully segregated and layered architecture. The original materials of the asteroid were processed both to the build the Brobdingnag and to have the unused mass in easy-to-use forms such as purified metals, silicates, water, and hydrocarbons. The Mass Reserve is basically a solid warehouse of materials for future development and propulsion of a ship with a planned flight of millions of years.
Just inside the multi-layered tank walls is several kilometers of fiber-reinforced water ice that serves as padding between the tank and the rest of the reserve. Below the ice is a thick crust of metals (separated into individual metallic elements) and non-metallic solids like boron and silicon. Finally, the largest part of the Reserve's volume is wedges and chords of water, nitrogenous compounds like ammonia, and hydrocarbons (mostly C7 to C10 to have a high melting point). A few "excitable" elements like uranium and sodium are kept in dispersed mineral forms to avoid problems like criticality events. Vast sheets and floors of carbon fiber honeycomb the reserve to keep the materials segregated and control slumping under acceleration or mining. And though the materials are segregated for ease of access, they are distributed to avoid mass concentrations. A fairly even mass distribution is important because the Reserve's gravity has a significant impact on Brobdingnag's design and operations. Liquid ocean layers were considered during the design phase, but sloshing and/or movement of solid inner cores were deemed undesirable problems.
The 268 million cubic kilometers of the Mass Reserve are not entirely solid, dumb mass. The core hosts moderately advanced plasma processors running Brobdingnag's S3shipmind and a number of S2 and S3 avatars for the MPA archailects that took interest in the project. This heavily protected center also has backup facilities for all residents and emergency power plants, manufacturing, and engines in case the ship encounters disasters capable of threatening 400 kilometers of solid mass. The interior is also littered with thousands displacement drive nodes that help distribute thrusts on the greatest part of the ship's mass. Some centi-G habitats are present for residents that prefer a centigravity cometary lifestyle while spherical habitats a couple hundred meters in radius surround some drive nodes to experience 1G without rotation. And, of course, there are vast "mines" where bots unload metals or use steam to melt-extract volatiles from the Reserve.
One reason for the low temperature of the Reserve was to help solidify the mass against acceleration. Another was to reduce storage volume and handling issues with volatiles like ammonia and light hydrocarbons. But a third reason was to make the Reserve a heat sink. During hypothetical emergencies with external damage, the Reserve is able to absorb energy far faster than temporary radiators could manage. Some of the secondary power plants and a fraction of the reaction engines' components (see: Propulsion) are plumbed into the Reserve to exploit this, while cryocoolers work over long interstellar cruises to maintain the Reserve's low temperatures in the face of heat from habitats and activities within the Reserve.
The Mass Reserve causes issues rarely seen on other ships. The most prominent challenge is the gravity created by the Mass Reserve, which imposes a diffuse but non-trivial load across the Fuselage. The frames are effectively huge compression towers with base loads similar to a kilometer-tall tower on Earth, a constant load that needs to be addressed prior to any maneuvering or thrust loads. The gravity means that the cores of the reserve sees pressures similar to the core of an asteroid and high accelerations (defined as those over about 1/10,000th G) can shift those pressures to the tank walls. Shifting and settling in the reserves can produce what is basically geological heating. Cryovolcanism is a valid concern for the tank wall. Naturally, Brobdingnag avoids such "high" accelerations except in emergencies. Or when the residents want to generate a couple of centuries of cryovolcanism in an open space inside the Reserve.
While a complication to Brobdingnag's design, the gravity has been integrated into the ship's operations. Humans on the hull cannot tumble free into deep space because escape velocities at even the extremes of the ship are in excess of 100m/s while gravity remains higher than any acceleration. Activities on or in the mass reserve occur under centigravity conditions. During the cruises between star systems, Brobdingnag has independent habitats orbiting it closely and anti-debris sensor platforms at distances of several thousand kilometers. Because the ship's accelerations rarely exceed 1/10,000th G, the free-flying habitats do not need to dock during those maneuvers. They are simply tractored along by gravity, albeit requiring some orbital corrections. One drawback of the gravity is that there are large parts of the ship's surfaces (such as the edges of the stern) where it is possible to suffer fatal falls, albeit falls that may take hours to play out.
This cylindrical module is mounted to the Reserve's stern. The aft-most section of the Fuselage holds the 150-kilometer long linear conversion reactors that feed the cluster of 19 engine bells and is segregated from the bow by an armored radiation bulkhead. This barrier is based on lessons from mishaps during the engines' development phase that evaporated merely Leviathan-sized sub-scale test ships, which were equipped with single prototypes of the Brobdingnag's engine. The final engines have worked flawlessly, but the barrier is considered a necessity to save some habitats in the fuselage and guarantee most residents may be recovered from backups.
The rest of the Fuselage between the engine section and the Reserve is a hollow, unpressurized, undeveloped frame enclosed in a skin of relativistic shielding. The framework consists of conventional stringers, longerons, and frames on an obviously giant scale. These also support habitats, manufactories, shipyards, docking ports, and all the other features of a generational starship. Part of the shipboard population lives in rotating habitats positioned within the empty interior of the fuselage, a position that gives them a maximum amount of well protected volume to explore whatever habitat configuration and environment has caught their fancy this century. The majority lives on the circular, 25-kilometer wide frames in centi-G habitats with exterior windows sometimes kilometers high. These regularly spaced rings of habitats and their lit windows give the Fuselage the appearance of a cylindrical skyscraper.
There are the two Main Habitats circling the equator of the Mass Reserve. Both are nearly flush with the Reserve's surface and located just ahead and behind the equator, respectively. They are toruses that run in tracks along the reserve's hull, each 820 kilometers diameter by 21 kilometers wide and rotating in opposite directions. These are in a position where a slight curve to its floor balances the Reserve's gravity. Unlike the oft-changing habitats of the fuselage, the Main Habitats are meant to be permanent parts of the ship.
The Main Habitats have terrestrial environments. Both rings use hot points on inner circumference to provide varied illumination that drives weather and seasons, and both have active wall and ceiling displays to simulate horizons and night skies. Both rings also feature complicated floors and shores on their bodies of water to serve as slosh baffles during maneuvering.
The "Bow Ring" (ahead of the reserve's equator) maintains a temperate, 4-season environment simulating Earth's northern hemisphere's "continental" biomes. The square cross-section of the bow ring has a mix of hills, plains, rivers, and lakes that provide diverse biomes, but all of that fits within the scheme of being in a deep, broad valley. The five kilometers of walls between floor and ceiling are hidden behind hollow mountains averaging three kilometers tall, some of which reach the ceiling. These wall-mountains host tableland and terraces with microclimates varying by altitude. About 1% of its terrain is urbanized in high density towns and villages averaging 1,000 humans were square kilometer, or about 5 million inhabitants in total.
The "Stern Ring" favors warmer climates, primarily tropical islands, which can enjoy the perpetual simulated "trade wind" of the ring. Some taller islands and mountains along the walls of the ring have other climates, much like the Bow Ring. An entire quarter of the ring is given over to a hot, dry desert created by a series of upwind rain-barrier mountains, which host jungles and cloud forests on their upwind flanks. Over the thousands of years of occupation, the Stern Ring has developed a rich shallow water ecosystem of coral reefs that surround the islands. A total of only 750,000 humans live in the Stern Ring, which is considered prime luxury property by ship residents.
As of 10,600AT, most of Brobdingnag's population of 75 million lives in the Fuselage's habitats. These habitats vary but are primarily conventional Stanford toruses and O'Neill cylinders with maximum dimensions of one hundred kilometers, though most reside in centi-G towers built up against the Fuselage's hull. At any time a few habitats are under construction while others are being scrapped to make way for some new habitat that has captured the imaginations of a group of residents. A wide variety of terrestrial environments are simulated in the Fuselage habitats, from dense metropoli to Hermenian vacuum wastes. Two thick-walled Stanford toruses hold to'ul'h environments and 100,000 to'ul'h travelers, while some warrens in the Reserve cater to the few dozen Muuh on Brobdingnag.
A diverse collection of about three thousand habitats and visiting spacecraft orbit Brobdingnag's equator in a band 425 to 500 kilometers from the core of the mass reserve. These habitats tend to be small, under a couple of kilometers long and under several million tons, so as to easily perform course correction maneuvers in response to Brobdingnag's flight plans. "The Belt," as this district is known, is considered a vacation zone where a sophont can escape the bustle of the Main and Fuselage habitats. Over 90% of the habitats are small freefall or tethered rotating pod habitats serving as "vacation cottages" with capacities for no more than a few hundred occupants, though a few are large enough for hundreds of thousands of vacationers.
Orbital velocity of the belt is quite low, 300 to 350m/s depending on altitude, so even modest chemical rockets may deliver a visitor from Brobdingnag to orbiting habitat. However, most transport to the Belt is performed by maglev launchers on the Reserve's hull, which fling transfer capsules to orbits with an apoapsis matching the targeted belt habitat. In case of an error, travelers may rest assured the launchers cannot reach Brobdingnag escape velocity. If necessary, the pod's reaction motors may supply an apoapsis maneuver but most residential habitats have tether capture systems to avoid that propellant expenditure. Likewise, the tethers can brake pods to let them fall to into orbits with periaspes that intercept maglev lines on the hull.
The Reserve has some internal centi-G tunnel warrens, caverns, and other habitats of many and varied forms. The low temperatures of the Mass Reserve require insulation for humans and terrestrial-type ecosystems, while low temperature vecs and bionts may endure the Kuiper-like conditions. A few habitats are located around displacement drive void motes in the reserve, which experience nearly 1G on shells two hundred meters in diameter.
The ship has two primary propulsion systems. The visually obvious system is the giant conversion rocket motors on the tail of the Fuselage. The redundancy of 19 separate engines is incidental to the design, which was attempting to address the manufacturing problem of building a multi-yottawatt reaction engine with more output than many red dwarf stars. At full power, the engine is able to accelerate the Brobdingnag at 0.001G, though it has only been used at half power during the 200-year boost to its 0.10c cruising speed.
The displacement drives are even more powerful and may accelerate the ship at 0.01G, still less than the gravity of the mass reserve, but this level of acceleration has been avoided. In theory, the ship's frame should endure even 0.05G, but there's been no reason to test this. This might lead to local failures in the Reserve's tank and a small leak of billions of tons of metals and ice falling through the Fuselage would be a large mess to clean up. The ship's acceleration limit is dictated by the all-dominating loads of moving the Reserve. Framework adequate to handle the Reserve at 0.05G is able to endure much greater loads from other parts of the ship. For example, the transverse loads imposed by the Main Habitats on the Reserve at 0.05G are less than 5% of what the Main Habitat's frames can endure.
While the gravity of the Reserve is predictable, the acceleration from maneuvers is less so. Ship operations and Habitat design must reflect this. Any acceleration is built up gradually to minimize sloshing in open bodies of water, instead allowing a gradual shift. Shores and beds of open bodies of water are designed to accommodate such changing tilts in the water, which never exceed a 100:1 slope compared to the original water level. As noted previously, the bottoms are designed with irregular roughness to act as anti-slosh baffles while flowing water uses riprap and curvaceous routes to prevent rapid changes in flow. The hollow, artificial terrain inside habitats is designed to endure much more than maneuvering loads. Indeed, stiff breezes may impose higher loads on hills and mountains than Brobdingnag's peak acceleration. Soil and rock are carefully secured by high-friction interfaces to the false terrain under them and abundant, long-rooted plants. All habitats in the ship are able to endure 0.05G without disaster, just like the frame.
Brobdingnag's onboard manufacturing systems may deploy many other means of propulsion given time.
The ship does use a pathfinder laser to sweep aside interstellar dust in a path 1,000 kilometers in diameter, but does not operate a conventional electromagnetic scoop. The powerful fields required of a ramscoop even for electromagnetic braking or interstellar steering would interfere with the ship's orbiting habitats and other external operations. Further, the ramscoop that the Brobdingnag could carry would only intercept modestly more dust and gas than vessels of conventional size. In proportion to its mass, this gas and dust collection are too modest to be worth the trouble. The pathfinder laser is supplemented by smart dust interceptors running up to 100AU ahead of the ship, and the leading edge of the Mass Reserve is covered in a 20-kilometer thick, spaced and layered barrier of relativistic shielding that protects both the Reserve and Main Habitats. The Reserve, in turn, functions as a final form of shielding for the Fuselage and engines.
An unusual habit of the crew, practiced throughout flight, is to alter velocities with microgravity accelerations at random intervals. By imparting random velocity variations of 0.1 to 2 meters per second, the Brobdingnag will shift off course by over one thousand kilometers in a matter of weeks and an AU over a period of years. This is done to confound any long range unguided weapons like Nicoll-Dyson beams. The crew hopes the flight will last over a very long period time, during which terragen space could fall prey to another round of star-shattering wars or other technological disaster. A large, useful ship like Brobdingnag could become a target simply because it exists.
Brobdingnag's bow shield supports batteries of large lasers. These are primarily used to form a conventional pathfinding beam that sweeps aside interstellar dust. Like most pathfinder lasers, smart dust is suspended in it to deal with particularly large debris threats. However, the lasers and their smart dust emitters are also capable of propelling beamriders and assisting sail-equipped vessels. These beams enable the ship's residents to tour systems ahead of their flightpath while using relatively little propellant. Such tourists must, of course, rely on other drive methods to return to the ship.
From time to time, Brobdingnag has acquired new material from passing systems by means ranging from Barnard Banger seeds deployed by the ship to spacetime catapults already present in the system. This was mostly done as proof of concept in case the ship ever wants to grow significantly or establish a wormhole connection to the Known Net.
VOYAGES AND COMMUNITY
The Brobdingnag launched from the MPA in 8,873AT and has been passing through the Inner Sphere at a leisurely 0.1c since then. It aimed for a high density of systems. By virtue of having launched in the Inner Sphere, it will pass systems both independent and belonging to multiple Sephriotics. In the past 1,700 years has passed within two light-years of 13 systems. It has executed small maneuvers to increase the number of relatively close passes. Over the next 250,000 years required for it to exit the Milky Way, Brobdingnag should encounter about 2,500 stars. All are likely to be settled by Terragens before the vessel reaches them. The final destination of Brobdingnag is NGC 300, some 6 million light-years away. The general assumption is that the ship will accelerate to 0.5 or 0.75c as it leaves the higher-dust environs of the galactic disk, though the final decision will not be made soon and a vocal minority of residents advocate maintaining the current cruising speed under the "million years" argument. ("Once you can make the first million years of flight, does it matter whether the remainder is eight or sixty million years? Sit back and enjoy the ride.")
The resident population of 75 million is mostly nearbaseline humans with an assortment of other modosophonts including (but not limited to) dotties, homo cosmoi, vecs, To'ul'h, and Muuh. Residents tend to be patient, not inclined toward excessive energy and mass demands seen among some post-scarcity cultures, and have the niche mentality of wanting to see new systems without resorting to virch techniques or forks. The onboard culture of the ship is self-reinforcing of that mentality, with non-compatible individuals leaving on the regular flights to nearby stars and interested immigrants replacing them.
Regarding immigrants, at any point several tens of thousands of tourists are physically visiting the ship. It has facilities to receive beamriders, torch ships, and other interstellar transports, and its communication facilities receive laser-transmitted forks, ais, and other sophtware. Of course, it is quite able to engenerate or build rental bodies for such visitors. Taking a cue from the New Brooklyn worldships, a higher toposophic Secdat filters communications. And in the years leading up to Brobdingnag's closest approach to a star system, up to 5% of residents may depart to tour the system.
Population growth is kept low. Even biont residents are nearly immortal, like most citizens of the Sephriotics, and the crew is currently planning up to 20 million years into the future. While hardly on the scale of a Negentropic star system's plan for the deep future, Brobdingnag's resources are also more limited. It could very easily convert the Mass Reserve into a shellworld for billions of inhabitants but the shipboard culture favors the current "cozier" population of some tens of millions of residents. Over centuries of life, it is possible for a modosophont to meet many fellow travelers.
During cruises between stars, the shipboard population keeps itself entertained in manners that differ little from any Sephriotic space habitat's population. Mass and energy usage are necessarily restrained to avoid endangering the flight or ship, so there is a preference for virch worlds and virch gardens. There are some unique hobbies on the ship, though.
For example, a percentage of residents entertain themselves by designing, building, and scrapping habitats, referred to as "L5ers" for their penchant of performing manual and teleoperated labor in the manner of Interplanetary Age Lagrange orbital developers. The slow construction that results from this keeps the L5ers engaged for decades per habitat and gives them a "hands on" appreciation for the fruit of their labors.
Another group participates in historical generation ship simulations ("Pretenders"). Some of the Fuselage habitats are built to resemble the habitats of Backyarder, First Federation, and later starships, where the inhabitants toil away centuries of starflight. Each habitat operates under different rules. Some are fully consensual roleplaying environments, while others depend on limited memory alteration to keep participants clueless for the duration of the flight. Per Information Age and Interplanetary Age fabulist stories, many Pretender scenarios expect participants to first realize they're actually on a ship and there's a greater universe outside, and then come to terms with the wider universe. Some Pretender scenarios overlap with the "Corpsicles."
Corpsicles, in the Brobdingnadian lexicon, are the less patient residents who "freeze" themselves for most of the period of starflight. Nanostasis and storage of a sophtware are the most common techniques. A smaller group amuses themselves by risking cryostasis to experience "authentic retro starflight." Another group willingly uses memory alteration to awaken with false memories so they can play out various generation and sleeper ship scenarios: "Slow boat finds its destination overtaken and populated by faster ships" is a popular scenario.
A tiny group is called "Spoilers" in polite society, but they are currently out of favor and generally called by less flattering terms derived from Wuppist and/or incestuous activities. Spoilers are pranksters who attempt to ruin Pretender scenarios.
Among uploads and ais, some run in extremely slow virches so that they pass time between stars aware of external events (and able to accelerate to normal speeds during excitement), but not fully halted.