The majority of the ships used by the Children of Earth are small, designed to fit a single extended family. Though larger ships, supporting populations of hundreds or thousands, do exist, they are comparatively rare, as they are far more expensive to construct and maintain. However, every fleet has at least one large ship, which holds the festivals, interfamily meetings, and other large gatherings.
Space on the smaller ships is at a premium, as every extra gram of weight leads to an increased need for fuel. Essential life-support systems –oxygen recyclers, hydroponic gardens, water purification systems, and the like — take precedence, as does cargo space, which leaves the living quarters relatively small and spartan. They are typically arranged along the edges of the ship, leaving the common areas like the gardens in the center. Passenger quarters also sit in the center, as the Children of Earth provide the main form of interstellar transportation. These, too, tend to be rather spartan.
The engines, purification systems, and cargo holds are below, sealed off from the living quarters via flexible, airtight membranes that function like cell membranes. Similar membranes, formed from synthetic chemicals that resemble lipids, seal off each compartment. A breach in the hull is therefore contained to a single section, allowing the rest of the ship to maintain oxygen and air pressure.
Such breaches do occur on occasion, though every attempt is made to protect the ships. The outer hulls are built from interlocking sheets of carbon nanotubes, while inner walls are constructed from lightweight, conductive ceramics. These support the creation of the magnetic fields that shield the ship’s inhabitants from the surrounding radiation.
Though the shields are strong enough to protect the ships during interstellar travel, they are not designed for planetary docking. The outer walls are not guaranteed to be strong enough to withstand the friction of entering atmosphere, and the heat generated by such entry could prove damaging to the inhabitants. Instead, ships approaching a planet to trade will dock at geostationary space stations, which provide pods — often in the form of space elevators — to allow the Children of Earth to transport their goods to the customers waiting on the planet.
Most modern ships are propelled using antimatter engines, with the antimatter safely contained in powerful magnetic fields. Older ships may still possess nuclear-powered engines, but they are both less reliable and less powerful, as the antimatter engines are very efficient at producing propulsion. However, they are expensive to maintain, and a single flaw in the magnetic field containment will quickly prove fatal, so some families have opted to keep their nuclear engines for as long as possible.
Gravity engines maintain an Earth-like level of gravity in all of the smaller ships, while larger ships and space stations use rotational forces to simulate gravity. Because the gravity engines require a significant amount of energy, an amount that increases exponentially with the amount of space that they sustain, they are often shut off for periods of transit. In an emergency, they are one of the first components to be shut down. However, they cannot be turned off for too long without causing serious health issues for the ship’s inhabitants.