Editing Joshua Pawlicki's Explanation of How It Works (section)

=='''How It Works'''==
When thinking about flight, there are two major modes to consider: in atmosphere and out of it. Flying in atmosphere gives you friction, which produces heat, which can pretty much burn you up if you go to fast and aren't aerodynamic enough. The upshot, however, is that you can lose heat to your surroundings (well, that's usually an upshot anyways), and that you can use the air itself for propulsion.
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===''Atmospheric Flight''===
The problem with fast in-atmosphere (atmo) flight is overcoming the resistance of the air against your hull. Anybody can fly a boat slow. Anyone can drive a car slow. But you never see anyone doing that. There are several solutions to generating efficient propulsion in atmo and beating the resistance of the air. Aerodynamicy will reduce the resistance of the air because you can channel it well so that it's bouncing off you less. The trick with the flight is staying up there. Modern aircraft use airfoils on the wing to keep them up (which, in small detail, uses air flowing over the wing to push up on the underside of the wing while also creating a lack of air that pulls up on the top of it). You may choose to include these in your boat or not. The further you get from the fuselage (the main body part of an airplane), typically the less distorted air you get, and the more stability. Thus, typically, a larger wingspan means more force directed properly on the airfoil, and better lift. Properly designed airfoils have minimal drag, slowing you down less than poorly designed airfoils. This is, however, limited by materials. The force exerted on the tips of the wings of a too-far-reaching boat will literally rip the wings right off, and then you're in trouble. Of course, the "screening" ability of the gravity drive makes this totally unnecessary.
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So right now you're probably thinking that you didn't want to talk about a plane, instead a spaceship. Airfoils are a neat thing for a mechanic to know, but your boat probably has big huge engines, not wings. In the Firefly/Serenity universe, most boats have large engines that swivel and provide lift to gain effects similar to a VTOL. Well, the design of these engines is (with modern materials) rather difficult to make reliably, although given perfect strength materials it could be done easily. The primary engine, known as a thruster or a pod, is a four-part engine. The basic principle relies on bringing in air, compressing it, superheating it, then letting it out the back of the engine. Since hot materials expand, it leaves at a speed considerably greater than the speed at which it entered, producing a force which then, by Newton's Third Law of Motion, pushes the engine forwards. This concept is called a ramjet engine. Given an constant source and concentration of fuel, a ramjet engine will accelerate until the forces of the air rip it into shreds. The trick is to thus limit the fuel that heats the air. Ramjet engines are extremely efficient, but will only work if you're already traveling at a certain speed roughly equal to half the speed of sound (around 620 km/h or 380 miles per hour), and are inefficient unless going even faster.
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The question, then, is how to get up to that speed, which is where the turbine comes in. In the engines of the 'Verse, a turbine exists in each engine, powered electrically from the electricity generated by the fusion reactor (we'll get to that later). Anyways, once you have this turbine (basically a big fan) rotating, you can "suck" in air at sufficient pressure to run a ramjet-like process on it and do the same thing. The problem is that you can only go so fast before the force of the air pushing on the turbine rips it apart. Also, this requires a lot more fuel and electricity, and thereby should be used as little as possible. Once you get up to a sufficient speed, the turbine blades fold back or retract depending on the design and cease to turn. In theory you could reverse engineer a turbine to rotate at high speeds as an electrical generator (I.E. a windmill/wind power), but they're not designed to do so, and fusion power systems really negate the need. Either way, this is when the engine becomes a ramjet engine. The speed varies depending on the design and power of the turbine, but is usually around 600 miles per hour or 1000 kilometers per hour.
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Once you pass Mach 1 or so (depending on design), forces of compressed air start bouncing around inside the ramjet engine due to the compression (it compresses the air to subsonic speeds). This can generate unwanted stress just about everywhere and eventually lead to all kinds of bad. The engines reconfigure somewhere within the transonic range to become scramjet engines (the method of how they reconfigure themselves depends on design, although the end products are similar if not the same). Scramjet engines are merely ramjet engines with a slightly different shape so as to allow supersonic air to pass through efficiently. They can usually get you up to Mach 28 or so (modern scramjets are capable of Mach 20-24, and it can be assumed that those in the 'Verse are constructed with better materials), which is more than enough to break the gravitational pull of the planet (you can orbit a planet from a low space orbit at Mach 22 safely, although of course scramjets don't work in space).
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The final configuration of the engines of Serenity/Firefly ships is a more optional use, at least in atmosphere. When in the rocket mode, the front of the engine closes, and superheated gases (likely helium exhaust from the fusion generator, although some designs use a fission reaction on the hydrogen fuel) are shot out the back. The upside of this is that it'll work in unusual conditions, such as a vacuum. The downside is of course that it burns tons and tons of fuel very quickly and, when compared to the ramjet-family, is extremely inefficient. But it is useful to know.
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===''Space Fight''===
Ah, finally, the most inexplicable topic of them all. The big problem with space travel is not losing energy to friction. It is quite simply the dog-gone massive distances involved. For short range travel in space (between moons, orbit, etc), one would use the reaction drives to save on energy (that will be expanded on in the next section). Reaction drives are simply your atmo thrusters in rocket mode. The problem is the amount of gas you're dumping into space while doing it.
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The key thing about space flight in the 'Verse is that it is unneccessary to go faster than the speed of light: star systems are very close to each other. However, you still need to go pretty darn fast, and there's one way to due that: The pulse engine. Due to the gravity drives (in a process later explained as inertia reduction, see Gravity Drive), one can effectively create a localized field in which the speed of objects can be accelerated greatly. Detecting someone who is moving in another inertial reduction field is tricky, but can be done pretty well by computers, although it's not a perfect science. The key to it lies in tracking the fore and aft parts of electromagnetic radiation exiting the inertial field of the other ship. The pulse engine is basically a really big rocket that provides a huge burst of acceleration within this field. It is more efficient than the pod rockets because some of the excess heat is converted into energy to power the localized gravity drive fields (see Gravity Drive).
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===''Gravity Drive''===
The gravity drive is the principle thing that makes the ship run. In addition to simulating the artificial gravity on the ship, it creates the pressure necessary to create the fusion reaction (see Fusion Reactor). This also sucks a huge amount of power, understandably. The gravity drive can be used to create the three assumptions (see Reference Tables), and is the key part of the ship. Without it, the fusion reactor will shut off, and that results in losing all power, air ventilation, and further systems. It is extremely difficult to repair, and almost impossible to cold start without a jump from another ship (most ships carry extra power cells that they can use to power it just in case: invest in these). The device works off the basic concept that quantum gravitation (gravity between atoms) is based on magnetic polarities. The hull of the ship is lined with electromagnets that, given sufficient power, can create an artificial gravitational field within and on the surface of the hull of the ship. The "gravity drive" in the sense that most people think of it is only a single major component of the entire drive (which is spread throughout the ship). This part is known as the gravity drive hub, and is typically seated nearby the fusion generator. It's primary purpose is to complete the complex mathematical calculations required to determine the pulses of energy that should be sent to each of the electromagnets throughout the ship. In theory, it can be engineered and modified to allow complete manual control of the gravitational fields in the ship, but most devices do not support this feature by default (for obvious security reasons). The largest electromagnet in the entire ship is attached to the pulse drive for the purposes of very fast travel, which uses inertia reduction to increase the local of objects. Look up Superstring Theory and Quantum Gravity for more.
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To reduce the need for power and required size of the fusion reactor, the fusion reactor's electromagnet is the only one that is constantly on. The rest of the electromagnets (those set in the hull that make you walk, not float, for example) are only on about 1/4th of the time (depending, as always, on design). The magnets turn on for a duration of 250 microseconds, then off for a duration of 750 microseconds. The pulse effect is similar enough to real gravity to fool any living being into thinking that it is constant, while only using 1/4th of the required power. Newtech systems have managed to get this into even smaller ratios, and average about 1/8th to 1/12th on time. The current record of minimal power consumption in the 'Verse while maintaining 1G is 1/45th in controlled lab conditions. In atmospheric flight, the ratio usually normalizes more, going to ½ the time or 2/3rds on time to allow upside down flight and so forth when another gravitational factor is an issue.
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As the gravity drive relies on electromagnetic waves, EM radiation becomes a huge issue. Most hulls have radiation shielding plated within them. Those that don't are short-range only and rarely have a pulse engine. Most of the radiation is in the exhausts of a ship, and enough of it is at a high enough frequency to completely strip an atom of electrons instantaneous. While flying in another ship's exhaust is a good way to remain hidden from heat sensing, it will slowly decay your hull, and eventually reduce your boat to a cloud of subatomic particles. How long a hull can hold out against this radiation depends on how much rad-shielding it has and design. A normal radiation suit or vac suit will not hold out long against this level of concentrated radiation, and shuttles, having much weaker hulls than boats, can't sit in there for long either. On the other hand, the radiation is a very good way to destroy the exhaust of a ship and not leave helium gas everywhere where you've been (which would be pretty easy to track with a decent computer).
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===''Fusion Reactor''===
The fusion reactor is the power source for the ship. By using a compressed artificial gravity field, it creates the pressure of a star and fires superheated hydrogen isotopes (specifically deuterium and tritium), which combine to form a helium atom and a free neutron that contains enormous energy (more than enough energy required to combine two more atoms). Ultimately, it's a self contained power generation system that requires hydrogen fuel and exhausts helium. This energy is used to superheat a plasmatic substance that is used as a medium (or a vector fluid) to heat up water in another chamber. The water evaporates, and the steam pressure turns a turbine that generates electricity. Look up Nuclear Fusion for more. There are two ways to fuel this: H2O packs, small backpack-sized tanks of specialized water, or the longer-term fuel cell (described in the book), which is basically a bunch of regulated  H2O packs. You have to switch it less often and it's slightly safer, so most mechanics prefer the fuel cell over the individual packs.
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===''Shipboard Recycling Systems''===
One of the major problems with modern spacecraft is limited oxygen. Firefly/Serenity solves this problem by constructing a miniature ecosystem on board the ship by utilizing tanks of algae. The algae recycles the carbon that humans release by respiration, producing breathable oxygen as a result (look up Photosynthesis for more). The carbon, however, is not taken from the algae, which maintains an equilibrium due to crowded conditions and starvation. The air is pumped by fans through the algae tanks, dissolved into the water, and then extracted by filtered evaporation. The upshot is that this can also keep the hydration levels of the atmosphere on board acceptable. The downside is that if your Gravity Drive breaks, your fusion reactor shuts off, the power shuts off, you lose ventilation, and the air goes bad. Human Waste is heated to evaporate as much water as economically possible, then compacted into cute little cubes using artificial gravity. You can filter contaminated water to some degree by evaporation, of course, if you have the spare heat (which most ships do), but few ships include designs for this, as water is a common resource and easily purchased anyways.
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