This post is an outspring of the Enterprise comments thread.
I always get interested in how space craft are designed in TV programmes and the movies. There is a delicate balance between the aesthetic and the practical that rests on the old maxim of nature being an equilibrium between form and function. So it must be for any machine, biological or otherwise. The ratio of power to mass must be right. Too many weapons for example just looks wrong. Consider a tank. Its main gun is large, but actually quite small when compared to the size of the tank. Secondary weapons systems are often completely underpowered and designed for anti personnel or soft hulled vehicles. Concepts which feature oversized weapons are most probably unrealistic.
Designed to exist in a hard environment, the power plant and armour take up much of a tank. A space craft by its nature shares the same needs. It must exist in the deadly shower of stellar radiation so some form of armour is essential even without combat and in order to power a vessel of such requirements calls for a serious powerplant. Weapons would be small in size but potent. Unless one discounts the notion of energy weapons being effective I cannot see the need for more than one primary weapon system either when one has a starship drive at ones disposal. Naturally, attack drones, torpedo's and other submunitions are to be considered but essentially these are secondary weapon systems (though drone fighters bearing energy weapons could conceivably be used as a primary weapon system). Modern warships use far more missiles now than they do cannon. So much so that guns have largely become defensive weapons due to their limited range. Energy weapons, moving at the speed of light would be far more effective at long range than drones. A single laser, powered by a starship drive and targeted by a machine mind could conceivable destroy an entire squadron of drones before these ever got into range.
Returning to the aesthetic design aspect though, a space ship, by its conjectured nature is like a sea faring vessel so its always a good idea to look at how sea ships are built. Big ships are always compact. Designed to face heavy sea's catamarans and trimarans above a certain size are extremely rare. Out riggers, which provide stability to smaller vessels only function so long as they are strong enough to bear the weight of the vessel. Once the pressures of the vessels weight increases, the out riggers fail. As Brando pointed out, the warp nacelle's of the Star Trek style vessels would be ripped clean off by the force of momentum once the ship moved beyond a certain speed. Thus we can conclude, that like an ocean going vessel, a space ship, designed to operate within the parameters of hard vacum, and without any form of 'energy shield/bubble' to compensate for the effects of velocity, would have to be as compact as possible. Thus, a single hull containing all the ships parts.
Below is Andrew Glazebrook's excellent HMS Camden Lock, from the British TV series 'Hyperdrive'. Based on a communications tower in central London it conforms to all the above critieria. I also find it aesthetically pleasing as it appears to have the form/function ratio that is all important for a realistic looking concept (though I'm not sure about the British having their own space craft). Link.
HMS Camden Lock has a nice set of holes in the back, so I guess we can assume it is driven by these. I'm not too sure about the cluster of smaller boosters since they are sitting outside the main structure and could be rippped off if their energy output exceeded the strength of what ever is holding them to the rest of the ship. The difference between this design and the Star Trek design is that HMS Camden Lock appears to have its main thruster in the centre of the configeration, thus the velocity of the main structure would match the outer boosters. It depends on how fast the ship is meant to travel. From the name of the series, it appears that the ship moves very fast (I haven't seen much of 'Hyperdrive' yet).
One of the biggest problems in designing space vessels lies in how to define the powerplant. Anything capable of producing the power output needed to move a ship at the speed of light would have to be a monster engine which by its nature would produce a lot of radiation thus shielding the crew from the effects of radiation would be a paramount consideration. The more powerful the powerplant, the more shielding required.
In the mid 1970's the British Interplanetary Society set about designing a realistic interstellar vessel named Project Daedalus (see below image). This vessel was designed with the specific goal of sending an unmanned probe to Barnards Star (6 light years from Earth). The vessel is in effect a pair of giant fusion engines, the larger being a super booster to get the smaller up to maximum velocity. The conjectured power output of the design is enourmous. Fully loaded with fuel and 500 tonnes of automated payload, the ship weighing an estimated 54,000 tonnes in total (20 times the size of a Saturn V rocket) would produce several times the entire energy output of planet Earth today!
The Daedalus design works on a very simple concept. A pellet of deuterium and helium 3 frozen to -270' C is injected by a special gun into the engine (the large dome to the left of the drawing). As the pellet reaches the target point (the centre of the dome) dozens of beam generators hit it with high energy electrons, causing it to ignite. When the pellet explodes it produces a fireball which pushes aside a magnetic field which is restrained by the metal walled dome chamber. The force of the detonation is transmitted by the field to the walls of this chamber and the remnants of the explosion are ejected. As well as driving the vehicle, the magnetic field also enables some energy to be drawn from the explosion by a coil placed around the engines propulsive exit. This energy then recharges the electron beam generators ready for the next fuel pellet. The repetion frequency of the explosions would be 250 explosions per second.
In other words, the Daedalus design is akin to a giant machine gun firing hydrogen bombs that push the ship forwards. The vessel is designed to continue doing this for almost four years so it is mostly all fuel and very expensive (it would take the entire Earths economy several decades to build). Being unmanned the shielding requirements are not as great as they otherwise would be, but put a few people on board and the ship would have to double in size in order to provide all the shielding, life support machinary and stores human beings would need.
The kicker is, this design wouldn't even get faster than 12% of the speed of light...
Then there is the small problem of gravity. Long term exposure to space on board the Mir space station and the current ISS have shown that human beings wither horribly fast. The rate of atrophy in zero gravity, even with constant exersize means there is a distinct time limit on how long a human being can survive without gravity. Star Trek and other sci fi drama's get around this by means of 'gravity plating' or a gravity field', but the truth is, there are only two ways to recreate gravity in space and that is good old fashioned centrifugal force or moving the ship forwards at a constant velocity of one G. The latter would mean the ships decks would be stacked one atop the other like a tower rather than a submarine, and the ship would lose its gravity when it reached orbital velocity around a planet. Another down side of using forward momentum is the crew would be incapacitated once the ship went to full speed. It was essentially this problem which has led to all serious interstellar designs being unmanned probes (that and the cost of building such a vehicle balanced against the pitiful rewards).
There is a simple way to get around this problem but it requires a leap of faith. One could put the crew into stasis and wire them up to the ships computer. They could live the whole voyage in an artificial reality which generated any form of interface required whilst their bodies, cushioned in liquid cells, 'slept'. So far I personally have not encountered any science fiction novel which has seriously looked at this idea, though the idea of sleeping during a space voyage is as old as the hills. I once had the idea of writing a science fiction novel around the concept of a stasis reality gone wrong, but I have since discarded the notion as my technical understanding of the matter (not to mention my story telling ability) is not up to the job.
So much for the Millenium Falcon then. It looks good on film, but as an interstellar vessel it defies everything in the book. At best it might pass for an in-system vessel. That is to say a vessel which operates within the confines of a single star system, but even then, the design is horribly unrealistic.
Some time back I set about trying to design star ships which were both pleasing to my eye and, if not wholly realistic, then at least as close as I could get them. In those days I favoured an open hull design that resembled the Eifel Tower with a lot of Daedalus style fuel cells clutterd about for interstellar ships. An electromagnetic spike to the rear to direct the flow of energy and an O'Niell torus at the front for life support. I later abandoned the torus idea as it was simply too fragile. A life support section could be deployed once a journey was finished perhaps, but along the way I realised only stasis makes sense. If you look at the lower right hand side of my drawing (below) you can make out a simple diagram of this design. The ships are meant to be 'realistic' interstellar spaceships. That is to say more realistic than the Millenium Falcon.
The ships are to scale and if you look closely there is a tiny figure of a man standing at the nose of the smallest ship to give a rough idea of the sizes I was thinking about then.
Looking back at these designs now I realise now that they were heavily influenced by the ships in the game Homeworld. The 'Apollo class cruiser' design (the big one) in particular resembles the design aesthetic from the game.
My basic design was simple enough. The ships are built around their power plants with weapons pylons and sensor towers mounted to the sides of it giving direct access to the ships power and bypassing the central section with its heavy shielding. To the fore are the crews area's, life support, drone and small ship bays &tc. The hull is heavily armoured and radiation shielded with all sensors residing within and being deployed only when needed. The crews for these vessels are small with every one being locked in stasis. Computers run everything (I've assumed AI is possible) with two thirds or more of the crew being artificial constructs with numerous back up copies in case of emergencies. Reduncy systems back up everything on the ship but the actual powerplant. I also pondered on energy shields, electromagnetic field generators and stuff like that, but my comprehension of how effective such things might be is pitiful at the best of times.
The flat looking ship in the centre of the drawing is a seperate concept. It is actually a design I borrowed from 'The Art of the film Judge Dredd' book (in which it was a concept design for a ground effect shuttle). I decided I liked the look of it and thought it looked like a ship that could be designed to skim the surface of a gas giant with large 'gills' in the front of the ship that would scoop up and process the atmosphere (to mine helium 3 for star ship fuel). I wrote a short story a few years ago featuring this ship (which I then gave a star drive despite myself) and called it Hasdrubal.
Looking back on my playful designs I realise now that they are far too 'submarine like'. They have a clear top and bottom which seems unrealistic. They ought to be more 'omni directional', like HMS Camden Lock.
Below are a few concept drawings from Homeworld2 which I've never played. I've incuded them as I like them. The bottom two in particular are nice, though obviously those are not interstellar craft.