Building a Space Battleship; the Technology of a Trope

Space Battleships?


    The trope of a 'Space Battleship' is one of the more persistent themes of SF, especially in the visual medium.  In most SF the trope takes the form of spacecraft classes that might not have any applicability to spacecraft; Battleship, Destroyer, and the often abused Dreadnaught.  It also extends to tactics, with many space battles in movies closer to a fight between two oceanic naval forces than a battle in 3D space.  In the most extreme form the spacecraft take the actual appearance of a seagoing battleship, as in the case of the Yamato, which was built from the wreck of the WWII battleship of that name.

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   The innumerable physics and engineering-breakers contained within most examples of this trope make it one sure to raise the hackles of any Hard SF fanatic.  Thrust at right angles to deck layout - what happens when artificial gravity fails and hallways turn into mines hafts of death.  Bridges that projects from the main body of the ship, robbing themselves of protection from the main armour of the mull, and not giving any advantage in the vastness of space.  Battles fought at close range with guns.  Turrets on only one side of the hull...   I could go on.

   But while a Space Battleship may not ever be the design of choice for the most science-centric 'Verse it does hold potential for those worlds which, while the author takes care not to 'break physics', are intended to follow the aesthetic of a battleship in space.  This post is intended to look at how that can be accomplished; what technologies and conditions are needed for a space battleship to be logical.




Design Brief: Space Battleship


In order to be recognisable as a Space Battleship our design is going to need several features, most of which are to do with the visual side of things.  The following is, then, an outline of the requirements of the design I'll be looking at.

Turreted Primary Weapons - nothing says 'battleship' like massive turrets with several massive cannon each.  Depending on how close to the classic image of a space battleship the creator wants to go the weapons can either be kinetic, which will resemble traditional cannon to a large extent; or DEW, which will be considerably different visually.  And definitely no missiles.

Armour - ultimately the whole point of a space battle in any fictional work is for the purpose of drama, tension, and excitement.  Thus from our point of view one shot kills are undesirable, despite the fact that kinetic weapons, nuclear warheads, and DEW all have the potential to make this the norm.  So we need armour.  Lots of it.

Long Tubular Hull - a hull that is several times longer than wide, and with a roughly square of circular cross-section is another must.  While the bow(end opposite the engines) of the spacecraft need not be shaped like a ocean going vessel it is one of the easier things to rationalise and is a solid indicator of the spacecraft's battleship status.

Prominent Superstructure - without the towering 'bridge' assembly the space battleship risks looking more like a submarine with turrets.  The extent of the superstructure is of course variable depending on the exact level of battleship-ish-ness the creator is considering.

Large Crew - while the chances of a spacecraft having a crew are pretty slim in the most realistic 'Verse when it comes to military craft, it is the people that make the story.

Flagship of the Fleet - for our Space Battleship to fit into it's 'Verse there must be a fleet, fleet battles, and a reason for a ship that is bigger, more armed, and more armoured than any other spacecraft.




Analysis & Design


Weapons

   In WWII Battleships had one main role - fight battleships.  While to an extent the number of battleships you had was a status thing they were also potent weapons.  Some were so well armed and armoured that only another battleship had any chance of taking one out without a massive numerical advantage.  While slower than smaller ship classes their weapons detractive potential meant that you couldn't risk them getting within range of a port or shipyard.  They were also good defensive assets, as the lack of speed made this less of an issue.  However there was one counter to them that in the end required an entirely new class of ships to be built.  Torpedoes could skin even the mightiest battleship, and could be launched by ships of far far less cost.  The vessels armed with torpedoes could also be much smaller and more manoeuvrable, meaning that the big guns of a battleship had a hard time hitting them.  The Destroyer class was originally conceived to defend Battleships against the small deadly torpedo boats.  And once the submarine, guided missile, and aircraft carrier offered ways to use similarly effective methods from even longer ranges the Battleship's fate was sealed.

   This is similar to the problem that missiles pose for a space battleship.  Missiles in space, unlimited by aerodynamics, are incredibly effective weapons(at least on paper).  They have unlimited range, coasting for hours, days, or even months between launch and the terminal boost stage.  They are accurate, with realtime data that a ship firing from vast distance away might not have.  They can manoeuvre, and being unencumbered with life support, weapons, etc. will be able to do so better than  the Battleship.  And they generate no waste heat for the firing craft.  And if a pod of missiles strapped to a converted cargo vessel can take down a Space Battleship none is going to use them.  Also, we want short ranged combat.  Point defence can offset this to an extent but even a laser based system would have trouble with hundred of independently homing missiles.

   They do have disadvantages.  Higher cost per shot than a round from a mass driver.  Needed a variety of materials to construct, not just the iron or aluminium a mass driver weapon uses.  More susceptible to active countermeasures, both soft and hard kill varieties.  More mass and volume per shot, meaning a ship of equivalent size will have less than a DEW or gun armed spacecraft.  Risk of secondary explosions due to battle damage, and relative fragility.  They are also less effective as the range drops of due to needing time for acceleration; this is seen in modern armed forces where cannon are used as short ranged or sustained fire and missiles are used as standoff or precision.  High acceleration can be given to point defence missiles, but making a 100g missile with good enough deltaV for long ranged work is going to result in a very large and expensive weapon, albeit an effective one(and a potential planet cracker).

    First off assume Jump Drives, FTL optional but recommended, and with the caveat that the drive cannot 'jump in' close to a planet.  Why?  If the drive can jump anywhere but close to a planet it allows it to be used in a battle to close range without running the gauntlet of missile fire.  At ranges of a few thousand or hundred kilometres unguided weapons become effective, even if they have to fire in a 'spread' to obtain a hit.  At closer ranges missiles cannot accelerate for as long and thus loose the advantage of speed that they would otherwise have, and the destructive potential it gives them.  Also, a missile with a active drive will be easy to spot, while a inert projectile or a laser beam cannot, preventing a 'tactical jump' to avoid them as could be done against a missile salvo.  If we make point defence quite good and missiles have to be fired in numbers to be successful the balance is further tipped in favour of a DEW of kinetic gun with its larger supply of ammunition.  The restriction on jumping close to a planet prevents a MAD scenario where a ship can jump into the atmosphere and deliver nuclear weapons without warning.

   Why interstellar travel?  By stretching out the supply line the ammo capacity of a ship becomes even more vital to overall victory.  If the ship can manufacture ammo from asteroids then it would have a great advantage.  No matter the level of technology it will be easier to make solid mass driver rounds than missiles, as well as requiring fewer materials.  Interstellar travel, if there isn't any FTL communication system, makes the tactical situation more complexed.  Add in the necessity for ships to stop at several solar systems while on their way to another stars system and there is a possibility for ambushes, as well as making the situation analogous to the strategic conditions in which battleships were used on Earth.

   So, we've managed to come up with good arguments against missiles.  Some of you have probably realised that while I keep mentioning unguided KEW DEW actually becomes more popular in the short ranged combat scenario.  Lasers can do away with large mirrors and lenses, preserving the look of the Space Battleship and at the same time have incredible accuracy.  Multiple high powered and accurate lasers one each ship also also make missiles less likely given their point defence ability compared to KEW systems.  Particle beams have the same advantages, although less so due to the lower beam velocity and the potential for the beam to be deflected by magnetic or electric fields.    The shear destructive power of a kinetic weapon also makes DEW good from a dramatic perspective as it could prevent one shot kills from ending the battle too abruptly.  Lasers and to a lesser extent particle beams are not as good at penetrating damage as are kinetic rounds, making armour more effective and prolonging the battle.  Any form of DEW also has a ammunition capacity limited only by the power supply and coolant system, a very big advantage in the 'Verse we are creating.

   Power and cooling are the two big drawbacks of DEW, followed by a probable increase in complexity and cost.  For a given damage output a laser is, at least based on current science, going to have more waste heat and require more power than a KEW.  Particle beams are probably between the two, although I'm unsure.  Big radiators are easy to damage and can quickly destroy the Space Battleship look.  How large the radiators are will depend on the exact technology used, but they will not be small.  It is possible of course to go the opposite direction and posit a 'Verse with technology roughly on par with our own.  With jump drives to close the range even chemical fuelled cannon could be sufficient, and have very little waste heat requirements, while the small amount of power needed for turret articulation could come from fuel cells.  While I won't discuss radiators in detail there are several options less visually annoying than simple flat surfaces; droplet radiators, retractable, and one sided radiators that double as the outer layer of a whipple shield.

Credit Edmond Barret
As some of you might have noticed the Space Battleship I
describe and the technology needed to make it  a logical
design are very similar to those of the Nameless War
Trilogy ships.  Convergent logic at work.

   Now that we have the rational for direct fire weapons at close range the placement of them has to be considered.  If the Space Battleship is facing kinetic weapons acceleration is likely to play a role in countering incoming fire even at very short range.  Since the Space Battleship will want to accelerate perpendicular to incoming fire its own weapons must be able to shoot at right angles to the direction of thrust.  If battles are typically one-on-one then this would favour ships with fixed weapons, perhaps withe only one side of the ship armed.  If there will be multiple combatants turrets make much more sense.  Putting turrets on opposite sides of the main hull retains the look of a space battleship and also gives a good field of fire.  Point defence will take the form of small scattered turrets, hardpoints, or laser/particle beam emitters.

   One final thing to mention is that particle beams can be shielded against using electric or magnetic fields.  A cloud of plasma might be effective if dense enough.  If the cloud uses charge to disrupt the beam, and the charge can only be replaced at a set rate, that offers the possibility of of 'shield' which can be dropped by sustained fire, much like the technobabble devices of star trek.  Particle beams do, however, have on flaw from our point of view; radiation.  A particle beam when impacting a object of field can produce intense ionising radiation, necessitating a lot of armour.  While this makes them more effective it also makes them more deadly and reduces the chances of the crew surviving an engagement.  Whether or not this is a problem depends on the exact story/'Verse.  Also, most of the arguments do not apply to defensive vessels or spaced stations which nave better supply chains or different conditions for engagement.

   Nuclear weapons require separate consideration.  While nuclear tipped missiles are excluded from most battles due to the short range nuclear DEW systems have some application.  Casaba howitzers and bomb pumped lasers could be launched from simple chemical or electromagnetic cannon, spearing their target with unstoppable fury.  Most such systems have a fairly short range so they fit tho 'Verse quite well.  Anything that reduces the number available is good as they threaten to be one shot kill weapons in any situation.  Shortages of fissionables, their outlawing after fusion was developed, or treaties could all be reasons that they are uncommon.  Or battles could just be really really short.

 
Armour

   Armour is a much debated topic amongst the space war enthusiasts.  Ultimately its incorporation into a design comes down to the prevalent weapons used in the 'Verse as each armour category has its own strengths and weaknesses.  It is a complexed subject, so I'll only do a brief overview, and that

The effects of the US Navy's 64 MJ railgun

only as it applies to the armaments already decided on.  As with anything to do with spacecraft Atomic Rockets has a wealth of detailed information.  Our Space Battleship can carry quite a good amount of protection since it has a reduced deltaV requirement thanks to the jump drive.

   Kinetic weapons are the hardest to armour against.  Take a look at the armour of a modern main battle tank, and then contrast the power of a antitank gun with the power of a spacecraft's railguns or gauss cannons.  On impact the projectile of a railgun can turn to plasma, burning through steel like it was butter.  Whipple Shields exploit this by having multiple vacuum separated layers.  While the outer layers will be easily penetrated the spreading plasma and liquid metal from the projectile has an increasingly difficult time getting through the other layers.  The other approach is to use incredibly dense materials, or composites of dense and hard armour layers.  Aerogels might have some use, but I'm not sure how they would react to HV impacts.  The whipple shield is likely be the lightest option if aerogels aren't any good.  It is likely though that any real-world spacecraft could not carry enough armour to stop high powered hits, and survival will be based on the internals being redundant and spread out so that one shot is not fatal, much as on a real Battleship.  A Space Battleship with a Jump Drive has a much smaller needed DeltaV, and so can afford more armour, granting the creator some leeway in the effectiveness of KEW in the 'Verse.

   Lasers have no real counter.  The RPG Traveller suggested creating clouds of sand to absorb the beam; any manoeuvring however, and protection is lost.  It has other problems and they are all discussed in depth at Atomic Rockets.  Ablative armour does deserve a mention, although not because it is a good choice.  With a continuous beam all armour hit by the laser is essentially ablative as the surface is heated up and boiled away.  If the beam is powerful enough or has a short enough pulse to create ablative shock this kind or armour will make things worse as the increased outgassing will increase the impulse the beam generates.  Likewise superconductive armour is not going to work; the power levels are required heat transfer is just too great once you move into anti-ship weapon range.  The trick, then, is to find the material that takes the most energy to vaporise while having a low enough mass that it can be used in sufficient quantity.  Ceramics might well be the choice here, perhaps of the kind used on the space shuttle's TPS.  A spray on compound might be useful even if less effective than other choices due to the ease of repair and replacement.

   Particle Beams are similar to lasers in most respects with two caveats.  They will not deposit all their energy on the surface, and they will produce secondary ionising radiation when the beam hits.  Dense armour is required as the effectiveness is determined by the mass per unit area.  While a metal is the most likely choice organic compounds could be used as secondary armour to soak up the radiation as they will produce less harmful tertiary radiation.  They can also generate a small EMP effect, meaning that particle beams are highly effective against electronic or under protected targets on the outside of the ship, and against missiles and satellites.


Hull Shape 

   The shape of the Space Battleship's hull is fairly important, especially for a visual work.  Having a roughly cylindrical hull is actually quite logical for several reasons.  given that the weapons are intended to fire in a broadside or forward arc the frontal and side cross section should be minimised.  While this might be taken to the extreme and a flattened hull shaped be used an extremely wide hull is in fact more vulnerable to critical damage.  In a cylindrical hull most major systems will be spread out and a penetrating hit is unlikely to take out more than one.  In a wider hull with room for several systems side by side a penetrating hit has more chance of taking out multiple systems.  A cylinder is also close to the ideal shape for the thrust structure of the ship.

   A bow section similar to a seagoing ship can be explained with a very simple handwave.  As the ship accelerates in that direction it is going to take the brunt of any collisions with debris.  Also it makes sense to give the bow thick sloped armour as a shot that penetrated could travel down the length of the ship causing huge amounts of damage.  That is more of a consideration if kinetic weapons are used, as is the matter of side profile.


Superstructure

A Early Warning Radar similar to what a Space Battleship
might use for point defence fire control, and navigation. 

 While a Space Battleship has no need for the collection of radio masts, gun laying stations, bridge, and funnels that for the superstructure of a seagoing battleship it does need sensors.  Mounting sensors some distance from the main hull could reduce interference from equipment in the hull, something that might be a problem with powerful magnetic weapon systems.  Having a sensor tower on the 'bottom' and the 'top' of the ship gives redundancy, as well as helping triangulate inching fire for the point defence.  Large phased radar arrays would also fit perfectly into the superstructure, looking something like the early warning radars used to detect incoming ICBM reentry vehicles and intruding military aircraft.  The exact size of the sensor tower is variable and while it will never contain the bridge of CIC can include an observation platform.


Crew

   Unfortunately for Romance(as in poets, not love-hearts) there are very good arguments against having a crew aboard a military spacecraft.  The mass, volume, and power requirements of a human crew are not significant.  A robotic ship can be lighter, doesn't need to carry life support systems or too maintain an internal environment.  It can be sent on suicide missions, and have reaction times far faster than any living human.

   This holds true while the action is constrained to a planet's orbital space, and is largely true while within a single solar system.  However, once the action moves to the interstellar stage things are different.  Without FTL comms the Captain of a ship is the highest authority next to God, and as such has to make decisions on behalf of his government, not to mention the complexed tactical and strategic decisions that do not need to be considered within the context of a single battle.  While A.I. does not suffer from the deficiencies of a below-human intelligence automata it has the same undesirable effect of removing humans from the equation.  While computers and a high level of automation are unavoidable Artificial Intelligence, as a technology in its infancy -  is much easier to handwave without breaking the setting.

   If A.I. is not an option for a Space Battleship then a command crew is the minimum.  This could be as few as five or six people, although longer voyages would probably be easier to stand psychologically with a larger crew.  Such things as navigation, point defence, direct reactor and thruster control, gun laying, and anything dependant on math will be handled by computers overseen by human crew.  They would also be responsible for the tactics - do we go in this formation or that, do we jump in this direction or stay here.  Since these roles are normally the ones filled by characters in works of SF this solves the problem quite nicely, but it is possible to go further.

   In the section on weapons one of the reasons against missiles was a long supply line due to FTL interstellar flight and war across many light years.  If the manufacture of munitions is a element of the ship's operation it will include specialists for that task.  It is also likely to carry the tools and manpower to effect repairs to the Space Battleship.  While it is possible to automate the repair facilities of a spacecraft the kind of problem solving needed is exactly the type of thing that has been found the hardest to program computers for; so without AI there will need to be a repair/maintenance crew.  How many crew members are needed is a difficult number to estimate, and might just be as many as can be fit aboard without any major issues.

   As voyages are long in this 'Verse there will need to be a good galley and skilled cook; good food makes hardship a lot less hard.  Almost as important is a spinning habitat section to provide 'gravity' via centripetal force.  Advanced biomedical science might conquer the effects of prolonged microgravity, but if that is absent from the 'Verse it can be a major problem; expect there to be a gym on even fairly small Space Battleships, helping stave off bone decalcification and muscle loss.  Recreation is no small deal when cooped up inside a tin can for months at a time and so the ship should have an extensive electronic library.

   All in all having a large crew aboard our Space Battleship is one of the more logical aspects, and one that fits right into the aesthetic of the trope.


Role of the Space Battleship Like its oceangoing counterpart our Space Battleship is a pure weapon of war, designed to decimate enemy fleets and exchange crippling barrages of fire with other capital ships.  Unlike a seagoing battleship it has less need of a escorting force, since its point defence is able to stop missiles and suicide drones, while its acceleration is the same as most other ships(or can be).  It is less manoeuvrable(longer ships are more difficult to turn, and will take longer in order to keep down stresses due to centripetal force).

   In the 'Verse we've created the battleship's tactics are simple; jump in close to the enemy and open fire.  The firepower of the Space Battleship, coupled with its armour, mean that smaller ships are unable to match it except in overwhelming numbers or with skilled tactics.  As such a battle is often won by the side with the most battleships, ore the side that manages to overcome the enemy battleships and turn their own on the smaller vessels first.  Just like the mighty warships of World War II the Space Battleship is a fearsome and potent weapon.




Other Technologies & Elements of Setting


Propulsion & Power

   Although having a jump drive drastically reduces the DeltaV a spacecraft needs to get anywhere it will still require propulsion of some kind.  It also needs power to run life support, weapons, and the reaction drives if they are electrical in nature.  For a Space Battleship going up against kinetic weapons or particle beams dodging is a variable strategy and so high acceleration is desirable, as are powerful attitude control thrusters.  With lasers it is still desirable but less effective against weapons that travel at the speed of light.  Lasers and particle beams do require large amounts of power which makes a electrical powered propulsion system a logical choice; it is also less likely to be a source of lethal radiation.  Plasma based engines like the VASMR drive would be good, especially with a mode that increases thrust by dumbing water or liquid gas into the exhaust stream.  Even a microwave thermal design might prove sufficient, depending on how often there is a chance to refuel, the acceleration needed, and the level of technology.  Open cycle designs like the thermal designs with energy input via electricity or fusion plasma from the reactors are especially good as they have less waste heat compared to high Isp designs like VASMR or direct fusion.

   Power systems are somewhat a problem.  They need to be relatively compact, powerful, and have manageable waste heat.  Radiation is also an issue.  In most real world concepts the reactor - fission or fusion - is located outside the ship to cut down on shielding waste heating imposed by the radiation.  Fusion is the best choice, especially a form of aneutronic fusion producing reduced amounts of radiation.  Not only does this allow less shielding but it also makes the location of the reactor less critical.  Preferably the design would not be based on a thermal working cycle, both to save mass(in theory) and to keep the radiators at a higher and more effective temperature(the high the temp the smaller the radiator for the same wast heat).  The actual design, as with that of the propulsion, has minimal impact on the Space Battleship's final appearance and setting.


Bridge & CIC

   Despite what almost all visual SF works try to tell us - the notable exception being Battlestar Galactica - the 'bridge' of a Space Battleship will not have huge panoramic windows.  In any military spacecraft the control area is going to be located deep within the hull where it has the most protection, both from the armour of the main hull and from the mass of the spacecraft surrounding it.  Civilian craft will also follow that design to maximise the protection from radiation.  A possible exception being craft expected to dock extremely often like shuttles, giving the pilot a valid backup to external sensors and automated docking.  Even the short ranged battles we've envisaged for the Space Battleship are of great enough distance that the Mark 1 eyeball is not going to suffice for any kind of information gathering; so it dons't even make sense in the case of a spacecraft with technobabble shields or forcefields.  

   The issue of the difference between and roles of the Bridge and CIC(Command & Information Centre) is a complicated one deserving of its own post, so I won't go into depth.  Atomic Rockets has as always a good supply of information, and the Wikipedia pages can help to clarify the roles of each.  If the Space Battleship needs a Bridge and a CIC or if the two can be combined is an interesting one, but ultimately up to the author of the particular 'Verse.


Space Marines, Pirates, & Smugglers

From the excellent
Colonial Marines Technical Manual 

   While it isn't directly to do with the Space Battleship I though I'd include this.  A marine contingent is pointless on a Space Battleship whose opponents are going to be vaporised by nuclear fire or gutted by kinetic energy.  If lasers and particle beams are prevalent however there is a possibility of the spacecraft loosing their weapons and manoeuvrability before being totally destroyed.  This opens up the possibility of boarding actions, a wonderful source of drama.  The jump drive makes smugglers and pirates more likely.  While they can't sneak into a very busy planet or one with good defences a colony would be simple enough; the smuggler ship jumps in, drops a high acceleration landing boat, and returns to collect it at a prearranged time.  It is even easier if the destination is a space station without the jump-in restrictions of a gravity field.  We've postulated widespread star systems and long travel times which means that pirates can lie in wait in some deserted star system, wait for a cargo ship to appear, and then jump in right on top of it.  While the smugglers still need something to smuggle and the pirates something worth stealing the jump drive does at leaf make it a practical if unlikely element of the 'Verse.





Overview


   So, we now have a Space Battleship.  It is recognisably shaped, with a long cylindrical hull, superstructure, and main gun turrets; a complete set of turrets and superstructure on the 'top' and 'bottom' of the hull.  It's main armament are DEW emitters or KEW cannon in each turret, and its hull is armoured against even the most powerful weapons.  Powered by a aneutronic fusion reactor deep within the hull, accelerated by a cluster of massive thermal rockets, and with a jump drive to give it FTL mobility.  It can take on an entire fleet of enemy ships, or blockade an entire planet.  With a large crew it is capable of repairing and rearming from the resources of asteroids, allowing long forays deep into enemy territory, and giving it almost unlimited endurance.  And all with only one handwave; the Jump Drive.  I think that that should fall close enough to the traditional concept of a Space Battleship that it would be recognisable in any medium and still manages to fall squarely within the real of 'Hard SF'.

AI & The Real World

   Well, a bit of a hiatus, but I should be posting more regularly again(although I remember saying that before).  In the pipeline, half written, are posts on Alien Physiology, Plasma Weapons, Residential Space Stations, and a few small 'Random Numbers' posts.

Honda's ASIMO

AI in SF

   Artificial Intelligence has to be one of the oldest themes in SF, both written and visual.  Rather than try to list the many ways it has been employed, or trying to pick the first, most famous, or best examples, I will simply link to the Wikipedia page on Artificial Intelligence in Fiction.  It is especially helpful as the entries are subdivided under the more common treatments.

   There are a wide range of fictional AI; from HALO's Cortana to the 'Minds' of Ian M. Bank's Culture series.  From the Replicant clones of Blade Runner to the disembodied mind of Jane in the Ender's Game series.  Most of them have one thing in common however; they are all very human.

   With more than a few this is intentional.  The question of if a AI can be considered 'Human' is as old as the concept of AI itself.  This is the basis of innumerable SF works, and will continue to be a cornerstone trope for the foreseeable future.  With others it is an indirect rather then direct result of the themes and plot.  The robot could be used as a metaphor for the dangers of logic untempered with emotion, or to show the dangers of blindly following a system.  In those examples the commonly surmised 'traits' of a AI are used to highlight the human characters and themes.  In others the AI might be perfectly moral beings, contrasted with fallible humanity.  Others yet simply use AI as a convenient and ominous foe.

   And for the most part this is not an issue.  It is a perfectly legitimate way to depict AI even before considering Burnside's Zeroth Law of space combat: SF fans relate more to human beings than they do to silicone chips.  If it is not necessary for the story you are telling why go to the extra effort to create a character that might be difficult for the readers/audience to understand, and will definitely be hard to write.

   But, will AI ever be Human-like.  Not will they be Human?  That is a question none can answer at this point in time.  But is it likely that a full AI, should we create it, be like it is depicted in SF?  I personally think it unlikely.

   Note, however, that there is an exception; AI designed to mimic Human behaviour.  Such a system may be possible through pure number-crunching, statistical analysis of someone prior decisions giving a accurate prediction of how they would respond.  For the point I am making AI is assumed to be an Intelligence that has not expressly been intended to be anthropomorphic.  AN AI created by copying a human mind might well act like its original to an extent, but one built from scratch is unlikely to do so.



Language, Data Processing, and Intelligence

   Laying aside philosophy, ethics, and religion the Human brain is fundamentally a computer; a device that processes information gathered through the senses, and produces a response.  It follows, then, that our intelligence is directly related to both how we receive information, and how we process it.  By extension of the first point language, or more strictly communication, is also vital as it is a major source of information for Humans, and seems likely to be so for any AI.

   But in all these areas - the gathering, processing, and transmission of data - humans are fundamentally limited.  We have relatively weak senses, have limited ability for some metal processes like mathematics and memorisation, and can only communicate throughout the inefficient process of speech.  What this means is that we tend to simplify.  What we perceive is a simplification of the world around us.  Our memories are prioritised according to what we need to remember.  And in communication!  The fact that two people never mean the same thing when using the same words alone is enough to make it inaccurate, but we are forced to simplify even further by the time it would take to transfer all the information we hold on a subject by speech.  Names are the product of this process, representing a huge amount of implied information with a single quickly spoken word.

   AI is different.  While there are limited to sensor technology there is no reason for an AI, if it should so wish, not to be connected to sensors that give it a view of an entire solar system.  It also sees things in more depth - all frequencies of light, electric and magnetics fields, gravity gradients, etc.  There is more precision - an AI would know exactly what it saw, down to many decimal places.  Given, of course, that its sensors are that accurate.

  Then too it has better memory.  Even with current electronic storage huge amounts of data can be recorded with little effort.  And unlike a human, who cannot select which stuff to remember, and AI can organises its memory as it desires.  Perfect recall is also a given for electronic memory.  The AI will never have to question if it remembers something correctly, and thus will have no need of the numerous devices - cameras, computers, etc - that humans use to store information.

  In processing the information the AI also is fundamentally different to a Human.  There would seem to be no limit to how much the AI can think of at once.  The intelligence itself could merely be a controller directing the operations of hundreds of subsidiaries, but doing so with an efficiency that a human with fallible memory and concentration could not manage.  It could also be free of bias, and be aware of exactly what impact any preconceptions have on its perception.  Humans are not aware of the working of their brain, but an AI could use diagnostic software to ensure that their thoughts were on track.

   When communicating the AI is faster than a human thanks to its ability to directly transfer information.  Nor will it be diluted and skewed by perception as a humans spoken word is - although the possibility that the AI can lie is a very real one.  AI might not use words, a person could be referred to not as 'bob' or 'Jane' but as a file reference that leads to the sum of all extant knowledge on that person.  And while this effect would be more pronounced the more powerful and AI is in processing capacity, it should be evident even in lesser versions.


   If these factors - information gathering, processing, and transmission -all shape human intelligence and consciousness, it is not logical to assume that an AI with widely different abilities would also have differences in its intelligence?


   So what will AI be like?  I don't know.  But the chances of a full AI being as similar to a human as is often portrayed seems to me to be unlikely in the extreme.  This is only my opinion however, the at the question is one that can only be answered by the development of a Artificial Intelligence(and then we'll have bigger questions, like who thought self modifying software was a good idea for a nuclear defence computer).  I intend to look at the more nitty-gritty details of AI in a future post, once I've read up on current developments in the field.

Random Numbers: How 'Powerful' is a 40 Watt phased plasma rifle?

Science Happens...

   For an Author writing SF can be challenging for many reasons.  Not least is the expectation that there must be some 'science' involved, especially for a 'hard SF' work.  Often this results in lengthy and boring expositions where the technology, setting, or related paraphernalia is explained in detail.  This isn't so bad; it is, after all, the reason many people read that particular kind of SF.  A bigger issue is when the author adds in a random number, not always necessary, in order to imbed more firmly in his reader/audience's mind that this is 'science' fiction.  But, often, the number is not as carefully selected as it should be.  Most SF fans will not care, but for some of us fanatics it is a major annoyance.

   The case in question is from Terminator, one of my favourite SF movies.  The terminator is buying guns and asks the shopkeeper if he has a 'phased plasma rifle in the forty watt range'.  So far so good. A single line that reinforces the fact that the terminator is a robotic killer from the future.

   But I got thinking, is 40W really a good number?  A big problem for hard SF authors wishing to include energy based weapons into their 'Verse is how much power to give them; making sidearms wight eh output of a thermonuclear warhead is an obvious no-no, for example.  So I made the following table, 'translating' the output of several modern kinetic weapons into a 'Power' rating.  It is not a perfect comparison, as directed energy weapons employ a different mechanism to do damage t the target than do KEW, but it provides a rough ballpark.

   It turns out that the terminator's preferred weapon is roughly equivalent to a .22 magnum rifle firing one round every fifteen seconds.  Not a very terrifying prospect.  If it had been forty kilowatts it would be another matter entirely.  While it is not an issue that detracts from the quality of a SF work overall getting details such as this correct is at the heart of hard SF, so hopefully this table will help with those details.  It also shows why multi-barrelled weapons are so deadly, even when they fire a relatively small projectile.  For anyone trying to do their own calculations, they are as follows;

Energy = (Mass * Velocity^2) / 2
mass in kg, velocity in m/s, energy in joules
Power = (Energy * RPM) / 60


EDIT
   It was pointed out in the comments that I had inadvertently used the wrong equation.  I've fixed that, and the table is updated as well.  If I've made any other errors feel free to point them out

Myths of SF: Do Nuclear Reactors Explode?

Fission, Fusion, Reactors, and Bombs

   Fear of nuclear devices is deeply engrained in modern culture as a result of the Cold War; years of imminent nuclear annihilation has that effect.  SF often reflects this, with many works from the Cold War period or later revolving around nuclear war as the cause of an apocalypse.  Even though that has been replaced in new works by climate disruption, genetic mishaps, etc. that reflect the newest scientific advances the negative connotation of nuclear devices remains.

   The most common example of this is the use of Fission bombs to show a person or faction as being 'uncivilised' or to show how desperate the situation.  In the Dune 'Verse all the noble families posses Atomics the use of which is seen as unthinkable, while in the movie Oblivion the use of nuclear weapons against the invading aliens was used to indicate the desperation of Earth's defenders.  The second example, more prevalent in movies at least as far as my own experience goes, is that of a reactor exploding.  As well as tapping into people's fear of radiation and their knowledge of the destructive potential of nuclear weapons it is an easy way to add tension to a story.  Alien did this, as is Aliens a classic example with the damaged Atmosphere Processor, and is the B-movie Nuclear Hurricane, although in the latter example the reactor did not explode its use as a literary device is the same.

   For a really fanatical 'hard SF' fan that is a problem.  Nuclear reactors don't explode.  Or more precisely - a nuclear reactor will not undergo a nuclear detonation, producing the feared mushroom cloud.  They can still explode, but this is due to high pressure steam or chemical reactions, and while it may severely damage the reactor facilities and spread radiation, it will not level everything within a kilometres wide blast zone.

   It is also important to understand that in a modern nuclear 'physics package' it is actually quite hard to achieve nuclear detonation.  The explosive compression of the fissile core requires incredible precise timing to achieve the required densities.  While gun-type devices are less precise they are still a mechanism dedicated to achieving a fission explosion.  Thus it is highly improbable that any nuclear reactor is eve able to achieve the conditions for a fission detonation; the required conditions are too precise.

   Yet an immanent catastrophe is the perfect way to spice up an otherwise lagging plot, are to up the stakes just that little bit more, so what can the hard SF writer do?  Firstly, arrange the setting so that a relatively small explosion is catastrophic - "if the reactor goes down the plasma shields fail and the solar flare will kill us all!"  Specify a non-nuclear explosion - fusion reactors could be quite cooperative in this regard, as I will explain later - to avoid the critics, and way you go.  For more specialised situations there is a possibility of nuclear detonation, most revolving around spacecraft due to the inherent danger of a system that can suffer catastrophic failure.

   I'm going to look at the first and second options.  For the non-nuclear explosion a quick look at the Chernobyl and Fukushima disasters will outline the basic failure modes.  Then for more futuristic settings will be a look a Fusion, Antimatter, Black Holes, NSWR, NPP, and more.

Chernobyl after the disaster
Source

Chernobyl & Fukushima

   The key to both Fukushima and Chernobyl hinges, to my (arguable limited) understanding on the fact that a fission reactor cannot be stopped instantly as, for example a car engine can.  A percentage of the power that the fuel outputs is not from the primary reaction but from the decay of short lived isotopes produced in the reactor.  This makes shutting down a fission reactor a tricky matter under the best conditions, as full cooling must be maintained uninterrupted through the process.  In Fukushima the failure of backup diesel genitors compromised the cooling system, and when the backup batteries run out it lead to a meltdown as the containment vessel overheated.  According to the wikipedia page

   "It is estimated that the hot zirconium fuel cladding-water reaction in Reactors 1-3 produced 800 kilograms (1,800 lb) to 1,000 kilograms (2,200 lb) of hydrogen gas each, which was vented out of the reactor pressure vessel and mixed with the ambient air. The gas eventually reached explosive concentration limits in Units 1 and 3. Either through piping connections between Units 3 and 4 or from the zirconium reaction in Unit 4 itself,^[27] Unit 4 also filled with hydrogen. Explosions occurred in the upper secondary containment building in all three reactors.^[28]"

   A similar situation occurred at Chernobyl.  Although it seems that the problem there was more due to the rapid boiling of the coolant water.  From the appropriate wikipedia page

  "Because of the positive void coefficient of the RBMK reactor at low reactor power levels, it was now primed to embark on a positive feedback loop, in which the formation of steam voids reduced the ability of the liquid water coolant to absorb neutrons, which in turn increased the reactor's power output. This caused yet more water to flash into steam, giving yet a further power increase."

   Basically the coolant flow dropped too low allowing steam to form.  As the steam does not absorb neutrons as well as the water the reaction rate in the core increased rapidly, finally reaching ten time the normal output.  This overpressure blew the containment vessel, venting all coolant and sending lumps of superheated graphite moderator into the air where they fought fire.  The secondary explosion was more powerful than the first and was probably a combination of chemical and steam. 

   The wikipedia pages provide more than enough information for any SF author to write a convincing plot centred around a failed nuclear reactor, and the citation links provide a huge mine of further information, so I won't go any further into the mechanics of a fission reactor failure.

A still of the atmosphere processor from
James Cameron's Aliens          Source

Fusion Reactor Failure

   One of the many advantages a fusion reactor would have over a fusion design would be its relative immunity to catastrophic failure.  The reacting fuel is a thin plasma that can be vented if problems arise, since most fusion fuels are non-radioactive.  Also, if the reaction is allowed to stop the fuel cools very rapidly, unlike solid fission fuel with its decay energy.  So it seems that with a good design catastrophic failure is unluckily in a fusion reactor.  There is, however, one possible medium through which it might occur. 

   Fusion reactors contain plasma through superconducting magnetics.  The superconductivity of such magnets is dependant on their being kept below a certain temperature, called the 'critical temperature'.  Above this point the conductors used in the magnetic become normal conductors, able to carry only a small fraction of the current that they can while superconductive.  If the cooling system was damaged it might be possible for the magnets to reach the critical temperature.  The resistivity of the coils would increase suddenly, heating them.  As the temperature rises so does the resistivity.  If the energy flowing through the coils is high enough it could be released in the form of an explosion as the coils are vaporised.  More energy would be added by the fusion plasma, although I have no idea how much that would be, given the extremely low densities.  If this is possible the effect would be most prominent in reactors with the strongest magnetic coils and high power outputs.

   Of course, any good reactor would be designed to prevent this from happening.  But incompetence, cost cutting, sabotage, and damage all offer an opportunity for any safety features to be circumvented.  The result will not be the nuclear blast of Aliens, but it could be more than enough to destroy a spacecraft or space station, two places where extremely powerful fusion reactors are likely to be found.  And of course boiling lithium or sodium coolant flying all over the place would add to the destruction, especially if there was large amounts of water present, or perhaps a fluorine atmosphere?

Warning sign by Anders Sandberg of
the Lifeboat Foundation

Antimatter

   This hardly needs explaining.  Atomic Rockets has a much better overview of the issues with storing antimatter than I could include here, so follow the link.

   Although not strictly speaking a 'reactor' antimatter might prove to be the only way to achieve certain things.  Interstellar flight, torchships via micro-fission or fusion sparked with minuscule amounts of antimatter.  However it has the fatal flaw of reacting with anything.  Which means no matter how good your containment is, damage through accident or design is a 'bad thing', which is why the containment cylinders on the starship Enterprise could be ejected.

   Superconductors also play into this scenario.  As a superconducting electromagnet does not loose all its power instantly when the power is cut off there might be a short delay between the failure and the magnetically levitated ball of anti hydrogen contacting the containment vessel and vaporising the ship.  It might be only seconds, but those seconds could mean the difference between the crew compartment automatically ejecting or getting atomised.

Robert Zubrin's NSWR from this paper

NSWR: Nuclear Salt Water Rocket

   For the people who think that the Orion Drive is impractical there is a concept known as the Nuclear Salt Water Rocket.  Innocent sounding name, but a rather terrifying mode of operation.  Water containing enriched uranium salts is pumped into the reaction chamber where it undergoes a continuous nuclear detonation.  Premature detonation is prevented by storing the fuel in a matrix of neutron absorbing material.  Once again I refer anyone interested in further details to Atomic Rockets.  The thing is that the NSWR offers such high performance that it might be used despite the obvious risks; military, interstellar probes, and massive commercial spacecraft all have obvious benefits.  They could even form the basis of a power system with the plasma from the exhaust guided through a MHD generator.  But should the neutron absorber be damaged or the 'nuke juice' accumulate to critical mass there will be a low yield fission explosion, perhaps powerful enough to cause detonation of the rest of the fuel.  Slightly safer than antimatter.

Credit Anders Sandberg

Black Holes

   Confusingly these favourites of SF are not, in fact, black.  Through some complicated physics I don't really understand black holes give off Hawking Radiation.  Not only that but they can evaporate.  The rate of evaporation is inversely related to the mass, as is the temperature of the radiation.  If you had a very small, as in atomic radius small, black hole it would give off quite a bit of energy.  If you could stabilise a micro-blask hole by forcing matter into it at the same rate as it lost mass it would be a 100% efficient mass to energy device.  Anyone with the tech to do this has a huge advantage in terms of starship propulsion as well as all the benefits of being a Kardashev level civilisation without having to build a Dyson Shell.  Obviously if the mass input was too low the black hole would 'explode', releasing far more energy than can be contained.  It is also perfectly predictable, if you know the mass of the hole then you know when that moment will come.  This, added to increasing output would be perfect for raising the stakes aboard a post-Singularity starship.  Note that as the amount of Hawking Radiation increases it becomes harder to get the black hole to accept matter due to the sheer energy output, exacerbating the problem.

NPP: Nuclear Pulsed Power

   In pulsed power reactor a tiny nuclear bomb is detonated and the resultant energy turned into electrical power.  A wide rang of techniques are used for both the bomb and the containment/energy capture.

   Most designs would be fairly safe, as under normal conditions the pulses do not put out enough energy to destroy the chamber even under worst case scenarios.  However, a system that had been modified to produce more power, run without spare parts, or one fuel it was not intended to use, could fail catastrophically.   If to the detonation produces to much plasma/debris the containment could be destroyed.  This is most likely in a overpowered magnetic containment design.  If the containment failed the impulsive shock of the detonation on the walls of the chamber could cause massive damage, although an 'explosion' as such is unlikely.

   The two main methods of energy capture are to harvest thermal energy, or to fuse the action of the plasma against magnetic of electric fields to directly generate power.  The former could fail in the method I have already described, but the latter has other modes.  If coolant flow was cut off but fuel detonations continued the coolant could boil, rupturing the system, and causing widespread devastation.  Also, and this applies to a magnetic design as well, the presence of material in the chamber - leaked coolant, gas, or a buildup of reaction products - could magnify the mechanical effects of the explosion, just as the atmosphere does for a nuclear warhead.


Other Systems

   Spacecraft need high performance more than any other application, so it is more than likely that technologies used in space will always be cutting edge, and thus posses more failure modes that tried and true technology.  There is also the slightly cold logic that an explosion in space will probably only harm the crew of one ship even if measured in megatons, while the same detonation on Earth could level a city.  Metastable helium, metallic hydrogen, and similar materials offer vastly increased performance in both spacecraft propulsion and in power generation, but also run the risk of catastrophic failure.  Even further into the haze of a speculative future there will be even more potent dangers.  Anyhow, that should be more than enough information to avoid the common misconceptions surrounding retain failures in SF, and to come up with a more realistic and original scenario.

Myths of SF: Bioships & Organic Spacecraft

The Fallacy of Organic Technology

   It is integral to the nature of SF(defined in the strictest sense) that the technology it portrays is advanced, or in some way unusual.  It is, after all, the reason that many people read SF over other genres.  Partially because of this biotechnology has become rampant in SF, never achieving widespread attention in the way that hyperdrives or blasters have, but appearing in many and varied works throughout the history of the genre.  Biotechnology of the kind needed to produce a spacecraft, or even part of one, is so far beyond current human understanding that it sets the story firmly in the far future, or ensures that a alien race is seen as more advanced.  And therein lies the problem, although a problem that only hard SF fans such as myself may object to.

   In almost all works biotechnology - especially bioships, which will be my focus - are far more powerful/effective than any comparable tech.  The Yuuzhan Vong(Star Wars), Species 8472(Star Trek), Edenists(Night's Dawn Trilogy), Shadows(Babylon 5), Wraith(Stargate Atlantis), Tyranids(WarHammer 40K), to name a few, all had spacecraft superior or equivalent to those that they faced.  Even when their superiority is not demonstrated through combat the organic spacecraft are often seen as more advanced than their mechanical counterparts, like the TARDIS from Doctor Who, or Moya from Farscape.  And although we have very little knowledge of how a bishop might function it seems certain that it would not be faster, be more resilient, have better weapons, etc than a mechanical ship.

   When confronted with this unfortunate truth the reaction of a SF addict is often to state that "its the future, they know things we don't", or "they're aliens and more advanced", or "its a story".  Of these only the last is a real excuse, and even then is only valid when writing 'soft SF'.  Why is this the case?  Mostly it is due to the difference between the structure of biological and nonbiological materials at a molecular scale, along with several restrictions imposed by the growth of the ship.  Because the non-biological structure is constructed externally it does not have to have provision for growth or del repair - instead of single cells it can be homogenous or structured solely to maximise a particular trait.  The result of this is that any material assembled biologically will be inferior to a nonbiological material.  It is not that simple however, the biological materials will have different properties and so designs will be different to make use of them, somewhat negating the less optimal materials.  The small applies to larger structures or constructs.

   Take rocket engines, or example.  A nuclear thermal rocket, at the low end of practical space travel in term of materials science, uses refractory metals and active cooling to keep from melting, not to mention the effects of radiation.  Any comparable biological system will have to withstand temperatures ranging from the cryogenic to thousands of K, be highly conductive to heat, have good mechanical strength, etc.  It will also need pumps to cycle the cryogenic liquid gas used as reaction mass or suffer the performance penalty associated with water or similar.  For their first requirements they are all characteristics that are increased by the homogeneity of the material, making an organic 'grown' substance unlikely.  For the pump not only does it have to cope with massive torques and insanely high rotational speeds but with the cryogenic temperatures.  Any living tissue will freeze solid and die at those temperatures, and if it is a dead material you loose the biggest advantage of a biological system - self repair.  The same applies to weapons, sensors, etc.  So while it may no be impossible to build a bioship it is unlucky that either the components or the whole will have greater performance than a purely technological system.

   So why bother?  Are there any reasons a bioship could be used?  To answer this it is important to consider this: biological systems are not inferior or superior to technological ones, they are merely optimised for a different scenario.  And this is their advantage.  A standard metal-and-composite hull would take a far amount of technology, resources, and effort to construct, making it an expensive item.  Likewise repairs are probably difficult without the resources used in construction, and may never return full strength or performance.  A bioship side-steps these disadvantages.  For construction it might need only a vat of nutrients, and can self repair to a high standard.  More advanced types might literally grow from eggs or embryos placed in the correct environment, like the Voidhawks of the Night's Dawn Trilogy who grow to maturity in the rings of a gas giant.  If so a fleet could require only time to construct, vasty reducing the const and increasing the huber of vessels available.  In a realistic space war, where it is likely that most hits will disable or destroy a ship, quantity may well be more important than quality.  And of course the whole ship does not have to biological; the Brumallian bioships in Neal Asher's Hilldiggers had implanted fusion drives.  

The Bioship Moya from Farscape 

Biological, symbiote, biomechanoid, cyborg?

   Bioships do not come in a single flavour.  As posited above they will not have the performance of a tech ship they do have the potential advantage of being much cheaper.  The disadvantage can be combated by adding modules of technology - engines, weapons, sensors - but this decreases the advantage.  As it turns out there are four main approaches to this trade-off, each with advantages and disadvantages.  Note that in practice these categories overlaps, some components of a single spacecraft falling under different classifications.  

   Biological
   In a fully biology-based bioship the spacecraft is one living organism.  It is still alive, perhaps even growing, and requires no external technology to function.  As such it is more an animal than a machine, and may even posses intelligence.  While this is one of the more common variations in SF it is the least likely.  Foremost is the lack of propulsion tech comparable with biological systems, often explained away by giving the bioship the ability to manipulate gravity(Voidhawks and the ships of the Yuuzhan Vong).  If these did occur in 'Real Life' they would likely live in the rings of a gas giant or in its moon system where energy and resources are potentially cheap while deltaV costs are low compared to interplanetary flight.  A fully biological organism could also be used as the basis of an artificial space-based ecosystem, harvested for their concentrated resources by humans or higher level animals.

   While they have the potential to require no human input in growth these bioships suffer from the most flaws.  Not only are they weak in terms of performance they need the most time to grow, need feeding, can get sick, be attacked with biological or chemical agents, and it intelligent suffer mental problems.

Symbiotes 

   A symbiotic spaceship is similar to a fully organic one except that it is composed of a colony of different organisms rather than single entity, similar to the Portuguese Man 'O War jellyfish.  It has the same disadvantages as the previous version of a bioship with only a few advantages.  The primary advantage is that by dividing the ship into separate 'subsystems' it is more robust against injury or attack, and it one segment fails - a drive unit, sensor cluster, etc. - there is the potential for it to be quickly replaced rather than regrown.  Although, of course, communication and commonality between the segments could be a problem.

   It is also important to realise that any of the other classifications can also be constructed of separately grown systems, although in that case it becomes a mere example of biotechnological engineering rather than a true bioship.

Biomechanoids 

   Biomechanical is a term that is often used to describe the work of H. R. Giger, who designed the alien from the Alien franchise, along with the derelict spacecraft in the first movie.  According to wikipedia it is also a term meaning the same thing as a cyborg.  Its actual meaning - or the most rigorous definition - is a living organism that incorporates elements of mechanical systems, but not as implants in the way a cyborg does.  In other words it is a biological system that rather than finding its own solution to a problem, utilises one that is a at least visually similar to the more technological approach.

   They are the most effective kind of bioship, and probably the hardest to create.  Although grown they are not necessarily still alive, wither in part or whole.  Because of this they can have greater performance.  Structures can be 'layered' in a kind of biological 3D printing.  Coral-like material could be used in rockets, reinforced by fibres on the outside, and cooled by transpiration.  It also makes them more resistant to temperature, radiation, and damage.  They don't need feeding, medical care, or a controlled environment.  And I imagine it is far more comfortable for the crew than  the inside of a living organism.  Of course it loses the ability to heal, but as this is going to be slow in any case, the loss is probably worth the improvement in performance.  It might also be possible to 'reactivate' parts of the ship when they are damaged.  Of greater concern is the fact that many biological materials loose strength when dead.  Many devices such as rotary pumps can be used, which would be hard in a living system, and weapons in particular should be easier.  Sensors and drives should also benefit by the greater degree of optimisation offered by not having living material.

Cyborgs

   Self explanatory for any fan of SF the cyborg bioship is probably the most likely ever to be developed or used as it combines the strong points of both biological and mechanical systems.  This approach is exemplified by the Edenist Voidhawks from The Night's Dawn Trilogy, which were sentient bioengineered creatures with the ability to manipulate gravity, and who carried a technological crew compartment, weapons, etc.  While the organism should be alive for it to be a cyborg in the strictest sense a combination of technology and biomechanical systems seems a good approach.  Structure, armour, remass systems, life support, these could all be biological while drives, sensors, communications, and weapons are technological.  The disadvantage is of course the added complexity of getting a biological and mechanical system to interface, and having components that must be manufactured rather than grown.


Aspects of Design

   For bioships in general there are several things to think about, points and suggestions for the way that they could be designed/grown.

Lifespan  Does the bioship age?  Does it have a childhood?  This probably applies only to sentient bioships, but raises interesting questions about how they are 'retired'.  Immaturity might also be a problem with young bioships.

Sickness   Can the bioship get sick?  Even if it cannot there is the possibility of biological attack.  The ship will probably have a immune system of some kind, although it may be closer to a diagnostic system than the immunological setup of a human.  Do they have allergies?  Can they get drunk?  These questions will add interest to any SF 'Verse, and have potential to push the plot in a particular direction without overt handwaving.

Crew   In SF it is common for bioships to 'bond' with a particular individual who then acts as their captain, even to the extent that Voidhawks gestate alongside their future partner.  More realistically the bioship's metabolism could provide life support for the crew or passengers, producing oxygen, food, and warmth, as well as processing waste.

Intelligence   Many bioships in SF are intelligent, making them a character in the story and allowing for many and varied plot twists.  This also brings up somewhat darker questions.  Can the ship feel pain?  Can it have emotions, does it choose its crew?  Do bioships have legal rights, or are they property/enslaved?  This is heavily dependant on the level of sentience - a dog-level ship can be euthanised if injured, but a sapient(human level) ship is another kettle of fish entirely.

   Another fact to consider is the bioship's piloting ability.  If it is sentient, and especially if part of a self-sustaining population, it is likely to be a far greater pilot than any human.  In the way that a bird can fly in winds no aircraft can face the bioship's mind and 'body' are perfectly suited to a 3D environment and the vagaries of orbital mechanics.  Even a AI might have trouble keeping up with them.

Sensorium   While there is no stealth in space a bioship's sensors are likely to be almost pathetically weak if organic in nature.  While 'giant eyeballs' could provide decent optical imaging other frequencies will be difficult to observe.  Communications will also be limited, especially since emitters of any kind of energy, even if possibly, are likely to be weak.  Biological systems do not like high power flows.  However, there is an advantage over tech systems in that sensors should be no more expensive to grow than other modules, allowing high redundancy.  Brightness filters could be in the form of translucent 'nictitating membranes'

Weapons   DEW are going to be impossible to grow, mostly due to the waste heat involved in lasers and the magnetic fields in particle beams.  For the same reason, along with power demand, electromotive weapons - railguns - are unlikely.  Missiles are presumably possible and the ability to grow them in large numbers makes one of their largest current problems, cost, invalid.  Distilling fuel might prove an issue, however.  Chemical guns might be possible, and of course any system can be added as a cybernetic implant.

Landing   While asteroids, low gravity moons, and comets will provide little difficulty to a bioship they are at a disadvantage in a gravity well or atmosphere.  This is to do with the greater performance required, specially in the acceleration area, and brings up another interesting problem.  While most spacecraft can be designed to hold up under far greater acceleration than the crew, a bioship might be limited to the ~5 g that living creatures can stand for short periods.  Reentry into an atmosphere could also pose a challenge.

Drives   Anything using magnetic fields, directed energy, or massive power requirements is a no go.  Thermal rockets will be the oder of the day, the most powerful being variations of a fission thermal rocket.  Being able to 'digest' a asteroid and extract fissionables could allow a ready supply of fuel and remass is only as far away as the next chunk of ice.  Chemical drives are much more likely, and provide adequate perforce for a bioship living in the ring system of a gas giant.  Solar sails are a possibility, although I see no way for the reflective surface to be formed.

Carboneering   Carboneering, the study and use of carbon allotropes and composites is at the forefront of modern material science, and unlike metallurgy and ceramics might be comparable with a biological system.  If carbon nanotubes and graphene sheets can be grown the strength and performance of a bioship will receive a massive boost.


   Doubtless there are many many more aspects to be considered, imagination is really the only limit.  For soft SF anything goes, and for reasonably hard SF all that needs be kept in mind is the poor performance Vs flexibility and cheap production of an organic system.



Implications

   Most of these have already been covered, things like the susceptibility to biological attack, possibility of sentience, etc.  Most of the ways they differ from a conventional spacecraft are immediately obvious, as are the consequences.  Also, most of these consequences do not extend beyond the environment in which the bioships are employed.  External effect will be mostly the same as those that a technological ship of similar performance, price, etc would have.  The implications of such advanced biotechnology are wider-reaching, and will be the focus of another post.