Sunday, 4 October 2015

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


   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 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.


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.


   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.


   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'.