Space Combat Part 2: Spinal, Broadside, and Turreted Weapons

Wherever nerds Science Fiction fans gather to debate the future of space warfare there are several debates that almost always pop up sooner or later, and which  seldom generate a consensus.    One of the most popular is the debate over fixed Vs turreted weapon mounts, with the fixed weapons divided into spinal mounts, and less commonly broadside mounts.  Related is the discussion over which of the three main direct fire weapons likely to be used in space combat - Laser, Particle Beam, and Kinetic - are most suited to each of the three mounting options.  In this blogpost I'm going to attempt a analysis of the specific strengths and weaknesses of each type of mounting, which weapon fits them best, and the tactical scenarios in which they offer the biggest advantages.  I'll also cover the worldbuilding needed to justify each option in your 'Verse.

The Spinal Mount

Definition: A weapon firing in a fixed forward arc, parallel to the direction of thrust, with limited elevation or traverse, and typically running through a significant portion of the spacecraft's length.

   Spinal or Keel mounted weapons are interesting because, unlike turrets or fixed weapons, they have no current real-world counterpart aside from fighter aircraft.  The sea going battleships that provide inspiration for many SF works used broadsides during the age of sail, and turrets in the era of Big Gun battleships, but a single forward firing weapon has never been used to my knowledge aside from a few submarines like the Surcouf, and that was neither common nor in line with the spinal mounts of SF.  If anything their closest analogy is the main gun of a turretless tank hunter.  Even that is a poor comparison given the role stealth plays in tank warfare, and the degree to which it is impossible in space.

   The rational behind the Spinal Mount is straightforward and pretty logical; the bigger the gun the better, right?  Most 'guns' in SF are in fact accelerators of some kind; railguns, coil-guns or gauss cannon, ram accelerators, and particle beams.  What this means is that muzzle velocity scales directly with the length of the weapon, rather than their being a optimum barrel length as their is with conventional firearms.  There are engineering limits, or those imposed by material science, but the highest theoretical velocity is as close to the speed of light as you can get.  A Spinal mount also translates the power of the weapon to the audience quite easily, especially when coupled with long recharge times and/or cool down.  The MAC guns of HALO and the Wave Motion Cannon of Space Battleship Yamato are pretty typical of this trope.

   There are a few disadvantages with the spinal mount, most of which revolve around the fact that the spacecraft must manoeuvre to aim the weapon.  Even if the finer adjustments are done internally rather than by the spacecraft's alignment it will still limit the speed that the spacecraft can edge widely separated targets.  It also means that if a enemy emerged unexpectedly from hyperspace the spinal mount might not have time to be oriented before it is destroyed.  Most spacecraft armed in this way are shown with only one main gun, with is a disadvantage if it breaks down or is disabled by enemy fire.  The spinal mount might well be a glass cannon, extremely dangerous, but needing other ships to contribute to its defence, especially if under attack by multiple enemy.

   While the time needed to aim, and the disadvantage of only being able to engage targets in the same direction at once are inescapable the problem of manoeuvrability may not be an issue.  A spacecraft equipped with a powerful gauss cannon, railgun, particle beam, or laser, will have plentiful electric power.  This can be used to power multiple thrusters distributed all over the spacecraft, rather than having them clumped together, and allowing acceleration in any direction.  With many fictional spacecraft the main drives are to large, expensive, or radioactive to allow this, but for more realistic low accelerations electrothermal or plasma based drives may do fine.

   The advantages are many.  A spacecraft can fit a larger spinal weapon than it could hope to fit into a turret, something likely to hold true for any size of spacecraft.  This is partially due to the fact that a turret has to turn, and so has limits on the mass and size of the weapon, and partially to the fact that recoil forces along the line of thrust can be absorbed by the thrust structure instead of by a complicated system of articulation.  This can also make the weapon more accurate as it will not have to cope with the vibration of turret articulation, or the fox in a unsupported barrel.  Greater muzzle velocity has the advantage of imparting a longer effective range on particle beam and kinetic weapons, helping to negate their inherent weakness.  Even if the energy they output is the same as a physically smaller weapon, the increased range will make them more effective at ranged combat, something there is likely to be a lot of in space.  And they do not need the cool down time shown in SF.  The most powerful might, but it should not be a surprise to find MAC gun like weapon with rapid fire capabilities. 

   Kinetic weapons benefit the most from a spinal mount as opposed to a turret or broadside since it helps to overcome their greatest weakness - low velocity.  Particle beams may also be common in this role since the long skinny shape of a particle accelerator fits the bill nicely.  Lasers on the other hand do not seem to be a good candidate.  Lasers do not benefit from having a longer physical shape, it is the diameter of the emitter that counts.  While there is an analogue - a spacecraft with a single massive mirror at the front - it has its own advantages and disadvantages, and does not really fit the description of a classic spinal mount.  Operationally it would be employed the same however, and have the advantage in rage over smaller turreted counterparts.

   It is this range benefit coupled with the low turning rate that define the use of spinal weapons.  They are the long ranged artillery of space.  If they can maintain range from the enemy the extra range might make them well right invulnerable, while if used in a defensive role that extra reach will fore the enemy to run a gauntlet of fire.  A battle between two of these spacecraft would be like a sniper duel - few tactics, with the one with the greatest accuracy coming out on top.  They would be at a disadvantage in any battle where there are multiple vectors of attack, or one that starts at close range. In a battlefield dominated by missiles they might not fare to well, but one that focuses on direct fire is likely to see them.

   The 'Verse that features spinal weapon can fall anywhere on the spectrum of scientific realism.  Given their long range and potential firepower it seems likely that any space force will have some in its ranks, and that they will form an important part of tactical doctrine.  One thing to note is that they become less attractive as the number and acceleration of ships increases as this brings out their weakness.  A jump drive that allows enemy to 'slip under the guns' as it were will also compromise them.  In any battle where missiles are unviable, massive firepower is needed from smaller ships, or the enemy will be engaged at extreme range a spinal mount is justified.  Another thing to remember is that a magnetic accelerator could be developed as a civilian cargo launcher on the moon, and repurposed as a weapon during a war, similar to in Heinlein's The Moon is a Harsh Mistress.  Even particle beams or lasers that fit the design requirements might be developed as part of beamed power stations.

The Turret

Definition:  A weapon or weapons mounted on or in an articulation that provides extreme ranges of traverse and elevation, as well as commonly housing the firing/loading mechanism and gun crew.

   The turret is one of the most common styles of weapon mounting in SF, and for good reason.  Nearly all wet navy guns are mounted in turrets, as are point defence weapons, and the main gun of tanks.  It was the invention and adoption of turreted main guns, along with the invention of the steam engine, that changed the face of ocean warfare forever.  A spacecraft armed with turrets can bring more of its weapons to bare on any enemy craft, and can do so regardless of its heading.  This is obviously important in a battle involving many spacecraft in close proximity, especially those capable of fairly pronounced manoeuvres and high acceleration.  Point defence weapons are far far more effective will a turret mount than without, allowing them to track incoming.

   There are two common mistakes with the representation of turrets in SF.  The first is the idea of a turret as a bolt on unit.  While this may be the case for smaller point defence units, it is almost never true of larger weapons.  Even the small gun turrets wet navy ships still use extend below the deck level, and old battleship turrets had more concealed than exposed.  The second issue is when turrets are placed in a position where the firing arc is limited by other turrets or by the hull of the spacecraft.  While the latter is to an extent unavoidable the former defeats the purpose of having a turret to begin with.  Yes, I'm looking at you Star Wars.

   Disadvantages of the turret are simple.  For any given weapon a turret to carry it will add complexity, mass, and power requirements to the design of the combat spacecraft, reducing the overall number that can be carried and increasing the cost.  Reduced accuracy can also be a problem due to vibration from the traverse motors, increased vibration in the flexible bearings, and flex in a unsupported barrel.  There amy also be a limit to the ammo that can fit in the turret, decreasing the overall firing rate.  Unique to spacecraft is the problem that recoil forces imparted on the spacecraft are not going to be constant, and will thus be harder to account for as they impact the trajectory of the whole craft.  

   Fundamentally turrets have a single advantage; they can be aimed independently of the spacecraft's orientation.  All the other advantages - reduction in number of guns needed to provide coverage in terms of point defence, ability to engage multiple targets in different directions etc are all derived from the former.  The advantage is most pronounced with point defence weapons, as they will face threats from many angles, and need to be able to track fast and close targets.

   Kinetic weapons are ideal for turrets given that unguided kinetics have short ranges, and it is in this envelope that turrets offer the biggest advantage.  Lasers also have a lot going for them.  Since the laser itself is likely to be in the main hull rather than the turret itself, with the beam reflected through a series of mirrors, there can actually be more turrets than the spacecraft can generate laser light for.  Whichever turrets are needed have laser directed into them, and the loss of a few to enemy fire is not such a disadvantage since the total energy output does not decrease.  Particle beams benefit the least.  This is both due tho their long skinny shape in most designs, and to the fact that bending a particle beam at any kind of angle will produce synchrotron radiation.  Tis could of course be overcome by having truely massive turrets or miniaturised particle beams.  In terms of point defence lasers are likely to be dominant given their accuracy at range, and the fact that a missile probably won't be too well armoured compared to a spacecraft.  Adaptive optics can also give point defence turrets quicker focusing and greater accuracy.  Kinetic point defence will be regulated to slower firing 'flak guns' that throw up a wall of shrapnel rather than targeting individual threats.

   Unlike broadside and spinal mounts turrets have the best chance of dominance in a softer SF 'Verse.  This is because they are best suited to short ranged, high relative speed combat where aim will have to be shifted quickly, and the spacecraft will be changing direction often.  They are also suited to battles where enemy spacecraft can emerge unexpectedly from hyperspace in any direction, and in which the spacecraft of both sides end up occupying the same volume of space.  Obviously force fields or shields help in this regard as they encourage ships to close to kinetic range where they can output more damage.  In a hard science 'Verse close quarters battles are unlikely as everyone will be seen long before they get into range, and with the ranges that are more realistic decrease the disadvantage of fixed weapons and emphasise range and accuracy.  Turrets will always be used as point defence installations however, so they will never be absent.  A lot of works also feature turret mounted kinetic guns as secondary weapons, like the Sulaco from Aliens; this is quite likly considering the relatively small size that kinetic weapons can have while remaining potent enough to be included.


The Broadside

Definition:  Weapons mounted at right angles to the direction of thrust, usually within the main hull of the spacecraft, and with limited traverse and elevation. 


   A fixed broadside battery is one of the most uncommon arrangements to be seen in SF, with turrets being far more common.  The only one that I can think of in visual SF is the gun deck aboard the Separatist ship at the beginning of Revenge of the Sith.  In written works the Black Fleet Trilogy by Joshua Dalzelle had what sounded like a fixed battery of laser weapons on the ship that acts as the setting for most of the first book, but it was never implicitly stated.  In the Honor Harrington books the beam weapons were, by memory, in broadside arrangement; a necessity imposed by the gravity drives used.  There are also the quite common examples in visual media where turrets are shown that would be unable to fire in any arc except that of a broadside.  Most of the turreted guns seen in the Star Wars movies fall into this category, with the Venator Class being a prime example.

   The scarcity of this arrangement is not unexpected.  With the prevalence of the 'Space is a Ocean' trope it is to be expected that a design philosophy that long ago gave way to turret armament should find little traction.  Where it is found it is most often for the visual effect, or because the work is intentionally trying to mimic the battles of the Napoleonic War transposed into space.

   There are not so many advantages to this type of design, and the conditions under which it become practicable are quite specific.  The main advantages are those shared by any fixed weapon mount.  Each weapon will mass less than an equivalent turret, and be simpler in construction.  It may be more accurate since it can be mounts straight to the spacecraft's structure via recoil absorbing mechanisms, reducing vibration.  Ease of access would also be a big factor, especially with advanced and perhaps temperamental weapons since turrets have never been known as spacious.  The weapon itself might also be more massive than a turret could cope with, or have a larger recoil force.

   Disadvantages are pretty obvious.  Limited traverse and elevation impose a greater need for manoeuvrability on the spacecraft, and run the risk that at close range or high traverse speed a more manoeuvrable target could stay out of the fire arc entirely.  This is partially avoided with lasers, since with adaptive optics they can have quite a good arc of fire without the actual emitter being articulated.  Since they cannot fire forward the spacecraft is at a disadvantage accelerating toward or away from a target, although this may not be a problem depending on the technology level of the 'Verse.  The broadside, and all fixed weapons, are at a disadvantage in a 'Verse where FTL can allow a enemy spacecraft to appear unexpectedly in any direction.  The need to rotate the entire spacecraft is going to slow down response times significantly compared to a turreted vessel.  Conversely the broadside is more attractive in a hard science 'Verse where you will always see the enemy coming.

   A broadside thus falls best into a 'Verse with fairly low accelerations and long engagement ranges.  It also becomes a lot more practical if the main offensive weapon is a missile attack from standoff range, especially if it is one involving tens or hundreds of missiles, and possible submunitions.  The ability to carry more weapons for the same mass than in turrets, coupled with the greater accuracy and potentially greater effective range would give the broadside ship a very good defence against missile spam attacks.  Against such an attack it is the volume, range, and accuracy of defensive fire that will stop your spacecraft from being ventilated by a hypervelocity penetrator, and in this regard the broadside holds the advantage.  Also, the greater the number of weapons, the more incoming can be targeted at once.

   Lasers or kinetic weapons would be the most practical.  Lasers would benefit from having many emitters, allowing more incoming to be targeted at once, and for kinetics it allows a greater overall rate of fire, important given their inaccuracy.  With kinetics it could also extend their offensive range by filling more space with metal than would be possible with fewer weapons and making it difficult to evade with low thrust levels; range would still be terrible compared to other weapons however.   Charged particle beams could interfere with each other, but a neutral beam wouldn't ave that issue.  The soft-kill ability of a particle beam might also prove handy against missile attacks; the beams could even be defocused to fill a huge volume of space with relativistic plasma, providing a potent radiation hazard for any incoming missiles.  But without exact numbers it seems impossible to give any of the three weapon types a clear advantage for broadside use; it depends doll on the details of the setting.

   Some of you might object to the idea that lasers are better with many emitters, and it is a common debate.  Do you use one emitter with longer range, or many smaller?  My reasoning is that in a 'Verse where missiles are a viable main offensive weapon they will broadly be able to fire enough missiles with enough submunitions that the extra range is not such a great advantage, more so since a accelerating missile at a half a light second or so is going to be phenomenally hard to hit, and could be travelling at a huge speed by that time.  In any case, a computer controlled array of smaller emitters can act as a single larger emitter to some extent, in the same way as many modern telescopes use mirrors composed of multiple segments.

   Although not strictly a 'broadside' a missile armed spacecraft might have its storage silos arranged in the same configuration to allow more rapid deployment.  With warfare based on missile spam the ability to unleash more missiles in less time might be the best chance at victory, and having the equivalent of a current VLS(Vertical Launch System) might be the ideal.  This could also look pretty cool visually while maintaining realism, so take notice Hollywood! 

  Well, there we go.  Part 3 is in the works, but no promises on how long it will take.  Anyone interested in a deeper discussion of this topic, along with the maths, can find a wealth of info on the Atomic Rockets website.  There is a lot there though, so this may be more helpful to someone looking at a overview of the subject.

Space Combat Part 1: Tactical Manoeuvres

NOTE

   I originally wrote this post as a guest post for the Future War Stories blog( link), where it generated a lot of very interesting discussion in the comments.  Since then, and mainly as a result of the comments, I've decided to expand on the theme of tactical manoeuvres.  I'm posting this so that anyone reading either part will be able to find the other; I do encourage reading the comments on Future War Stories though, they have almost as much stuff as the post itself.

   Hopefully this will develop into an extended series of posts, some of which will be design related like my  Building a Space Battleship, and some will be looking at tactics, strategy, etc.

  SF Worldbuilding has been on a bit of a hiatus, but I'm going to be posting again, hopefully.  I remember saying that before though, so don't get to excited.  If anyone has any ideas for non-military future tech they'd like a post on please leave a comment; my main interest is military SF, so I find other things hard to think of, but want the blog to have a broader scope than that.

"I am a leaf on the wind" - Wash

The hand can't hit what the eye can't see

   As both 'Wash' Hoban(Firefly) and Han Solo(Star Wars) have demonstrated on numerous occasions firepower is not the only asset that can win a fight.  Quite often in movie SF the heroes of the story will be aboard a smaller spacecraft than their opponents, their only hope of survival lying in their superior abilities.  While this is largely due to dramatic reasons, it does draw attention to the importance of manoeuvrability in space combat.  When dealing with hard SF - no handwavium forcefields or technobabble shields - one shot kills are very probable: nukes, mass drivers, particle beams, lasers, all posses more than enough potential to negate any form of armour we know about today.  And while no real spaceship will every fly with the grace of a X-wing starfighter this does mean that the ability to avoid hits may be more important than surviving them(structurally, the crew is still a concern), much like the situation in arial combat today.

   For SF writers this is a boon.  A battle that requires manoeuvres is intrinsically better suited to one in which humans might play a role.  Randomness and intuition could be vital, and so far computers don't offer that.  Even if the ship can fly and fight itself this leaves room for a human tactician, negating Burnside's Zeroth Law of Space Combat - SF fans relate more to humans than they do to silicon chips.  However, it can also pose difficulties.  Space is not a familiar environment, and movement in it is counterintuitive at best.  It is also radically different for a spacecraft in orbit around a single planet, in a planetary system, or in deep space.  And for those of us who try to avoid the dreaded 'Space is a Ocean' trope this can be very...frustrating.

   So, I'll look at four basic situations; deep space with low relative velocity, deep space with high relative velocity, single planet, and planetary system.  For each I'll also take a look at the changes in the situation that different tech will have.  This post is not so much about manoeuvring itself, but about how different situations shape it.  An in depth discussion of tactical manoeuvring down to the level of orbital physics or specific technologies would make the article far to long.  In the future I'll attempt to do follow up articles that look at manoeuvring in the context of a specific spacecraft, but for now this should provide an indication of what a spaceship would be doing.  For simplicity's sake I'm only going to consider one-on-one battles in detail, not constellation engagements.  Fleet actions are a whole separate ball game, and will warrant a separate post.

Deep Space - low relative velocity

   Just what is 'deep space'?  For the purposes of a story it is that area of space which only the bigger spacecraft can reach, so interplanetary or interstellar, depending on tech levels.  From a navigational perspective it could be defined as 'flat' space.  That is, space in which the gravitational acceleration is insignificant.  Insignificant is defined by the power of the drives your spacecraft is using, so this adjusts itself to match the setting.
   Manoeuvres here are closest they will get to those found in Space Opera.  The lack of a gravitational source means that movement in any direction is equally easy, and the fight becomes truly 3D.
   For high tech - multi-gee acceleration and big delta-V - the fights will be 'dogfights' to some degree.  This will be more marked if the craft use spinal mounted weapons, or if they have large blind spots in offensive or defensive weaponry.  If kinetics are the main weapon then the fight could become quite interesting, with KE rounds restricting the possible choices for manoeuvring, a possible tactic for the adept captain to employ.  Missiles will be very effective, with s straight line of flight to the target, as will beam weapons.  Particle beams will benefit, as they are degraded in accuracy and rage in the presence of a planet's gravity or magnetic field.  If lasers are the primary weapon then the fight will be less of a dogfight, and more of random 'drunk-walking' to throw off targeting.
   For low tech - milligee acceleration and limited delta-V - visually this would be quite boring.  The ships cannot perform elaborate manoeuvres to get in each other's blind spots, nor can they expect to dodge beams and kinetic weapons at short ranges(ranges dependant on velocity of the weapon).  Instead orientation and sensor data is the most vital.  The spaceship must bring the most weapons to bear, while at the same time keeping a small target profile, and reducing signals that might give its opponent an effective targeting solution.  The ships orient themselves, enter weapons range, fire a few salvoes, and the battle is decided.  In this case missiles are very effective, as they can come in at an angle to the primary attack vector, distracting sensors and absorbing point defence capacity.  Kinetic rounds are also more effective, not only can the score a hit from longer range, but they can be more easily used to 'box in' an opponent than if accelerations were high.  As before, 'drunk-walk' will be used to throw off targeting.

Deep Space - high relative velocity

   The chances are that spaceships will rarely intercept each other in deep space.  It is simply to large, and too easy to see someone coming.  When they do it is likely to be a head-on pass at high relative velocity for two spacecraft following the same or similar orbit in opposite directions.  Note that once unrealistically powerful torch-drives become common, interception is possible, if still unlikely unless both parties wish it, or one slips up.
   It turns out that for both high and low tech the manoeuvres are much the same in this situation.  Any reasonably fast orbit will result in the two ships passing with Rv of tens if not hundreds of km/s. At this speed there is not time to dogfight.  Even a torch ship, which will have a much higher intercept velocity, will take so long to cancel its Rv and return to the battle it would be considered as a separate engagement, rather than a second pass.  For a ship with foreseeable tech it would be nearly impossible.  If anything it will resemble a joust between two medieval knights on horseback.  Unlike a joust, however, they might not be a winner.
   The longest commonly accepted range for a laser weapon to target effectively is about one light second, or 3*10^8 meters.  At a very low end relative velocity - I randomly chose 40 km/s, which means that each ship has ~half solar escape velocity, which is not unrealistic, nor is it that high for a advanced ship.  At this range and closing speed the time for targeting the incoming ships and its projectiles is ~2 hours.  Plenty of time to shoot down incoming projectiles, you say.  But at this speed one kilogram of inert matter has an energy of 8*10^8 J.  And how many of those is the opposing ship going to throw out in your path?  You can make considerable sideways movement relative to direction of travel in an effort to avoid the projectiles, but the opposing ship can easily see any move you make, and at charter ranges dodging will become impossible.  Pretty much any kinetic hit at this speed will be fatal, so it will be the ship with the best point defence, sensors, and emergency manoeuvring that will survive.
   Durin the approach both ships fill space with inert projectiles, possible with last ditch terminal guidance.  They will be hard to spot at long range, tiny, inert, and possibly cooled down so that they have no discernible thermal signature.  So it will be only in the last stage of the pass that the combatants can begin to dodge the projectiles.  High lateral acceleration and powerful attitude control will help to weave through the incoming fire like a skier on a slalom course.  Good sensors will be needed to sport the incoming, and good PD to shoot those that can't be avoided.  However, it is my personal opinion that this sort of situation would be 'two men go in, half a man comes out'.  If energy wagons are primarily used, them this is even more so the case, as dodging becomes effectively impossible.

Orbital Space - single planet

   Most space battles in SF take place in orbit around a planet.  This makes sense in both hard and soft SF 'Verse's for several reasons.  Primarily it is the place where hostile spacecraft are most likely to meet.  It also adds a new layer of complexity to the fight, introducing 'terrain' to the tactical considerations.  The planet can hide opponents, restricts manoeuvres, sucks up delta-V, and provides something to crash into.
   Aside from hiding spacecraft who are on the other side a planet can slo provide some cover for combatants.  Picking up a spacecraft against the disk of a planet is significantly harder than spotting one against the backdrop of space after all.  A low orbit that brushed the atmosphere prevents opponents from attacking from most of one hemisphere, a great advantage.  For a craft equipped to reenter the atmosphere it also offers the possibility of manoeuvres not possible with the amount of delta-V they posses.  From reading Atomic Rockets kinetic weapons seem to hold the advantage shooting from a higher orbit at a lower.  A DEW is not effected so much, and so the orbit used is less of an advantage or disadvantage aside from the detection aspects.  Lasers also posses the potential to be 'bounced' around the horizon by remote drones, meaning that the attacker can shoot without exposing themselves.
   So the aim of any manoeuvres is pretty simple.  Orientation to bring weapons to bear, and the standard 'drunk-walk' are a given.  The opposing captains will try to gain the better position in an orbit underneath the enemy ship, or perhaps between the enemy ship and the sun, which might help to blind sensors.  This will be complicated by the fact that change orbital inclination is very hard compared to other manoeuvres, restricting the spacecraft to a 3D layer of space, although not  2D plane shown in so many soft SF works.  Forcing the ship into a lower orbit will decrease its orbital period, and vice versa.  Combined with changing the orbit from circular to the elliptic and back this gives spacecraft commanders the ability to surprise their opponents by appearing around the planet at a different place or time than expected.  There will also be a large amount of 'minelaying' of a kind, seeding or its will kinetic projectiles in order to herd the enemy into a bad position.
   But while the aim of the manoeuvres is simple, execution is not.  Trying to explain it is beyond me, so I suggest that anyone serious about grasping orbital mechanics begins by playing the Kerbal Space Program game, or browsing youtube for anything helpful.  It makes a lot more sense visually than it ever will in writing.
   High tech - for advanced ships a planet is a much smaller piece of terrain, a hill rather than a mountain.  They can more easily afford to change orbits, to drop below minimum orbit al velocity or go over the maximum, and can perform delta-V heavy manoeuvres such as change the orbital inclination.  The ultimate of course is a ship that has drives powerful enough to reverse its orbit completely, surprising its opponent when it emerges around the opposite side of the planet to what was expected.  With higher acceleration and delta-V the seeding of orbits becomes less effective, much easier to dodge than with a low powered spacecraft.
   Low tech - with low levels of acceleration, even if the spacecraft has a high delta-V, changing orbits can take days if not weeks.  The position of the enemy will be highly predictable, and so kinetic weapons become very important.  The advantage converted by different orbits will be much more apparent, as it is harder for anyone to turn the tables on their opponent.  Most tactics would be a combination of manoeuvring into a good position, and using kinetics to force the enemy into a bad one.  Low tech ships would also gain a large advantage by being able to dip into the atmosphere, as this provides essentially free deceleration, saving reaction mass.

Orbital  spaghetti

Planetary Systems

   Adding more heavenly bodies to the mix vastly increases the tactical possibilities.  While 'planets' per se do not do much, moons do.  A gas giant with seven or eight moons is a extremely complicated system, and has travel times of only hours or days as opposed to years between planets, and that is with Hohmann orbits.  High acceleration, low delta-V spacecraft could follow complicated routes, sling-shoting themselves around the moons to gain an unexpected position. For much of the time they could be out of sight of the enemy, making it a scenario reminiscent of The Hunt for Red October.  The fact that moons often have lower gravity than planets also means that the manoeuvres in proximity to them can be more extreme given the same tech level.  It even brings up the possibility of landing on a moon, camouflaging the spacecraft, waiting for the enemy to pass by, and then launching and taking them by surprise.  The changes imposed by tech levels are the same as those for a single planet, so I won't both to go into detail.  This kind of setting will be the most complicated for a SF aficionado to get right, and I would suggest finding a solar system simulator to model the setting before attempting to figure out a complicated battle.  It does lend itself to far more interesting scenarios, however, and will be far more rewarding.

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.