Thursday, January 15, 2015

Space Combat in Conjunction: Basic Assumptions

This is sort of a digression from our Building a Space Navy series, but a necessary one.  In order to finish filling out the Building a Space Navy chart, we will eventually have to add in some actual ships and rockets and stuff.  For their capabilities and armaments and other particulars to make even a lick of sense, we must establish what design assumptions are in place in the Conjunction setting.  That's what this post is about.
Dis iz Doin it Rong.

As always, special thanks to Rick Robinson for waxing lyrical on these topics on his Rocketpunk Manifesto blog, and Winchell Chung Jr. for his indispensable Atomic Rockets website.  I will be referencing their work throughout.

Assumption #1: Purple vs Green is a Draw

For those of you not familiar (lucky!) with "Purple vs Green", it refers to the debate among Hard SF fans about which type of weapon system is better: Lasers or Kinetics?  The subject is passionately discussed in a variety of places.  This blog is not one of them.  For an in depth analysis, Rick Robinson has a couple of posts that Atomic Rockets already linked to, so that's where you should start, with further discussion here.

In the Conjunction universe, a laser capable of destroying any and all kinetics attacks is too expensive to build, especially in terms of power.  While a big laser Combat Mirror would have the power to vape anything massing less than a small asteroid, the thing is impossible to aim fast enough to do the job, so there you go.  Contra wise, with enough small lasers massed on a single side, there is no amount of kinetics capable of overwhelming a determined defense.  The cost in delta-V is to high to move that much mass.

This is how you do it.

This is important to the setting for two reasons:  First, having only one type of weapon system dominate is kinda boring.   By having both swarms of Kinetic Kill Vehicles and eye-burning lasers, you get variety to spice up your setting.  Two, by making both banks of lasers and swarms of kinetics just about even, things like maneuvering, tactics, fire discipline and other stuff you can lump under "human factors" become important.  After all, it it's just a matter of "whoever has the most lasers/missiles wins", then why write about it?  With beams and kinetics evenly matched, the choice of which one to use, under which circumstance, can be critical.

Assumption #3: The Light-Second Limit

This isn't a real limit, but a practical consideration that comes from the first assumption.  Basically, in the Conjunction universe, you can't effectively remote control something more than a light-second away.  By "effectively control" we mean, things like evasive maneuvers, coordinated fleet movements, synchronized fire from lasers, and the direction of flights of missiles.  What this means is that even the largest, most sophisticated swarm of missiles and autonomous combat craft will have a control ship with real people somewhere within three hundred thousand kilometers.    The Light-Second Limit also refers to the fact that the closest distance you can get to an attacker and still reasonably dodge a laser is a light-second, because it gives you (duh) a second's time to move.  You cannot, of course, actively dodge, because by the time you see the laser, it's cooking you.  But if you stay moving around, the laser's targeting system can only see where you were a second ago, due and then guess where you'll be by the time the laser actually gets there.  So, the goal of the attackers is to get inside the light-second range, while the defender will want to keep the attackers at least a light-second out.

Assumption#3: Most Combat Takes Place in Orbital Space

Beware smiling patrol craft...
In a realistic setting, where's all the interesting stuff going to be?  In orbit, of course.  That's where ninety percent of all live fire incidents in the Conjunction universe have taken place.  This type of environment is a loathsome cross between brutal house-to-house urban fighting and dreadnaughts in the open ocean, only at 7 km/s in free fall.  I chose those two examples most deliberately;  In orbital space, you can fight over the horizon, and you can hide in a crowd.  There is a horizon in orbital space for the simple and unavoidable reason that there is some planetary body in the way.  because of this, unless there is an existing satellite network you can use, you will need scouts to check out the opposite side of the planet and probably a relay craft as well to insure communication.   Or you can use smaller, more maneuverable Patrol Craft that have the crew - and the authority - to make command-level decisions.  You really need that level of authority because of the other consideration, where a baddie can hide in the debris, the sovereign orbits of another nation, or even hide on or in space stations and spacecraft that are otherwise kosher.  In order to prevent a diplomatic incident, you would need an organization with broad powers to stop and search and international oversight.  An organization like the UN&C Space Force and Espatier Corps, for example. 

Aassumption #4: The Staring Contest - Lasers Against Lasers

Again, thanks to Rick Robinson for pointing this out.  You can armor a spacecraft, obviously, you can even armor radiators, if you make them out of the right stuff.  But you can't armor the lenses of your own lasers, therefore, the lasers themselves are the best target on a spacecraft.  The thing is, both sides know this.  This is why those nifty swarms of KKVs also pack a handful of laser tipped missiles that home in on the defenders lenses when they light up to break up the swarm.  Given a close enough range, a disposable pulse laser can in fact burn a hole in those nice, heavy lasers on our space warrior's bad-ass battlestars that will have to be put out of action and repaired.  Assuming, of course, that you get the chance.

Let us remember, however, that only the mirror will be kaput.  The laser generator, which is the heart of the system, will probably not be damaged.  Spacecraft will probably have multiple emitters for a single laser generator, so they can remain combat effective even with the loss of a mirror or two.  This is also a plus in that larger mirrors can be fixed-mounted in multiple places for a given generator, while a turret is unavoidably smaller - and therefore of shorter effective range - than a fixed mount of the same length.

Because of the cost of a laser system of this type, most lasers are mounted on non-disposable spacecraft.  Manned spacecraft have the opportunity to perform damage control and replace burned-out mirrors.  But probably not during a battle - it will all be over quickly, one way or another.
You may have other things to think about.

There will be a couple other posts in this category as we continue with the main series of articles.  Now that we've established our basic assumptions, we can discuss the types of spacecraft that our "space navy" will need to deploy.  We can then discuss some of the combat doctrines that will be in force in Conjunction.  But before all that, we will discuss fleet posture in our next Building a Space Navy post, in order to establish the final group of criteria we need to know before we design a fleet.

See you then!



  1. I've been thinking about laser combat recently, and wondering how difficult it would be to create automatic mirror replacement mechanisms.

  2. Interesting...of course, the easier the optics are to replace, the easier they can be accidentally knocked out of alignment.

  3. Isaak Kuo, our resident Jovian, has this to say about Lasers:

    "It is possible to armor laser mirrors, and it's also possible to use optics which are inherently difficult to damage. We've had extensive discussions about this (with Rick and others) on sfconsim-l.

    Armor is based on protecting an otherwise delicate mirror with grids of armor. This assumes the use of a pulsed laser. Each armor grid is a bundle of parallel sheets. When the grid is rotated, it briefly lines up with the target in passing--that's when a pulse laser can fire. With two or more grids, the window of vulnerability can be made arbitrarily short. And the duty cycle can be made unpredictable.

    So, for example, a pulsed laser that could only pulse 1/10000 of the time. Incoming laser fire would only hit the mirror 1/1000 of the time. The other 99.99% of the time, it hits the grid armor.

    If you want to get even fancier, you can space apart the grids by, say, 1/1000 light seconds (300km). This requires the use of an armor drone, or a pair of warships. This lets you have a duty cycle of almost 50% and still have armor protection 100% of the time. The time delay is sufficient that your photons can pass through to the target, while photons going the other way will get blocked by either one grid or the other.

    Still, this grid armor is very bulky. Assuming the grids block 10% of the outgoing photons, it takes 100cm thick grid armor to provide the equivalent protection of only 10cm of solid armor. And it's possible that damage to these grids may significantly diminish their efficiency.

    Another interesting possibility is to use damage resistant optics. If you use diffraction rather than reflection or refraction, you can make your focusing element arbitrarily thick. Your focusing element is a zone plate drone some distance away from the beam generator ship. The zone plate is a sturdy thick set of concentric cylinders. It can be arbitrarily thick...if you want, it can be 1m thick. All that really matters is the pattern of concentric circles. Enemy lasers could blast away at this thing all day, and it still functions perfectly so long as there's enough left over to block the concentric circles.

    Such a zone plate is not the most efficient focusing element--it only focuses about 25% of the source beam's energy on target. But if you want the ultimate in damage resistance, it can't be beat.

    The bottom line is...don't bother shooting at the laser optics. It can be HEAVILY armored."


  4. COOL.
    This way, when one side gets it's ass kicked, rotating armored grids can be part of the next generation of warship!

    1. Isaac Responds:


      Yes, perhaps, but anti-laser armor protection in general seems like a pretty obvious idea once lasers become powerful enough to require armor protection. I wouldn't think it would be something that requires an ass kicking to realize should be done.

      However, if you want to justify laser warship with no anti-laser armor...

      You might posit that up until the time of your setting, missiles have been overwhelmingly dominant over weapons lasers. As such, warships are designed purely with missile combat in mind. It's not that weapons lasers don't exist, it's just that no one bothers to put them on spacecraft because missiles are superior weapons.

      In this situation, it might make sense to design a laser armed spacecraft designed to fight only missiles because there are lots of enemy missiles and no enemy lasers. It's like how the first tanks weren't designed to fight enemy tanks because enemy tanks didn't exist yet.

      Then, when the enemy sees them and reacts by slapping some laser on their own spacecraft, the first guys are like, "Derp, we didn't think that would happen."

      (No really, people can be that stupid.)

      Aaarggh...this scenario really hurts my head. It just doesn't seem to make sense from the start. Weapons lasers seem to be inevitably useful thing to have around. If the POTUS wants to zap terrorists from orbital drones, a near future laser will be able to do it with precision but a missile would take minutes to cross the distance required. Orbital lasers could zap hostage taking pirates like a team of snipers, while orbital missile launchers just...can't. There's just no way missiles will ever be better than lasers for this, and it's hard to imagine a future where that isn't one of the first things mankind does with space weaponry."

    2. I see what you mean about missiles being inferior to lasers in that sense. One of the saving graces in the Conjunction setting is that there has never been a interplanetary war, or any kind of space war for that matter. just a series of police action and the like. In this case, I envisioned rogue states and "pirates" or more likely smugglers and the like using kinetic because rockets , if you have a large orbital presence of any type, will be dirt cheap to procure and convert in KKVs. It not even a case of Tanks not having anti-tank capability - it's more like how Coast Guard cutters don't have armor belts because they go up against speed boats and small arms fire.

      But all that said, the wouldn't the armor on a laser lens be thinner than on the rocket's flanks?

    3. More from Isaac Kuo:

      "Anyway, getting back to your original article...I understand the motivation for wanting missiles and lasers to have an uneasy balance. I tried for years for this to be a guiding principle, for the same reason you have.

      But I've pretty much given up on the idea. The fundamental problem is that missiles aren't fun. They are a pain to keep track of, in any numbers, and missile combat basically just boils down to numbers.

      If you want things to be tactically fun, it may be a better idea to look at different sorts of weapon systems instead. In particular, electron beams can be an interesting weapon system in your setting. Electron beams can be interesting complements to laser weapons, because they can share hardware with a free electron laser.

      A couple years ago, I came up with this interesting way to use a planet's ambient magnetic field to focus electron beams over long distances. But the beam spot size is smallest when shooting perpendicular to the magnetic field. The further the target is from this, the larger the beam spot size. Interestingly, the beam spot size does NOT directly depend on range to target--only direction to target, and strength of the ambient magnetic field. (This strength diminishes quickly with distance from the planet, so there is in fact a practical range limit.)

      The bottom line is that if you're setting involves mainly space combat near planets, an electron beam is an interesting complement to laser armament. There are some directions and ranges where the electron beam is superior, and others where the laser is superior.

      Furthermore, different sized vehicles have different defensive abilities. A relatively large vehicle can completely defend itself from an electron beam with a strong large magnetic field. Small vehicles are vulnerable, though, and an electron beam could be an order of magnitude more efficient at delivering beam energy. (Free electron laser will only convert a fraction of the electron beam's energy into photons, and then the target material may be reflective enough to only absorb a fraction of the laser's energy.)

      So, even though the electron beam may be useless against large warships, it's so much more effective against small warships that it's still a useful secondary weapons mode.

      Also, the firing port of an electron beam weapon is tiny. The example I calculated out was a weapon with a 4mm spot size and a 4mm firing port. The beam can actually be aimed with electromagnets even after the firing port. Anyway, it's a lot less bulky than a laser turret.

      And then there's space weather. Besides the fact that different planets have magnetic fields of different strengths, these magnetic fields are constantly shifting. This results in "windiness" that throws off your electron beam's aim. Earth's magnetic field shifts in the timeframe of around a second, so it's going to be impossible to stay on target at .5 light seconds away. Your practical range is likely much lower than that. Space weather can result in large variations in magnetic field strength--affecting beam spot size--as well as how "windy" it is. The effect on beam spot size effectively changes how wide your firing arc is against a particular target (a smaller spot can penetrate deeper). The effect on windiness changes the effective range of the weapon.

      My point's an interesting weapons system that can make tactical maneuvers an interesting puzzle. It's not just about numbers, you've got firing arcs that matter. You've got formations to cover each other's blind spots. You've got situations where a polar orbit is radically different, tactically, than an equatorial orbit, even when neither side has any relevant surface assets.

      And from a playability perspective, a really nice thing about these firing arcs is that they don't depend upon dealing with complex 3D rotations. They depend purely upon a spacecraft's position, not its orientation."


Questions, comments, criticisms? All non-Trolls welcome!