In Fire Forged: Worlds of Honor V-ARC (47 page)

The Star Kingdom of Manticore pursued an independent path to laser head armament. Always admirably well informed on galaxy-wide research trends due to command of the Manticore Wormhole Junction, the Bureau of Weapons (BuWeaps) presumably learned of the laser head concept when it first became public knowledge in the late 1830s. Thus began a low-level development effort which confirmed the validity of the basic physics without developing a functional weapon. Even Manticore’s vaunted research and development establishment struggled with the complex problems of gravitic technology miniaturization, timing, and nuclear processes for many years. Manticoran work paid off in 1870 with the introduction of their first laser head capable missile—the Mk-19 capital ship missile.

The advent of the laser-head armed impeller drive missile put a premium on keeping enemy missiles far away from one’s ships and forced defensive system designers to make dramatic improvements in countermissiles, point defense laser clusters, gravitic sidewall strength, and armor. Armor and structural designers in particular were challenged as it became clear that a laser head strike, even against an intact sidewall, could penetrate dozens of meters into a target. Against an open impeller throat or stern the new weapons could literally punch straight through meters of even capital ship grade heavy armor. Warship armor experienced a general thickening in this period and much greater emphasis was placed on bow and stern hammerhead active defenses and armor design. It also became slightly more common to see dorsal and ventral armor during this period to protect against freak hits from laser-head armed missiles.

State of the Art in Laser Head Armed Impeller Drive Missiles: The Mk-13 Anti-Ship Missile

Armor design is based on the expected threat. BuShips would use intelligence estimates of Havenite weaponry to model the threat but such information is somewhat scarce in the public domain. This article will instead use the Royal Manticoran Navy’s standard heavy cruiser/battlecruiser (CA/BC) weight anti-ship missile, the Mk-13. Even here, though more information is available, specifics are usually classified. The reader will soon see, however, that publicly available information gives us a good appreciation of the Mk-13’s capabilities and the basics of the armor design problem.

Design and Construction

BuWeaps began the Mk-13 design in 1879 intending to produce the first RMN CA/BC weight anti-ship missile designed from the start to use laser heads. Previous RMN laser-head equipped weapons had required gravitic lens arrays too massive to fit into the smaller missiles fired by heavy cruisers and battlecruisers. Since operational experience with the laser head was relatively scarce, BuWeaps decided that flexibility would be the central feature of the design. It was felt important to support all attack modes into a single weapon. Proposals had been circulating for several years within BuWeaps speculating on the possibility of a multifunction gravitational lens array (MGLA) and fusion warhead combination small enough for use in a CA/BC weight missile, yet flexible enough to support laser-head attack, detonate in a counter-sidewall role, or act as a contact nuke as the situation demanded. BuWeaps began work on the Mk-86 general purpose fusion warhead and the Mk-13 program was initiated to carry it.

The Mk-13 impeller drive anti-ship missile bus is a 12 meter long 78 ton weapon capable of a maximum 88,000 gee acceleration and carrying the 15 megaton Mk-86 pure hydrogen fusion warhead with six Mk-73 three meter independently targetable laser submunition vehicles. It was designed to be fired from the even then venerable Mod-7 series launcher. Development of the necessary components took over three years with major difficulties encountered in the miniaturization of the MGLA and synchronization of all of the different parts of the system. Towards the end of that period when the first prototypes were nearly complete, information indicating that the Republic of Haven had somehow acquired laser-head technology began to flow out of Haven sector. While the RMN had little operational experience with the laser head, it paid very close attention to the experience that the Havenites were getting with it as they annexed their neighbors. Additional lessons learned regarding Republican electronic countermeasures delayed the roll out of the final Mk-13 design by almost another full year. Its final release in 1883 is considered to have been worth the wait.

Figure 1 (see end papers) shows the general internal arrangement of the Mk-13 bus configured for the anti-ship role. The schematic shows the features typical of most of the galaxy’s shipkilling missiles. The Mk-13 consists of four component groups. The foremost, called the “nosecone group.” holds the warhead and MGLA. Its outer skin also carries sensors for target acquisition and tracking. The two-meter effective diameter of the nosecone group does not give the seeker much sensitivity, so the primary guidance during most of its flight is provided by the launching unit. Behind the nosecone group is the payload group. It contains the six Mk-73 laser submunitions, ejectable payload bay doors, and short range high bandwidth laser telemetry transceivers for communication with the submunitions immediately before detonation. Comprising most of the rest of the weapon, the propulsion and power group contains a single impeller ring with eight nodes and the superconducting capacitor storage rings that power the weapon’s flight. This group also includes the missile’s thrust vector control systems and control moment gyroscopes for rapid, fine, low vibration pointing. Finally, the tailcone group contains the weapon’s telemetry transceiver and guidance package. The system consists of no fewer than five independent molycirc computer systems with cross checking routines to avoid the radiation induced upsets common during a space nuclear exchange. The computers are heavily radiation and electromagnetic pulse shielded to further reduce the chance of guidance failure.

Factors Affecting Performance

A variety of design factors control how effective a laser head will be. In simple terms, the laser head will be most effective when it puts the most energy into the smallest possible sized spot on the surface of the target. Other important characteristics include the wavelength of the photons in the beam and the rate of total energy flow (beam power). The discussion here ignores the weapon’s function in a pure counter-sidewall or contact nuke role to focus entirely on its performance as a sidewall piercing anti-ship weapon.

Nuclear Device Yield

Increased device yield tends to increase beam power up to a point whose exact practical limit is a matter of intense debate in some circles. Above a certain device yield, the laser head’s efficiency begins to drop off, indicating a maximum limit to possible laser output for a given system. The physics of this are beyond the scope of the present work but numerous schemes have been proposed in the open literature and on public boards to find ways around this fact. What BuWeaps is doing about it they decline to say.

Gravitic Lens Array Amplification

Generally, the more tightly focused the grav lens array pattern is, the more intense the resulting laser beam becomes. Increased grav lens amplification also directs more of the bomb energy that does not go into energizing the laser rods onto the target’s sidewall. Beyond a certain point, however, more grav lens amplification doesn’t mean a more powerful laser beam. Just as with increased device yield, laser efficiency starts to fall off as the radiation bombarding the laser rod gets too intense.

Lasing Material

The laser material in the Mk-73 remains classified and the composition of the laser rods is known only as Special Laser Material or Special Lasant outside of BuWeaps. Sources cognizant of the relevant physics speculate that the lasant is a high atomic number material with favorable quantum structure such as tungsten or hafnium but are quick to point out that many materials could potentially be used. The lasant not only determines the wavelength of the X-ray laser beams but also influences how long the weapon will operate and what sort of focusing will be possible.

Spot Size

The focusing length and diameter of the lasing rods, any X-ray optics built into them, and the standoff distance between the rod and the target at the time of detonation all conspire to fix the beam spot size on target. Smaller spots mean that the weapon’s power is focused on a smaller area to burn through the target. Smaller is always better for the weapon because the target’s sidewalls will defocus and spread out the beam. The importance of spot size becomes clear once one realizes that the better part of a kiloton of energy can be flowing into that spot. Indeed, one Grayson Navy officer of the author’s acquaintance, upon his first introduction to the Mk-13, proclaimed it “the Tester’s Own Cutting Torch.”

Rod Jitter

In an ideal engagement, the weapon would deposit all of its energy into a single spot on the target. The real world of space combat is typically devoid of this idyllic situation. Not only is there a large closure velocity between the missiles and the target but the laser rods must eject from the missile bus, reach their appointed positions, and slew to face a target with a nearly microscopic visible spot size in a very short period of time. The forces required to get a laser rod into position and rapidly point it are considerable and the laser submunitions are long and relatively thin. Vibration is common in this environment, and stabilization is a non-trivial engineering challenge. If the rod is still in motion or if it is oscillating as its thrusters and control gyroscopes steady it, then the laser spot on the target can move a great deal, smearing the beam across the target’s surface, or causing it to miss entirely. Any geometry that forces the missile bus to deploy its laser rods later than normal or the submunitions to slew a great deal will induce more jitter and tend to do less damage.

Weapon Effects and Armor: How Does a Weapon Damage the Target?

The most important thing from the armor designer’s perspective is what the beam does to the target. One might define a modern space-to-space weapon as a device which deliberately changes the material properties of a distant spacecraft in a way undesirable to that spacecraft’s owners. Most every anti-ship weapon damages a target by focusing some type of photon beam onto it. Beams disrupt spacecraft systems by breaking up the molecular structure of those systems so that they no longer perform as designed. When these beams consist of light of a single color, they fall under the archaic heading of “laser” beams. This term was originally an acronym standing for Light Amplification by Stimulated Emission of Radiation. Only some classes of modern beams rely upon the “stimulated emission” principle and the bomb-pumped laser is one of them. Understanding how these beams damage targets requires detailed knowledge of how the individual photons interact with atoms in the target. Only a cursory summary can be made of this rich field. Interested readers should consult an introductory radiation hydrodynamics course for more detail. Contact the author for several excellent resources.
 

Three factors conspire to predict beam behavior in a target: the wavelength of the beam photons, total beam energy delivered by all those photons to the target, and the rate at which that energy is deposited. Combined, these allow one to predict how deeply the beam will penetrate different materials, how much of the target’s molecular structure will be disrupted, and what kind of shock waves will result.

The author begins with the photon wavelength. One might as well use frequency or energy because they are all mathematically equivalent but weapons designers fairly consistently use wavelength. Early space energy weapons used photons in the ultraviolet, visible, infrared, and even the radio range. These wavelengths are impractical to focus at contemporary combat ranges so modern weapons use shorter wavelength photons in the X-ray to gamma ray range. Indeed, modern space weapon lasers are so commonly X-ray lasers that the term “laser” is generally synonymous with “xraser” in naval parlance. Their rarer gamma emitting cousins are called “grasers.” Both of these words have their obvious origin with the ancient “laser” though the fact that many such weapons do not operate on the principle of “stimulated emission” is generally forgotten. Confusion sometimes results because different scientific and engineering communities have different definitions of exactly what constitutes the cutoff between X and gamma rays. An astronomer’s X-ray might be a particle beam engineer’s gamma ray and so on. There appears little hope at this writing of ever clearing this up completely. This article uses the terminology of the Interstellar Association of Astronautical Engineers that a photon with a wavelength greater than one picometer (10
^-12
meters) is an X-ray and light with a wavelength shorter than that is a gamma ray. This value was chosen because one pm is a good cutoff point when discussing armor and weapons effects. This is because light begins to exhibit deep penetrating characteristics in common spacecraft materials for wavelengths shorter than this so that a graser cannon operating at 0.1 picometers damages a target in different ways than a laser at 10 picometers.

Weapons designers prefer shorter wavelength photons because they are (up to a point) easier to focus at the ranges of modern beam weapons. Shorter wavelength photons also tend to penetrate more deeply into armor and deposit into denser spacecraft structures like impeller nodes, fusion reactors, and weapon mounts. If preferred, the reader can imagine the shorter wavelength packets of energy in a graser beam “slipping” in between atoms in less dense materials to penetrate more deeply into the target and hitting the more closely packed atoms of more dense materials. Shorter wavelength photons also (again up to a point) deposit more energy and thus do more damage to any structure they hit. Needless to say, any characteristics which make short wavelength photons the friends of weapon designers do not to endear them to armor designers. The downside to shorter wavelength photons is that they tend to be harder to efficiently produce than their longer wavelength siblings. That means less energy on target for a given amount of input energy from the fusion reactors for ship mounted weapons or the nuclear device for bomb pumped ones. This is one fundamental physical reason why graser mounts are usually best practically mounted only on heavy cruisers or larger.