by David Weber
Literally hundreds of different armor nanoconstruction techniques can be used to form and machine the different layers, but one deserves particular mention. Designers sometimes use special structures within the armor surface to attempt to reflect a portion of the incident beam back out towards space. Most often used near the surface and called “face-mirroring” these tiny X-ray mirrors are formed by spacing highly absorbing layers of boundary material separated by precisely machined transparent spacers that are one beam wavelength in thickness. That this is only possible when the weapon wavelength is known precisely is the major reason that wavelength and any other information useful in deriving it (such as laser rod composition) is classified. The technique becomes progressively less useful as wavelengths get shorter and even under the best of circumstances does not reflect much beam energy. The precision machining required is time consuming and the materials used are typically expensive. However, it still finds application, particularly where there is risk of direct strike against bare hull as on hammerheads. Every reflected photon helps in these situations. Face-mirrored armor designed for the wrong wavelength means that the design wastes mass and construction effort for no improvement in protection.
Armor Materials
Armor materials are classified by their function in the armor system as described above: boundary, scattering, and structural. It is economics that determines which materials are used after the physical characteristics dictate which could be used. Cost-benefit tradeoffs are a grim necessity in war and it does a navy no good to design armor systems that it cannot afford to build. Even in an age of counter-grav spacelift it is expensive to mine planets for millions of tons of heavy elements and lift them to orbital construction yards for use as disposable armor for a fleet. Armor and other bulk space construction materials consist largely of alloys and composites of elements common in asteroids. This makes silicon, carbon, aluminum, titanium, iron, and so on particularly common in bulk armor substrates. That is not to say that rarer elements are not found in armor—just that they do not typically make up its bulk.
BOUNDARY MATERIALS
Boundary layers need high total ionization energies, density, structural strength, and good thermal properties. These properties can usually be achieved with a variety of available space resources. The most common boundary layers are ceramics such as silicon carbide and titanium carbide. These materials are sometimes combined with heavier elements in composites to provide greater mass and particle density at critical areas.9 Iron, being abundant, is the most commonly used element for this purpose but rarer and more expensive elements can and have been used. These elements most often allow thinner layers to produce the same effect as a given thickness of iron and can result in significant mass savings.
SCATTERING MATERIALS
While these layers do soak up some beam energy to ionizations, their main function is to scatter the incoming beam by releasing as many electrons as possible when ionized by it. The more electrons that lie in the beam’s path, the more scattered and diffuse it becomes. This requires materials delivering the most electrons at the highest total ionization energies in the lowest possible density. It is here that spacecraft structural gels are most often used. They are nanocomposite materials with very porous microstructures. The term derives from the old word “aerogel” and referred to the original process of replacing the liquid component of a gel with a gas (typically air) to produce low density materials with various useful properties. Modern spacecraft structural gels are made through a variety of different processes but retain many of the characteristics of their ancient predecessors: high strength for low density and low thermal conductivity. They commonly include foams of silicon, carbon, titanium, and aluminum as well as other rarer elements or compounds. It is very common for foams of light common elements to be doped or filled with quantities of other elements with more electrons per atom to increase the scattering effect. The great volume occupied by the scattering materials (sometimes a meter or more) means that they also play an important role in slowing down fragments and stopping heat transfer from nearby beam strikes.
STRUCTURAL MATERIALS
Battlesteel is the single most common spacecraft structural material in known space. It is the universally accepted term for a whole family of carbon-based nanocomposite materials used to build starship hulls and supports. While battlesteel is not used as armor, it is used to form structural elements within armor systems. Battlesteel comes in a bewildering number of varieties and an entire branch of modern material science exists to document new forms. The general advantages of all forms of battlesteel are extremely high tensile strength for a given mass, the ability to withstand great amounts of heat without changing physical properties, and an affinity for nanoalloying. The benefits are offset to some extent by low strength in compression and the amount of industrial infrastructure required for working battlesteel. The carbon that forms the raw feedstock for battlesteel production is almost universally obtained from the asteroid belts. Battlesteel has such low density that it is relatively transparent to the short wavelength radiation used in modern weapons, making it less than ideal as an armor component. A much greater thickness of battlesteel is required to stop a given intensity beam than with higher density materials found in armor.
LIQUID MATERIALS
While not technically armor, many liquids stored aboard starships have a role in the armor system. Liquid hydrogen and water are most commonly seen in this role. Tankage for these fluids can frequently be found wrapped around vital components. These liquid barriers, not as effective as dedicated armor materials, tend to be meters in depth and act both to absorb residual beam energy that gets past the outer armor and to stop splinters of shattered outer hull components from reaching deeper into the ship. The design and subdivision of these specialized tanks includes fast acting one way valves leading to vacuum filled flash expansion tanks to prevent overpressure rupture.
Overall Armor System Design
Viewed locally at the exact place where a beam strikes the ship, armor design seems a simple affair. The problem is that one never knows where a beam will strike and using the same thickness of armor everywhere is not practical. Armor designers, like all others, have to fit their system within the available mass and volume and armoring everything is simply impossible because of the mass cost. This means the designer must choose which areas will be protected . . . and which will not. Four principles guide this decisions process.10
1.Armor cannot do all the work. It has already been mentioned that armor works in concert with gravitic sidewall and radiation screen generators. Without these screens operating at design levels, some damage will typically occur to a target which is engaged by a ship of its own class once missiles begin to detonate or the enemy gets within energy range. Notable exceptions to this principle are the hammerheads which are more likely to be hit on bare hull (i.e. without the benefit of sidewalls).
2.Armor cannot protect everything. Armor designers have experienced this problem for thousands of years: something (usually speed or firepower) is sacrificed to add greater protection. On an impeller drive starship, the problem arises because of limits to the mass and volume that a given propulsion system can economically move. This imposes limits on how much mass can be allocated to each system and armor is no exception.
3.Combat starships are designed to fight their equals or inferiors—not their betters. A heavy cruiser’s armor scheme is perfectly adequate for fighting other heavy cruisers or lighter craft. Yet a battlecruiser would likely shatter it beyond recognition.11 It is the ancient wisdom, “quantity has a quality all its own,” which drives this practice. It would be desirable for every warship to be able to withstand a superdreadnought’s fire but that would effectively mean that every ship was a superdreadnought. While this would be good for crews, the Royal Manticoran Navy could not afford enough ships to be all of the places that it is required to be at once.
4.Armor’s job is to limit damage—not stop it. The
job of armor is to minimize damage, contain it to the maximum possible extent, and channel it away from vital areas. Of course, there are exceptional situations. One example might be a desperate light cruiser or destroyer engaging a dreadnought. The DN’s sidewalls and armor in this case might very well be heavy enough that the lighter ship would find it effectively impossible to do meaningful damage. This should not be thought of as complete invulnerability for the heavier unit but rather as the lighter ship’s chance of doing any serious damage to the heavier being so small that a sane captain just wouldn’t try.
Armor design therefore requires study of the ship to separate that which is vital from the merely critical or nonessential systems and to identify those components which cannot be practically armored. These decisions are subjective and each navy has detailed definitions backed up by ship modeling, mission analysis, probabilistic risk vs. threat simulation, trade studies, and so on. The definitions below are sufficient for the present purpose.
VITAL
Systems or volumes whose loss will result in loss of the ship or inability to accomplish a primary mission. The RMN includes returning safely to base as part of the primary mission and armors components accordingly. Examples include fusion reactors, hyper generators, impeller rooms, some structural members, control spaces, and at least a portion of the life support system.
CRITICAL
Systems or volumes whose loss will result in significant risk to the ship or primary mission accomplishment. Examples include individual power conduits, weapon mounts, and gun-crew capsules.
NONESSENTIAL
Systems or volumes whose loss results in minimal or no risk to mission accomplishment. Examples include the captain’s day cabin, viewing galleries, and some storerooms.
UNARMORABLE
Systems which, by their nature, cannot be armored, regardless of their importance to ship safety or mission accomplishment. Typical examples include impeller nodes, sensor emplacements, communications arrays, and other surface features.
Distinctions like these govern the design of almost every warship built today and govern what goes into the core hull and what does not. The core hull layout puts as many vital systems and spaces as possible in the smallest practical volume at the center of the ship, puts an armor envelope around it, and then wraps this round with other critical, nonessential, or unarmorable systems and more armor. The nonvital systems effectively provide extra layers of armor by stopping damage that would otherwise reach vital components in the core hull. This layout maximizes the protection of a given armor mass because that mass offers greater protection when applied over a smaller volume. This is an almost universal warship design feature, with battlecruisers and higher having complete core hull armor systems. It is increasingly common to see extensive core hull armoring on new construction heavy and even some light cruisers. The notion is evident also in destroyers where fuel bunkerage and water tankage are often wrapped around vital spaces on ships with no true armor at all.
State of the Art in Heavy Cruiser Armor: The Star Knight class
BuShips began working on the Star Knight-class heavy cruiser in the late 1880s. The threat from laser heads was more or less fully understood from reports of the People’s Navy’s battles against Haven’s neighbors at that time. Star Knight was in fact the first Manticoran heavy cruiser built with laser heads in mind. This had a major and not entirely happy effect. While widely thought to be the best protected ship of her type in known space, many actually criticize the vessel as having too much mass devoted to defense and not enough to offense. Be that as it may, a study of the armor system’s salient features provides much insight into laser-head era protective system design.
The general arrangement of a Star Knight’s systems is shown in Figure 3 (see appendix) with the author’s interpretation of which systems might be labeled vital or critical indicated. Exact internal details are not available to the public, but the plans BuShips has released and a basic knowledge of her missions are sufficient to draw conclusions about system criticality. Manticoran heavy cruisers’ primary peacetime missions are commerce protection and long duration system pickets, while they are given additional commerce raiding tasking in wartime, as well as screening duties. They are designed to stand up to other heavy cruisers, crush lighter units in action, and conduct merchant interdiction. These mission sets emphasize mobility and long-range endurance before combat power and might lead to the following system classifications under the general definitions described above.
More than their larger battlecruiser brethren, heavy cruisers must have propulsion at all times. For this reason, the hyperdrive, impeller, and fusion reactors are certainly vital on the Star Knight. Also vital to maximum propulsion capability are key structural members which take the load from the impeller rings. Other vital systems included in the core hull are life support and all of the ship’s maintenance shops. The life support systems obviously might be called upon to support a crew on a long journey to a friendly base after suffering damage during a raid or convoy action. Less intuitively, the maintenance shops, spare parts, and damage control remote storage are protected inside the core hull to ensure that the ship, which is often the largest hyper-capable warship in a convoy, has abundant repair capability. The offensive and defensive armament constitutes the bulk of the critical protection priority systems and is concentrated on the gun decks and in the hammerheads. A desire for redundancy may be why the designers have chosen to carry more defensive launchers and emitters than strictly required on a ship of this size at the expense of fewer offensive mounts. If this were indeed the case, one might expect the design team to have downgraded the defensive weapon suite to critical rank in the armor priority scheme to save mass. A final critical component would be sidewall generators—they are necessary for defense but this ship carries more than she needs. These are, as discussed below, probably another case where increased redundancy would seem to justify reduced protection priority.
Protective Features
After determining what needs protecting, the designer looks at how to protect it. Significant laser-head influence appears before even looking at the armor. Atypically for RMN heavy cruisers before her class, Star Knight is reported to carry a 20% redundancy in her sidewall generators, meaning that she carries enough extra generating capacity to retain her rated strength even if 20% of her generators are out of action. This is an unprecedented level of redundancy for a heavy cruiser. It is indeed higher than that of some older battlecruisers. It represents recognition of the ultimate impracticality of stopping a bomb-pumped beam with material armor. The wealth of highly educated recruits and trained gravtechs which Manticoran society produces allows this. By contrast, Haven is short on technicians, and places more faith (and mass budgets) into armor.
A related ship design choice gave the Star Knight a truly astonishing second redundant fusion reactor above the normal one. Each reactor is alone capable of carrying the full combat load of the ship and the addition of a second spare at considerable cost in mass is a good indication that the design team was dedicated to ensuring that the sidewall generators continued to receive power no matter what. Ongoing criticism of the design’s defensive emphasis cast doubt on the utility of this particular innovation.
The Star Knight’s armor scheme shows features common in heavy cruisers and quite a few borrowed from battlecruiser and capital class units. A general declassified arrangement of the armor system appears in Figure 4 (see appendix) as available on public datanets and enhanced by the author. Key armor system features are described below.
GENERAL OUTER HULL ARMOR
The skin of the Star Knight’s outer hull on the broadside has an armor system probably consisting of scattering layers of structural gels sandwiched between ceramic boundary layers. Due to the massive area covered by the general armor, it is likely built on a cheap abundant silicon substrate which means silicon carbide would be the ceramic of choice for boundary layers. The outer hull is generally fifteen or twen
ty meters from the vital systems in the core hull. Hence, a beam scattered on impact with the outer hull armor has fifteen to twenty meters to spread out before contacting the core armor. Public sources estimate that the outer hull is armored to a thickness of some half a meter or more. Localized specialized protection such as the impeller room belts tends to be grown or layered on top of the general outer hull armor substrate.
HAMMERHEAD ARMOR
Without benefit of sidewalls, the hammerheads are usually the single most heavily armored portion of a warship’s exterior hull. Unofficial estimates from Jane’s and other open source intelligence indicate that over half of a Star Knight’s armor mass might go to hammerhead armor. External holo inspection indicates an armor depth upwards of a meter in some places, though the sloping portions probably have less thickness than the vertical faces. Some sources report the use of a heavy metal additive as a boundary layer absorption enhancer in the outer surface hammerhead armor. The most common material for this purpose would be silicon or carbon based nanocomposite weave loaded with high concentrations of iron. Research papers by firms known to have been employed by BuShips while Star Knight class was being designed, however, described experiments doping silicon structural gels with tungsten, lead, and osmium. These have led to speculation that these materials may have been used in Star Knight’s armor. Such additives, if used, were probably a mass saving measure though they would also provide modest increases in graser resistance in thicknesses above a few centimeters. Another oft-commented feature is the bow hammerhead’s longer and more angular shape compared to the stern’s. This is due to key structural members which must run from the impeller rings forward to brace them under acceleration. The longer, sloping portion of the bow hammerhead armor envelope encloses the forward set of structures while those at the stern are covered by the impeller room belts.