In Fire Forged

by David Weber

  Further change hinged on many years of work on practical miniaturization of gravitic generators in the commercial sector. Their introduction made possible the long sought after pure fusion warhead in the 1650s. This was a nuclear bomb whose only fuels were relatively common light elements like hydrogen and its isotopes. Cheap gravitic implosion made it economical to fit devices with previously unheard of yields into a missile body. The pure fuel made it possible to predict the output radiation of the bomb explosion precisely and ultimately control (to a small degree) the spectrum and duration of the explosion’s radiation. Since most nuclear weapon damage to space targets is caused by X-ray radiation from the explosion, the ability to tune that radiation, even slightly, made the defender’s problem significantly more difficult. Missile warhead yields of hundreds of megatons became commonplace in this time period and heavy weapons in the gigaton range were not unheard of. Ship to ship actions once again became brutally short. Warhead designers quickly realized that they could change the compression pattern and sequence of the new gravitic imploders to somewhat shape the resulting release of radiation. In 1669, a series of tests by several navies quietly confirmed the ability of the new warheads compressing fuel in different patterns to produce modest increases in stand-off ranges for impeller missiles in some cases. The necessary software to sequence the imploders and optimize the blast pattern at the moment of detonation appeared in routine upgrades all over known space, because essentially no new hardware was required. Little remarked at the time, these early nuclear directed energy weapons (NDEW) portended more lethal technologies to come.

  The defense was not at all idle during this period. Advances in gravitic deception technologies raced neck-and-neck with seeker improvements. Sidewall systems largely took the lead in thwarting penetrator improvements and improved materials and designs kept the defense almost in step as missile warheads grew. The pure fusion warhead might have had more disruptive consequences if the impeller drive countermissile had not appeared on scene in 1701. Essentially a smaller version of the shipkiller, this weapon destroyed incoming missiles by wedge to wedge interaction. This added a new depth to the missile defense problem which allowed nearby ships to defend each other cooperatively as never before. The countermissile dramatically reduced the effectiveness of shipkillers. This was followed some eighty years later by the widespread introduction of numerous small point defense laser weapons. The new active defenses ensured that even a weapon whose seeker was not decoyed by the target’s ECM would be stopped short of the sidewall. The point defense laser cluster created the final layer of light speed defense that resulted in the now familiar geometrically increased chance of the missile being destroyed in the last 50,000 to 60,000 km of its run. Hits against intact defenses became rare. This relegated the impeller drive missile to a counter sidewall role in which the best that could typically be achieved was a close aboard detonation of a multiple missile salvo to burn out sidewall generators and soften the target up for an energy range attack. Sidewall burning was in fact the end to which the largest pure fusion weapons were built.

  That most navies kept building dual mode (sidewall burning and contact nuke) impeller missiles after this point surprises some. Dual mode weapons provided tactical flexibility. Opportunities occasionally arose in large counter-sidewall salvos to get a contact nuke through. Under those conditions, the ability to have a dual mode weapon capable of performing both as a contact nuke and in an anti-sidewall role gave a chance for a decisive strike at the slight cost of the space and mass of sidewall penetrating equipment and extra software. The RMN chose to retain the dual mode capability, and it is became known colloquially to old spacers (such as the author) as “boom” or “burn” presets. Other navies followed the same logic to the same capability.

  Though retained, “boom” settings were rarely useful, so missile designers seeking ways to increase sidewall burning effectiveness kept trying for longer standoff range. The development of another generation of powerful practical micronized grav generators marked the next evolutionary step in missile warfare in 1806 with the introduction of the first nuclear gravitically directed energy weapon (NGDEW). The key components were grav lens arrays derived from those that had dramatically increased shipboard laser/graser effectiveness roughly fifty years earlier. The very first of these arrays was called a “plate array” and simply reflected the bomb’s energy off a flat artificial grav wave similar to an impeller or sidewall behind the warhead. Research continually tightened the focus of the grav arrays as impeller missile standoff ranges grew from tens of hundreds to tens of thousands of kilometers over the ensuing decades. The early grav lens arrays were quite large, however and frequently displaced the sidewall penetrators until further refinements could reduce their sizes. By 1826, a state of the art RMN impeller drive nuclear armed missile could boast a standoff range of 8,000 to 10,000 kilometers in sidewall burning mode.

  That same year, a small Solarian defense contractor, Aberu and Harmon, developed the unique combination of a state of the art grav lens array with a series of multiple submunitions carrying rods that emitted short wavelength X-ray laser light when exposed to the broadband X-ray pulse from a nuclear explosion. The idea was that these rods would produce intense laser beams which would impact on a target whose sidewall was weakened by the portion of the blast front that did not impact the rods. The slight delay produced by the lasing process ensured that the bomb energy which missed the rods would hit and weaken the target sidewall before the laser beams arrived. Initially called a laser enhanced nuclear gravitically directed energy weapon (LENGDEW), the device quickly earned the handier title of “laser head.” It promised to end the stalemate in missile arms and net the first star nation adopting it serious advantages over those which did not. Aberu and Harmon leveraged heavily to develop the laser rods, specialized submunitions to carry them, and telemetry links that allowed the main missile body and its deployed warheads to operate in concert. The Solarian League Navy, however, was less than enthusiastic about the effect of a potentially destabilizing weapon on its unchallenged naval supremacy. Strong Aberu family influence within the SLN and the lure of being first eventually won modest funding for a short series of live tests in 1833.

  The tests proved embarrassing failures. Characterized by one Solarian League Battle Fleet observer as “anemic.” the system’s submunitions proved difficult to position accurately, focusing was much harder than predicted, and the beam output itself was too low to make an effective weapon. Some of these problems were easy to solve, but others could not be overcome with the technology of the day. The lasing process in the rods, in particular, was significantly less efficient than predicted. Recriminations, accusations of falsified data, and scandal ensued. The resulting media attention brought word of the laser head briefly into the public eye where it came to the attention of Astral Energetics, Ltd. Sensing an opportunity, the company bought out Aberu and Harmon, collected all existing research materials, and began a long term incremental development program. Astral’s huge sales of gravitic and nuclear physics packages for military, mining, and scientific uses meant a steady flow of resources to their extensive project team located amidst the sprawling industry of the 70 Virginis system. Their work took over thirty years, but it produced the first complete laser-head-armed impeller-drive anti-ship missile system in 1866. The key advance that made the laser head practical was the perfection of a gravitic lens array with a much tighter focus than previous units. This new array increased the bomb power fed to the laser rods and resulted in increased laser output. It also had the happy side effect of directing much more of the bomb output energy that missed the laser rods into a narrower cone. This dramatically increased standoff range and made the weapon significantly more effective against targets protected by active defenses.

  Once they had a product, however, Astral found that they could no longer interest their intended buyer. Time and negative political repercussions from the Aberu and Harmon tests had solidified the SLN�
�s habitual disinterest in destabilizing technology into an abiding disdain for anything that altered the status quo. Convinced that the weapon was nothing more than a passing novelty, the SLN rejected the best efforts of Astral’s sales department and lobbyists for years. Desperate, Astral eventually began advertising the weapon for export. The Imperial Andermani Navy was their first official buyer in early 1872. Successful, though infrequent, use of laser heads against pirates in Silesia over the ensuing decade encouraged the People’s Republic to begin acquiring laser heads and the capability to produce them in the early 1880s in the midst of its forcible expansion into much of the Haven sector.

  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 BuW
eaps. 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.