Ship Design: Shielding
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Ship Design: Shielding |
Deep space is not empty, but rather filled with a very diffuse gas (about 1 hydrogen atom per cubic cm), occasional dust particles, and electromagnetic radiation. For a vessel travelling at even a small proportion of the speed of light, these can become potentially deadly hazards, and the danger increases the closer to C the vessel travels. This is shown by the formula for relativistic kinetic energy:
K=mc²(gamma -1), where gamma = 1/sqrt(1-(v/c)²)For 0.3 c, a one milligram impact would give 4.3456e+09 J of energy, equivalent to one ton of chemical high explosive. For 0.9 c the figure rises to 1.1647e+11 J, and for a 0.99c ship 5.4799e+11 J
During the interplanetary age, when the first interstellar probes and then manned missions were launched, this problem was solved by using an ablative shield, almost always ice (although during the later interplanetary age this was generally reinforced with carbon buckytube weave and fibre bundles, which together produced a hard composite called pycrete). This added greatly to the weight, but was nevertheless effective in protecting crew, passengers, and payload. By the time the probe, ship, or particle stream shuttle had reached its destination, almost all of the shield had been eroded.
The early First Federation began with little more than late Interplanetary age technology, that had been preserved and sometimes refined during the nanoswarm period. While First Federation superturings and hyperturings were sometimes far advanced over their interplanetary age predecessors, the technology of interstellar travel was still based on the tried and true technology of particle stream, laser/maser, and (more expensive and less often used) amat-fusion hybrid propulsion, and passive ablative shield protection.Many of these groups became incredibly rich, as wealthy as the amat corps, through cunningly manipulating and raising the prices, frequently cooperating with each other against the predations of the big corporations and the Federation, both of whom they held in contempt.
If interstellar expansion was to be viable, it was obvious that there was need for something beyond passive ice shields. The megacorporations and their AIs embarked on a rush to discover an alternative.
Over the next few centuries several options were tried. Active shielding was becoming more sophisticated in this period, generally consisting of a cloud of fluid droplets projected in front of the ship by magnetic means. During the acceleration phase fluid droplets would fall back toward the ship and could be recycled, but in cruising mode (which generally lasted many years or decades) such droplets would be lost over time, making active shielding expensive. Alternately a small cloud of charged plasma could be maintained in a magnetic field with somewhat smaller losses over time.
Those ships which used used a Ram Augmented propellant collection system of magnetic scoops were actively protected by the powerful fields, which channelled almost all interstellar material into the throat of the scoop; powerful lasers ionised neutral dust so that it could also be gathered in this way. Later Conversion drive ships often used such scoops to augment their supplies of propellant.
At the same time advanced materials improved the passive shields in the ship. These almost always involved laminates of nanofabricated alloys using atomic dot waveguides (so-called smart matter). Energetic radiation would strike the smart matter and be channelled off. There were however a number of technical problems to be overcome before this became viable. Interstellar dust however remained a serious problem, as it would automatically destroy the quantum dots when it hits, and that will reduce the protection on that spot, leading to further erosion. One option that was often used was a layer of nano-aerogel (the properties and brand name generally varied according to the corporation and licensing deals) on top of the outermost layer. Very low mass and expendable, but at near-c speeds these layers helped to reduce the energies of oncoming particles before they hit the main cladding. Another problem was protons from hydrogen atoms striking the surface and creating secondary rays. The most common solution settled on was a layer of a proton-reflective moderator (boron and boron compounds were frequently used).
Compared to interplanetary vessels, interstellar ships were streamlined, or more properly shadowed, in order to reduce impact surface at relativistic velocities. The forward shield would thus shadow the entire ship from the radiation and dust in front of it.
This new shielding was not only expensive (in research, fabrication, and resource-material terms) but also far heavier and not as strong as classic buckyboard and diamondoid materials, and was generally used as a cladding over the diamondoid hull. Even so, the weight was increased tremendously, requiring in turn even larger engines and more amat. Many of the corporate ships of this period massed many tens or even hundreds of millions of tons. Moreover, the cladding was very vulnerable to erosion (a single hydrogen atom striking at relativistic velocities would blow a huge hole) so a further layer of protective diamondoid was required. Some ships had several laminates of diamondoid - nanoalloy - diamondoid. Inevitably, by the time even the best-hulled corporate ship had reached its destination system, major hull repair and maintenance was required. Most corporate ships included extensive nanofacturing facilities for just this purpose; some (especially if it was a system that was poorly developed or unpopulated) also included mining bots as well. The best solution was to bring in-house licensed dot-writing nanodevices to restore the shields. They would also be used during the flight to repair the local damage; these themselves being used up at a high rate.
Not unexpectedly, this technology helped encourage the simultaneous development of military shielding, and in fact there was quite a bit of cross-fertilisation between the two areas of research.
The late federation period saw the emergence of Efficient Amat Drive, and more efficient shielding, often using photonic-nanotech and pico-nanotech hybrid technology, and in some cases a magnetic ring or fine plasma film. This was even more expensive and difficult to construct than the nanoshielding, often (especially in the early days) unreliable, and in addiction it was active rather than passive, requiring an extensive "dumb"-processing network which usually had to be supervised and integrated by a superturing AI.
By the early fifth millennium refinements in technology had increased the efficiency of shielding, and a variety of passive, active, reactive, dumb, smart, unlaminated, laminated, multilaminated, nano, photonic-nano, pico-nano, and pico- tech shieldings were available and used by various clades and empires. Each of these and their almost infinite combinations and variations had particular advantages and disadvantages. e.g. plasma, magnetic, and pico-tech shielding tended to have a very high energy signature and high AI requirements, and hence was disliked by hider groups like the Backgrounders and haloers, but widely used by peaceful ultra tech clades like the Minskyis. This technology inevitably found a use in the Consolidation Wars and among some relativist clades, where it was further developed and refined.
At the same time, the introduction of reactionless drives was a revolution in both civilian and military ships. Reactionless drive had many military uses, but in civilian spaceflight the drive technology also allowed the construction of limited gravitational lensing, which made the very high velocities possible. The drive fields were simply designed to cause infalling particles and energy to be refracted away from the ship.
Having reached the most optimal configurations there were only very minor modifications until the Emple-Dokcetic development of chromodynamically stabilised metallic hydrogen enabled a new, cheap, larger-scale form of shielding that can applied not only to ships but to entire biospheres.
