Ship Design: Shielding

Protection against radiation and particle collision during interstellar flight

Catch-Me-Who-Can
Image from Steve Bowers
The Catch-Me-Who-Can, a First Federation Antimatter Beam Core drive ship with carbon-nanofibre-reinforced ice shielding at the bow

The Dangers of Impact in Interstellar Flight

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

Even at 10% of light speed, the most common velocity of spacecraft in the first thousand years of interstellar flight, a shield might be expected to lose about 1 kilogram of mass per square metre.

Early Interstellar Shielding

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 First Federation

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 boostbeams and antimatter-catalysed fusion.

At this time passive ablative shield protection was still adequate for protection. Unlike interplanetary vessels, interstellar ships were designed to be streamlined, or more properly shadowed, in order to reduce impact surface at high velocities. The forward shield would thus shadow the entire ship from impact with the gas and dust in front of it; interstellar hydrogen is more evenly distributed than dust, and erodes passive shielding more gradually and evenly than dust impact.

Ice shields could protect vessels at speeds of 0.1c or so, but at faster velocities friction with interstellar hydrogen caused the outermost layers to evaporate. Reinforced ice could withstand somewhat faster velocities, but as starships became faster erosion became a real problem. 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. At the same time, modosophont-built antimatter drive ships began to have enough available energy to accelerate to faster speeds, and to use more active shielding methods.

Over the next few centuries several options were tried. Slightly more advanced shields used a separate sacrificial shield, a portion flying a few miles in front of the ship proper, so that massive dust hits have space for the energy released to dissipate. Another active shielding concept consisted 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. Such matter-based semi-active shields are commonly called "pebble fountains" or "vapor shields." Alternately a small cloud of charged plasma could be maintained in a magnetic field with somewhat smaller losses over time.

Those ships which 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.

Transapientech Shielding Technology

The late Federation period saw the development of transapienttech conversion drive and of more efficient shielding, often using photonic-nanotech hybrid technology and in some cases a magnetic ring or a 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.

Conversion technology allowed much more power to be available for active shielding, but at S:1 level the lack of permanent monopoles kept electronic shields and ramscoops weak and short-ranged, as mere superconducting electrons are sharply constrained in their abilities. This lack, and the imperfect state of programmable matter photonics, made converting the abundant power available into a useful shield difficult. S:1 shielding was mainly passive, and magnetically-levitated passive shields travelling a few dozen kilometers in front of the ship were commonplace.

At <{T492d6fafbef2aS:2 level}> permanent monopoles allow enormously more energy to be available, and advances in programmable matter makes photonics also much more potent and powerful. This allows photoelectric cooling of the conversion drive to generate vast amounts of electricity, which is readily converted back to tuned photons at the front of the ship, leading to the development of the "pathfinder laser" the first truly active ship defense method. Using a pathfinder laser, the main forward shield of the vessel is no longer a passive or active block of matter, it is a beam of high-energy photons. This light beam serves to ionize any gas or dust, allowing monopole-strengthened electromagnetic fields to be much more effective. The combination of the photons and the electromagnetics serve to enormously improve the defense possible compared to a passive block or ice or a simple pebble fountain.

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).

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.

High Transapient Shielding Tech

At S:3, ship shielding methods reach maturity. The pathfinder laser becomes tremendously powerful and for the first time is integrated with active shielding pebbles using tiny lightsails that levitate inside the beam, along with ram field effects (if present) and levitated magmatter hoops for photoelectronic/magnetic effects. Controlling such an array of actively flying units in such a way that the following ship is never exposed is a huge challenge, and requires the vast mind power and efficient modes of thought of an S:3 mind. Using these advanced, multi-layer shields, such Conversion-ships can reach steady-state cruising speeds of 0.88c (the improvement comes from high speed reactions in the mass-stream from the ramscoop, or improved mass fractions if not.) They can also sprint up to 0.93c to 0.95c, and have the shields to handle those speeds for very long distances even without a ramscoop. In addition, at S:3 enough computational power can be applied to the active shielding to allow very comprehensive shielding solutions, with the semi-autonomous 'pebbles' sailing on miniature light sails in the pathfinder laser. By using a levitated magmatter hoop for magnetic lateral braking, the pebbles can redirect some of energy of the pathfinder laser laterally in the space before the ship, either sweeping the area more efficiently or concentrating the mass more effectively.This effect, combined with long-baseline sensory arrays based in the pebbles and the extremely powerful magnetic fields possible with monopole enhanced electromagnetic shields allow the pebble fountain to provide effective shielding even to the side of the vessel.

In essence, the output of the pathfinder laser is directed forward, where there is a vast cloud of shield pebbles, each with a tiny grain of computronium, a basic sensor suite, and a small lightsail. The pebbles intercept the light and are kept from wafting way by the grip of the electromagnetic shields/ramscoop. A portion of the pathfinder laser is allowed to shine forward, where it acts to illuminate the ship's path so dust can be detected earlier and it ionizes the background gas. A portion of the light is focused sideways, to push gas and dust into favorable places for shielding or scooping, and a portion of the light is directed backward toward the ship, and in this reversed light, millions of pebbles sail sedately along, using their sensors to search in every direction. At least one layer of pebbles is arrayed between the ship and any possible vector of a dust collision. At the back of the ship, spent pebbles are directed into the hugely powerful drive beam, and they reflect a portion of that light also lateral to the ship, where it is re-reflected by the cloud of pebbles, making them more mobile. Pebbles along the side of the ship are kept from escaping by magnetic fields. More pebbles are created from mass scooped as the ship travels. This effective and 360 degree shielding combined with the high power levels allows such ships to have effective ranges of 1000 to 2000 light years.

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, magtech 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 magtech 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. More details on shielding of reactionless drive vessels here.

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.

Radiation Shielding

At the same time as the front of the ship must be protected from friction with the interstellar medium, the motor at the rear of a rocketship using a high-energy drive is a source of dangerous radiation. Fission, fusion, antimatter reactions and even Conversion Drive all emit large amounts of radiataion, in the form variously of neutrons, neutrinos, gamma rays, and other particles. The amount of radiation that reaches the crew accomodation can be reduced by locating the motor as far away from the polulated parts of the ship as possible. The bulk of fuel and propellant tanks can also be used to reduce exposure.

But most ships use dense, specially designed radiation shields located as close to the source of radiation as possible. In early ships these shields were made of dense metals; later, exotic materials became available, icluding thin but dense sheets of bonded magmatter. A specialised form of Emple-Dokcetic shielding using metallic maghydrogen is now available which can reduce radiation levels from almost any thrust system to safe levels.

 
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Development Notes
Text by M. Alan Kazlev, Mauk Mcamuk and Chris Shaeffer
suggestions by Anders Sandberg and Xaonon
Initially published on 02 February 2001.

References
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