Spacecraft Power Generation and Propulsion Technology
Florence Clemens, Head of Engineering
Octavarium Fleet Research and Development
Submitted to the Neural Net Public Archives
This paper is intended to be a primer on power generation for Sirian spacecraft and techniques used in modern propulsion, both slower and faster than light. It is not intended to be a how-to guide on building and maintaining spacecraft drive sections.[1]
Clean Power Generation
The ultimate in power generation would be a byproduct-free matter-to-energy converter, but while those are theoretically possible, they're practically impossible. As a result, the next best thing is aneutronic fusion, a category of nuclear fusion reactions that release little to no free neutrons. Free neutrons created by fusion reactions can impact other atoms and transmute them into radioactive isotopes, which is harmful both to organic and inorganic matter, especially when the transmuted atoms compose the complex engineering inside your fusion reactor itself.
Most common in Sirian fusion reactors is the aneutronic reaction of deuterium and helium-3, which fuses one deuterium atom and one helium-3 atom into one helium-4 atom, one proton, and eighteen million electron-volts of energy (2D + 3He → + 1p + 18.3 MeV). Production of neutrons from D-D side reactions is made rare through the use of magnetic reactant steering, and with conventional technology, D-3He fusion requires relatively little initial energy investment to kickstart. Initial ignition is generally provided via a microgram-scale antimatter annihilation, far smaller than that used as a payload in cryogenic antimatter projectors such as the "Mortar" and "Supernova" series of weapons.[2]
Demonstrated in research reactors with a lower yield than D-3He fusion but expensive in both sustenance and fuel cost is 3He-3He or "pure helium-3" fusion. The availability of helium-3 is the chief concern in this situation, which, while partially mitigated by the unusually large free deposits of helium-3 in the Sigma systems, is still a concern long-term. Improvements in the D-3He fusion process has generally made helium-3 fusion research obsolete, and as a result, production of these types of reactors in the future is unlikely.
Theoretically possible and under consideration to supplant D-3He fusion is proton-boron fusion. p-B fusion uses commonly-available fuel and releases no neutrons and helium-4, along with energy that is directly usable as electrical power (1p + 11B → 3 4He + 8.7 MeV). Proton-boron reactors in research environments have required far less shielding to lower radiation to acceptable occupational doses than D-3He reactors of equivalent output. However, the reactor method of colliding streams of protons with streams of boron atoms requires a significant investment in either time -- unsuitable for large-scale power generation -- or thermal energy -- difficult to accomplish without creating large amounts of radiation as a byproduct.
The increase in complexity surrounding aneutronic fusion differs by fusion type. The availability of helium-3 is mitigated through the proliferation of GMG H-Fuel, distributed as "packets" containing segments of deuterium, helium-3, and a small amount of elemental hydrogen for utility. However, the Crow Nebula will run out of easily-accessible helium-3 eventually, though current estimates place that timeline in excess of a millennium at conservatively-extrapolated consumption rates. Proton-boron fusion addresses this concern by using naturally-available boron-11, which while rare compared to the majority of elements, is a fuel source that shifts the difficulty of procurement to the required catalyst; large-scale proton-boron fusion reaction chains requires significant energy investment, which has been best demonstrated at station scale in several test cases and in at least one known production reactor[3] through the use of sub-nanoscale antimatter annihilations. No known ship-scale p-B reactor exists at this time that is capable of generating its own power while being considered "acceptably sustainable".
Dirty/Obsolete Power Generation
Among circles where initial investment and fuel costs are more of a concern than drive longevity, deuterium-tritium fusion reactors can be found aplenty. One of the easiest types of fusion to accomplish due to low temperatures needed and low fuel costs, D-T fusion is an inexpensive nuclear fusion reaction that generates similar amounts of energy on paper per input mass to D-3He fusion, but at the cost of generating energetic neutrons that will irradiate reactor internals through neutron activation. To accelerate the rate of reaction with larger amounts of fuel per pulse, subcritical decay of a fissile catalyst is induced.
In Bretonian-derived D-T fusion reactors, whose designs date to before the discovery of the Sigma border worlds' helium-3 deposits, plutonium MOX is used as a fissile catalyst. The decayed, spent fissile fuel is ejected through the drive assembly's propellant stream during sublight travel, leaving a faintly-detectable, lightly radioactive "trail" behind the ship. Lobbyists throughout the colonies have been working to outlaw MOX-based reactors due to their potential for adverse health effects when used near both spaceborne and planet-based settlements, as well as their potential for damaging spacecraft and harming maintenance technicians.
A variant of MOX-boosted D-T fusion reactors from Rheinland replaces the uranium in the catalyst pellets with thorium. The fission products from the use of the pellets in a MOX-boosted reactor retain their structure at higher temperatures, theoretically lowering the chance of unwanted spread of radioactive contaminants. Long-term studies have not yet been concluded on what the efficacy of replacing plutonium MOX with thorium MOX is in practically reducing the effects of releasing spent catalysts in propellant streams. Short term studies by Octavarium Fleet Research and Development concluded that the primary advantage of a ship switching from plutonium MOX to thorium MOX is in making it easier to separately track.
Replacement of MOX-boosted power plants with ones using GMG H-Fuel and other brands of D-3He fuels is an ongoing process that tends to be done on an individual basis when ordering or retrofitting a ship, due to the engineering hacks needed to replace the reactors, generators, and engine assemblies. Engineering efforts are being conducted at this time by Aquila Defense System to build a drop-in replacement for MOX-boosted drive assemblies for the Pitbull series of grey-market bulk transports that converts the drive section to use aneutronic D-3He reactions instead.
Sublight Engine Technologies
There are three methods of propulsion for spacecraft: go slow, go fast, and go tricky.[4]
Going slow is infeasible for interstellar and even interplanetary travel in the modern world. This requires accelerating to a small fraction of the speed of light and riding out the transit duration either in cryonic hibernation or suspension for interstellar travel or with a very good book for interplanetary travel. The applications for "going slow" for the majority of the years since settlement and even before the exodus from Sol are built entirely around ship-to-ship combat, and are therefore outside the scope of this article except from a theoretical standpoint.
Going fast is the method by which the human and temporal components of a ship's crew are ignored to an extent by accelerating to relativistic speeds and letting time dilation "collapse" the time spent in transit significantly. At 0.7c (seventy percent of the speed of light), time dilation makes the speed perceived by the crew to be that of light in a vacuum, and any faster in actual speed appears to the crew that the ship is exceeding the speed of light while staying within the confines of unmolested relativistic space. This has several side effects including, most severely, psychological issues associated with temporal disconnect between a crew spending several months of a year at relativistic speeds under the effects of noticeable time dilation.
Both of these methods use the same concept: propellant, sometimes known as "reaction mass", is combined with the energy generated by the fuel from a reactor to create an energized mass that is directed out a nozzle. By Newton's first law, this action causes a reaction in the form of kinetic energy being applied to the vessel. In cases where the fuel is a chemical compound, this fuel-propellant-engine combination is often called a rocket.
The same principles applied to chemical rockets are applied to nuclear fission and fusion based reactor-engine combinations. Combined with high rates of acceleration cushioned by modern inertial dampening technology (sometimes referred to as "kinetic sumps" or "gravsinks"), "go fast" can be achieved in short bursts, closing the arena of combat from several thousand kilometres as experienced before the proliferation of fighter and bomber type spacecraft to fifteen kilometres or less in the average fleet engagement.
For all modern interplanetary travel, though, the preferred technique is to go tricky.
Go Tricky: Cruise Engines
The method of "going tricky" is, in essence, bypassing special and/or general relativity. In other words, superluminal travel.
Cruise engines are a form of non-relativistic, pseudo-linear faster-than-light (FTL) drive derived from supercarrier-scale, pre-exodus FTL technology and miniaturized over the course of multiple centuries alongside the miniaturization of nuclear fusion power plants for spacecraft. More scientifically known as a self-sustaining relativistic reference frame shift apparatus, cruise engines generate a static relativistic reference frame detached from the general reference frame of the universe that is then shifted through space at superluminal speeds, creating an effect by which a ship travels through space faster than light without actually breaking the speed of light.
Minimal side effects have been observed in the use of cruise engines. The most significant and easily noticeable disconnect between superluminal reference frames and the "static universe" is a visual "skipping" that can be seen when looking "into" one reference frame from another -- a ship travelling faster than light at cruise speeds will appear to be visually skipping from an external observer at a fixed point due to the microsecond-scale pauses in between reference frame shifts, and vice versa. The flare of a sublight engine appears to "grow" during a shift due to the gravitational lensing caused by the propellant exiting the reference frame abruptly and being "decelerated".
Gravitational effects from the "bubble" of space surrounding a solar system known as the heliosphere limits the top speed of a ship travelling via self-sustaining relativistic reference frame shifts. Test drones attempting to surpass approximately 5.1c have been observed to partially lose sustenance of their reference frame, causing different failure modes depending on the point at which the frame's stability is damaged.[5] In tests where reference frame stability is lost towards the beginning of a shift, the shift merely fails and cannot be restarted for several minutes. When the stability is lost towards the end of a shift, the cruise engine has been found to be damaged and is unable to function at any speed. In cases where stability was lost mid-shift, the test craft did not rematerialize properly.
Trade lane technology, while thoroughly protected by its producers, has been observed by independent researchers to be similar in function to cruise engines, just at faster rates of travel due to the static nature of the trade lane stabilization rings. Ships in trade lanes are able to reach upwards of twenty times the speed of light, or four times the speed of a cruise engine within a solar system's heliosphere. It is unknown whether or not the effects of a heliosphere on cruise engines also affect trade lanes, and if trade lanes beyond a heliosheath could propel ships to higher multiples of the speed of light than those inside a solar system.
Due to the commonality of jump gates and metastable jump holes (both of which are considered to be variants on traversable wormholes or four-dimensional bridges through three-dimensional space), cruise engines are not commonly used for interstellar travel. There have been exceptions in recent years, such as the Octavarium Fleet safely traversing interstellar space at an average speed of 9.8c in 824 A.S.,[6] but for the most part, transit between systems is done non-linearly through these bridges due to their ability to cross several lightyears in minutes to hours.
Footnotes
[1] Consult an actual drive assembly manufacturer. [2] Clemens, F., Keighley, A. (825). Report: Cryogenic Antimatter Projection. Aquila Technical Reports Database. [3] Wilson, D. (825). Report: CORINTHIAN. Aquila Technical Reports Database. [4] Woodcock, G., Chung, W. Propulsion Methodologies for Modern Space Travel. Neural Net Public Archives. [5] Kane, G., Pearson, L. (788) Speed Limits In Space: Effects of the Heliosphere on Superluminal Relativistic Frame Shifts. Ageira Technologies Experiment Results Collection. [6] Clemens, F. (825) Report: Field Modifications for Extrasolar Relativistic Frame Shifts. Octavarium Fleet Research and Development Reports Database.