Reaction Drives

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Reaction Drives

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Reaction Drives

Going nowhere fast


Steam Rocket

The Steam Rocket is the most primitive reaction drive known. Fuel is typically coal or some other fossil fuel combined with pure oxygen. Propellant is typically water, but other materials are also used. Advanced versions of the Steam Rocket replace oxygen-enriched fossil fuel with a nuclear reactor.


Solar Thermal

The Solar Thermal Drive uses an array of mirrors to focus the local sunlight on a boiling chamber, expelling the resulting steam for thrust. Beyond a certain distance depending on the star in question, Solar Thermal drives have to rely on propulsion lasers in order to get a decent amount of thrust. For this reason they are also known as Laser Thermal drives.


Coulomb Drive

Named after an ancient Earth physicist, the Coulomb Drive uses electromagnetic fields as a medium to push against via negative and positive charges. The Coulomb Drive works best when it is in a strong electromagnetic field such as near a gas giant, star, pulsar, magnetar, and any other object with a powerful electromagnetic field.


Ion Drives

A catch-all term for a class of low-power plasma thrusters using ionised gases such as Krypton, Hydrogen, Nitrogen, or Argon. Advanced Ion Drives may use a supply of femto-engineered buckyballs instead.


External Pulse Drives

This class of reaction drive is defined by a series of rapid explosions thrusting against an external pusher plate, magnetic field or forcefield. Orion drives are powered by a series of fission explosions pushing against a physical armour plate with an ablative graphite layer. Advanaced versions may use ultra-strength materials instead. Helios drives improve on the performance of the Orion by containing the explosion, mixed with some propellant, in an armoured chamber usually constructed of diamond alloys at the very least. Helios drives are strictly speaking not "external" pulse drives, but since the armoured chamber is kept well seperate from the rest of the ship they are placed in this category for simplicity.
The Medusa External Pulse Drive instead uses the radiation pressure of a series of thermonuclear explosions to push along a gigantic solar sail, which pulls the payload behind it.
Fusion EPDs use either thermonuclear warheads or pure fusion devices to produce a greater amount of thrust than a traditional Orion Drive, and are far more likely to magnetic fields or forcefield pusher plates. Antimatter EPDs are the most powerful, and almost always use forcefields.


Fission Rockets

There are many designs in the Fission Rocket class of reaction drives. The Solid Core Fission Rocket is the most basic, heating propellant by passing it through a rod matrix or particle bed before expelling it out of the nozzle. Liquid Core Fission Rockets allow higher temperatures and thus a higher thrust, with Gas Core and Plasma Core allowing correspondingly higher temperatures and thrusts.


Plasma Rockets

Plasma Rockets heat up their propellant to plasma state, providing the highest possible temperature and thus the highest possible thrust. Because no fission, fusion or antimatter is involved, Plasma Rockets are the preferred engine of choice for spacecraft capable of entering an atmosphere. Magnetoplasmadynamic Thrusters consist of a central columnar cathode surrounded by an annular anode. The magnetic field and current creates a Lorentz body force on the plasma particles, accelerating them along the thruster nozzle. The anode can be supplemented by an external magnetic field, greatly enhancing the plasma acceleration. MPD Thrusters can be operated in either steady-state or pulsed mode. The pulsed mode takes advantage of high-current capacitors discharging every few hundred microseconds. This involves a more complicated power conditioning system design than the steady-state mode, but allows for higher instantaneous discharge powers for a given steady-state power level. One of the major limitations of MPD Thrusters is that the end of the cathode is subjected to extreme temperatures, often in excess of 2500 degrees Celsius, causing rapid wear and tear. The main propellants for MPD Thrusters are typically Argon, Lithium, and Xenon.
The Variable Specific Impulse Magnetoplasma Rocket (VASIMR) uses an array of powerful microwave emitters to heat its hydrogen fuel into a plasma state, and manipulates it using powerful superconducting magnets, which further ionize and heat the plasma as it flows through. The superconducting magnets can be put to other uses when the drive is not in use, such as shielding. Finally, the Electron Beam Plasma Rocket injects a relativistic (sped up to near-light speed by a linear particle accelerator) electron beam into a compressed reactive fluid, most typically hydrogen, superheating it to a plasma state. Powerful magnetic fields hold both the ignition reaction and directs the plasma out of the vehicle for thrust. The extreme high energy of the beam heats the hydrogen explosively fast compared to the VASIMR model, requiring very powerful magnetic fields to contain and direct it. Like MPD Thrusters, Electron Beam Plasma Rockets would give their best performance in pulsed mode, taking advantage of high-current capacitors to achieve best possible thrust energy, firing every few milliseconds.


Fusion Drives

Faster, easier to fuel and immune to the catastrophic explosions that can occur with antimatter drives, fusion drives nevertheless need a high technology base in order to obtain maximum energy effeciency. A nominally efficient fusion drive can reach up to a third of C. Gas Dynamic Mirror Fusion Propulsion is the simplest to build and uses a long, thin magnetic bottle where most of the fusion reaction is contained by straight, easily-aligned magnetic field lines, generated by toroidal shaped superconducting magnets running the length of the reaction chamber. At either end of the reaction chamber are stronger "mirror" magnetic fields, which help "focus" the plasma and prevent it from escaping except for select apertures in the rear magnet, where exhaust is vented for thrust. The plasma is heated with a powerful microwave antenna and the magnetic fields of the bottle further compress and heat it in order to achieve a fusion reaction. Ships equipped with Gas Dynamic Mirror Fusion Propulsion have a very distinctive set of large radiators.
In Deep Plasma Focus Fusion Drives plasma is forced into a long, cone-like magnetic "funnel" that continually compresses the plasma until, at the cone’s apex, the pressure of the magnetic field becomes greater than the particle pressure of the plasma, forcing the atomic nucleii together into a fusion reaction. The flow of the plasma forced into the magnetic funnel at ultra-high pressures keeps the entire system firing continuously. By adjusting the magnetic field strength as well as the width of its fusion apex, this scheme can be scaled down somewhat for use as a plasma rocket.
Like the Electron Beam Plasma Rocket, the Electron Beam Fusion Drive uses a high-energy relativistic electron beam to catalyze a fusion reaction in a magnetically-bottled plasma, which is then released for thrust. The beam produces the fusion reaction explosively fast, requiring very powerful magnetic fields to contain it, and the system is usually operated in rapid pulse mode.
In Contained Inertial Confinement Fusion Drives, powerful magnetic fields and forcefields are used to completely contain and direct the reaction generated by crossed laser or particle beams compressing pellets of fuel. Unlike External Pulse Drives, this internal reaction is considerably more efficient, especially the more technologically sophisticated versions.
Combined Cycle Plasma/Fusion Rockets take advantage of the fact that some Fusion Drives (Electron Beam, Deep Plasma Focus and Pulsed Compression) can be scaled down for use as a plasma rocket. A combined cycle plasma/fusion rocket has a dynamic controlled thrust system, where the magnetic fields and/or catalyzing electron beam are easily adjustable so the same engine can function as both a plasma and a fusion rocket of varying outputs, depending on circumstances.
This can prove very advantageous in craft designed to operate both within an atmosphere as well as in deep space, as the vessel can use the plasma rocket mode for travel on or near planets, Habitats and similar Megastructures and not have to worry about radioactive exhaust threatening a biosphere or human population. Once away from any planets and habitats, however, it can kick up the power to fusion mode for rapid deep space travel.
Pulsed Compression Fusion Drives are the most conceptually simple and powerful system, using super-strong collapsing magnetic fields or collapsing forcefields to near-instantly squeeze fuel plasma into a fusion state. Used in rapid pulse mode, from several hundred to several thousand reactions per second, it can provide extremely high thrust.


Metastable Fuels

This is a class of fuels defined by the ability to release large amounts of energy under certain conditions, providing thrust directly or greatly enhancing the performance of a reaction drive. Metastable Helium is an example of a metastable fuel that does not need an oxidiser, as simply heating it will cause it to release its pent-up energy. Metallic Hydrogen is a very dense form of hydrogen, which can be made to revert back into it's normal form, releasing some of the energy used to compress it in the process. As well as providing thrust directly through this process, the hydrogen can be used in a Plasma Rocket or Fusion Drive immediately afterwards, giving additional thrust. Bose-Einstein Condensates (BECs) can be electrically stimulated to release approximately twice as much energy as the same weight of Metallic Hydrogen, and like the aforementioned can be used to supply a Plasma Rocket or Fusion Drive at the same time if the correct elements are used.
Degenerate Matter Metastable Fuels are the most powerful available, but also the rarest as it's manufacture requires exacting submicrotech and a high level of technology. Drives using Degenerate Matter Metastable Fuels use a multistep process, dependant on the level degenerate matter the drive can accept. The most advanced drives use Metastable Preon Hyperfluid as their raw fuel. In the course of drive operation, the Preon Hyperfluid is destabilised, releasing energy and creating quarks. The energy is used and the quarks are directed to a further destabilisation chamber, releasing more energy and creating a soup of hydrogen nuclei (protons), neutrons and perhaps a few helium nuclei. This soup is then further processed, fusing the protons and other nuclei together, releasing energy while the reaction products and the neutrons are expelled out of the drive's nozzle for thrust. More primitive drives can only deal with quark matter or metastable protonium.


Antimatter Drives

Highly energetic matter/antimatter reactions are either used to directly produce thrust or the energy is used to heat propellant. A basic Antimatter Drive can achieve speeds of ~0.20C. Carrying around large quantities of highly reactive antimatter is a dangerous proposition, and some spaceports will refuse to allow ships with antimatter drives to dock. Antimatter Catalyzed Fusion Drives greatly mitigate this by using only microscopic amounts of antimatter, in the form of anti-protons, to catalyze fusion reactions. Antimatter Boosted Fusion takes this up a step, using micrograms of antimatter. In Solid Core Antimatter Drives, antiprotons annihilate protons, heating a tungsten or graphite heat-exchanger. The tungsten and/or the graphite helps to absorb the gamma rays and pions produced by the reaction. Hydrogen fuel is pumped through narrow channels between the heat exchangers, heating the hydrogen to a plasma state, which is then expelled for thrust. Gas Core Antimatter Drives inject antiprotons directly into the hydrogen fuel stream. Magnetic fields are used to contain only the energetic charged pions which spiral into the hydrogen gas to heat it. The resultant plasma is then expelled through a conventional rocket nozzle. Gas core antimatter rockets are less efficient than solid core models, but they are less constrained by the melting points of their material components.
Plasma Core Antimatter Drives inject a much larger amount of antimatter into the hydrogen fuel, using powerful magnetic fields and forcefields to contain the high energy pions that result from the annihilation reactions to heat the resultant plasma to a superheated state. This plasma is then exhausted for thrust. This engine is not limited by the material melting points of its components. It does, however, require full kilograms of antimatter to go any significant distance.
The Beam Core Antimatter Drive employs a diverging magnetic field just upstream of the annihilation point between the antimatter and low-density hydrogen. The magnetic field then directly focuses the energetic charged pions as the exhausted propellant. This design has a matter/antimatter annihilation ratio of nearly 1:1 and requires tons of antimatter to function. However, this is compensated by extremely high fuel efficiency, able to obtain speeds of up to 0.40C.


Antimatter Sail

More closely related to External Pulse Drives than Solar Sails, this drive system consists of a sail coated with U-235. The ship, dragged behind the sail, launches "puffs" of antimatter particles at the sail. When the antimatter hits the sail, it detonates when it comes in contact with the normal matter. The heat of this reaction also creates miniature fission reactions in the U-235 coating of the sail. Both effects push the sail forward, dragging the ship behind it for the next pulse. Using this one-two punch of matter/antimatter detonations and fission reactions, speed in excess of 417,600Kph can be achieved. Obviously, the sail would have to be thick and ablative to handle continuous bombardments of antimatter, with each layer interwoven with enriched uranium.


Interstellar Ramjet

Interstellar Ramjets make use of the Interstellar Medium (ISM) as a source of fuel or propellant. The traditional design is the Fusion Based Interstellar Ramjet, which gathers up the insterstellar hydrogen with its massive electromagnetic scoop, using some of the gathered hydrogen as fuel while using the rest of it as propellant.
The Scramjet is a more powerful variant of the traditional design, able to achieve much greater speeds due to carrying it's own source of fuel, thus foregoing the need to slow down the gathered interstellar hydrogen in order to fuel the ship. The ship uses the ISM purely as a source of propellant.
Both designs can be Antimatter Enhanced, injecting a steady flow of antimatter into the stream of interstellar hydrogen. If you have the technology, you can forget about faffing about with antimatter and simply use Energy Conversion to turn the stream of interstellar hydrogen directly into energy.


Antimatter-Photon Hybrid

Matter-Antimatter reactions produce lots of gamma rays, a form of light. Some Antimatter Drives are enhanced by the addition of gamma ray mirrors, which increase the amount of usable energy from the reaction by as much as 40%, greatly improving its performance and power.


Photon Drive

The Photon Drive uses an advanced, concave gamma ray mirror that reflects the intense and highly energetic gamma rays created by 1:1 matter-antimatter annihilation. This gamma ray mirror reflects nearly 100% of the incoming energy, but has to be regularly replaced as it wears down. The matter-antimatter reaction would take place directly on the focal point of the concave mirror on the aft end of the spacecraft, which would act like a pusher plate similar to the External Pulse Drive designs. Because the reaction takes place at the mirror’s focal point, all the light hitting it from the annihilation reaction is reflected in the same direction.


Conversion Drive

The Conversion Drive converts a store of matter directly into energy, resulting in twice as much power as a Photon Drive. Primitive Conversion Drives require heavy shielding due to intense amounts of gamma radiation produced, but more advanced models are geared to produce energies at less penetrating wavelengths.


Laser Drive

Based on the Conversion Drive, this converts matter into energy which is collimated and lased to increase thrust efficiency. The thin, up to 300,000km long exhaust blast (which is quite literally a continuously running laser) can be very hazardous, capable of vapourising small moons and devastating planets with it's raw power.


GUT Drive

GUT Drives take advantage of the virtual particle effect for propulsion. As the zero-point vacuum fluctuations are happening in every square centimeter of the universe, a ship that can tap into it has an essentially endless supply of energy it can use for thrust. Black holes can strip away one half of the particle/antiparticle pair before they annihilate and return to the vacuum, so a captured singularity is used in primitive GUT Drives. More advanced methods use neutronium structures on board the ship to supply the gravitic fields necessary for zero-point energy acquisition.
The energy harnessed from the vacuum can be used in one of several ways. The charged vacuum-derived particles can be accelerated and expelled out a nozzle directly for thrust, very similar to a Beam Core Antimatter Drive. Or more simply, they can be used to superheat a reactive fluid such as hydrogen, which is in turn expelled for thrust. The antimatter particles can also be used to catalyze fusion reactions. As the zero-point rocket has an essentially endless supply of energy, it can theoretically accelerate to near lightspeed. How fast it can do so and how much thrust would be available to it would depend on how much energy the drive can liberate from the vacuum at any one time. For this reason the GUT Drive is considered the ultimate "wilderness drive" allowing ships to operate indefinately without requiring refuelling.


Superunification Drive

The Superunification Drive builds on the GUT Drive, consisting of a spherical array of GUT Drives pointing at the centre of a reaction chamber. When the drive is activated, the GUT Drives simultaneously activate, creating conditions in the centre of the chamber not seen since the Big Bang. Manipulating the GUT Drive array and the spherical reaction chamber allows almost total control over the exhaust products, enabling the Superunification Drive to function as an Antimatter Drive, a Photon Drive, a Conversion Drive, or a Laser Drive. The exhaust tuning also has stealth applications, as one can tune the Superunification Drive to produce mirror photons or mirror particles.
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