"Prologue: A Guide To Useful Rockets"
16th Buri, 25 U.R.
Estrili Sakati
Governance Faculty, Orion Commonwealth Advanced Studies Institute
"The dreams and desires of any aspiring leader are constrained by what they have the technological capability to do.
I presume all of you are at least interested in governance of some kind, and therefore, you will one day face that constraint. Many of you will of course be taking elective modules that consider engineering in greater detail - nevertheless, a basic understanding of rocketry is a required component of this course.
So, we will begin.
We will start with chemical rockets. Chemical rockets come in three fundamental types - monopropellant solid rocket, monopropellant liquid rocket and multi-propellant liquid rocket. Single fuel solid rockets are simple to make and have good thrust characteristics, but are very inefficient and cannot be shut-down once lit, making them much more dangerous. They consist of a tank and an ignition circuit that lights them up. Generally, they are used as booster stage rockets to help lift things off a planet. Monopropellant liquid rockets are much more controllable, however, they tend to be lower thrust. Generally they are used in Reaction Control Systems. multi-propellant liquid rockets are the main workhorses among chemical rockets. The two most commonly used fuels are liquid oxygen and liquid methane, and liquid hydrogen and liquid oxygen. The first is cheap and easy to use and store, but has a lower exhaust velocity. The second has a much higher exhaust velocity, but suffers hydrogen bleed-off, meaning the tanks soon empty. Both are only mildly dangerous, unlike anything involving flourine. You do occassionally see tri-propellant rockets that add a combustible metal to release more energy, however this also adds controlability difficulties.
These rockets have core anatomies of a tank or tanks for the fuel, a combustion chamber where the fuels are burned, and then an expansion nozzle where the resulting explosion is ejected and applies pressure to the nozzle and thereby moves the ship.
Following on from chemical rockets are generally open-cycle nuclear-thermal rockets; nuclear power is typically first harnessed safely around the time of the first space-capable rockets. An open-cycle nuclear-thermal rocket uses a nuclear reactor to heat propellant, which is then ejected. The exhaust is radioactive - especially in the more technologically advanced variants of liquid, gas and plasma core nuclear-thermal rockets - and the nozzle suffers neutron embrittlement from absorbing neutrons released. They also suffer the drawback that you can't simply just shut them down; they use nuclear reactors where the propellant is used to cool the reactor, which means propellant must still flow while you shutdown the reactor. And unless heavily shielded, they cannot be stacked because the neutrons emitted from one engine can cause fissions in another, with potentially disastrous results.
These are usually followed by metastable propellant rockets. While extremely similar to monopropellant liquid rockets, only much more powerful, the key differenceis that the a propellant is not combusted - instead, it undergoes a phase transition from a high energy state to a low energy state, the difference released as heat and kinetic energy that impact the nozzle. As 'metastable rocket propellant' is read as 'extremely volatile explosive', and the fuel tanks are the size of conventional chemical rocket fuel tanks, these rockets are not suitable for warships.
Nuclear power is of course capable of acting in fission explosions. This is the basis of Project Orion, the nuclear pulsed propulsion Naomi Of Unity relied upon to guide Life2.0 back to space as it was much easier than trying to develop fusion, but there is another kind - the nuclear salt water rocket, in which a continous stream of enriched fissile salts in water solvent are expelled from numerous injectors into a fission chamber where they combine into a continously detonating fission reaction that offers very high thrust and very high exhaust velocity, with relatively low neutron enrichment of the ship. The downside is that the exhaust is extremely radioactive and that most people are not comfortable with continously detonating fission reactions. These are all factors that led to the adoption of nuclear pulsed propulsion.
Nuclear pulsed propulsion is still widely used across the Orion Commonwealth today. At the smallest scales, nuclear pulsed propulsion is simply too inefficient; really, any pulse unit below several kilotons is too inefficient to use, which has a mild problem, as that means any ship smaller than several hundred tons cannot effectively use it - NSWRs by contrast, can be made to work at smaller scales much more comfortably. The upside of this is NPP gets better as you go bigger, which is why the Holocron developed his 400m pusher-plate design that used megaton nuclear devices in pulse units that propelled vessels of millions of tons mass with giganewton thrusts and exhaust velocities in excess of a million m/s. A variant on this theme uses a antimatter device instead of a nuclear or thermonuclear device, with similar performances obtained.
This brings us to the main rocket of today - the true antimatter rocket. There are two key types you need to understand - the solid nozzle rocket, in which a very small amount of antimatter is injected into a propellant, leading to an annhilation reaction that heats the propellant and kicks it out the nozzle with extreme thrust and comparable exhaust velocity to nuclear-thermal with lower radiation hazard, and the electromagnetic confinement rocket, in which antimatter is reacted with equal amounts of matter in extremely strong magnetic fields produced by superconductors that lead to immense exhaust velocities with moderate thrust-weight owing to the very high mass shielding around the superconductors, especially in high-efficiency designs that comrpise multiple rings of superconducting electromagnets.
The last type you need to be familiar with is the monopole conversion rocket. We do not yet use them in wide distribution because while they can be produced fairly easily after the initial symetry-breaking regime particle accelerators are built, the geometries needed imply accelerators with radii on the scale of planets, meaning he prefers to invest the resources in the much lower mass requirement antimatter producing accelerators, while working towards them in the background; he expects to field the first Commonwealth captured monopoles within the decade. Monopoles can be used to act like catalysts in fusion reactions, increasing the power output and reducing the size. In rockets, an additional innovation is the grid-core engine, where monopoles are bound to a grid of sufficient density that propellant is fused as it passes through the compression of the grid, releasing huge amounts of energy and radiation at high exhaust velocities.
In terms of missions these rockets are able to perform, chemical rockets struggle to exceed 5km/s exhaust velocity, with many designs achieving far less; as a result, refuelling is essential, and missions are constrained by requiring launch windows to get Hohmann transfers which makes transit times very high. Open-cycle nuclear-thermal rockets can do much better, with solid-core designs peaking at 10km/s exhaust velocities using liquid hydrogen propellant, with liquid and gas cores in the region of two to three times better. Metastable can achieve comparable performance to solid core nuclear-thermal. Nuclear pulsed propulsion depends very heavily on the size of nuclear or thermonuclear device and the geometry of the pulse unit, however, in general 12m systems achieve results that match gas core nuclear-thermal, 26m systems achieve results that exceed gas-core nuclear-thermal by an order of magnitude, 56m systems achieve results that are torch-like for short interplanetary transfers, while 400m systems can achieve torchdrive performance across a star system. Nuclear Salt Water Rockets are broadly similar, as are the antimatter pulse units. Antimatter and monopole rockets are true torchship drives.
There are also various kinds of fusion rockets, but as the Holocron has skipped them to jump straight to higher performance antimatter, for the purposes of this course you don't have to know about them."
