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Chemical Rockets

Propulsion using rockets which use chemical energy

Hummingbird Pods
Image from Steve Bowers
Hummingbird pods use chemical rockets to manouvre around larger ships and near space installations

Chemical Rockets

Summary:The oldest and most primitive type of rocket propulsion are chemical rockets, in which two or more chemicals are mixed together to produce a powerful chemical reaction. The reaction produces hot gases that are forced out a nozzle at high speed, creating thrust and propelling the rocket forward. There are two types, solid and liquid.
Solid FuelSummary: The most primitive type of rocket; various uses; Lo tech.

Basic Propulsion: Reaction

Specific Impulse: Usually no more than 150 to 280

Fuel: Monopropellant or bipropellant solid fuel

Minimum Technology Required: Late Agricultural Age to early Industrial Age (Iron Age / Medieval)

Matter Manipulation: Macroscale

Controller required: None

First Introduced: First rockets Iron Age Old Earth (Chinese fireworks) - Earth Orbit Atomic Age Old Earth

Used By: Mostly worlds off the main nexus, medium tech polities, outposts, backwaters, etc. Also quite popular with some S<1 hobbyists

Used In: Close range ordinance (military); strap-on boosters for orbital launch; fireworks; lo tech hobbyists

Construction Costs: Industrial Age: depends on size, not over-expensive; Autofac: very cheap; Hylonano: very cheap (assuming presence of component materials)

Running Cost: Very cheap or n/a (once-only use)

Advantages: Can be stored for months or years without any sort of maintenance, regulation, stasis, or inert gas, even in atmospheric conditions, and still will not degrade. Simplicity of structure means can easily be replicated or produced

Disadvantages: Extremely low ISP. Useless even for short-range interplanetary vessels. Once ignited cannot be shut off until it burns itself out.

Normal Acceleration: less than 3G
Liquid FuelSummary: Liquid Fuel chemical rocket engines are used in the smallest vehicles and for specialist lo tech short-range high-acceleration applications. They have poor fuel efficiency and are not generally used for interplanetary operations.

Basic Propulsion: Reaction

Specific Impulse: Up to 450; higher with exotic fuels

Fuel: Monopropellant or bipropellant

Minimum Technology Required: Middle Tech - Late Industrial Age (Atomic Age)

Matter Manipulation: Nacroscale

Controller Required: None for motor

First Introduced: Atomic Age Old Earth

Used By: Still widely used for cheap inter-habitat transport on many Middle and some High Tech systems. mostly worlds off the main nexus, medium tech polities, outposts, backwaters, etc. Also, quite popular with some S<1 hobbyists. A number of medium-tech worlds prohibit the use of high energy drives for launches from the surface of inhabited planets, especially where there is a risk of radioactive fall-out; for this reason chemical launch vessels (either HOTOL or Big Dumb Boosters) are still used in some locations.

Used In: Short range shuttles (interorbital), boosters and launchers in isolated outposts and lo tech worlds, medium range missiles.
also used as parts of larger units: manoeuvering rockets for docking and course correction (more expensive but better isp than arcjets)

Advantages: Simple lo tech solution for getting vehicles into orbit (large thrust for short periods)

Disadvantages: Fuel highly explosive, often requires special storage (cold temperature, corrosive, etc), very low ISP. Interorbital and near-planetary only

Construction Costs: Industrial Age prim: Expensive Autofac: Very Cheap; Hylonano: Very cheap, can be produced simply in many asteroid and moon environments

Running cost: Expensive to very expensive

Normal Acceleration: Less than 3G
An invention as old as the Industrial Age, with late Agricultural Age (Iron Age or Medieval) precursors with uses by the Old Earth Chinese circa 800 BT (1000 c.e.), chemical fuel rockets have been used as missile weapons and as cheap and effective lo-tech near space transportation ever since. S:0 chemical rockets typically fall into three broad categories, cryogenic, stable, and hybrid.

Chemical cryogenic rockets use fuels that demand active storage measures in almost all star systems if used inside the "snow line." By far the most common such system is the liquid hydrogen/liquid oxygen rocket, which uses plain water as fuel, split into its component elements.Such rockets typically have Isps of 400 to 500 seconds, a thrust to weight ratio of less than 100 to 1 and a total delta-v of no more than 10 km/sec.

Chemical stable rockets use fuels that are stable in most star systems up to or beyond the inner region of the habitable zone. Most such are also solid fuel rockets, although not all. One of the most common such fuels is aluminum powder and a non-cryogenic oxygen or fluorine source. Another popular version uses lithium and a non-cryogenic hydrogen source. Such designs typically have Isps of 200-400 seconds, a thrust to weight ratio of less than 80 to 1, and a total delta-v of no more than 8 km/sec.

Chemical hybrid rockets use fuels that are cryogenic and non-cryogenic in combination. There are many reasons for such choices. Typically, the solid fuel component is chosen such that it can serve as insulation for the cryogenic one. Some popular combinations are aluminum powder and liquid oxygen, or lithium and fluorine. Such designs typically have Isps of 500-600 seconds, a thrust to weight ratio of 120 to 1, and a total delta-v of no more than 12 km/sec.

Both solid- and liquid-propellant forms utilize a chemical reaction between a fuel and an oxidizer. Although chemical rockets can develop great thrust, they are not capable of long continuous operation, due to the very poor isp [specific impulse], which generally varies from 150 to 450, with the LOX-LH2 (Liquid Oxygen-Liquid Hydrogen) mix used on the early (late 20/early 21st century) space shuttle system giving 450 to 475, and the O-BeH bipropellant as the most energetic natural chemical propellant providing 705.

Metastable helium and other nanofactured synthelements can give specific impulses as high as 3000, but these are so unstable and expensive it is generally easier to use fusion propulsion.

The use of chemical rockets for space exploration really came into its own during the second half of the 21st and the early to mid 22nd centuries, when increasingly cheap nanofactured buckyfibre and diamondoid materials reduced structural weight sufficiently for the very poor isp to be viable at least for Earth orbital and near orbital flights. Rockets were of greater utility in low gravity worlds like Luna and Mars. In fact, their cheapness, robustness and (with the less exotic propellants) reliability made them very easy to manufacture by robot factory or autofab during the middle interplanetary age, and they remained the standard short range transport right up until the nanoswarm crisis, and again during the First Federation period.

Even today many systems, especially in the outer volumes or on low tech worlds, use chemical rockets as a standard space propulsion, especially when lifting off from the surface of moons and planets, or for small workhorse craft which need only light acceleration, such as the widespread Hummingbird Pod shown above. In these instances, small unmanned craft and single manned construction and mining ships use chemical rockets for movement between closely spaced orbital structures. Many asteroids and Selenese-class Moons are rich in aluminium and oxygen, candidates for chemical reactants, and hence can be very easily and cheaply nanogrown.


Chemical Fuel Performance Table

Solid fuelisp 150 to 280 Advantages Cheap, reliable, very simple and lo tech Disadvantages Cannot be controlled once ignited Usage Many independent and low tech polities (booster rockets, short range ordinance, etc)
LOX LH2isp 450 to 528 Advantages Easily available fuel, simple components, high thrust to weight ratio Disadvantages Explosive, Usage Many independent and low tech polities (booster rockets)
hydrogen and ozoneisp 580 to 607 Advantages Easily available fuel, simple components, high thrust to weight ratio Disadvantages Highly explosive Usage Some independent and low tech polities (booster rockets)
F2 Li H2 hydrogen and fluorineisp 546 to 703 Advantages high thrust to weight exhaust product Disadvantages (hydrofluoric acid) is highly corrosive Usage Some independent polities (booster rockets)
beryllium and oxygenisp 705 Advantages simple components, high thrust to weight ratio Disadvantages beryllium is toxic. Usage Some independent polities (booster rockets)
Free H Radicalsisp 2130 Advantages high isp Disadvantages very unstable, requires advanced tech Usage A few independent polities (boosters and interplanetary rockets)
Metastable Helium and other metastable materialsisp 3150 Advantages high isp Disadvantages very unstable, requires advanced tech Usage A number of independent polities (boosters and interplanetary rockets)
 
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Development Notes
Text by M. Alan Kazlev, Richard Baker, David Dye, Mauk Mcamuk and Chris Shaeffer

Initially published on 03 December 2008.

 
 
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