The below will form the basis of my poster at PUP, and the subsequent paper. It's at a relatively early stage, and references haven't yet been added. Comments on or off list would be appreciated.
Thanks A -------------------------- Ballistics for delivery of SRM materials - an engineering principles approach Introduction ------------ Ballistic delivery of materials for the purpose of Solar Radiation Management has been proposed and appraised by various authors. Evaluation of technologies has been generally limited to redeployed military hardware, such as tank or battleship guns. Such technologies were not designed to deliver SRM materials, and are poorly suited to the purpose, leading to high cost estimates in previous analyses. The design of ballistic systems is reappraised with geoengineering use in mind, and a literature review of alternative launch technologies is given. The intent is to inform later engineering studies and cost analyses which may seek to design in detail, or to cost, a suitable gunnery system. Design requirements -------------------- Modern military weapons *Infrequent firing *Portable/vehicle mounted *Operating costs relatively unimportant *Accuracy critical *Shells never recovered Geoengineering guns *Frequent or continuous firing *Potentially static *Operating costs relatively important *Accuracy relatively unimportant *Shells may be recovered Engineering differences ----------------------- The objectives listed above will result in geoengineering guns being very different from military weapons. Below are detailed a range of design principles to guide the development of appropriate guns. *Large calibre: Energy costs are reduced substantially by the lower aerodynamic drag per payload kilo on larger rounds (assuming constant shape). *Static installation: Guns will likely be stationary, but may rotate to disperse projectiles widely. *Elevated, mid latitude firing position: Firing from a tall tower or mountain top will reduce muzzle velocities significantly, both by increasing altitude and limiting aerodynamic drag. It will therefore reduce propellant costs and require a less robust shell. Inserting precursors into the ascending arm of the Brewer-Dobson circulation may also reduce insertion altitudes, as well as aiding dispersion. As an alternative, an ocean-submerged gun could be used, which will allow easy repositioning and reorientation, as well as a very long barrel. However, submerged guns will necessarily require a longer trajectory through thicker atmospheric strata to attain the same elevations. *Barrel length unrestricted: Static guns can use long barrels. This means lower pressures are needed, as the propellant can act for longer. This will permit less robust shell designs. *Barrel wear costs are significant: Conventional barrels need relining or replacing regularly due to the friction between the projectile and the barrel. System design which minimises barrel wear is important. (See projectile design, below) *Propellant costs are significant: Hydrocarbon fuel/air mixtures are alternatives for evaluation. *Accuracy is unimportant: Minor trajectory changes resulting from barrel distortions and sub-calibre projectile designs are largely irrelevant. This allows a lighter barrel with a lower-friction fit. *Shell costs are significant: Within the limits of a given manufacturing technique, costs generally fall with a larger shell, as the ratio of volume/surface area changes with size. Further, lower pressures resulting from a longer barrel allow the use of less robust shells than would otherwise be the case. *Externally stabilised barrel: Military barrels are typically self-supporting, whereas a scaffolding can be built to stabilise a geoengineering gun. Where available, the gun may be built against terrain. This additionally has the advantage of allowing easy access to all barrel sections for maintenance. Projectile design ---------------- *Lighter shell casings: Geoengineering projectile casings perform no direct function, which differs from military uses where the casing is itself a weapon. Casing contains the payload (which may be under pressure), allows the propellant to act on it, and acts as a faring during its travel through the atmosphere. The need to reduce casing cost/weight suggests a more fragile casing, requiring lower propellant pressures, and necessitating a longer barrel. *Gradual payload release: Military guns rely on a momentary detonation; geoengineering guns will likely benefit from a 'slow-bleed' release of payload, to better aid dispersal. To this end, a small dispersal aperture may be preferable to a fully frangible casing. *Low frontal area to volume ratio: Longer, thinner projectiles experience less drag per unit mass. This has to be traded off against higher casing costs from a relatively larger surface area. *Payload dispersal: If explosive dispersal is not used, a similarly cheap design for payload dispersal will be required. High-pressure gases will self-disperse through any aperture. Liquids will need to be forced through nozzles to achieve controlled particle size and payload delivery at the desired location. Liquid-filled projectiles will require a significant force to evacuate the payload from a large shell on a short flight time, especially if fine droplet control is required. Where rifling is practicable, centrifugal force may assist dispersal. However, not all launch technologies permit rifling or equivalent (eg railguns). Throughflow of external air in the payload chamber could provide pressure to distribute the payload. A propellant charge could alternatively be used. A simpler alternative would be to dissolve gas into the propellant, allowing it to generate its own force by effervescence. *Shell recycling: Projectiles would ideally be recovered for recycling or reuse. Predictable fall patterns from a static gun may make this practical. More complex shell designs are harder to recycle, so a simple design with few materials and components is preferable. *Low-friction driving bands: Swaging bands are used to seal projectiles to the barrel, maintaining a pressure differential. They are usually metal, but plastic bands are used, such as in the GAU-8/A Avenger fitted to the A-10. A low acceleration, long-barrel gun will require a less demanding band design. Some guns, eg GC-45, do not require driving bands at all. *Base bleed: A slow-burning propellant can be added to the base of a projectile in order to stabilise airflow over the rear of the shell. This 'base bleed' technology improves aerodynamics to improve range at a given muzzle energy. Alternative Technologies ---------------------------------- A broad range of alternative technologies has previously been proposed for gunnery, much of which has been motivated by a desire to allow ballistic space launch. Below some technologies are considered which superficially appear suitable for geoengineering. Light gas gun: This uses a tapering combustion chamber filled with light gas (eg H2 or He) to provide potentially high muzzle velocities. The mechanism of action is the same as that of a pellet gun (ie a hydraulic force converter), but with a gas pressure (eg explosive) propellant rather than a spring. This would be of interest were long flight paths required, as the high muzzle velocity would allow low angles of elevation to be used whilst still enabling the projectile to reach the stratosphere. This would result in low payload ejection rates and better dispersion. Cheap fossil fuels can be used, with methane being deployed in experimental systems. Accelerations are high, complicating projectile design. Ram accelerator: This launch system relies on a teardrop shaped, sub-calibre projectile, which passes through a fuel/air mix. Due to aerodynamic effects, the passage of the projectile controls the combustion of the surrounding fuel, resulting in a zone of combustion behind the projectile. This has two crucial advantages: very low barrel wear (only stabilising fins contact the barrel) and very cheap propellant (fuel-air mixture). However, the projectile has to be launched into the ram accelerator at supersonic speeds, necessitating a secondary launch system and increasing both complexity and cost. Coilgun: Electrically powered coilguns rely on electromagnets to attract and accelerate a ferromagnetic projectile. This would require the use of a significant mass of ferromagnetic material in the projectile, increasing energy costs and making recovery/recycling more important. Nevertheless, the frictionless design, and entirely electrical power system, makes this an attractive system. Coilguns are well researched, and various military uses are envisaged with some space-launch projects specified. Ablative laser propulsion: A sulphur mass can be lifted and gasified by the action of a ground based laser. This propulsion technology could be combined with alternative lifting technologies, such as gunnery. It has the advantage of potentially being made to work with a solid sulfur projectile, thus eliminating the need to loft other chemical species, which can instead be sourced from atmospheric air. Other projects ------------------- Various supergun projects have been tested, which indicate some useful design features and principles: *V3: German WWII V3 gun designs used a smooth-bore barrel and an aerodynamically-stabilised projectile. Propellant was multi-stage solid rocket boosters, inserted into the barrel and fired against the projectile as it passed. *Startram: This proposed space launch project relies on MAGLEV propulsion to accelerate craft to orbital velocities. Acceleration takes place in a vacuum, with a plasma window protecting the open end. *Superguns: Conventional artillery pieces, such as Big Bertha, Dora and Project Babylon have all demonstrated heavy lift capability with extended range. Conclusions ------------ Previous evaluation of gunnery for geoengineering use is inadequate, as the military technology evaluated is wholly different in design objectives from custom-build geoengineering equipment. The design of geoengineering guns will likely be based on alternative design principles and may use alternative propellant technologies. Of the alternative gunnery technologies presented, ram accelerators appear to have particular promise because: *Low barrel wear *Very cheap propellant *Low acceleration allows a cheaper, less robust shell A secondary launch system would be required, and a conventional gun could be used. A light gas gun or coilgun would be likely to reduce costs, once developed, due to low propellant costs. Laser-ablation systems are worthy of consideration, but are at an early research stage. A typical geoengineering gunnery system may therefore be a large 'supergun' style design, based on a two-stage system with ram accelerator technology providing the terminal stage. The angle of elevation would be non-vertical, to enable bleed-dispersal of payload. One design variant would rely on terrain support, being built against the slope of a mountain. An alternative would be a rotating turntable on a high plateau, which would give broader dispersal but would be more costly per gun. Projectiles would likely be lightweight and substantially less robust than military designs. An effervescent liquid, or high pressure gas, will likely be the cheapest dispersal technology, should a slow release be preferred. It is likely that spent projectiles would be recovered and recycled. Base bleed technology may reduce costs, although there is a tradeoff between energy and complexity costs. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en.
