Wednesday, 27 April 2016

Particle Accelerators and Coilguns.


Many of the space warships in Transhuman Space (TS) include neutral particle accelerators as part of their armament.

 In TS 3e ship-building rules particle accelerators were brought in 50 foot increments, the longest known example being 400 ft long. One of the reasons for the popularity of cylindrical hulls was that a linear particle accelerator could be installed running down most of the longitudinal length of the hull. This arrangement only allows the particle weapon to fire into the ship’s forward arc. Spaceships 8 design rules represent this by treating particle weapons as fixed mounts on the forward hull. While the weapon extends most of the length of the vessel it is generally not massive enough to count as a spinal mount. If you had a ship that expected to get chased a lot it might be prudent to build a vessel with a rearward firing particle weapon! The Archangel-class SDV [Spaceships 8 p.29] design has a pair of particle beams but both are mounted for forward fire. Legally only warships are permitted to mount particle accelerators. In Spaceship 8 rules particle beams can only be mounted on ships of SM+8 or larger and must be major, medium, or spinal batteries, installed as fixed mounts (a +2 to hit) with either the rapid fire or very rapid fire options. The Salahudin Samboja [Spaceships 8, p.31] appears to be an exception, mounting a 3GJ weapon, the maximum size of non-rapid major battery weapon for the SM+10 hull.

The Atomic Rockets webpage has some interesting discussion of the real word strengths and limitations of particle beams as weapons. Particle beams cannot be focused as tightly as a laser, giving them less range than a laser of equivalent power. On the plus side the particle beam has greater penetration. A laser beam stops on the surface of a target and attempts to burn through. A particle beam will penetrate deeper, causing local heating and also producing levels of radiation dangerous to both electronic and biological systems. In Transhuman Space laser weapons are limited to 300MJ or less. Particle beams are available in the GJ range.

The requirement for a forward mounting raises some interesting questions. The spacecraft can only fire its particle beam at a target the hull is pointing towards. Of course, in space combat a ship can point in a different direction to the one that it is travelling in. Most of the ships in TS appear to be “tailburners”. They have one large engine at the end of the vessel. Presumably they decelerate by pointing the drive forward and change course by orientating the drive in the appropriate direction. Suppose such a ship is heading “north” and wants to head “east”. The ship would reorientate so that its drive is pointing “northwest”. Thrust from the drive would cancel the northward motion and move the ship eastward. It should be obvious that during this process the forward-firing systems of the ship can only engage targets to the “south-east”. The ship cannot fire and manoeuvre at the same time! This is why I have proposed designs of military spaceship with multiple major thrust ports, permitting changes of direction or speed without reorientation.

Another consideration for the fixed mount is one of accuracy. When a target is thousands of miles distant the margin of error will be in terms of fractions of a degree. It seems unlikely that a ship hull of 10,000 to 30,000 tons can be orientated with sufficient finesse. The particle weapon itself will weigh 20-40 tons for every 50ft of length, [TS (3e) p.182] so sufficiently fine movement of this mass is unlikely to be practical either. The spaceship will need some mechanism to influence the path of the beam magnetically. The particle beam is neutralized just before it leaves the “muzzle”. Beam trajectory will need to be set while the beam is still in its charged state.

Coilguns are another weapon found on some large TS spacecraft. In TS 3e all coilguns were 333mm [p.181] and fired “munition packs”. A Kinetic Kill Munition Pack (KKMP) held several canisters of tungsten pellets. A X-ray Laser Munitions Pack (XLMP) had canisters holding several nuclear bomb-pumped X-ray laser weapons [TS 3e p.102, p.188]. Both types of munition pack massed 9.5 tons, occupied 250 cubic feet and held 10 shots [p197]. (This implies each coilgun round is more than 26ft/8m long! Perhaps each shot is a fusillade of smaller canisters.)
In Spaceships 8 coilguns are considered to be equivalent to electromagnetic guns and their power varies. AKVs carry coilguns equivalent to 10cm or 12cm guns. Larger vessels carry guns of 14 to 24cm equivalence, representing that larger vessels can mount more powerful coilguns that can fire the same munition packs at greater velocities. Potentially a coilgun as long as the ship could be created. These may in fact be the systems represented by fixed forward mounts of medium size or greater. Despite this, coilguns are relatively low velocity weapons in the context of space warfare and are thus limited to shorter range engagements. Minimum relative velocity modifier is 2 mps. See Spaceships 4e [p.58, p.68] for effects of 10-24cm electromagnetic guns and space combat. (Note that the p.68 table is subject to a correction in Spaceships Errata. dDamage for 10cm-24cm is actually 3dx5 - 6dx6)  Spaceships 8 [p.9] has rules for X-ray laser munitions. KKMPs are treated as conventional 10-24cm rounds for damaging purposes with no armour modifier. Each coilgun bay contains one munition pack giving 10 shots. It is up to the GM as to whether a coilgun bay can be reloaded during a combat. Given that each munitions pack weights nearly 10 tons this will only be practical on larger spaceships if allowed.