Magnetic linear accelerator

Magnetic linear accelerators (MLA) or linear motors are a class of ballistic weaponry utilizing electromagnetism to propel projectiles to high speeds. Magnetic weapons are capable of achieving far higher muzzle velocities than conventional firearms, and typically rely on the sheer kinetic energy of the projectile to do most of the damage rather than using a separate payload. Though their technological complexity has historically limited them from fully replacing conventional powder-based weapons, they dominate in space warfare due to the exceedingly high muzzle velocities required to make unguided weapons useful.

The two main categories of magnetic accelerators in use with the United Nations Space Command are coilguns and railguns.

Coilguns
Coilguns, also known as Gauss guns or asynchronous linear induction motors, accelerate metallic projectiles using a series of electromagnetic coils arranged in a linear path. The coils are rapidly switched on and off as the projectile moves along the firing channel. Coilguns lack a barrel in the usual sense as the projectile is levitated between the coils instead. Generally seen as heavy-hitter weapons, coilguns are most effective on a large scale and with comparatively large projectiles. They are more technologically complex than railguns and usually more massive.

A common non-weaponized application of coilgun technology is the mass driver, a form of large payload-delivery structure also known as an electromagnetic catapult or a lobber. Ground- and space-based mass drivers have seen use since the Golden Age of Space Colonization. Up until the 24th century, mass drivers were massive structures up to dozens of kilometers in length, more infrastructure than weapons. Military adoption first came in the form of the MAC gun, the first examples of which were station-based and likewise too enormous in scale to produce in large numbers. The technology was first downscaled to large ships during the UNSC-CMA Cold War of the 25th century, and miniaturized to fit destroyers and frigates by the advent of the 2500s.

Today, naval coilguns are widely used as weaponry on human ships, including the heavy spinal-mounted Magnetic Accelerator Cannons. The technology is also found in ground weapons such as the M68 ALIM Gauss turret or the M99 Stanchion heavy anti-materiel sniper rifle.

Railguns
While coilguns accelerate projectiles along a linear set of coils, railguns use a pair of conducting metal rails to create a current loop that runs through the projectile from one rail to another, perpendicular to the axis of acceleration. While various designs exist, railguns commonly employ a sabot as a contact between the projectile and the rails. This is one of the technology's weaknesses in comparison to coilguns, as the direct contact between the projectile and the rails causes the latter to wear down relatively rapidly. While materials advances over the past century have improved the longevity of rails, it is still common for them to require changing after fewer than ten shots. Railguns are less efficient than coilguns and tend to have lower velocities due to rail friction, but excel on a smaller scale, are less technically complex, and more affordable.

Railguns are present in the UNSC arsenal mainly in various groundside applications, which started to become common by the 25th century. By the mid-26th century, railguns could be miniaturized down to the infantry scale, though the size and weight of the power packs required limited widespread deployment at first. The first infantry railguns were squad specialist weapons powered by a backpack-mounted power source, though the later decades of the 26th century saw the development of power sources compact and lightweight enough to be integrated to the weapon itself.

A proposed further advancement of the technology is the virtual railgun or plasma railgun, which uses two shafts of charged particles generated as the weapon fires in lieu of physical rails. Although this would solve the issue of rail wear, as of the 2580s such technology is not yet viable for deployment in the field.