Mass Driver

A Mass Driver (マスドライバー) is an electromagnetic catapult which is used to accelerate and launch payloads at high speeds.

Principles
A mass driver is a catapult launch system, primarily consisting of a path which payloads travel down, powerful electromagnets positioned down along that path and a magnetizable holder containing a payload. The rows of electromagnets are used to accelerate the payload down the path, which then continues travelling after leaving the path on the momentum it has acquired.

Aside from the linear track types, there are also silo-type mass drivers, such as the one in School District 23, which fire payloads from a cylindrical space (in the case of the District 23 driver, about 20m across and over 300m deep) with an accelerated plasma flow. These mass drivers can be fired just for the cost of the electricity needed to power its low-temperature superconductor electrodes and to generate the plasma flow from catalysts. At least in the case of Parasatellite 01, the mass driver launch is single-stage and doesn't require any complex trajectory management, with the payload leaving the atmosphere and being placed into the desired orbit less than ten minutes after being fired. The mass driver launch can achieve a payload velocity of over Mach 20. After the mass driver is fired, excess electricity remains in the 'barrel', preventing people from entering the space immediately afterwards, with the risk of losing an arm, a leg or more.

Outside of Academy City and its cooperative institutions, the Logistic Hornets, giant airborne launch platforms developed by Space Engage, have built-in mass drivers for launching spacecraft and objects into ballistic orbits from an altitude of 30km. Built around the hole in the center of the craft's wings (with exposure to air to cool the electromagnets after use), the linear motors build up circular acceleration around it before launching their payload through a launch port mounted on the craft's tail wing. Although limited to ballistic trajectories, the launches were still sufficient to deliver payloads to the opposite side of the planet in around 20 minutes.

Toaru Majutsu to Kagaku no Ensemble
A mass driver in an Academy City cooperative institution in Australia was used to send a biopod to Academy City, with the city attempting to shoot it down using Debris Storm.

Magic God Invasion Arc
An underground silo-type mass driver in School District 23 was intended to be used to launch Parasatellite 01 to investigate the Arrowhead Comet. It was used by Kamijou Touma and Misaka Mikoto to launch the High Priest into space.

Los Angeles Arc
The Logistic Hornets developed by Space Engage and their built-in mass drivers played a key role in R&C Occultics's global drone-based distribution network, as well as the incident in Los Angeles on December 26th.