Death Star
Warning: Plot details follow.The Death Star is a moon-sized planetoid military space station in the fictional Star Wars universe.
The Galactic Empire's ultimate terror weapon, the Death Stars were battle stations several hundred kilometers in diameter and mounting a directed energy weapon capable of completely destroying an Earth-sized planet with a single shot. Planetary shields that could have held off entire Imperial fleets were useless against such a weapon.
Two such Death Stars were featured in the original movie trilogy, the first in A New Hope, and the second in Return Of The Jedi. In the first movie, the plans, stolen by Rebel spies (according to the LucasArts video game Dark Forces, Kyle Katarn), are transported by Princess Leia (with help from Han Solo, Luke Skywalker and two droids) to Rebel leaders. Luke Skywalker pilots an X-Wing starfighter through a trench-like indentation on the surface of the Death Star, evading a pursuing Darth Vader long enough to launch a proton torpedo down a ventilation tube that reaches right down into the "reactor core", causing a chain reaction to destroy the battle station. In Return of the Jedi, Bothan spies steal the plans, unaware that their theft was orchestrated by Emperor Palpatine, and General Crix Madine and Admiral Ackbar devise a plan for its destruction. Han Solo leads a team to the forest moon of Endor to destroy its shield generator, while group of fighters and the Millennium Falcon piloted by Lando Calrissian fly into the centre of the ship through a narrow maze of pipes and destroy the reactor directly, rushing out in just enough time to escape the ensuing explosion.
The first Death Star was 160 kilometers in diameter; the second one was some 900 kilometers in diameter. It should be noted that earlier literature places them at 120 kilometers and 160 kilometers in diameter, respectively. However, in-movie scaling and newer references argue for the larger sizes.
Outside of the movie trilogy, there was also a prototype in the Maw installation near Kessel that was destroyed by the New Republic. Durga the Hutt also built a small version with only the central laser core and a small living quarters, which was destroyed in the asteroid field around Hoth. This was known as the Darksabre but shoddy construction techniques meant that this attempt was an abject failure even before its destruction.
It has been calculated that blowing up an Earth-sized planet takes on the order of joules of energy; this is roughly the total output of the sun in a week. More detailed estimates place the violent destruction of Alderaan as requiring joules of energy, or roughly one million times that necessary to permanently break apart the planet.