Orbital bombardment is the act of attacking the surface of a planet from a spaceship, satellite, or other object orbiting in space above the planet. From the 1950s onward, various militaries have considered ways to attack surface targets from orbit, but no actual system has been developed to date. Article IV of the 1967 Outer Space Treaty prohibits the orbiting of weapons of mass destruction in space.
At present, modern human civilization has no defense against a spacecraft parking itself in orbit and bombarding the planet, and as such we are currently defenseless in the unlikely event of an alien invasion.
Orbital Bombardment in Science Fiction
Orbital bombardment by various means is quite common in science fiction, for both precision strikes and indescriminate mass destruction.
- In Star Wars, the best known example of orbital bombardment is the Imperial Base Delta Zero operation, in which one or more Imperial Star Destroyers systematically destroy all life and all useful assets on a planet's surface with a continuous turbolaser barrage. The Death Star is also technically a weapon of orbital bombardment, but it destroys the entire planet instead of just devastating the surface.
- In Star Trek, starships have occasionally used phasers and/or photon torpedos to destroy specific targets on a planet's surface from space, and in DS9's "The Die is Cast", a fleet of Cardassian and Romulan warships attempted to destroy the Founders by bombarding their homeworld. Starfleet also has General Order 24, which directs a ship to use its weapons to destroy a planetary civilization.
- In Babylon 5, a variety of methods were used for attacking surface targets from space, including directed energy weapons, missiles, and mass drivers that hurled asteroids at the planet's surface. The ancient Shadow and Vorlon races possessed dedicated planet-killing warships that could make a planet uninhabitable in a matter of hours.
- In the Stargate universe, the Goa'uld and the Wraith make heavy use of orbital bombardment using heavy energy weapons to eradicate civilizations that are evolving technologically towards a point where they might pose a threat. The forces of the Tau'ri equip their spacecraft for orbital bombardment, having them carry gigaton range Naquadah-enhanced themonuclear devices.
- In the Warhammer 40,000 universe, the Navy of the Imperium of Man is capable of destroying all life on a planet with a variety of methods, including use of capital ship weapons and biological weapons delivered from orbit in an operation known as Exterminatus. Other factions also make use of orbital bombardment.
- In the Command and Conquer: Tiberium universe, the Global Defense Initiative (GDI) controls a network of orbital ion cannons for bombarding surface installations.
- In Mass Effect, dreadnoughts are capable of bombarding planets with triple-digit terajoule mass accelerator cannons, but interstellar treaties forbid use of such weapons on habitable worlds. Traces of past such bombardments by extinct civilizations have been found on some planets.
- In Halo the Covenant destroyed numerous terran colonies through orbital bombardment, sterilizing numerous worlds in the process. This was referred to as "Glassing".