The Outer Space Treaty of 1967 and Space-Based Weaponry
The idea of the militarization of outer space was a real fear in the heady days of the Space Race between the USA and USSR. The Soviets had put up military space stations and a few of them were armed with an 23mm cannon. There was also worry that the arms race would continue into the void of outer space with orbital nuclear missile platforms. In 1967, the United Nations passed the Outer Space Treaty that established legal frameworks on the ownership of celestial bodies, like Luna and Mars. One of the elements of the treaty was preventing orbital weapon platforms that bore nuclear weapons and othe r WMDs. This treaty shaped the research on orbital weapon systems.
The Types of Orbital Artillery
One of the most common type of orbital bombardment/artillery is directed energy beams that can be used more like knife than an club or even a shower of directed energy death-laser-beams that tear through the planetary surface. Shooting freaking laser beams on the surface of Luna is much easier than shooting them down to Earth or Mars, due to the atmosphere. Any military-grade lethal DE beam would have to be powerful enough to punch through the atmosphere and hit the target with enough energy to be lethal. It is unlikely that lasers will be the orbital DEW system of choice, instead, it is likely that particle beam DEWs would fulfill that role. The use of DE is common in science fiction "kill satellites" as seen in works like Akira.
Kinetic Projectiles or "Rods from God"
Unlike orbiting nuclear weapons, kinetic projectiles are legal under the 1967 Outer Space Treaty (as well as space-based lasers) and instead of those dirty nuclear weapons, these rods from god are able to delivery some serious punch without the nasty after effects of nukes. If we examine the USAF's proposed kinetic bombardment system, these six meter long tungsten rods impacted the surface of the Earth with the road going at MACH 10 (7,700 MPH). The impact of the rob was equal to between 10 and 120 tons of TNT, less than the 2,000 tons of TNT that the Fat Man and Little Boy Atomic bombs produced when dropped on Japan. Unlike long-range bombers like the B-52 and B-1, the tungsten rods at able to reach their Earth-based target at between 10-15 minutes, and are extremely difficult to intercept like ICBMs or bombers. While this form of orbital artillery is not as effective as nuclear weapons, they can be used in more of combat supporting role and even pre-invasion artillery softening up operations, along with being a effective "bunker buster" system. The data for this section, comes from the Game Theory video: https://www.youtube.com/watch?v=rx5XyspHldk
The Dangers of Orbital Artillery/Bombardment
Defense Against Orbital Weapon Platforms
Real-World Examples of Orbital Weapon System
The THOR Project (USA 1950's-today)
Boeing in the 1950's became working on a kinetic bombardment system called THOR. The idea was to have an orbital artillery system that could not provoke a nuclear exchange, and THOR later would conform to the 1967 Outer Space Treaty. The heart of THOR was long tungsten rods that were the size of telephone poles and could delivery a punch without the risks of nuclear or conventional explosives. Even today, the US Air Force has been continuing the work on THOR as late as 2003. While Project THOR is technical possible, there are challenges with controlling the rod through atmospheric reentry, the cost of putting the system in space, the political heat for having orbital weapons system, and lastly, maintenance. A massive military orbital weapons system would need maintenance, and with the Space Shuttle fleet gone, it would require something like what was seen in COD: GHOSTS to keep the system running.
Fractional Orbital Bombardment System (USSR 1968-1983)
The Rumored X-37B Space Drone Orbital Weapon Delivery System
The 3rd Reich "Sun-Gun"
The Role of Orbital Artillery/Bombardment in Future Warfare
This is were the orbiting warship comes into play. Any planetary invasion would be first conducted via control of orbital space, much like air superiority. Once that condition has been met, the warships could soften up the planetary defenses via some form of orbital artillery. That could be kinetic rods-from-god or DE weaponry, but either way, the weaponry of the warship would be used in a similar manner to the US Navy using their battleships in World War II to shore bombard prior to an ambitious invasion force landing. After the planetary LZ is secure, and field artillery and CAS are being established, the orbiting warship could be setting up so-called "kill-satellites" to further support the ground forces. This Kill-Sats could be dual-role as well, supporting ground planetary operations with support fire and protecting the planet from any counter-strike.
From the Fox Mulder Corner...
One of the most infamous video footage of UFOs (or something) in Earth orbit being engaged by some type of weapon systems came from Space Shuttle Orbiter Discovery during STS-48 in September of 1991. Some believe that the amazing footage shows an Earth anti-UFO defense system being use, and missing the alien craft. Of course, NASA and others claim it is ice particles. Even before this, there were claims that the US maintains an orbital weapons system that was piggybacked on the old SDI program. Why does the US military maintain an secret orbital weaponry program. Aliens. Some believe that the US and other nations are fighting a secret war with an alien intelligence.
Orbital Bombardment and Science Fiction
During the 1980's, with the rise in science fiction and war gaming, and SDI; orbital bombardment became a hot topic. This fueled a number of examples in sci-fi, and one of the greatest lines fucking ever in a sci-fi film: I say we take-off and nuke the site from orbit. It's the only way to be sure. In 1986's magnum opus, ALIENS, the idea of orbital bombardment was wrapped into one of the best lines of the one of the best sci-fi movies of all time, and that triggered a number of other sci-fi creators to include orbital weapon systems, including nuclear, into their stories and creations.
The Attack on the Founder Homeworld from Star Trek: DS9
It was hoped that this assault on the heart of the Dominion would produce its collapse, however, the Battle of the Omerian Nebula was the result. At first, the combined fleet was able to pound the homeworld with torpedoes and directed energy fire, it seemed too easy, and that was because the Founders learned of the plan, allowed to be carried forward, and setup a trap for the combined fleet. The Founders left their world, and allowed the fleet to destroy 30% of the planet's crust, and during this moment, 150 Jem'Hadar warships descended on small attack force. It was a slaughter, and wiped out the majority of these intelligence services power and influence, allowing the Founders to have an easier time subjugating the Cardassian Union and the Romulan Star Empire.
The Fithp Invasion of Earth from Footfall
The Covenant "Glassing" from the HALO Universe
It just has to be said...the Covenant are just dicks. It is not enough for them to destroy human colonies and kill everyone there, but then they have to go and burn the world black with ship-mounted plasma artillery. The massive plasma cannons on Covenant warships are altered to allow them to project plasma in linear beams that hit the surface of a planet with vastly intense heat, alter top soil to lechatelierite, a form of silica glass. It takes the aliens days to glass an UNSC colonial world. The world suffers global environmental damage that forever alters the planetary environment and leaves the atmosphere in a state of nuclear winter. Covenant glassing operations can be conducted from orbit or even endo-atmospherically. It is believed from some footage from the end of Reach, that the future UNSC has a slow method of reversing the effects of glassing.
The Zentraedi Holocaust from the ROBOTECH Universe
The USAF ODIN and the Federation's LOKI Space Platforms from Call of Duty: GHOSTS
To finally end the US, the Federation takes survives elements of the ODIN space station, and creates their own space-based weapon platform, LOKI. Unlike ODIN, LOKI could be controlled by a ground based operations center, the robds were smaller allowing for them to be used in a close fire support role, and there were more platforms, allowing the Federation to carryout further offensive operations. During the apex of Ghosts, the USAF space warfare team, LCARUS, mounted an assault on the Federation LOKI space station, and turned the Federation's weapon against them, wiping out the ground-based control center, and the Federation naval force. LOKI was destroyed by the USAF LCARUS team. ODIN and LOKI may be one of the most accurate real-world examples of space-based weapons platforms in popular media.
The Centauri Mass Driver Bombardment of Narn from the B5 Universe
During the Narn-Centauri of 2259, the superior Centauri Republic gained the upper hand, and finally arrived at the homeworld of the Narn. When the Narn refused to surrender, the Centauri did not mount an invasion of the planet, but instead used retrofitted mass drivers on their Primus class battlecrusiers to propel asteroids. This form of planetary bombardment is illegal and ban by the League of Non-aligned Worlds, but te Centauri gave zero fucks, and did it anyway. For four days, the Centauri warships bombarded the surface of Narn, and finally, the Narn government gave in and surrendered to their former masters. Narn was already a world still scarred by the Centauri strip-mining efforts during their occupation, and the pounding from space didn't help. For over a year, Narn was a world under a nuclear winter, and it would take over ten years with the help of Minbari atmospheric processors to clean most of the air.
Londo Mollari: Refa, any force attempting to invade Narn would be up to its neck in blood—its own!
Lord Refa: We have no intention of invading Narn. Flattening it, yes—but invading it? We will be using mass drivers. By the time we are done their cities will be in ruins, we can move in at our leisure!
Londo Mollari: Mass drivers? They have been outlawed by every civilized planet!
Orbital Bombardment from DUST 514
In the EVE Online military sci-fi shooter, DUST 514, players can call down three types of orbital strikes as fire support and even turning the tide in the online gaming arena. The first type of orbital strike is the Pulse Laser Strike that fires a high damage laser beam, but it only covers a small area. Next is the EM strike that used electro-magnetic energy blast to strike an larger area, but is a non-lethal strike, bring down shields and electronics. Lastly, there is the Hybrid Strike that combines lasers and other times of ammunition that the most devastating. Of course, giving the offensive power of the orbital strike, it is harder to achieve battlefield reward.
The Lunar Catapult from The Moon is a Harsh Mistress
The Xindi Probe Attack from Star Trek: Enterprise "The Expanse"
The USSD Particle Satellites from Bubblegun Crisis: 2033
The Slug's Rod Attacks from Orphanage by Robet Buettner
The Hammer of the Dawn from the Gears of War Universe
The AEGIS Orbital Defense Platforms from Babylon 5 "Endgame"
In the final showdown between the forces loyal to dickhead President Clark and B5's liberation force, Clark was losing and decided to turn the planetary defense grid of orbital weapons platforms called AEGIS back onto Earth. AEGIS platforms were equiped with missiles and heavy-duty particle cannons that could level wide areas of the surface. The liberation fleet destroys the AEGIS platforms and saves 40% of Earth's population from certain death. The AEGIS defense grid is rebuilt just in time for the Drakh attack on Earth in 2266.
The SOL Weapon Platforms from Akira
The Alien Relativistic Missiles from The Killing Star
Imperial of Man's "Exterminates" from WH40K
The Nerve Gas Orbital Modules from Moonraker
HERCULES and PETER the GREAT from Meteor (1979)
In the much panned 1979 disaster film, a massive asteroid is headed to Earth that will produce an extinction level event, and there seems to be little to stop it. But wait! The United States and the USSR both have secret nuclear weapon platforms that completely volatile the Outer Space Treaty. In the film, Sean Connery was the developer of the American HERCULES weapon platform, he is brought on to help with redirecting the asteroid from hitting the Earth and killing everyone. The Soviets have the PETER the GREAT nuclear weapon platform.