A kinetic bombardment or a kinetic orbital strike is the hypothetical act of attacking a planetary surface with an inert projectile, where the destructive force comes from the kinetic energy of the projectile impacting at very high speeds. The concept originated during the Cold War.
The typical depiction of the tactic is of a satellite containing a magazine of tungsten rods and a directional thrust system. (In science fiction, the weapon is often depicted as being launched from a spaceship, instead of a satellite.) When a strike is ordered, the launch vehicle would brake one of the rods out of its orbit and into a suborbital trajectory that intersects the target. As the rod approaches periapsis and the target due to gravity, it picks up immense speed until it begins decelerating in the atmosphere and reaches terminal velocity shortly before impact. The rods would typically be shaped to minimize air resistance and maximize terminal velocity.
Kinetic bombardment has the advantage of being able to deliver projectiles from a very high angle at a very high speed, making them extremely difficult to defend against. In addition, projectiles would not require explosive warheads, and—in the simplest designs—would consist entirely of solid metal rods, giving rise to the common nickname "Rods from God". Disadvantages include the technical difficulties of ensuring accuracy and the high costs of positioning ammunition in orbit.
Real life concepts and theories
During the Vietnam War, there was limited use of the Lazy Dog bomb, a steel projectile shaped like a conventional bomb but only about 25.4 mm (1") long and 9.525 mm (3/8") diameter. A piece of sheet metal was folded to make the fins and welded to the rear of the projectile. These were dumped from aircraft onto enemy troops and had the same effect as a machine gun fired vertically. Observers visiting a battlefield after an attack said it looked like the ground had been 'tenderized' using a gigantic fork. Bodies had been penetrated longitudinally from shoulder to lower abdomen.
Project Thor is an idea for a weapons system that launches telephone pole-sized kinetic projectiles made from tungsten from Earth's orbit to damage targets on the ground. Jerry Pournelle originated the concept while working in operations research at Boeing in the 1950s before becoming a science-fiction writer.
The system most often described is "an orbiting tungsten telephone pole with small fins and a computer in the back for guidance". The system described in the 2003 United States Air Force report was that of 20-foot-long (6.1 m), 1-foot-diameter (0.30 m) tungsten rods, that are satellite controlled, and have global strike capability, with impact speeds of Mach 10.
The time between deorbit and impact would only be a few minutes, and depending on the orbits and positions in the orbits, the system would have a worldwide range. There would be no need to deploy missiles, aircraft or other vehicles.
The idea is that the weapon would naturally contain a large kinetic energy because it moves at orbital velocities, around 8 kilometers per second in orbit and 3 kilometers per second or Mach 10 at impact. As the rod would reenter Earth's atmosphere it would lose most of the velocity, but the remaining energy would cause considerable damage. Some systems are quoted as having the yield of a small tactical nuclear bomb. These designs are envisioned as a bunker buster. As the name suggests, the 'bunker buster' is powerful enough to destroy a nuclear bunker. With 6–8 satellites on a given orbit, a target could be hit within 12–15 minutes from any given time, less than half the time taken by an ICBM and without the launch warning. Such a system could also be equipped with sensors to detect incoming anti-ballistic missile-type threats and relatively light protective measures to use against them (e.g. Hit-To-Kill Missiles or megawatt-class chemical laser).
In the case of the system mentioned in the 2003 Air Force report above, a 6.1 m × 0.3 m tungsten cylinder impacting at Mach 10 has a kinetic energy equivalent to approximately 11.5 tons of TNT (or 7.2 tons of dynamite). The mass of such a cylinder is itself greater than 9 tons, so the practical applications of such a system are limited to those situations where its other characteristics provide a clear and decisive advantage—a conventional bomb/warhead of similar weight to the tungsten rod, delivered by conventional means, provides similar destructive capability and is far more practical and cost effective.
The highly elongated shape and high mass are to enhance sectional density and therefore minimize kinetic energy loss due to air friction and maximize penetration of hard or buried targets. The larger device is expected to be quite effective at penetrating deeply buried bunkers and other command and control targets.
The weapon would be very hard to defend against. It has a very high closing velocity and small radar cross-section. Launch is difficult to detect. Any infrared launch signature occurs in orbit, at no fixed position. The infrared launch signature also has a much smaller magnitude compared to a ballistic missile launch. One drawback of the system is that the weapon's sensors would almost certainly be blind during atmospheric reentry due to the plasma sheath that would develop ahead of it, so a mobile target could be difficult to hit if it performed an unexpected maneuver. The system would also have to cope with atmospheric heating from re-entry, which could melt non-tungsten components of the weapon.
In science fiction
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In the mid-1960s, popular science interest in orbital mechanics led to a number of science fiction stories which explored their implications. Among these was The Moon Is a Harsh Mistress by Robert A. Heinlein in which the citizens of the Moon bombard the Earth with rocks wrapped in iron containers which are in turn fired from an electromagnetic launch system at Earth-based targets.
In the 1970s and 1980s this idea was refined in science fiction novels such as Footfall by Larry Niven and Jerry Pournelle (the same Pournelle that first proposed the idea for military use in a non-fiction context), in which aliens use a Thor-type system. During the 1980s and 1990s references to such weapons became a staple of science fiction roleplaying games such as Traveller, Shadowrun and Heavy Gear (the latter game naming these weapons ortillery, a portmanteau of orbital artillery), as well as visual media including Babylon 5's "mass drivers" and the film Starship Troopers, itself an adaptation of a Heinlein novel of the same name.
The re-purposing of space colonies for use in kinetic bombardment (referred as a "colony drop") is a frequent element of the Gundam franchise and is central to the plots of Mobile Suit Gundam: Char's Counterattack and Mobile Suit Gundam 0083: Stardust Memory.
A smaller "crowbar" variant is mentioned in David's Sling by Marc Stiegler (Baen, 1988). Set in the Cold War, the story is based on the use of (relatively inexpensive) information-based "intelligent" systems to overcome an enemy's numerical advantage. The orbital kinetic bombardment system is used first to destroy the Soviet tank armies that have invaded Europe and then to take out Soviet ICBM silos prior to a nuclear strike.
From the mid-1990s, kinetic weapons as science fiction plot devices appeared in video games. Appearing in Bullfrog Productions' 1996 Syndicate Wars as a player-usable weapon, it also featured prominently in the plot of Tom Clancy's Endwar, Mass Effect 2 and Call of Duty: Ghosts, to name some.
The Warren Ellis comic Global Frequency (issue #12, "Harpoon", August 2004) featured the threat of kinetic spears, weapons designed to be dropped from satellites, heat up on re-entry, and strike the ground with the force of a tactical nuke, and as hot as the edge of the sun. Rather than being a weapon of war, they were depicted as part of a 'die-back' protocol designed to reduce Earth's human population to a sustainable level.
In 2013 a kinetic weapon bombardment system consisting of tungsten rods in an orbiting platform, codenamed Project: Zeus, was featured in the movie G.I. Joe: Retaliation, where it destroys London. However, the movie misrepresented physics by claiming the rod would not be "launched" or "fired" but merely "dropped". If it were released without force it would orbit the Earth in the same manner as the platform itself. In order for a rod to fall straight toward the center of Earth, it would need to be launched away from the station with a tangential velocity equal in magnitude and opposite in direction from the orbiting station. This velocity would be in the range of approximately 7–8 km/s for satellites in low earth orbit, however, the actual velocity change needed to merely deorbit within half an orbit would be much less, likely a few hundred m/s for a low-orbiting satellite, if even that much.
In John Birmingham's Stalin's Hammer (a part of his Axis of Time series), Soviet scientists use 21st century technology obtained from a fleet thrown back to World War II to create a satellite capable of launching tungsten rods from orbit and launch it by the early 1950s.
In David Weber's Honorverse series, kinetic strike weapons are a standard armament of all space navies that conduct orbit-to-ground operations. The version used by the Royal Manticoran Navy is a six-hundred-kilogram iron slug equipped with a small gravitic drive, capable of variable yields ranging from that of a large artillery shell to an intermediate-yield nuclear device, and packaged in six-shot satellites that are deployed from starship counter-missile tubes.
In Peter F. Hamilton's The Night's Dawn trilogy, "kinetic harpoons" are being used to bombard the surface of a planet. The book in which the event occurs also specifies how the staggering of the harpoons' impact caused the shockwaves from the impacts to resonate and result in an artificial earthquake.
In the 28 August 2005 strip of Schlock Mercenary by Howard Taylor, the sentient race Tohdfraug intend to destroy the extant civilisation on the planet Qlaviql, by bombarding it with "a few thousand depleted uranium projectiles ... no bigger than a roll of Terran toilet paper", although accelerated to 250 Mm/h. 
- Concrete bomb
- Kinetic energy penetrator
- Prompt Global Strike
- Brilliant Pebbles
- Fractional Orbital Bombardment System
- Pelt, Michel van (2005). Space Tourism: Adventures in Earth Orbit and Beyond. Springer Science & Business Media. p. 107. ISBN 978-0-387-40213-0.; - the word "brake" in this paragraph refers to the act of braking; the fact that by slowing the rod's orbital trajectory, the satellite can de-orbit it in order to drop it onto the planet below.
- Eric Adams (June 2004). "Rods from God". Popular Science. Retrieved 27 May 2010.
- David Karmes (2014). The Patricia Lynn Project: Vietnam War, the Early Years of Air Intelligence. iUniverse. The Lazy Dog Bomb. ISBN 978-1-4917-5228-9.
- Ralph A Rowley (12 April 2013). Close Air Support In Vietnam. Lulu.com. p. 43. ISBN 978-1-939335-12-8.
- Jonathan Shainin (10 December 2006). "Rods From God". New York Times.
- Jerry Pournelle (6 March 2006). "Chaos Manor Mail". The View from Chaos Manor. Archived from the original on 28 August 2008.
- "US Air Force Transformation Flight Plan" (PDF).
- Giuseppe Anzera (18 August 2005). "Star Wars: Empires strike back". Asia Times. Retrieved 25 May 2010.
- John Arquilla (12 March 2006). "RODS FROM GOD / Imagine a bundle of telephone poles hurtling through space at 7,000 mph". San Francisco Chronicle. Archived from the original on 2013-02-02. Retrieved 25 May 2010.
[Such] bundles of metal are not specifically disallowed by the 1972 Anti-Ballistic Missile Treaty, which explicitly prohibits only deploying nuclear weapons in space. The rods, however, would violate the spirit of the more general Outer Space Treaty.
- Julian Borger (19 May 2005). "Bush likely to back weapons in space". The Guardian. Retrieved 25 May 2010.
- Jack Kelly (28 July 2003). "Rods from God". Pittsburgh Post-Gazette. p. A5.
- History Television, The Universe, season 4, episode 8, "Space Wars"; referring to rod from God
- Noah Shachtman (20 February 2004). "Pentagon Preps for War in Space". Wired. Retrieved 25 May 2010.
- Michael Goldfarb (8 June 2005). "The Rods from God". The Weekly Standard. Retrieved 28 May 2010.