Wednesday 31 July 2013

Project Thor :: Kinetic Bombardment

A kinetic bombardment (sometimes called a mass drop) is a fairly simple concept. Mass is dropped. In other words, the idea behind a kinetic bombardment is to take something massive, and well, drop it.
It is the 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 velocities. The concept is encountered in science fiction and is thought to have originated during the Cold War.
Non-orbital bombardments with kinetic projectiles, such as lobbing stones with siege engines such as catapults or trebuchets are considered siege warfare, not kinetic bombardment.

And wouldn't you know, humanity has been using kinetic bombardments (in a sense) for thousands of years. If it comes from a non-horizontal direction, doesn't use explosives, and has a blunt impact then it's technically a kinetic bombardment. A particularly ancient example occurred during the ice age when hunters would lure mammoths and other prey into lower areas, then drop heavy rocks on them from above. More modern examples can be found in the World War 2 and Cold War eras when multiple bombs were developed that were designed to weigh as much as possible and be dropped from large heights. While the intended purpose of this was to have the bombs penetrate the earth and explode underground, testing revealed that the massive forces involved (imagine 22,000 pounds being dropped from almost 12,000 feat and moving at nearly supersonic speed upon impact) would effectively cause two shock-waves, one when the bomb landed and one when it exploded.

Now imagine, instead of using a bomb or a small load of rocks to attack the earth, you decide to use something a bit more massive.

Project Thor is an idea for a weapons system that launches kinetic projectiles from Earth 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 most described system is "an orbiting tungsten telephone pole with small fins and a computer in the back for guidance". The weapon can be down-scaled, an orbiting "crowbar" rather than a pole.The system described in the 2003 United States Air Force (USAF) 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 deorbiting and impact would only be a few minutes, and depending on the orbits and positions in the orbits, the system would have a world-wide range.[citation needed] There is no requirement to deploy missiles, aircraft or other vehicles. Although the SALT II (1979) prohibited the deployment of orbital weapons of mass destruction, it did not prohibit the deployment of conventional weapons. The system is prohibited by neither the Outer Space Treaty nor the Anti-Ballistic Missile Treaty.

The idea is that the weapon would inflict damage because it moves at orbital velocities, at least 9 kilometers per second. Smaller weapons can deliver measured amounts of energy as small as a 225 kg conventional bomb. Some systems are quoted as having the yield of a small tactical nuclear bomb. These designs are envisioned as a bunker buster.

In the case of the system mentioned in the 2003 USAF report above, a 6.1m x 0.3m 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 it is clear that the practical applications of such a system are limited to those situations where its other characteristics provide a decisive advantage - a conventional bomb/warhead of similar weight to the tungsten rod, delivered by conventional means, provides similar destructive capability and is a far more practical method.

The highly elongated shape and high density 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 good at penetrating deeply buried bunkers and other command and control targets. The smaller "crowbar" size might be employed for anti-armor, anti-aircraft, anti-satellite and possibly anti-personnel use.

The weapon would be very hard to defend against. It has a very high closing velocity and a small radar cross-section. Launch is difficult to detect. Any infra-red launch signature occurs in orbit, at no fixed position. The infra-red launch signature also has a small 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 any unexpected maneuvering. The system would also have to cope with atmospheric heating from re-entry, which could melt non-tungsten components of the weapon.

While the larger version might be individually launched, the smaller versions would be launched from "pods" or "carriers" that contained several missiles.

The phrase "Rods from God" is also used to describe the same concept. A USAF report called them "hypervelocity rod bundles".


What kind of damage could it do? 
 It turns out you can do quite a bit of damage just dropping something massive enough on something else, especially at a high speed. However, most sci-fi writers tend to drastically overestimate the mass required to cause widespread destruction.

While many sci-fi writers weave terrifying tales of asteroids or even moons hundreds to thousands of miles across, the fact of the matter is that they are drastically underestimating the power of a smaller asteroid. The asteroid we think contributed to the extinction of the dinosaurs? 10 kilometers wide. Sure, that seems pretty large for a single rock, and it is, if you're only looking at rocks here on earth. It turns out there are an expected 12,000 asteroids that are that size or bigger in our asteroid belt alone and that number gets multiplied by 7 if you want to count the asteroids half that size.

And while I could go into excruciating detail into the effects of and size of numerous impacts that have occurred here are some pictures instead:





 Artist's impression of a major impact event. The collision between a planet and an asteroid a few kilometers in diameter may release as much energy as several million nuclear weapons detonating simultaneously.










Trees knocked over by the Tunguska blast








Depending on the type of asteroid, its size, and where it lands, we could face everything from earthquakes and volcanic activity to slightly more startling events.

If the impact occurs in or near water, we can expect absolutely massive tsunamis reaching miles into the air. In fact, an impact 35 million years ago into the Chesapeake Bay area is suspected of causing a tsunami that topped the Blue Ridge Mountain Range.

Other devastating effects of a sizable impact include fires being started by super-heated fragments of ejecta thrown into the air, an (ever popular) dust cloud -- hindering photosynthesis and devastating vegetation -- and acid rain caused by various sediments lingering in the atmosphere.

Perhaps most terrifying of all is the massive burst of infrared radiation that most life would be subject to. It turns out that if enough heavy ejecta is thrown into the atmosphere then the force and heat generated by re-entry would cause a short but intense burst of infrared radiation.

Altogether this means that, should an alien force decide to attack us with an asteroid, even if we survive the impact, the aftermath will not be pretty.

In science fiction
 The film G.I. Joe: Retaliation showed a kinetic bombardment of Central London from one of the seven orbital weapons in space, dubbed "Project Zeus". The projectile is a hollow platinum tube filled with a tungsten rod and appears to be a pole shaped object with a motor, very much in line with the speculated design of such a weapon. Instead of an explosion, a violent earthquake appears to take place, which is again a characteristic of kinetic bombardment.

Here is the Clip:
 
 

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