Space gun

A space gun is a method of launching an object into space using a large gun, or cannon. It provides a method of non-rocket spacelaunch.

In the Project HARP a U.S. Navy 16 in 100 caliber gun was used to fire a 180 kg slug at 3600 m/s or 12960 kph, reaching an apogee of 180 km, hence performing a suborbital spaceflight. However, a space gun has never been successfully used to launch an object into orbit.

Technical issues
The large g-force experienced by a ballistic projectile would likely mean that a space gun would be incapable of safely launching humans or delicate instruments, rather being restricted to freight, fuel or ruggedized satellites.

Atmospheric drag also makes it more difficult to control the trajectory of any projectile launched, subjects the projectile to extremely high forces, and causes severe energy losses that may not be easily overcome.

Getting to orbit
A space gun, by itself, is not capable of placing objects into stable orbit around the object (planet or otherwise) from which it is launched. The laws of two-body gravitation make it impossible to reach a stable orbit without an active payload which performs orbital correction burns to change the shape of its orbit after launch. The orbit is a parabolic orbit, a hyperbolic orbit, or part of an elliptic orbit which ends at the planet's surface at the point of launch or another point. This means that an uncorrected ballistic payload will always strike the planet within its first orbit unless the velocity was so high as to reach or exceed escape velocity.

Isaac Newton avoided this objection in his thought experiment by positing an impossibly tall mountain from which his cannon was fired. If in a stable orbit, the projectile, however, would still tend to circle the planet and strike the point of launch (see Newton's cannonball).

As a result, all payloads intended to reach a closed orbit need at least to perform some sort of course correction to create another orbit that does not intersect the planet's surface. A rocket can be used for additional boost as planned in both Project HARP and the Quicklaunch project. The magnitude of such may be small; for instance, the StarTram Generation 1 reference design involves a total of 0.6 km/s of rocket burn to raise perigee well above the atmosphere when entering a 8 km/s Low Earth Orbit.

In a three-body or larger system, a gravity assist trajectory might be available such that a carefully aimed escape velocity projectile would have its trajectory modified by the gravitational fields of other bodies in the system such that the projectile would eventually return to orbit the initial planet using only the launch delta-v.

Acceleration
A space gun with a "gun barrel" of length ($$l$$), and the needed velocity ($$v_e$$), the acceleration ($$a$$) is provided by the following formula:


 * $$ a = \frac{v_e^2}{2l} $$

For instance, with a space gun with a vertical "gun barrel" through both the Earth's crust and the troposphere, totalling ~60 km of length ($$l$$), and a velocity ($$v_e$$) enough to escape the Earth's gravity (escape velocity, which is 11.2 km/s on Earth), the acceleration ($$a$$) would theoretically be more than 1000 m/s2, which is more than 100 g-forces, which is about 3 times the human tolerance to g-forces of maximum 20 to 35 g during the ~10 seconds such a firing would take. However, a space gun with a circular track could utilize much lower accelerations because its effective track length is infinite (though the centripetal acceleration at high speed would be enormous, depeding on the size of the circle).

Practical attempts


The German V-3 cannon program (less well known than the V-2 rocket or V-1 flying bomb), during the Second World War was an attempt to build something approaching a space gun. Based in the Pas-de-Calais area of France it was planned to be more devastating than the other Nazi 'Vengeance weapons'. It was destroyed by RAF bombing using Tallboy blockbuster bombs in July 1944.

On the practical side, the most prominent recent attempt to make a space gun was artillery engineer Gerald Bull's Project Babylon, which was also known as the 'Iraqi supergun' by the media. During Project Babylon, Bull used his experience from Project HARP to build a massive cannon for Saddam Hussein, leader of Ba'athist Iraq. Bull was assassinated before the project was completed.

Super High Altitude Research Project
Since Bull's death, few have seriously attempted to build a space gun. Perhaps most promisingly, the US Ballistic Missile Defense program sponsored the Super High Altitude Research Project (SHARP) in the 1980s. Developed at Lawrence Livermore Laboratory, it is a light gas gun and has been used to test fire objects at Mach 9.

Quicklaunch
After cancellation of SHARP, lead developers John Hunter founded the Jules Verne Launcher Company in 1996 and the Quicklaunch company. As of September 2012, Quicklaunch was seeking to raise $500 million to build a gun that could refuel a propellant depot or send bulk materials into space.

Ram accelerators have also been proposed as an alternative to light gas guns. Other proposals use electromagnetic techniques for accelerating the payload, such as coilguns and railguns.

In fiction
The first publication of the concept may be Newton's cannonball in the 1728 book A Treatise of the System of the World, although it was primarily used as a thought experiment regarding gravity.

Perhaps the most famous representation of a space gun is in Jules Verne's novel, From the Earth to the Moon (made into a silent movie called Le Voyage dans la Lune), in which astronauts fly to the moon aboard a ship launched from a cannon. Another famous example is the hydrogen accelerator cannon used by the Martians to launch their invasion in H. G. Wells' book The War of the Worlds. Wells also used the concept in the climax of the 1936 movie Things to Come. The device was featured in films as late as 1967, such as Jules Verne's Rocket to the Moon.

In the video game Ultima: Worlds of Adventure 2: Martian Dreams, Percival Lowell builds a space gun to send a ship to Mars.

In the Nintendo game Paper Mario: The Thousand Year Door the protagonist is fired to the moon from a large cannon powered by the explosive deaths of thousands of anthropomorphic bombs. This is depicted in a somewhat comical fashion.

Gerald Bull's assassination and the Project Babylon gun were also the starting point for Frederick Forsyth's 1994 novel The Fist of God.