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[[Image:FETMlaunch.jpg|right|thumb|150px|The imaginary firing of a space gun in [[Jules Verne]]'s ''[[From the Earth to the Moon]]''.]]
A '''space gun''' is a method of launching an object into space using a large [[gun]], or [[cannon]]. Though it is the earliest envisioned method of space launch, a space gun has never been successfully used to launch an object into
A space gun cannot, by itself, put an object into stable orbit around the planet from which it is launched. Since [[Kepler's laws of planetary motion]] were discovered, it has been known that any
[[Isaac Newton]] avoided this objection in his thought experiment by positing an impossibly tall mountain peak, above the sensible atmosphere, from which his cannon
▲Since [[Kepler's laws of planetary motion]] were discovered, it has been known that any payload fired from a planet's surface would follow an elliptical path with one focus of the ellipse at the center of the planet. This ellipse will obviously contact the planet's surface at the point of launch, and at least one other point. This means that a ballistic payload without orbital correction will always strike the planet within its first orbit unless it reaches vacuum at escape velocity, in which case its trajectory would be a hyperbola.
As a result, all payloads intended to reach stable orbit would have to perform some sort of course correction to move very soon to another orbit that does not intersect the planet's surface (or result in aerocapture if the planet has a significant atmosphere.) The
▲[[Isaac Newton]] avoided this objection in his thought experiment by positing an impossibly tall mountain from which his cannon was fired. The projectile, however, would still tend to circle the planet and return to the point of launch.
▲As a result, all payloads intended to reach orbit would have to perform some sort of course correction to move to another orbit that does not intersect the planet's surface or result in aerocapture if the planet has a significant atmosphere. The amount of fuel carried would thus reduce the payload-to-fuel ratio, decreasing the efficiency and increasing the complexity of such a system. It is conceivable that in a multi-body gravitational system, like the earth-moon system, a trajectory from earth could be found that does not re-intersect the earth's surface, although these paths would likely not be very simple or desirable, and would require more energy.
If acceptable solutions to these problems can be found, a space gun could offer access to space at costs significantly lower than those seen with rocket launch. However, the very high accelerations experienced by a [[Ballistics|ballistic]] projectile
▲Atmospheric drag also makes it more difficult to control the trajectory of any projectile launched, subjects the projectile to high pressures and heat loading, and causes significant energy losses that may not be easily overcome.
▲If acceptable solutions to these problems can be found, a space gun could offer access to space at costs lower than those seen with rocket launch. However, the very high accelerations experienced by a [[Ballistics|ballistic]] projectile would mean that a space gun would be incapable of launching [[human]]s or delicate instruments intact, restricting its applications to orbiting[[freight]] with high acceleration tolerance, and highly ruggedized satellites.
Perhaps the most famous representation of a space gun is [[Jules Verne]]'s novel, ''[[From the Earth to the Moon]]'' (made into a silent movie, ''[[Le Voyage dans la Lune]]''), in which astronauts fly to the moon aboard a ship launched from a cannon. [[Isaac Newton]] once used as an example a [[cannon]] placed on top of a [[mountain]] and fired with the correct [[velocity]] as a demonstration of his law of universal gravity, and the concept was featured in films as late as [[1967]] in films like [[Rocket to the Moon]]. Another famous example of a space gun is the hydrogen accelerator cannon used by the Martians to launch their invasion in HG Wells' book The War of the Worlds.
On the practical side, the most prominent and successful attempt to make a space gun was ballistics and cannon genius [[Gerald Bull]]'s [[Project Babylon]]. During Project Babylon, Bull used his experience from [[Project HARP]] to build a massive cannon for [[Saddam Hussein]] of [[Iraq]]. This gun, had it been completed, would have been the first true space gun capable of launching objects into space. However, it appears that he was assassinated, perhaps by [[Mossad]] or the [[CIA]],
Since Bull's death, few have seriously attempted to build a space gun. Perhaps most promisingly, the US [[Ballistic Missile Defense]] programme sponsored the [[Super High Altitude Research Project]] in the 1980s. Developed at [[Lawrence Livermore Laboratory]], it is a [[light gas gun]] and has been used to test fire objects at [[Mach number|Mach 9]]. One of the lead developers [[John Hunter]] has since founded the [[Jules Verne Launcher Company]] in [[1996]], though has as yet been unable to find funding for the multi-billion dollar project.
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