A ram accelerator is a device for accelerating
projectiles
or just a single projectile to extremely high speeds using
jet-engine
A jet engine is a type of reaction engine discharging a fast-moving jet (fluid), jet of heated gas (usually air) that generates thrust by jet propulsion. While this broad definition can include Rocket engine, rocket, Pump-jet, water jet, and ...
-like propulsion cycles based on
ramjet
A ramjet, or athodyd (aero thermodynamic duct), is a form of airbreathing jet engine that uses the forward motion of the engine to produce thrust. Since it produces no thrust when stationary (no ram air) ramjet-powered vehicles require an as ...
or
scramjet
A scramjet (supersonic combustion ramjet) is a variant of a ramjet airbreathing jet engine in which combustion takes place in supersonic airflow. As in ramjets, a scramjet relies on high vehicle speed to compress the incoming air forcefully ...
combustion processes. It is thought to be possible to achieve
non-rocket spacelaunch
Non-rocket spacelaunch refers to theoretical concepts for launch into space where much of the speed and altitude needed to achieve orbit is provided by a propulsion technique that is not subject to the limits of the rocket equation. Although al ...
with this technology.
It consists of a long tube (barrel) filled with a mixture of combustible gases with a
frangible
A material is said to be frangible if through deformation it tends to break up into fragments, rather than deforming elastically and retaining its cohesion as a single object. Common crackers are examples of frangible materials, while fresh bre ...
diaphragm at either end to contain the gases. The projectile is fired by another means (e.g., a
light-gas gun
The light-gas gun is an apparatus for physics experiments. It is a highly specialized gun designed to generate extremely high velocities. It is usually used to study high-speed impact phenomena (hypervelocity research), such as the formation of ...
or
railgun
A railgun or rail gun is a linear motor device, typically designed as a weapon, that uses electromagnetic force to launch high velocity projectiles. The projectile normally does not contain explosives, instead relying on the projectile's high ...
) supersonically through the first diaphragm into the tube. Then the projectile burns the gases as fuel, because it is shaped like a ramjet or scramjet core, and accelerates under jet propulsion. Other physics come into play at higher velocities.
Description
In a normal ramjet, air is compressed between a spike-shaped centerbody and an outer cowling, fuel is added and burned, and high speed exhaust gases are expanded supersonically out of the nozzle to generate thrust. In a ram accelerator, a projectile having a shape similar to the ramjet centerbody is fired, (often from a conventional gun), into the accelerator barrel, causing compression between the projectile and the barrel's walls. The barrel contains a pre-mixed gaseous fuel-air mixture. As the ram accelerator projectile compresses the fuel-air mixture, it is ignited and the combustion is stabilized at the base of the projectile. The resulting pressure differential generates a prodigious amount of thrust that can accelerate projectiles to in-tube Mach numbers greater than 8. Thus, if propellant mixtures with a
speed of sound of 1000 m/s (e.g. fuel-rich H
2-O
2 mixtures) are used, muzzle velocities in excess of 8000 m/s are possible.
To span a wide range in a typical ram accelerator system, multiple stages with propellants with different sound speeds are used to maintain high performance. Membranes or diaphragms that are easily punctured by the projectile are used to isolate the propellant stages. Each section is filled with a different fuel-air mixture chosen so that later sections have higher speeds of sound. As such, the ram can be maintained at optimal speeds of
Mach 3–5 (relative to the mixture that it travels through) during its entire acceleration period. Ram accelerators optimized to use
supersonic combustion modes can generate even higher velocities (Mach 6-8) due to the ability to combust fuel that is still moving at supersonic speed.
Testing
Scramjet projectiles were tested in
Project HARP
Project HARP, short for High Altitude Research Project, was a joint venture of the United States Department of Defense and Canada's Department of National Defence created with the goal of studying ballistics of re-entry vehicles and collecting ...
in the 1960s.
Advantages
The chief advantage of a ram accelerator over a conventional gun is its scalability. In a normal gun, maximum pressure is exerted at the time of the charge ignition. As the projectile moves further down the barrel, the amount of acceleration upon the projectile decreases as the gas behind it expands, eventually reaching amounts trivial enough that a longer barrel is no longer justified . With a ram accelerator, the projectile is propelled primarily by the pressure generated by the reaction of the propellant gases burning just behind the projectile. This leads to constant pressure being put both on the gun and the projectile itself. Consequently, far longer barrels are possible than conventional guns, while still delivering a strong constant acceleration to the projectile.
Uses
Ram accelerators have been proposed as a cheap method to get payloads into space. Impulsive launched projectiles need some means to circularize their trajectory for orbit insertion, so
rocket
A rocket (from it, rocchetto, , bobbin/spool) is a vehicle that uses jet propulsion to accelerate without using the surrounding air. A rocket engine produces thrust by reaction to exhaust expelled at high speed. Rocket engines work entirely fr ...
s, such as those designed in the 1960s in
Project HARP
Project HARP, short for High Altitude Research Project, was a joint venture of the United States Department of Defense and Canada's Department of National Defence created with the goal of studying ballistics of re-entry vehicles and collecting ...
, are typically incorporated into the projectiles. With multi-stage rocket projectiles the launch cost was estimated at US$500 per kilogram in 2004.
Ram accelerator technology has also been envisioned for military applications such as ultra-long range striking and intercepting capabilities against stationary and on-the-move threats. The fact that the projectile accelerates and travels at very high velocities makes it a perfect alternative to
anti-ship warfare, giving it abilities to evade defense systems. Only systems such as
railguns could have such striking abilities against high alert threats. Such projectiles could even be integrated into railguns themselves to allow even higher acceleration at a cheaper cost and effectiveness against a wide variety of targets.
Technologies related to a ram accelerator for direct space launch applications are: two-stage gas guns (
SHARP
Sharp or SHARP may refer to:
Acronyms
* SHARP (helmet ratings) (Safety Helmet Assessment and Rating Programme), a British motorcycle helmet safety rating scheme
* Self Help Addiction Recovery Program, a charitable organisation founded in 19 ...
), multiple sidewall injection gas guns (JVL),
railgun
A railgun or rail gun is a linear motor device, typically designed as a weapon, that uses electromagnetic force to launch high velocity projectiles. The projectile normally does not contain explosives, instead relying on the projectile's high ...
s, and
coilgun
A coilgun, also known as a Gauss rifle, is a type of mass driver consisting of one or more coils used as electromagnets in the configuration of a linear motor that accelerate a ferromagnetic or conducting projectile to high velocity. In almos ...
s.
Ram accelerators are currently used primarily for research into supersonic combustion. As of July 2007,
the Ballistic Flight Group
''The'' () is a grammatical article in English, denoting persons or things already mentioned, under discussion, implied or otherwise presumed familiar to listeners, readers, or speakers. It is the definite article in English. ''The'' is the m ...
has been promoting commercial investment into the ram accelerator technology. The ''scram cannon''
science fiction
Science fiction (sometimes shortened to Sci-Fi or SF) is a genre of speculative fiction which typically deals with imaginative and futuristic concepts such as advanced science and technology, space exploration, time travel, parallel uni ...
weapon was inspired by ram accelerators.
See also
*
Light-gas gun
The light-gas gun is an apparatus for physics experiments. It is a highly specialized gun designed to generate extremely high velocities. It is usually used to study high-speed impact phenomena (hypervelocity research), such as the formation of ...
*
Railgun
A railgun or rail gun is a linear motor device, typically designed as a weapon, that uses electromagnetic force to launch high velocity projectiles. The projectile normally does not contain explosives, instead relying on the projectile's high ...
*
Plasma railgun
A plasma railgun is a linear accelerator which, like a projectile railgun, uses two long parallel electrodes to accelerate a "sliding short" armature. However, in a plasma railgun, the armature and ejected projectile consists of plasma, or hot, io ...
*
Helical railgun Helical railguns are multi-turn railguns that reduce rail and brush current by a factor equal to the number of turns. Two rails are surrounded by a helical barrel and the projectile or re-usable carrier is cylindrical. The projectile is energized co ...
*
Coilgun
A coilgun, also known as a Gauss rifle, is a type of mass driver consisting of one or more coils used as electromagnets in the configuration of a linear motor that accelerate a ferromagnetic or conducting projectile to high velocity. In almos ...
*
Mass driver
A mass driver or electromagnetic catapult is a proposed method of non-rocket spacelaunch which would use a linear motor to accelerate and catapult payloads up to high speeds. Existing and contemplated mass drivers use coils of wire energized by e ...
External links
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{{Non-rocket spacelaunch
Spacecraft propulsion
Artillery by type