Missile guidance
[citation needed] In World War II, guided missiles were first developed, as part of the German V-weapons program.
In the case of glide bombs or missiles against ships or the supersonic Wasserfall against slow-moving B-17 Flying Fortress bombers this system worked, but as speeds increased MCLOS was quickly rendered useless for most roles.
It is similar to MCLOS but some automatic systems position the missile in the line of sight while the operator simply tracks the target.
SACLOS has the advantage of allowing the missile to start in a position invisible to the user, as well as generally being considerably easier to operate.
Semi-active radar homing (SARH) is by far the most common "all weather" guidance solution for anti-aircraft systems, both ground- and air-launched.
[6] It has the disadvantage for air-launched systems that the launch aircraft must keep moving towards the target in order to maintain radar and guidance lock.
For ships and mobile or fixed ground-based systems, this is irrelevant as the speed (and often size) of the launch platform precludes "running away" from the target or opening the range so as to make the enemy attack fail.
[6] Contrast seekers use a video camera, typically black and white, to image a field of view in front of the missile, which is presented to the operator.
Contrast seekers have been used for air-to-ground missiles, including the AGM-65 Maverick, because most ground targets can be distinguished only by visual means.
However they rely on there being strong contrast changes to track, and even traditional camouflage can render them unable to "lock on".
All of the guidance components (including sensors such as accelerometers or gyroscopes) are contained within the missile, and no outside information (such as radio instructions) is used.
[11] Inertial guidance uses sensitive measurement devices to calculate the location of the missile due to the acceleration put on it after leaving a known position.
Early mechanical systems were not very accurate, and required some sort of external adjustment to allow them to hit targets even the size of a city.
Modern systems use solid state ring laser gyros that are accurate to within metres over ranges of 10,000 km, and no longer require additional inputs.
Gyroscope development has culminated in the AIRS found on the MX missile, allowing for an accuracy of less than 100 m at intercontinental ranges.
Many civilian aircraft use inertial guidance using a ring laser gyroscope, which is less accurate than the mechanical systems found in ICBMs, but which provide an inexpensive means of attaining a fairly accurate fix on location (when most airliners such as Boeing's 707 and 747 were designed, GPS was not the widely commercially available means of tracking that it is today).
[2] Additionally, the relatively low precision of this guidance method is less of an issue for large nuclear warheads.
The USAF sought a precision navigation system for maintaining route accuracy and target tracking at very high speeds.
[citation needed] Nortronics, Northrop's electronics development division, had developed an astro-inertial navigation system (ANS), which could correct inertial navigation errors with celestial observations, for the SM-62 Snark missile, and a separate system for the ill-fated AGM-48 Skybolt missile, the latter of which was adapted for the SR-71.
As the accuracy of a missile is dependent upon the guidance system knowing the exact position of the missile at any given moment during its flight, the fact that stars are a fixed reference point from which to calculate that position makes this a potentially very effective means of improving accuracy.
that the missiles from Soviet submarines would track two separate stars to achieve this), if it was not quite aligned to where it should be then this would indicate that the inertial system was not precisely on target and a correction would be made.
[13] TERCOM, for "terrain contour matching", uses altitude maps of the strip of land from the launch site to the target, and compares them with information from a radar altimeter on board.
TERCOM is the typical system for cruise missile guidance, but is being supplanted by GPS systems and by DSMAC, digital scene-matching area correlator, which employs a camera to view an area of land, digitizes the view, and compares it to stored scenes in an onboard computer to guide the missile to its target.
