Laser Seeker

The seeker itself can be programmed from the cockpit while en route to seek a particular coded burst. This burst pattern differentiates the laser designator from other designators on the battlefield, thus ensuring that the missile will strike the target is was intended for. The AGM-114's seeker sends information to the guidance section, which in turn sends steering cues to the control section. Through this series of hand-offs, the missile is able to determine where its target is located, and then guide itself in order to strike it.

While the AGM-114 is classified as a fire-and-forget missile, this label actually depends on the how the missile is employed. The Hellfire system features two guidance options: autonomous and remote designation. Autonomous designation refers to an engagement where the launching aircraft is responsible for both target designation missile launch. This particular engagement requires that the helicopter expose itself so that the designator has a clear line-of-sight to the target. For the AH-64, which houses its designator in the nose of the airframe, this requires that nearly the entire aircraft be exposed to potential enemy fire.

Remote designation allows the helicopter to conceal its location behind a terrain feature such as a hill. Known as masking, this technique significantly reduces the chances of detection as well as the danger from opposing fire. Relieved of the burden of missile guidance, the helicopter essentially becomes a launch platform, with targeting and guidance delivered through the use of other helicopters, ground vehicles, or Combat Observation Lasing Teams (COLTs) inserted into the area equipped with man-portable lasers. This latter method of delivery requires a significant degree of coordination between launch and designation units. Timing and position is crucial to the success of the attack - both requiring a great deal of preparation and communication.

Multiple Delivery Options

The AGM-114 provides four delivery options for the pilot to choose from. Each option has a direct impact on the exposure of the aircraft to enemy fire, and thus the safety of the crew. However, each option carries its own set of advantages and disadvantages. A skillful crew will weigh these factors and select the best guidance option for the situation at hand. The options are as follows:
• Lock-on Before Launch (LOBL)
  LOBL is one of the autonomous engagement methods. The aircraft locks onto the target with its own designator, launches the missile and then continues to designate the target until missile impact. The advantages are that the crew is assured that the correct target is designated and that the target is within the seeker constraints of the missile. However the disadvantage of this method lies in the trajectory of the missile's flightpath.

  In most cases, the terminal stage of the Hellfire flightpath is a top-down approach in excess of 60 degrees. This angle allows the missile to strike an object such as a tank at its weakest point, the top armour, as well as overcome obstacles such as berms or revetments.

  If the missile is at maximum range, it must gain much more altitude in order to achieve the same terminal angle. Due to the fact that more altitude must be gained, this must take place during the initial boost period, where kinetic energy is greatest. Upon launch at maximum range, the missile will climb to nearly 2000 feet above the launcher - one of its highest trajectories - in order to achieve that optimum dive-angle.

  On a clear day, this does not pose a problem. However, should the weather be overcast with a low cloud base, it is possible that the target lock may be broken as the missile reaches its apex just prior to the terminal stage. In order to reduce this trajectory, the launching aircraft must be positioned closer to the target. However, given that the aircraft must be exposed in order to provide a clear line-of-sight for its designator, this option is less desirable as it places the aircraft in greater danger.

  
  
  
• Lock-on After Launch - Direct (LOAL-DIR)
  Another of the autonomous delivery modes, LOAL-DIR still utilizes the aircraft to select and designate, however the missile flies the lowest of trajectories for all engagement methods while still maintaining maximum range. Essentially, the missile is fired in the general direction of the target and upon launch, the missile gradually increases altitude at an angle of about 20-30 degrees. After a delay of a few seconds, the aircraft will then designate the target. At this point, the missile locates the laser emissions reflecting off of the target and adjusts its path in order to strike the object. However, this option carries with it a reduced probability of successful employment as it is possible that factors beyond the control of the crew could interfere with this chain of events as the missile essentially flies blind for those few seconds.

  If the missile is able to achieve a lock, it then pitches up in order to gain altitude for optimum dive-angle. However, since the missile is much closer to the target at this point, the altitude required is much less than necessary at maximum range, usually only a few hundred feet. The result is a much lower apex than that of LOBL delivery. At twelve seconds - the longest possible delay before designation - the apex is only approximately 1000 feet above the launch vehicle, almost half that of LOBL mode. While the longer the delay the lower the trajectory, the increased period of blind flight also increases the chances that the missile will be unable to successfully acquire the target.

  
  
  
Lock-on After Launch - Low (LOAL-LO)
The first of the remote designation methods, LOAL-LO mode is utilized when the aircraft is masked behind low terrain features such as tree lines, buildings, or low hills. This mode allows the missile to pass over an obstacle 260 feet high providing that there is adequate horizontal standoff distance between the aircraft and the highest point of the terrain feature - about 1800 feet minimum. Again, delaying designation by the remote source, influences the trajectory as well as the probability of a successful strike. A maximum delay of 15 seconds from launch to designation results in an apex of approximately 1200 feet. No delay results in a maximum height of 1800 feet, increasing the potential that weather affects will influence success.



• Lock-on After Launch - High (LOAL-HI)
  Similar in nature to the previous remote designation mode, LOAL-HI is utilized when masking behind much higher terrain features. This mode allows the AGM-114 to clear features up to a maximum of 1000 feet in height. As with LOAL-LO, the helicopter must be a minimum horizontal distance from the highest point of the obstacle, about 4500 feet in the case of a 1000 foot-high feature. This mode also extends the maximum effective range of the missile to over 8 km.

  However, LOAL-HI produces the highest trajectory of any of the Hellfire's launch modes, with a corresponding increase in the likelihood that low clouds may break the seeker's lock on the target, causing the missile to go blind. As with the other guidance options, delaying the designation does have an impact on the trajectory. A maximum 15-second delay produces a trajectory of 1900 feet. An almost immediate lock results in an apex of 2300 feet.




Each mode possesses its relative merits, those advantages dependant on a number of circumstances. As stated before, different conditions will dictate which option is most appropriate. The most capable crews will be those who can weigh the various factors and select which guidance mode will be the most effective. In addition, preparation, coordination, and communication will be key factors in the success of the strike, particularly in the case of the various remote designation engagements._