How Laser Guided Bombs Works

[Carl Fredrik Ahl]

Hi,

I know that laser guided bombs works by projecting a laser to an object and the bomb will have a photosensor that tries to keep the reflected laser in the center of the sensor, right? What I wonder is how does it know how to move in order to keep the laser in the center of the photosensor? Is this the only thing it requires to hit the target? Trying to move little all the time to keep the reflected laser in the center of the photosensor? 

[swansont]

That's probably it. An algorithm that steers the fins to keep the target centered. If it drifts, the feedback steers it back to center. PID controllers do stuff like this all the time. (Proportional, Integral, Derivative feedback)

[dimreepr]

3 hours ago, swansont said:

That's probably it. An algorithm that steers the fins to keep the target centered. If it drifts, the feedback steers it back to center. PID controllers do stuff like this all the time. (Proportional, Integral, Derivative feedback)

 

Pigeons do stuff like this all the time.

[swansont]

1 minute ago, dimreepr said:

Pigeons do stuff like this all the time.

Without the lasers.

[dimreepr]

24 minutes ago, swansont said:

Without the lasers.

indeed

[Sensei]

If photo-sensor is basically camera (could be IR camera too), and we have two servos able to spin in range -90...+90 angles, no engines, algorithm is very easy.

1) convert image from camera to bitmap (so computer will be able to analyze it).

2) analyze bitmap to find where is "spot" (the easiest would be compare the all pixels to check if some of them is in specified range of colors).

for( int j = 0; j < height; j++ ) {
   for( int i = 0; i < width; i++ ) {
      if( Color.compare( bitmap.get( i, j ), Color.Red, tolerance ) {
         spot_x = i; spot_y = j;
         break;
      }
   }
}

(smarter would be going from the center to outside)

3) calculate distance between "spot" x,y and center

delta_x = spot_x - width / 2;
delta_y = spot_y - height / 2;

If delta_x > 0, servo X, must rotate one direction e.g. 0...+90

If delta_x < 0, servo X, must rotate opposite direction 0...-90

If delta_y > 0, servo Y, must rotate one direction e.g. 0...+90

If delta_y < 0, servo Y, must rotate opposite direction 0...-90

4) convert delta_x and delta_y to corresponding servo rotation

servo_x_angle = delta_x * 90 / ( width / 2 ) * tolerance;
servo_y_angle = delta_y * 90 / ( height / 2 ) * tolerance;

5) couple milliseconds delay

6) go to 1)

 

If object is flying from higher altitude to the ground, it does not require engines.

 

You can see how to program Arduino micro servo (probably it has 9 grams, if I recall correctly), watch f.e. this video:

They are widely used to make remote controlled airplanes, robots and stuff like that. Single one costed me 2.7 USD, the last time I bought.

If intended to be used in remote controlled object, better replace Arduino by Arduino Nano. It will reduce mass of object quite considerably.

Edited April 1, 2019 by Sensei

[MigL]

Weapon systems, whether bombs or missiles, use three types of guidance systems.
Active, passive and GPS.

An active system uses a missile's self-contained radar to illuminate the target, and correctly steer itself toward it. Alternatively the 'seeker' can receive information ( such as IR emissions ) directly from the target.
A passive system requires illumination from the launcher, firing vehicle, or independent ground based source. The major drawback to this is that the target must be continuously illuminated during the bomb/missile's flight. This is a problem for strike aircraft as it makes them visible/vulnerable to AA systems.
The third option, is used only for non moving targets, and only by bombs or cruise missiles, where the target location is pre-programmed, and 'steering' is by GPS

[theHassan]

On 4/1/2019 at 7:55 PM, MigL said:

Weapon systems, whether bombs or missiles, use three types of guidance systems.
Active, passive and GPS.

An active system uses a missile's self-contained radar to illuminate the target, and correctly steer itself toward it. Alternatively the 'seeker' can receive information ( such as IR emissions ) directly from the target.
A passive system requires illumination from the launcher, firing vehicle, or independent ground based source. The major drawback to this is that the target must be continuously illuminated during the bomb/missile's flight. This is a problem for strike aircraft as it makes them visible/vulnerable to AA systems.
The third option, is used only for non moving targets, and only by bombs or cruise missiles, where the target location is pre-programmed, and 'steering' is by GPS

Dear MigL,

 

Please allow me to correct You a little. What You described as "passive" is actually called semi-active. As there is an active part in it, the illuminator. Which can be radar (Sparrow air-to-air missile is my example) or laser.

Passive guidance relies on the emissions of the target itself, like IR/UV emissions of a fighter jet engine to be homed on by a SAM (Stinger, for example) or a Sidewinder-like air-to-air missile, home-on-jamming missiles to take out jammer aircraft, antiradiation (antiradar) missiles to target air-defence radars (HARM) or imaging sensors in air-ground weapons like in some versions of Maverick.

[MigL]

Did not want to confuse the issue too much as it did not relate to the OP.
You are right, and no version of the Sparrow missile used active guidance.
IOW, its own radar does not illuminate the target and home in on it.
That is what active means. So semi-active is the correct classification ( which I omitted ), because it does have a targeting radar.
Active imparts fire and forget capability to a missile ( see AMRAAM or Meteor )

Targeting by emissions or other than own illumination, I termed passive ( see Sparrow and Skyflash/Aspide versions or Sidewinder )

Good talking to someone who shares similar interests.