Detect to Engage - Fire Control Solution

Detect to Engage/The Fire Control SolutionNaval Weapons Systems

We will learn:How the target is detected, How the target is tracked, How the weapon is launched, How the weapon is propelled, How the weapon finds the target, How the weapon knows when to detonate,How the weapon detonates.What is missing is the Fire Control SolutionThis is normally a topic for the end of this course but I put it here at the beginning so you can see the big picture. Then as we go over the parts, you will be able to see where they fit.

Learning Objectives:Comprehend the basic geometry of the fire control problem.Apply the basic fire control problem.Know the basic factors of the fire control problem.Comprehend the factors effecting the solution of the fire control problem. Comprehend the basic concepts of relative target motion, bearing rate, and speed across line-of-sight.Comprehend the following exterior ballistic effects upon the trajectory of the weapon: gravity, drag, wind, drift and Coriolis force.Know the basic concepts of the detect-to-engage sequence.

Detect-to-engage sequence:Target is detected by one or more sensors.Additional sensors are used to gain better information on the target.Target information sent to other units through the NTDS or other means.Target is identified.Original unit or other unit completes a threatanalysis.Operational commander evaluates the threat and the ability to counter the threat.Operational commander assigns a launch platform, if necessary, based on threat evaluation.Launch platform completes the fire control solution, assigns a weapon, and attacks the target.

Detection, with RadarDetection is normally achieved by a radar optimized for long range detection of targets. The compromises in radar design in order to achieve detection at long range often results in radar characteristics that require another radar optimized to provide the accuracy required for a Fire Control Solution.Examples of Detection radars (often called Early Warning Radars) are the SPS-49, SPS-48, AN/SPS-145 (E-2C)

The Fire Control ProblemFire control problem can be divided intotwo components:

1. Effects of relative motion during flight

2. Effects of physical phenomena on the weapon or exterior ballistics

Relative Motion and Target Motion Analysis (TMA)Present target positionRelative velocityOwn ship motionTarget motionBearing rateSpeed across line-of-sightFuture target position

Relative MotionThe apparent motion of an object when viewed from a point.10 mph10 mph20 mphABC

Affects of Target Relative Motion on Range and Bearing PresentPosition FuturePosition Ships HeadingPresent RangeFuture RangeRange ChangeBearing ChangePresent Bearing

Solving the Relative Motion Problem Launch Platform SensorsTarget Position Navigation Systems (location)Gyrocompass (course)Electromagnetic Log (speed)Dead reckoning Analyzer Depth indicatorRadar (search and fire control)SonarElectronic warfare equipmentData Systems (NTDS)INPUTTarget CourseTarget SpeedTarget RangeTarget BearingOutput

Exterior BallisticsGravityDragWindDriftCoriolis force

Effects of GravityLine of SightLine of FireGravity tends to accelerateobjects downward. (The longerthe flight time the more the curve)

Effects of DragDrag is loss of energy of a projectile during flight.Energy is lost through: a. Creation of air waves (function of projectile shape) b. Creation of suction and eddy currents (shape) c. Formation of heat (friction)Drag will change the aim point by changing the speed of theprojectile, increasing flight time, increasing curve caused bygravity.

Effects of DriftDrift is caused by the rotation of a projectile (rifling).Drift results in a lateral displacement in flight path.Vertical PlaneDriftHorizontal PlaneLine of Fire

Effects of WindLine of FireHorizontal Effects

Line of FireVertical Effects

Coriolis EffectCaused by the earths rotation. Results in an apparent right curve in the northern hemisphere, left in southern.20 mph10 mph

Fire Control ProblemInputTarget dataOwn ship dataComputationsRelative motion procedureExterior ballistics procedure

Fire Control Problem Cont.SolutionsWeapons time of flightBearing rateLine of Sight(LOS): The course the weapon must follow to intercept the targetSpeed across LOSFuture target positionLaunch anglesLaunch azimuthLaunch elevationWeapon positioning orders

The Iterative Process to the Fire Control SolutionStep 1Step 2Step 3Last StepThe aim point is where the target is at the time of fire. At impact the target will move down its track. a. The bearing error is used to change the bearing of the aim point. b. Note: If only used bearing error, the weapon would always fall short so the range error is also usedThe iterative process continues until the weapon and the targets solution intersect at the flight time of the weapon.

A 3-Dimensional ProblemWhat Information does the computer need to solve this problem? 1. Target position 2. Target data over a period of time to determine target course speed and range.Weapons speed to compute time of flightNOTE: it is actually a lot more complicated.

Solving the Fire Control ProblemContinuously MeasurePresent Target PositionStabilize Measured QuantitiesCompute RelativeTarget Velocity BallisticCalculations Relative Motion CalculationsTime of Flight Future TargetPositionPrediction ProcedureUnstabilized Launch AnglesEnvironmental Inputs Launch Angles (Stabilized)Weapons Positioning orders

Questions?

Go over graphic as a review.

What is missing???? Where do we aim the weapon to get a hit.

This is very important with a weapon that doesnt know where it is and where the target is and continuously corrects, like a gun.

Its even important for very smart weapons to keep from wasting time and fuel by shooting in the wrong direction.

Solving the problem of where to aim is called solving the FIRE CONTROL PROBLEM.The fire control problem begins when the target is assigned and ends when the target is destroyed.Currently this is becoming less and less the case. Technological improvements are allowing development of radars that have fire control characteristics (wave length, beam widths etc) but can put out enough power to act as a detection radar and thus the two radars (Long Range detection and Fire Control) can be combined into one, For example (SPY-1 series)The fire control problem would be easy if we could just point the weapon at the target and shoot and a magical beam of energy instantaneously got to the target and destroyed it. (The future of laser weaponry.)

It will take some period of time to for the weapon to get from the launcher to the target. That time is call flight time. If the weapon is shot directly at the target and there is any movement of the target during the flight time, then the weapon will miss the target (unless the weapons flight path is changed during the flight).

This motion will effect the fire control problem.

The fire control problem consists of determining target position, target motion, and a weapon path that intercepts the target at a particular point.Relative Motion is the apparent motion of another object when viewed from a location that is considered to be standing still.

Relative motion problem does not deal with the weapon, only the firing platform.

Use the diagram to ask students what the relative motion of each car is when view from standing on the curb or if they were in each car.

It doesn't matter if the target is moving or the launch platform is moving or if both are moving, under the relative motion the problem can be reduce down to the launch platform is not moving and the target is. Example: Car A sees the man on the curb closing at 10mph. The man on the curb sees car A closing at 10 mph. Car A would see car B opening at 10mph.

Rather than solve the the fire control problem calculating the motion of both the target, weapon and launch platform we consider the relative motion as if the launch platform is standing still. Our frame of reference is from the launch platform. a. This works out well because thats where the radars, etc. are located which will track the weapon.

So our analysis of the motion will always be from the aspect of relative motion or movement of the target, viewed as if the launch platform was stationary.

Go over diagram to show the geometry of the problem. Show a. Development of Bearing Change b. Development of Range Error

Goal is to determine the targets course and speed so we can predict where the target will be at the time it takes the weapon to reach the target.

We are trying to solve a solution with respect to time: ie. We want to adjust the aim point such that the target and the weapon arrive at the same point at the same time. We then convert the Bearing change to a time reference by calling it a bearing rate. ie. how much the bearing changes with time. We do the same thing with range.

Getting this solution is just a little better than a trial and error process. It is a multiple step process when one solution is tried and the errors fed back to improve the next solution trial. This is called an iteration process.

To summarize what has been presented:

Cover the graphic explaining the inputs that go into determining the targets relative motion.If the flight path of the weapon was straight then we would have the problem solved. Unfortunately life isnt that easy.

1. The environment effects the flight path of the weapon.

Go over list. The slides following also discuss the items in the list.

3. These items have the tendency to make the weapons flight path to curve.

4. This curved path will effect the weapons flight time and the aim point so they must taken into account.

This solves the problem of getting the weapon to the target.

1. Gravity pulls an object down resulting in a curved flight path.

2. The longer the flight time the more the effect of gravity (more curve).

3. This means there is an entirely new flight path needs to be calculated each time the flight time is varied.

Cover the graphic.Drift is caused by the rotation of the projectile. a. Remember the barrel rifling (grooves) that cause the projectile to spin. We did this to set up a gyroscopic motion to keep the projectile aligned so it didnt tumble. b. A draw back to this spin is drift. c. The physics of this effect is called the Magnus Effect but it will not be covered. You can read more in the text (p556). d. Just understand that drift is of concern and will cause the aim point to be shifted.

Similar effect as a curve ball.The wind has an effect on the performance of a projectile which may cause the projectile aim point to be moved.

Traverse (or crosswind) effect: a. Can move the projectile either left or right horizontally. b. Can also effect the vertical flight path of the projectile.

Range Wind effect: a. Either retards or aids projectile speed and thus range. b. Either pushes the projectile faster or slows it down varying the flight time and the resulting aim point.Coriolis Effect is because the earth is rotating.1. A point on the equator is moving faster than a point near the pole (less distance to travel in one rotation).2. If viewed from space watching the earth go by, a point on the equator will move from left to right at one speed and a point near the pole will be moving from left to right at a slower speed.3. Now lets shift to two cars speeding along as shown on the graphic. One car is moving faster faster than the other.4. Looking at the slower car from the reference of the faster car, What is the relative motion? Answer: The slow car would be moving to the left.5. If at the exact time the fast car passes the slow car, you throw a ball straight at the slow car aiming at the same window you through the ball through. Would the ball hit the car? Where would the ball hit? It would hit forward of the car. Dont for get the ball has the same for ward motion as the fast car

6. From the frame of reference of the the fast car you threw the ball straight the slow car was just moving to the left and that is why you missed.7. From the frame of reference of the slow car the ball was aimed at the slow car but curved.8. Now view the same thing from the curved surface of the earth. The iterative process starts with an initial guess of the solution. The aiming point is put into the computer and the position of the target is computed at the time the weapon reaches the aim point. The error is fed back to refine the aim point. For example:

Step 1 a. The aim point is where the target is at the time of fire. At impact the target will move down its track.Step 2 a. The bearing error is used to change the bearing of the aim point. b. Note: If only used bearing error, the weapon would always fall short so the range error is also used

The iterative process continues until the the weapon and the targets solution intersect at the flight time of the weapon.

As a review:What Information does the computer need to solve this problem? 1. Target position 2. Target data over a period of time to determine target course speed and range.3. Weapons speed to compute time of flight1. In the previous examples we were concerned with two dimensions. The actual problem could be 3-dimensional.

2. The problem is essentially the same but have different names. 1. Continuously measure target Position.

2. Stabilize Measured Quantities a. Remove the effects of own ship roll pitch and yaw b. Standardize points of reference (difference between location of sensors and weapons.

3. Compute Relative Velocity of the Target

4. Prediction Procedures a. Does the trial and error flight calculation to weapon and target interception at the flight time of the weapon. b The output is the launch angles as if the launch platform is stabilized. (i.e. not rock, roll, pitch and yaw)

5. Motion of the launch platform is added to the launch angle to give the weapons position order.

6. Sequence is repeated.