MDTS 5705 : Guidance Lecture 2 : Line-of-Sight Guidance. Gerard Leng, MDTS, NUS

Transcription

1 MDTS 5705 : Guidance Lecture 2 : Line-of-Sight Guidance

2 2. Line of Sight (LOS) Guidance Definition - In LOS guidance the missile follows the line of sight (LOS) from an external tracker to the target View through the MILAN tracker Target

3 MILAN ATGM Tracker Missile Launcher

4 Three point guidance missile target tracker LOS There are three points of interests 1. the tracker, 2. the missile 3. the target. Hence LOS guidance is also referred to as three point guidance.

5 Type of LOS Guidance Depending on where the guidance commands are generated, LOS guidance can be divided into 2 important variants 1. Beam Rider 2. Command to Line Of Sight (CLOS)

6 Definition - If the missile generates its own guidance commands to follow the LOS then the LOS guidance is referred to as beam rider guidance Deployment The typical set up for a beam rider SAM is as shown Note that two radar beams are used to track the target. 2.2 Beam Rider One for each plane of symmetry in the missile

7 A typical set up for an ATGM using a laser beam as the LOS is shown The laser beam has to be coded to enable the missile to sense its position relative to the LOS. Note that in LOS guidance the missile is blind. It does not see the target.

8 2.3 Command to Line of Sight (CLOS) Definition - If the guidance commands to follow the LOS are generated externally and transmitted to the missile, then the LOS guidance is called Command to Line Of Sight (CLOS) guidance Deployment The deployment of a CLOS ATGM is shown. Note the wire command link

9 Features of CLOS systems Question : What is a typical command link? Note The presence of a command link. means that there is no intelligence on-board the missile. (think R/C models)

10 Types of CLOS guidance Classification of CLOS There are 3 types of CLOS guidance depending on whether the tracking of the target and the missile are automated i) MCLOS or Manual CLOS The operator tracks both target & missile, and generates guidance commands for the missile. Any problems?

11 AT-3 Sagger (9K11 Malyutka) ATGM HEAT warhead can penetrate over 400 mm of armour at 500m to 3000 m AT-3 used by the NVA.

12 AT-3 Sagger Guidance Platform Carrying case doubles as launch platform Wire -guided via control stick & periscope on the case AT-3 Sagger, an example of a MCLOS ATGM

13 ii) SACLOS or Semi Automatic CLOS The operator tracks the target only. Guidance commands are generated automatically The guidance kinematics are similar to a beam rider except that commands are up linked to the missile. Used in 2 nd generation ATGM s and SAM s

14 Computer-generated (SACLOS) guidance commands are relayed via wire link. Rear-mounted coded IR beacons on the missile TOW 2A ATGM IR tracker on the launcher detects deviation from the LOS TOW 2A, an example of a SACLOS AGTM

15 iii) ACLOS or Automatic CLOS No operator tracking of target and missile is required. Sounds great, right?

16 Jernas/Rapier(FSC) SAM Based on the Rapier Mk2 + Blindfire tracking radar and Dagger surveillance radar Automatic command to ( radar) line of sight guidance Jernas/Rapier(FCS), an ACLOS SAM

17 2.4 LOS guidance characteristics 1. How does the missile keeps itself on track? 2. Should we use a wide or narrow tracking beam? 3. Does a narrow tracking beam cause any complications? 4. What are advantages of LOS guidance? 5. What are the disadvantages of LOS guidance?

18 Moral LOS guidance means that missile is blind to the target. No tracking beam no guidance no hit

19 2.5 LOS Guidance Analysis Most missiles have two planes of symmetry. yaw plane (azimuth) This reduces the guidance analysis from 3D to 2D. pitch plane (elevation)

20 Y LOS Guidance Planar Geometry a t V t T target g t LOS V m R t a m g m q t q m R m M missile O tracker X

21 Kinematic equations The dimensional kinematic equations are : missile target dr m /dt = V m cos(g m - q m ) R m dq m /dt = V m sin(g m - q m ) V m dg m /dt = a m dr t /dt = V t cos(g t - q t ) R t dq t /dt = V t sin(g t - q t ) V t dg t /dt = a t

22 We non dimensionalise the equations to reduce the number of parameters. Using the initial range R o and the missile speed V m, we define non dimensional time = t V m / R o non dimensional distance r = R/ R o Hence d( )/dt = d( )/d V m / R o Substitute this in the kinematic equations and clean up the algebra...

23 2.5.3 The non dimensional kinematic equations are : missile dr m /d = cos(g m - q m ) dq m /d = sin(g m - q m ) / r m dg m /d = m target dr t /d = cos(g t - q t ) dq t /d = sin(g t - q t ) / r t dg t /d = t / where the speed ratio = V t / V m ( 0 < < 1 ) and the non dimensional accelerations are defined as m = a m / (V 2 m / R o ) t = a t / ( V 2 m / R o )

24 2.6 LOS guidance law design Question: What should a m be to intercept the target? Hint : What can be measured? LOS D a m V m q t q m R m M O

25 LOS Guidance Law Idea! The acceleration to keep the missile on the LOS is proportional to the measured deviation of the missile from the LOS. a m = K D = K R m sin(q t - q m ) Question : What happens if the angular error is small?

26 2.6.2 Trajectory characteristics There are a few quirks in LOS guidance. Consider this engagement scenario for a speed ratio of 0.8. target LOS missile

27 2.6.3 Appreciating the kinematics 1. Is the missile aligned with the LOS? 2. Is this increasing body to beam angle desirable? 3. Are there any effects on warhead effectiveness? 4. Just how large can this misalignment get?

28 Body to beam angle Question How significant is a misalignment of 18 o?

29 Exercise : Estimating the operational constraints ATGM intercepts target at a range of 3 km tracker LOS target d 18 o 18 o body to beam angle at 3km means a misalignment d of = 3000 x tan(18 o ) = 975 m at the tracker

30 Lateral acceleration Question : What is the dominant feature of the latax behaviour? Question : What does a non dim latatx of 0.4 mean?

31 Exercise : Estimating the latax requirements Consider an ATGM, speed 250 m/s engaging a target at an initial separation of 2 km A non-dim latax of 0.4 means that the actual acceleration required is = 0.4 x /2000 = 12.5 m/s 2 Question : Is this large? How does this compare with the pickup of a car?

32 Question : Can we improve on the performance? Answer : Yes, if we account for the beam motion as well. Idea We have used beam angles, what about using beam angle rate and beam angle acceleration?

33 Anticipating the target motion LOS a m V m Suppose the missile is on the LOS and aligned with it. R m q t M As the LOS rotates with the target, the missile must generate latax to rotate with the LOS O

34 LOS guidance with feedforward latax terms The required latax can be derived as : a m = 2 V m dq t /dt + R m d 2 q t /dt 2 and this serves as an additional command to the guidance system. Note 1. It is a feed forward command because q m is not involved in the generation of dq t /dt and d 2 q t /dt 2 2. There s a price to pay. Can you spot the catch?

35 Feedfoward LOS guidance - latax Comments : Look at the latax Any differences with the earlier LOS guidance law?

36 Feedforward LOS guidance - body to beam angle Question What is the effect of the feedforward terms?