MDTS 5734 : Guidance Lecture 3 : Homing Guidance. Gerard Leng, MDTS, NUS

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1 MDTS 5734 : Guidance Lecture 3 : Homing Guidance

2 3. Homing Guidance Definition -In homing guidance the missile steers itself towards a target using an onboard seeker which is able to detect some distinguishing characteristics of the target. Millimetre wave seeker Gimballed imaging seeker

3 Spike AGM

4 Maverick AGM

5 Types of homing guidance Homing guidance can be divided into 3 main variants depending on how the distinguishing feature is generated. i) Active homing ii) Semi-Active homing iii) Passive homing

6 Active Homing Definition : In active homing guidance the source for illuminating the target, and the receiver for detecting the reflected energy are carried onboard the missile Comments? autonomous guidance but relatively heavy & expensive missile

7 Harpoon AGM, example of a active homing missile Harpoon AGM Sea-skimming mid-course guidance with radar altimeter Active seeker radar for terminal homing Price tag SGD$ 1 M/unit

8 Semi-Active Homing Definition In semi-active homing guidance the missile seeker uses reflected energy from the target which is illuminated by an external source

9 Bloodhound SAM 1st generation SAM used by the RSAF Semi-active homing guidance using the ground control continuous wave radar

10 AMRAAM AIM-120 A combination of active and semi-active homing Medium range (50 km) Mach 4 Datalink with aircraft

11 Passive Homing Definition : In passive homing guidance the missile seeker uses energy radiated by the target itself as the guidance signal Thermal signature of an APC

12 Mistral SAM Passive infrared homing guidance Indium arsenide seeker detector array 3 to 5 micron waveband Mistral deployed by the RSAF Low-drag transparent hexagonal pyramid shaped nose cone housing

Sidewinder AAM AIM9L/M passive IR homing guidance seeker uses an indiumantimonide (InSb) detector element, cooled by an open cycle Joule-Thompson cryostat

13 Sidewinder AAM AIM9L/M passive IR homing guidance seeker uses an indiumantimonide (InSb) detector element, cooled by an open cycle Joule-Thompson cryostat Sidewinder - A simple & successful AAM design price tag about SGD$ 150K / unit Magnesium fluoride (MgF 2 ) seeker window Seeker scans both IR and UV wavelengths

14 3.2 Homing guidance analysis In homing guidance, as the seeker is onboard the missile, there are only two points of interest : the missile & the target. Hence homing guidance is also called two point guidance. For missile with two planes of symmetry,. we need only consider the motion for one plane.

15 Geometry of homing guidance Y target a m a t T R q LOS g g t V m m V t M missile O X

16 Kinematic equations The dimensional kinematic equations are : missile target dx m /dt = V m cosg m dy m /dt = V m sing m V m dg m /dt = a m dx t /dt = V t cosg t dy t /dt = V t sing t V t dg t /dt = a t

17 LOS angle & distance to go Define the LOS angle and distance to go as : LOS angle q = tan -1 ( (Y t - Y m )/ (X t - X m ) ) Distance to go R 2 = (X t - X m ) 2 + (Y t - Y m ) 2

18 LOS rate & closing velocity Differentiating the previous expressions with respect to time yields : LOS rate dq/dt = ( V t sin(g t - q) - V m sin(g m - q) ) / R Closing velocity V c = - dr/dt = - V t cos(g t - q) + V m cos(g m - q)

19 Concept of an intercept triangle What must be satisfied for an interception course? t f Vm t f V t g t - q target g m - q LOS missile t f : time to intercept

20 Condition for an interception course Using the sine rule t f V m = t f V t t f Vm t f V t g t - q sin( - (g t - q) ) sin(g m - q ) g m - q This simplifies to ( V t /V m ) sin(g t - q) - sin(g m - q ) = 0 looks familiar? or dq/dt = 0

21 3.3 Proportional navigation In proportional navigation (PN) homing guidance, the latax command is generated as follows : a m = K x V c x dq/dt guidance gain closing velocity LOS rate Question : Does this make sense?

22 Non dimensional kinematic equations guidance dr/d = cos(g t - q ) - cos(g m - q) r dq/d = sin( g t - q) - sin(g m - q) m = K (-dr/d ) (dq/d ) missile target dx m /d = cosg m dy m /d = sing m dg m /d = m dx t /d = cosg t dy t /d = sing t dg t /d = t /

23 Characteristics of PN guidance Engagement scenario Speed ratio = 0.3 PN gain = 3 Non maneuvering target

24 PN latax behaviour Question Any problems with this latax behaviour?

25 PN seeker to missile angle Question : How does the seeker to missile angle vary? Can you spot a possible problem?

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

MDTS 5705 : Guidance Lecture 2 : Line-of-Sight Guidance 2. Line of Sight (LOS) Guidance 2.1.1. Definition - In LOS guidance the missile follows the line of sight (LOS) from an external tracker to the target