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Chapter 6 / Missile Guidance
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6.6 Missile Guidance - Command to Line-of-Sight
Although CLOS has received relatively little attention in public literature
compared with PN, Roddy [R.10-12] et. al. (1985) published several papers on
the control of Bank-to-Turn (BTT) missiles that provide a useful insight to
CLOS guidance. Their work treats YP control as separate LQR problems
using quadratic PI to minimise differential angle, aileron effort and roll rate
induced cross-coupling. Conceptually, CLOS guidance commands consist
of feed forward, feedback, Command Of LOS (COLOS) and gravitational
acceleration components,
CLOS α D : = αFB
+ ϕ ⊗ α
FF FF + αCOLOS
+ αGA
6-20
Equation 6.6-1
The elemental parts to this expression perform the following functions:
• αFB minimises the angle between the missile LOS and the target LOS
• αFF compensates for target sight line dynamics
• αCOLOS places the missile off the target LOS to aid optical tracking
• αGA compensates for gravity as described in §6.5.2.4
A feed-forward weighting (ϕFF) was introduced by Lee [L.4] to compensate
for the errors introduced using polar dynamics for non-manoeuvring targets.
Combining these elemental parts, excluding the gravitational component
common to both CLOS and PN,
CLOS α D : = CLOSαS
+ αG
Equation 6.6-2
To generate the required acceleration normal to the missile body the
guidance demands are again scaled to take account of the body-to-beam
angle. Applying the results of §6.5.2 when transforming from Target LOS
to the Missile Body axes,
CLOS
B
S
6.6.1 Guidance Loop Definition
α
B
( 5 ) , T ( 6 )
⎡ B
T
⎤
T
T
1 ⎢
⎥
: = ⋅ B ⎢
⎥ ⋅ CLOSα
TT
( 1 ) ⎢ B
B
TT
( 8 ) , TT
( 9 ) ⎥
⎣
⎦
T
S
Equation 6.6-3
In the idealised 2D CLOS guidance scheme shown in Figure 6-3 the target
and missile dynamics are assumed to be identical at impact. The missile
angular acceleration is doubly integrated and passed through a weave tuned
α−β−γ filter F1(s) described in §21.4 providing smoothed target angular