Thesis - Leigh Moody.pdf - Bad Request - Cranfield University

Glossary
_ _
9.6 Discussion
9.6.1 PN Study
The studies undertaken so far have proven the simulation infrastructure,
target, tracking and missile simulators. The reference and state observer
parameters listed in §22.3 were verified, as was the launcher, in-tube and
free flight missile dynamics, in particular the low speed thresholds applied
for stability when using the simplified generic model.
A study of PN and CLOS guidance laws provides a performance baseline
against which other guidance laws and trajectory optimisation can be
judged. The laws, stimulated by reference data, were used to stimulate the
guidance laws and a STT autopilot whilst engaging Target 3 (crossing) and
Target 7 (weaving GOT) with an avoidance manoeuvre 2 s from impact.
The IMM filters are tuned in isolation to determine suitable system noise
levels when tracking targets with matching dynamics using range, range-rate
and angle measurements corrupted by Gaussian noise.
The ATPN guidance law from §6 was selected on the basis of this study
trajectory optimisation initialisation. For the crossing target a gain of 3 to
3.5 results in maximum impact speed and minimum effort. The miss
distance dropped sharply as the gain increases from 2 to 3, and only
marginally thereafter as expected. It is known that miss distance and control
effort minimisation against manoeuvring targets requires a gain of 4 to
maximise the no escape region.
PN performance against weaving targets was poor but improved as the gain,
and hence bandwidth, were reduced. The implication being that PN
performance can be improved given target manoeuvre discrimination,
perhaps using the IMM filter probabilities, or the output from the missile
state observer. For example, make the PN gain a function of the IMM
weave filter probability with an upper threshold of 0.5,
λ
m
9-28
0.
5
( 1 − UL 4 )
: = 4 ⋅ µ
0
Equation 9.6-1
This places the onus on the IMM to properly reflect the dynamic mode of
the system. At low speeds, target acceleration compensated PN performs
badly as it tries to establish a collision course against the weaving target.
This form of compensation should be introduced as a function of Mach
number limited to a value of 1.