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

Chapter 6 / Missile Guidance
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are simply defined by height and speed dependent incidence lag
implementation of which requires a high state update rate.
The simulator is configured so that missile guidance and autopilots can be
stimulated using reference, sensor measurements, or state observer data.
STT and BTT lateral autopilots are provided, with a fast roll autopilot for
the latter. Limits are imposed on lateral acceleration and angular rate
commensurate with motion in a rotating launcher, low speed manoeuvring,
and high speed “g” limiting.
The simulator takes a modular approach to guidance law construction
providing a test-bed for basic PN and CLOS laws augmented by numerous
correction terms. The objective was to separate trajectory optimisation and
be able to switch between PN and biased CLOS to study transitions between
the two. This approach is rapidly becoming outdated since fusion of ground
radar and missile IMU information means pseudo-PN guidance laws can be
formulate throughout flight.
The historical development of PN guidance laws provides a useful insight
into how analytical trajectory optimisation came to influence the subject.
Studying missile trajectories generated by simple cost functions is the ideal
starting point for complex cost functions and trajectory optimisation.
Three areas of special interest are considered. The first is PN, and the
requirement on the missile state observer to stabilise the seeker preventing
missile body motion from cross coupling into the missile sight-line rate.
This can severely reduce the acquisition range as the motion of the detector
during the stare time smears the IR energy returns. The cross-coupling
equations are provided so that the source and characteristics of the parasitic
errors can be clearly identified.
The other two areas concern CLOS. Weave frequency estimation accuracy
for acceptable performance against weaving targets is presented as a
function of the target tracking bandwidth. Finally, CLOS guidance demand
corrections are provided when the target is travelling at constant velocity.
Clearly target manoeuvre detection is required which may be provided by
the IMM filter probabilities up-linked to the missile.
The is little in the way of further work generated by this chapter which in
essence supports the main research topics of state observation and trajectory
optimisation. The verification of the constant velocity correction, and its
interaction with the IMM filter probabilities, is of some academic interest
however, such laws are gradually being overtaken by pseudo-PN command
generation.
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