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

Chapter 5 / Missile State Observer
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The sensors provide raw measurements (plots) that are integrated, usually
asynchronously, by a central state observer. Although this places a large,
and often unacceptable, computational load on the central processor, it is the
only architecture that can achieve fully optimal results. In de-centralised
systems, initially studied by Singer [S.22] , the output from each sensor is
processed to form an optimal track. The local tracks are passed to a central
processor that selects the appropriate data using a voting algorithm, or
performs track fusion as shown in Figure 5-2. Although track fusion is
more robust for multiple target engagements, it being less sensitive to
measurement cross correlation errors than measurement fusion, the results
obtained are sub-optimal.
MISSILE
SEEKER
TARGET IMM
TRACKS
IMM
TARGET FILTER
FUSION
5-4
MISSILE
MEASUREMENT
AND TARGET
TRACK FUSION
MISSILE
IMU
MISSILE
MEASUREMENTS
GROUND
TRACKER
Figure 5-3 : Hybrid Fusion Architecture
The hybrid architecture in Figure 5-3 fuses the external tracks received by
the central processor into an observer that is also updated by local sensor
measurements. This is the architecture of choice for air-defence in which
ground based radar target plots are processed and the resulting track uplinked
to the missile. The ground tracker invariably possesses more
computing capacity than the missile and can accommodate relatively
complex tracking algorithms thereby reducing the load on the central
processor. The down-side is the increased up-link bandwidth required to
deliver the track data compared with simple target plots.
The missile state observer provides optimal data for guidance. This data is
obtained from the observer state that combines gyroscope, accelerometer
and seeker data, with up-linked radar target tracks from the IMM, and
missile position and range rate measurements as shown in Figure 5-4. The
observer is partitioned into target linear, missile linear and missile angular
states. The IMU drives both missile partitions, whilst the seeker data is used
by all of them, thereby providing the sensor measurement redundancy
needed for sensor error estimation. The gyroscope triad plays a pivotal role
and is the one critical sensor for missile stabilisation and seeker acquisition.
The up-linked missile data is used in the missile linear state partition. The
up-linked target track states cannot be treated simply as measurements since
the IMM states are correlated and may destabilise the fusion filter.