Autofilter: automatic code generation for mathematical state estimation

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Autofilter automatic code generation for
mathematical state estimation

• Jon Whittle
• NASA Ames Research Center

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Motivation

• Lack of reuse between missions
• Inadequate documentation
• Inability to respond to unforeseen events
• High cost in cycle from model to implementation

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Code Generation now future
stub code
is it what I want?
simulink model
model specific optimization
domain knowledge
gain pminus mtrans(h) minv(h pminus
mtrans(h) r) xhat1 xhatmin gain (zhat
- zpred)
explicit assumptions
Autofilter model
certified code
synthesize code
multiple programs
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Autofilter
Generic algorithms
Symbolic solvers
Knowledge base
program synthesis
Transformation system

• Enables rapid reuse
• Model to code generation
• Reduces testing
• Can help with flight certification

pseudo code
C/Matlab code
C code
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Autofilter Spec Language
Process noise variables
State variables
Filter architecture
Process model
Sensor specs
variable
Measurement model
- units
- frames
- coordinate systems
Measurement variables
Measurement noise variables
- distributions
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Smart Systems Spacecraft Simulator
Ed Wilson 3/23/01
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Kalman Filter Design I
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Kalman Filter Design II
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Kalman Filter Synthesis
filter architecture
linearized kalman filter (with nominal trajectory)
extended kalman filter (no nominal trajectory)
basic kalman filter
information filter
fundamental solution matrix
linearize over time (continuous ? discrete)
compute estimate
propagate estimate
approximate matrix exponential
linearize over state space
interpolate estimate
Taylor series expansion
linearity check
UD-factorization
Laplace transform
jacobians
numerical integration
differentiate
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DS1 Attitude Estimation
gyros
quaternion
quaternion
startracker
quaternion
Initialization/Parameter Updates

• Estimator Software
• Interface software
• State machine
• Algorithm

Inputs (sensors)
Outputs (Guidance/ Controller)
Mode
Telemetry/ Debug data
Event Reporting/ Fault Monitoring
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Test procedures

• A Set of DS-1 Spacecraft commands were generated
  to maneuver the S/C into RCS mode.
• While in RCS mode some eight different turns were
  performed.
• Modified the downlink telemetry filter to display
  and log the estimated attitude and rate data.
• Attitude and rate data have been gathered from
  the log file and been plotted on Matlab.
• The above procedures were performed on the
  original DS-1 code and the Autofilter generated
  KF code.

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Test Comparison