Page 1 Livingstone: Livingstone: System Architecture Model-based - - PowerPoint PPT Presentation

Page 1

Chart: 1

Autonomous Sequencing and Model-based Fault Protection for Space Interferometry

i-SAIRAS June 21, 2001

Michel Ingham, Brian Williams

MIT Space Systems Lab MIT Artificial Intelligence Lab Cambridge, MA

Thomas Lockhart, Amalaye Oyake, Micah Clark, Abdullah Aljabri

Caltech Jet Propulsion Lab Pasadena, CA

Chart: 2

Outline

• Technical Goal & Motivation
• Basics of Optical Interferometry
• Background on Remote Agent
• System Architecture
• Livingstone: Model-based MIR
• Executive: Autonomous Sequencing
• Lessons Learned
• Future Work

Chart: 3

Technical Goal

Demonstrate autonomous control of an interferometer instrument by implementing a model-based fault protection system (Livingstone) and autonomous sequencing (Exec) on a ground-based interferometer testbed, in the context of a representative observation scenario.

Chart: 4

Motivation

• Model-based autonomy has

significant potential for NASA missions

• Learn to represent system

engineering knowledge of a complex instrument:

– numerous components – significant component interaction – multiple failure modes – multi-step recoveries

• Successful ground test-bed

demonstration: 1st step toward broader acceptance TPF SIM

Chart: 5

Optical Interferometry

Baseline Internal Metrology Laser Source Fiducial Fiducial Siderostat Siderostat External Delay

Stellar Wavefront

Delay Line

α

Fringe Detector Beam Combiner

Acquire starlight (L & R)

• slew Siderostat to estimated

target angle

• with Siderostat tracking,

perform Star Tracker search

• Star Tracker locks onto target

star

Acquire fringe

• calibrate PZT Dither
• homeset Delay Line, zero

Laser Counter, lock Internal Metrology

• slew Delay Line to estimated

delay position

• with Delay Line tracking,

perform fringe search

• Fringe Tracker locks onto

fringe

Perform science measurement

Chart: 6

Remote Agent

integrated with interferometry RTC s/w

• sophisticated monitoring and control s/w
• AI technology used to encode operational rules and system constraints

within flight s/w

• ground operators rely on RA to monitor s/c and achieve mission goals
• flight validated on DS-1 in May ‘99
• 3 primary modules:

– Planner/Scheduler – Smart Executive – Livingstone model-based MIR

Model- based MIR Mission Manager Scripted Executive Planner/ Scheduler

Page 2

Chart: 7

EXEC Livingstone

Recoveries Commands

RTC Telemetry Server

REMOTE AGENT

CLASH MESSAGES CORBA MESSAGES

Telemetry Data Telemetry Data ACE-TAO ORB ACE-TAO ORB ALLEGRO ORBLINK CLASH IPC

Monitors

Recovery Requests State updates Commands Pseudo- Commands Monitor Values

System Architecture

Chart: 8

Livingstone: Model-based MIR

Controller Plant

mode identification mode reconfiguration

s’(t) µ(t)

f f

s (t)

g g

• (t)

Model Goals

• Livingstone provides the following capabilities:

Monitoring of predicted vs. observed state (consistency checking) Mode identification in case of discrepancy Reconfiguration suggestions

• Performs significant deduction in the sense/response loop

Chart: 9

Livingstone: Model-based MIR

• Use common-sense behavioral models of spacecraft components &

subsystems

• Transition system formulation, based on qualitative representations
• ver finite domains:

counter-delta = { hold, track, slew, out }

• Represent dynamics with probabilistic automata
• Models compile to propositional logic:

mode = locked ⇒ (not (counter-delta = out)) mode = reset ⇒ (not (counter-delta = out)) (mode = unlocked) Λ (cmd-in = homeset) ⇒ (next (mode = reset) Internal Metrology Internal Metrology Component Model Component Model

Locked Locked Reset Reset Unlocked Unlocked

homeset homeset-

• cmd

cmd reached reached-

• homeset

homeset-

• cmd

cmd homeset homeset-

• cmd

cmd Mode constraint: (not (counter_delta = out)) No mode constraints Mode constraint: (not (counter_delta = out)) “ “likely likely” ” “ “likely likely” ” Chart: 10

Interferometer Model

Chart: 11

Delay Line

• Inputs: limit switch signals, home-sensor signal,

counter-delta, DL-command

• Outputs: servo-mode

Not all possible transitions shown

Chart: 12

Limit Switch Sensors

• Inputs: none
• Outputs: signal-out, health-state
• Pair-Switches module consists of two sensors: one

soft limit switch, one hard limit switch

• STB-3 soft limit switches are disabled

Page 3

Chart: 13

Executive: Autonomous Sequencing

• robust, event-driven, goal-oriented, multi-threaded sequencing engine
• written in rich procedural language (ESL):

contingency handling

Signaling failures, specifying recovery procedures

timekeeping

Integrating with external timekeeping sources (e.g.timeout specification)

goal achievement

Decoupling achievement conditions and achievement methods

task management

Multi-threading, synchronizing concurrent tasks

logical database

Monitoring state variables of system

property locks

Coordinating concurrent tasks, controlling inter-task conflicts

Chart: 14

Executive: Autonomous Sequencing

• Exec constructs:

general component-specific

• Define “composite” (subsystem-level) constructs by layering and

combining component-specific constructs, e.g.:

achievement & maintenance of fringe tracking

• 2. establish internal metrology lock
• 3. establish delay line tracking
• 4. close fringe tracker servo loop
• 1. activate & calibrate path dither

Chart: 15

Demonstrated Scenario

• Interactive commanding

– (send-command :DL :back) – (send-command :DL :homeset)

• Nominal fringe acquisition scenario:

– send Delay Line to front of track – calibrate PZT Dither – homeset Delay Line (zeroes Laser Counter & locks IM) – slew Delay Line to estimated delay position – with Delay Line tracking, perform fringe search – Fringe Tracker locks onto fringe

• State achievement and maintenance (IM lock, DL tracking)
• Break IM lock, see autonomous recovery

Chart: 16

Lessons Learned

• Interface complexity

– Livingstone/EXEC/RTC – importance of clear i/f specifications

• Scoping of models

– primitive components vs. subsystems – “abstract” components

• Flexibility of IDL

– fixed RTC commands, telemetry – feedback from RA model development

• System observability

– inaccessibility of some desired telemetry

• Multi-step recoveries

– Livingstone implementation limited to 1-step reconfigurations

• Commanded nominal transitions

– nominal transitions conditioned on explicit commands – workaround via pseudo-commands

Chart: 17

Future Work

• Continue MIR modeling and Exec sequence development
• Deployment to other testbeds
• Replace CLASH layer with a CORBA interface
• Integrate Burton multi-step reactive planner
• Integrate C++ MIR system
• Replace Exec:

Model-based executive (MIT)

IDEA integrated planning/execution (Ames)

Chart: 18

Backup slides

Page 4

Chart: 19

SSI Sequence

• 2. Acquire

right starlight

• 5. Acquire

left starlight

• 6. Measure delay

& delay rate

• 7. Cool formation
• 4. Acquire

linear metrology

• 3. Acquire

angular metrology R θ

Representative acquisition sequence

1. Move Spacecraft… 8. Find/track/measure fringe

StarLight

Chart: 20

Interferometer Sequence

• Initial state:

– L & R STs, L & R Sids, DL, FT idling – LC not zeroed

• Acquire starlight (L & R)

– Slew Sid to estimated target angle (OL) – w/ Sid tracking, perform ST search – ST locks onto target star

• Acquire fringe

– Calibrate PZT Dither – Homeset DL, zero LC, lock metrology – Slew DL to estimated delay pos’n (OL) – w/ DL tracking, perform fringe search – FT locks onto fringe

• Perform science measurement

Combiner Spacecraft Relay Spacecraft

up to 125 m up to 600 m Lay & Dubovitsky – May 2000 Chart: 21

Livingstone Algorithm

Truth Maintenance System

New Conflicts Observations Checked Solution

Conflict Database

Candidates

Best-first Agenda

Most Likely Candidate All Conflicts Diagnosis Theory (Including Predicted State)

Conflict- directed A* Search

Chart: 22

Path Dither

• Inputs: PD-command, DL-command
• Outputs: health-state
• Model requires dither must be “on” before calibrating

Chart: 23

Fringe Tracker

• Inputs: FT-command
• Outputs: FT servo-state

Not all possible transitions shown

Chart: 24

SSI-specific Models

Angular-metrology Siderostat

Not all possible transitions shown

Page 5

Chart: 25

Exec Details

Initialize State Database Define Device Types Define Command Timeout Values Define Raw CORBA Command Define State Observation Predicates Define Command Constructs for all Components Define “to-achieve” Functions Define Recovery Procedures Define MIR/Exec CLASH-CORBA Command Top Level Entry Points General Constructs Component Specific Constructs Chart: 26

Recovery Procedures

EXEC Livingstone

• 3. Recovery

Suggestions

• 4. Dispatch Recovery

Commands to RTC

• 2. Recovery

Request

• 1. State

Updates

• 4. Execute

Commands

• Livingstone implementation limited to single-step recovery suggestions
• Multi-step recoveries had to be procedurally coded within Exec, e.g.:

(defun RESET_DL (dl) ;;This is a recovery suggested by MIR to get metrology re-locked (achieve (:op_state :IM :locked)) (format t "Delay line recovery done (~s).” dl))