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Timed Model-based Programming: Executable Specifications for Robust Mission-Critical Sequences

This paper introduces a visual programming paradigm for encoding and executing robust mission-critical spacecraft sequences, addressing issues of complexity and low-level system interactions. It adopts timed, state-based control specifications and models nominal and off-nominal plant behavior. Illustrations and examples are provided.

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Timed Model-based Programming: Executable Specifications for Robust Mission-Critical Sequences

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  1. Timed Model-based Programming: Executable Specifications for Robust Mission-Critical Sequences Michel Ingham, Seung Chung, Paul Elliott, Oliver Martin, Tazeen Mahtab, Greg Sullivan and Brian Williams Model-based Embedded Robotic Systems Group Space Systems Laboratory Massachusetts Institute of Technology

  2. Objectives & Outline • Timed Model-based Execution “in a nutshell” • Timed Model-based Programming: a visual programming paradigm • Illustration of Timed Model-based Execution • Executive implementation: Timed Control Sequencer • Executive implementation: Timed Mode Estimation • Executive implementation: Symbolic Reactive Planner

  3. Motivation • Mission-critical sequences: • Launch & deployment • Planetary fly-by • Orbital insertion • Entry, descent & landing images courtesy of NASA

  4. Problem Statement • Traditional programming can lead to “brittle” sequences: • complexity of control specification • complexity of plant interactions • lack of robustness (management of off-nominal behavior) • Time is central to the execution of mission-critical sequences: • plant spec: component behavior includes latency and evolution • control spec: hard-coded delays in sequence capture state knowledge • Robust executive must consider time in its control and behavior models, in addition to reactively managing complexity Approach: Timed Model-based Programming

  5. Timed Model-based Programming • Approach for graphically encoding and executing robust mission-critical spacecraft sequences. • Addresses issues of sequence complexity and low-level system interactions • Adopts timed, state-based control specifications • Reasons through probabilistic, timed models of nominal and off-nominal plant behavior.

  6. Mars Entry Example engine to standby planetary approach switch toinertial nav rotate to entry-orient& hold attitude separatelander

  7. Mars Entry Example heating 30-60 sec standby off engine to standby planetary approach switch toinertial nav rotate to entry-orient& hold attitude separatelander Descent engine to “standby”:

  8. Mars Entry Example engine to standby planetary approach switch toinertial nav rotate to entry-orient& hold attitude separatelander • Spacecraft approach: • 270 mins delay • relative position wrt Mars not observable • based on ground computations of cruise trajectory

  9. Mars Entry Example Switch navigation mode: Switch navigation mode: “Earth-relative” = Star Tracker + IMU “Inertial” = IMU only engine to standby planetary approach switch toinertial nav rotate to entry-orient& hold attitude separatelander

  10. Mars Entry Example engine to standby planetary approach switch toinertial nav rotate to entry-orient& hold attitude separatelander • Rotate spacecraft: • command ACS to entry orientation

  11. Mars Entry Example engine to standby planetary approach switch toinertial nav rotate to entry-orient& hold attitude separatelander • Rotate spacecraft: • once entry orientation achieved, ACS holds attitude

  12. Mars Entry Example engine to standby planetary approach switch toinertial nav rotate to entry-orient& hold attitude separatelander Separate lander from cruise stage: cruisestage landerstage pyrolatches

  13. Mars Entry Example • Separate lander from cruise stage: • when entry orientation achieved, fire primary pyro latch cruisestage landerstage pyrolatches engine to standby planetary approach switch toinertial nav rotate to entry-orient& hold attitude separatelander

  14. Mars Entry Example • Separate lander from cruise stage: • when entry orientation achieved, fire primary pyro latch cruisestage landerstage engine to standby planetary approach switch toinertial nav rotate to entry-orient& hold attitude separatelander

  15. Mars Entry Example • Separate lander from cruise stage: • in case of failure of primary latch,fire backup pyro latch cruisestage landerstage engine to standby planetary approach switch toinertial nav rotate to entry-orient& hold attitude separatelander

  16. Mars Entry Example • Separate lander from cruise stage: • in case of failure of primary latch,fire backup pyro latch cruisestage landerstage engine to standby planetary approach switch toinertial nav rotate to entry-orient& hold attitude separatelander

  17. Key Features of Executive engine to standby planetary approach switch toinertial nav rotate to entry-orient& hold attitude • simple state-based control specifications • models are writable/inspectable by systems engineers • handle timed plant & control behavior • automated reasoning through low-level plant interactions • fault-aware (in-the-loop recoveries) separatelander

  18. TMBP for Mars Science Lab Technology Demo 2005 MSL Mission (2009) courtesy NASA JPL

  19. Related Work Visual Representations State-based Specifications Harel, ‘87; Kesten & Pnueli, ‘92 Closed-loop Control Timed Control Programs, Timed Plant Models, Semi-Markov Semantics Goal-driven Execution RMPL and Control Sequencer Model-based Programming TMBP Firby, ‘89; Simmons, ‘98; Gat, ‘96 Embedded Programming Constructs Constraint Modeling Williams, Ingham, Chung & Elliott, ‘03 Synchronous Programming Constraint Programming Saraswat, Jagadeesan & Gupta, ‘94 Berry & Gonthier, ‘92 Halbwachs, ‘93 Non-deterministic Timed Transitions Timed Formal Modeling Deductive Estimation & Control Mission Data System Model-based Execution Alur & Dill, ‘94 Henzinger, Manna & Pnueli, ‘92 Kwiatkowska, et al., ‘00 Largouet & Cordier, ‘00 Dvorak, Rasmussen, et al., ‘00 deKleer & Williams, ‘87-‘89 Williams & Nayak, ‘96-’97 Kurien & Nayak, ‘00

  20. Objectives & Outline • Timed Model-based Execution “in a nutshell” • Timed Model-based Programming: a visual programming paradigm • Illustration of Timed Model-based Execution • Executive implementation: Timed Control Sequencer • Executive implementation: Timed Mode Estimation • Executive implementation: Symbolic Reactive Planner

  21. Timed Model-based Program

  22. Timed Model-based Program

  23. Timed HierarchicalConstraint Automata primitive locations composite locations • graphical specification language for control programs • in spirit of Timed StateCharts (Kesten & Pnueli, Harel) • writable, inspectable by systems engineers • compact encoding: multiple locations can be simultaneously marked

  24. Timed HierarchicalConstraint Automata goal constraint (hidden state) clock initialization • graphical specification language for control programs • in spirit of Timed StateCharts (Kesten & Pnueli, Harel) • writable, inspectable by systems engineers • act on hidden state • clocks provide timing mechanism

  25. Timed HierarchicalConstraint Automata transition guard maintenance constraint transition • graphical specification language for control programs • in spirit of Timed StateCharts (Kesten & Pnueli, Harel) • writable, inspectable by systems engineers • conditioned on time & state constraints

  26. Timed HierarchicalConstraint Automata parallel sequential iteration preemption • graphical specification language for control programs • in spirit of Timed StateCharts (Kesten & Pnueli, Harel) • writable, inspectable by systems engineers

  27. Timed Model-based Program

  28. Timed ConcurrentConstraint Automata pt(t) nominal modes t 0.1 0.2 fault modes Pt = 99.9% • variant of factored POSMDP (time continuous, but observations and decisions at discrete points) constraints guarded & timed probabilistic transitions modal rewards

  29. Objectives & Outline • Timed Model-based Execution “in a nutshell” • Timed Model-based Programming: a visual programming paradigm • Illustration of Timed Model-based Execution • Executive implementation: Timed Control Sequencer • Executive implementation: Timed Mode Estimation • Executive implementation: Symbolic Reactive Planner

  30. Timed Model-basedExecutive Architecture

  31. Mars Entry Example engine to standby switch toinertial nav planetary approach rotate to entry-orient& hold attitude separatelander

  32. Mars Entry Example engine to standby switch toinertial nav planetary approach rotate to entry-orient& hold attitude separatelander Control Sequencer executes THCA

  33. Mars Entry Example engine to standby switch toinertial nav planetary approach rotate to entry-orient& hold attitude separatelander pt(t) t 30 60 goal: Standby obs: Deductive Controller provides state estimates and command sequences that achieve goals

  34. Mars Entry Example engine to standby switch toinertial nav planetary approach rotate to entry-orient& hold attitude separatelander

  35. Mars Entry Example engine to standby switch toinertial nav planetary approach rotate to entry-orient& hold attitude separatelander

  36. Mars Entry Example engine to standby switch toinertial nav planetary approach rotate to entry-orient& hold attitude separatelander

  37. Mars Entry Example engine to standby switch toinertial nav planetary approach rotate to entry-orient& hold attitude separatelander

  38. Mars Entry Example engine to standby switch toinertial nav planetary approach rotate to entry-orient& hold attitude separatelander

  39. Mars Entry Example engine to standby switch toinertial nav planetary approach rotate to entry-orient& hold attitude separatelander

  40. Mars Entry Example engine to standby switch toinertial nav planetary approach rotate to entry-orient& hold attitude separatelander

  41. Mars Entry Example engine to standby switch toinertial nav planetary approach rotate to entry-orient& hold attitude separatelander

  42. Mars Entry Example engine to standby switch toinertial nav planetary approach rotate to entry-orient& hold attitude separatelander

  43. Mars Entry Example engine to standby switch toinertial nav planetary approach rotate to entry-orient& hold attitude separatelander

  44. Mars Entry Example engine to standby switch toinertial nav planetary approach rotate to entry-orient& hold attitude separatelander goal: Separated primary pyro misfired! backup pyro fired obs: Model-based executive provides robustness in the goal-driven control loop

  45. Mars Entry Example engine to standby switch toinertial nav planetary approach rotate to entry-orient& hold attitude separatelander

  46. Mars Entry Example engine to standby switch toinertial nav planetary approach rotate to entry-orient& hold attitude separatelander

  47. Mars Entry Example engine to standby switch toinertial nav planetary approach rotate to entry-orient& hold attitude separatelander

  48. Full Demonstration • Proof-of-concept on a representative mission scenario: “Full” Entry, Descent and Landing scenario • Control program (57 locations, 16 state vars, 6 clock vars) • Plant model (~25 components, avg. 3-4 modes per component)

  49. Demonstration: Highlights Key Capabilities • Nominal operations: • execution conditioned on state constraints • execution conditioned on time constraints • nominal mode tracking through commanded and timed transitions • accept configuration goal and generate appropriate command sequence (single-step, multi-step reconfigurations) • Operations in the presence of faults: • fault diagnosis through commanded transitions • fault diagnosis through timed transitions • recovery by repair (deductive controller) • recovery by leveraging physical/functional redundancy (control sequencer)

  50. TMBP for Mars Science Lab Technology Demo 2005 MSL Mission (2009) courtesy NASA JPL

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