Space Systems Engineering

Transcription

1 Lecture #02 September 5, 2013 Background of Systems Engineering NASA program planning phases Scheduled milestones Requirements document Work breakdown structure Technology readiness levels Project management tools Design reference missions and CONOPS Earned value management Risk tracking David L. Akin - All rights reserved

2 Announcements No lectures next week Lectures will be podcast on web Use class time to meet with your group and work on Systems project assignment When posting in Piazza, don t use anonymous mode unless it is appropriate! Check the course web site(s) regularly (at least daily) for news and announcements 2

3 Overview of Systems Engineering Developed to handle large, complex systems Geographically disparate Cutting-edge technologies Significant time/cost constraints Failure-critical First wide-spread applications in aerospace programs of the 1950 s (e.g., ICBMs) Rigorous, systematic approach to organization and record-keeping 3

4 NASA Lifecycle Overview 4

5 NASA Formulation Stage Overview 5

6 Space Systems Development Process Pre-Phase A Conceptual Design Phase Development of performance goals and requirements Establishment of Science Working Group (science missions) Trade studies of mission concepts Feasibility and preliminary cost analyses Request for Phase A proposals 6

7 Space Systems Development Process Pre-Phase A Phase A Preliminary Analysis Phase Proof of concept analyses Mission operations concepts Build vs. buy decisions Payload definition Selection of experimenters Detailed trajectory analysis Target program schedule RFP for Phase B studies 7

8 Space Systems Development Process Pre-Phase A Phase A Phase B Definition Phase Define baseline technical solutions Create requirements document Significant reviews: Systems Requirements Review Systems Design Review Non-Advocate Review Request for Phase C/D proposals Ends with Preliminary Design Review (PDR) 8

9 Historical Implications of Study Phases from J. A. Moody, ed., Metrics and Case Studies for Evaluating Engineering Designs Prentice-Hall,

10 Implementation Stage Overview 10

11 Space Systems Development Process Pre-Phase A Phase A Phase B Phase C/D Development Phase Detailed design process Cutting metal Test and analysis Significant reviews: Critical Design Review (CDR) Test Acceptance Review Flight Readiness Review Ends at launch of vehicle 11

12 Space Systems Development Process Pre-Phase A Phase A Phase B Operations and End-of-Life Launch On-orbit Check-out Mission Operations Maintenance and Troubleshooting Failure monitoring End-of-life disposal Phase C/D Phase E/F 12

13 NASA Project Life Cycle - Milestones from NASA SP rev. 1, NASA Systems Engineering Handbook 13

14 NASA Project Life Cycle - Acronyms from NASA SP rev. 1, NASA Systems Engineering Handbook 14

15 Requirements Document The bible of the design and development process Lists (clearly, unambiguously, numerically) what is required to successfully complete the program Requirements flow-down results in successively finer levels of detail May be subject to change as state of knowledge grows Critical tool for maintaining program budgets 15

16 Akin s Laws of Spacecraft Design - #13 Design is based on requirements. There's no justification for designing something one bit "better" than the requirements dictate. 16

17 DYMAFLEX Stowed Configura7on Deployed Configura7on

18 Mission Overview Mission Statement Investigate the coupled dynamics and associated control mitigation strategies for a free-flying vehicle with a high-performance manipulator performing tasks analogous to satellite servicing Mission Objectives Develop a microsatellite in the university environment through a program which maximizes opportunities for students to be involved in all aspects of the development process. Leverage three decades of advanced space robotics research in the development and flight demonstration of a space manipulator system Investigate the coupled dynamics and associated control mitigation strategies for a free-flying vehicle with a high-performance manipulator performing tasks analogous to satellite servicing Technology Demonstrations Lightweight, high-performance manipulator Space manipulator adaptive control

19 Mission Requirements M-1 DYMAFLEX shall include a robotic manipulator M-2 DYMAFLEX shall be able to move the manipulator sufficiently fast as to cause larger dynamic coupling between manipulator and host vehicle than currently experienced on flown systems M-3 DYMAFLEX shall be able to downlink telemetry of experiments to validate success of algorithms on the ground M-4 DYMAFLEX shall operate in an environment where system dynamics dominates perturbations due to environmental effects M-5 DYMAFLEX shall be able to introduce unknown values to control system by changing the mass configuration of its end effector M-6 DYMAFLEX shall be able to return to a stable attitude after or during dynamic motions of the manipulator M-7 DYMAFLEX shall simulate a variety of payload motions to cover desirable sets of future trajectories M-8 DYMAFLEX shall maximize useful life on orbit by accepting new experiments from the ground

20 System Requirements S-1 DYMAFLEX shall be able to perform a minimum set of trajectories: a single DOF, multi-axis linear and extended nonlinear S-2 DYMAFLEX shall meet launch program's requirements (see UNP7 Users Guide) S-3 DYMAFLEX shall be able to know its position, orientation, manipulator configuration, and lock state of tip masses S-4 DYMAFLEX shall have sufficient communications capability to downlink a minimum of TBD Mb of experiment data within life of spacecraft S-5 DYMAFLEX shall generate sufficient power (# watts TBD) to execute the minimum set of experiments and communicate results to ground S-6 DYMAFLEX shall have multiple interchangeable tip masses for the manipulator S-7 DYMAFLEX shall have sufficient computational power to perform realtime kinematic and manipulator control calculations S-8 DYMAFLEX shall be able to put itself into a safe mode in the event of a critical anomaly

21 ROBO Requirements S1-1 ROBO shall have a 4 DOF manipulator S1-2 ROBO shall be able to change tip masses S1-3 ROBO shall be capable of minimum end effector velocity of TBD m/s S1-4 ROBO shall sense joint position, velocity, and torque S1-5 ROBO shall sense motor controller temperature and current draw S1-6 ROBO shall not extend below the Satellite interface plane (during or after deployment)

22 STRM Requirements S2-1 The STRM shall have a natural frequency of at least 100 Hz with a goal of TBD Hz S2-2 The STRM shall withstand g's in the x,y,z direction S2-3 The STRM shall have a factor of safety of 2.0 for yield and 2.6 for ultimate for all structural elements S2-4 STRM shall have a mass less than TBD grams with a goal of less than TBD grams S2-5 STRM shall interface with lightband at satellite interface plane with 24 #1/4 bolts S2-6 STRM shall not extend below Satellite interface plane (during or after deployments) S2-7 STRM shall provide system with solar panels that will provide sufficient power for experiments S2-8 STRM shall ensure CG for DYMAFLEX is within envelope (less than 0.5cm from lightband centerline, less than 40cm above satellite interface plane) S2-9 STRM shall ensure final dimensions of DYMAFLEX meet requirements (50cm x 50cm x 60 cm tall) S2-10 STRM materials shall meet all outgassing and stress corrosion cracking requirements S2-11 STRM shall provide adequate venting such that the pressure difference is less then 0.5 psi with a factor of safety of 2

23 Requirements Verification Matrix Single spreadsheet tracking all requirements, sources, status, and documentation Broken down to successively finer levels of detail (frequently 4-6 levels) For a major program, the printed version can run to hundreds of pages Ensures that nothing gets overlooked and everything is done for a purpose 23

24 483/484 Level 1 Requirements The habitat system shall be capable of being positioned and used anywhere in cislunar space beyond the Van Allen radiation belts The system shall be compatible with Orion and provide crew support for up to 30 days The system shall provide an airlock or other means of supporting extravehicular activity without depressurization The system design shall incorporate launch, delivery, and stationkeeping 24

25 ENAE 483/484 Level 1 Requirements The system shall be designed to accommodate multiple missions and potential repositionings over the course of the habitat lifetime The system shall support an overall mission loss of crew probability no greater than The system shall maintain crew cumulative radiation dosage within current NASA limits Habitability of the habitat design and crew interfaces shall be assessed using physical mockups in 1g and neutral buoyancy 25

26 ENAE 483/484 Level 1 Requirements The system shall be capable of being launched on a single existing EELV or Falcon Heavy TBD 26

27 RASC-AL Judging Criteria Synergistic application of innovative capabilities and/or new technologies for evolutionary architecture development to enable future missions, reduce cost, or improve safety; Scientific evaluation and rationale of mission operations in support of an exciting and sustainable space exploration program; A mission concept of operations that includes what occurs at the facility before, during, and after crewed visits (over a period of years); Key technologies, including technology readiness levels (TRLs), as well as the systems engineering and architectural trades that guide the recommended approach; Reliability and human safety consideration in trading various architecture options; Realistic assessment of project plan and execution of that plan, including inclusion of a project schedule and test plan, as well as development and realistic annual operating costs (i.e., budget) 27

28 DYMAFLEX Requirements Verification Matrix

29 Interface Control Documents Used to clearly specify interfaces (mechanical, electrical, data, etc.) between mating systems Critical since systems may not be fit-checked until assembled on-orbit! Success of a program may be driven by careful choices of interfaces KISS principle holds here ( keep it simple, stupid ) 29

30 System Block Diagrams Shows interrelationships between systems Can be used to derive communication bandwidth requirements, wiring harnesses, delineation of responsibilities Created at multiple levels (project, spacecraft, individual systems and subsystems) 30

31 Exo-SPHERES S/C Block Diagram Regulator! RCS! Thrusters (x 16)!! Tank!! Valves!! EPS! Charger! Batteries! STRM! Tank!! Kibo Airlock! Interfaces! Access Hatches! Restraints! Cushioning! C&DH! Disk Storage! CPU! Sensors! (TDB)! Wiring Harness! ADCS! Reaction Wheel (TDB)! (x3)! 9 DOF IMU (TDB)! (x 3)! THRM! SFT! OS! Scheduling! ADCS! RCS! COMM! ROBO! Active (TDB)! Passive (TDB)! High Bandwidth! XPNDR! (TBD)! Low Bandwidth! XPNDR! (TBD)! COMM! VIS! Forward Camera (x2)!! Aft Camera! Lights (TDB)! AMP! Payload! Antenna! (TBD)! Antenna! (TBD)! Antenna! (TBD)! Antenna! (TBD)! 31

32 Exo-SPHERES RCS Block Diagram 32

33 Akin s Laws of Spacecraft Design - #15 (Shea's Law) The ability to improve a design occurs primarily at the interfaces. This is also the prime location for screwing it up. 33

34 Work Breakdown Structures Detailed outline of all tasks required to develop and operate the system Successively finer levels of detail Program (e.g., Constellation Program) Project (Lunar Exploration) Mission (Lunar Sortie Exploration) System (Pressurized Rover) Subsystem (Life Support System) Assembly (CO 2 Scrubber System) Subassembly, Component, Part,... 34

35 NASA Standard WBS Levels 1 & 2 35

36 Standard WBS for JPL Mission WBS Levels Project Management 01 Project Mgmnt Project Sys Eng 02 Project Sys Eng Mission Assurance 03 MA Mgmnt Science 04 Science Mgmnt Project Name Payload 05 P/L Mgmnt Flight System 06 Spacecraft Contract Mission Ops System 07 Mission Ops Mgmnt Launch System 08 Launch Services Business Mgmnt Mission & Nav Design System Safety Science Team P/L Sys Eng Flt Sys Mgmnt MOS Sys Eng Risk Mgmnt Project SW Eng Environments Sci Data Support Instrument Flt Sys - Sys Eng Ground Data Sys Project Plng Spt Information Systems Reliability Sci Investigatio & Ops Spt Instrument N Power Subsys Operations Review Support Config Mgmnt EEE Parts Eng Sci Environment Characterization Common P/L Systems Command & Data S/s MOS V&V Facilities Planetary Protection HW Q&A Education & Outreach P/L I&T Telecomm Subsys Foreign Travel/ITAR Launch Sys Eng SW Q&A Mechanical Subsys Project V&V Contamination Control Thermal Subsys SW IV&V Propulsion Subsys GN&C Subsys Spacecraft Flt SW Testbeds Spacecraft assembly test & verification ENAE 483/788D - Principles 06.12of Space Systems Design

37 Detail across JPL WBS Level II 1. Project Management 2. Project Systems Engineering 3. Mission Assurance 4. Science 5. Payload 6. Flight System 7. Mission Operations System 8. Launch System 37

38 Standard WBS for JPL Mission WBS Levels Project Management 01 Project Mgmnt Project Sys Eng 02 Project Sys Eng Mission Assurance 03 MA Mgmnt Science 04 Science Mgmnt Project Name Payload 05 P/L Mgmnt Flight System 06 Spacecraft Contract Mission Ops System 07 Mission Ops Mgmnt Launch System 08 Launch Services Business Mgmnt Mission & Nav Design System Safety Science Team P/L Sys Eng Flt Sys Mgmnt MOS Sys Eng Risk Mgmnt Project SW Eng Environments Sci Data Support Instrument Flt Sys - Sys Eng Ground Data Sys Project Plng Spt Information Systems Reliability Sci Investigatio & Ops Spt Instrument N Power Subsys Operations Review Support Config Mgmnt EEE Parts Eng Sci Environment Characterization Common P/L Systems Command & Data S/s MOS V&V Facilities Planetary Protection HW Q&A Education & Outreach P/L I&T Telecomm Subsys Foreign Travel/ITAR Launch Sys Eng SW Q&A Mechanical Subsys Project V&V Contamination Control Thermal Subsys SW IV&V Propulsion Subsys GN&C Subsys Spacecraft Flt SW Testbeds Spacecraft assembly test & verification ENAE 483/788D - Principles 06.12of Space Systems Design

39 Detail in JPL Flight Systems Column 1. Spacecraft Contract 2. Flight Systems Management 3. Flight Systems - Systems Engineering 4. Power Systems 5. Command and Data Handling Systems 6. Telecommunications Systems 7. Mechanical Systems 8. Thermal Systems 9. Propulsion Systems 10.Guidance, Navigation, and Control Systems 11.Spacecraft Flight Software 12.Testbeds 13.Spacecraft Assembly, Test, and Verification 39

40 Akin s Laws of Spacecraft Design - #24 It's called a "Work Breakdown Structure" because the Work remaining will grow until you have a Breakdown, unless you enforce some Structure on it. 40

41 Technology Readiness Levels TRL 9 TRL 8 TRL 7 TRL 6 TRL 5 TRL 4 TRL 3 TRL 2 TRL 1 Actual system flight proven through successful mission operations Actual system completed and flight qualified through test and demonstration System prototype demonstration in the real environment System/subsystem model or prototype demonstration in a relevant environment Component and/or breadboard validation in relevant environment Component and/or breadboard validation in laboratory environment Analytical and experimental critical function and/or characteristic proof-of-concept Technology concept and/or application formulated Basic principles observed and reported 41

42 PERT* Charts Task Title Task Duration Slack Time Earliest Starting Date Earliest Completion Date *Program Evaluation and Review Technique 42

43 The Critical Path and Slack Time 43

44 The Critical Path and Slack Time 44

45 Cascading Slack Time 45

46 Gantt* Charts ID Task Name Duration Start Finish Predec 1 Design Robot 4w Tue 9/3/02 Mon 9/30/02 2 Build Head 6w Tue 10/1/02 Mon 11/11/ Build Body 4w Tue 10/1/02 Mon 10/28/ Build Legs 3w Tue 10/1/02 Mon 10/21/ Assemble 2w Tue 11/12/02 Mon 11/25/02 2,3,4 September October November 9/1 9/8 9/15 9/22 9/29 10/6 10/13 10/20 10/27 11/3 11/10 11/17 11/24 12/1 *developed by Charles Gantt in

47 Some Pitfalls of Project Management 47

48 Akin s Laws of Spacecraft Design - #23 The schedule you develop will seem like a complete work of fiction up until the time your customer fires you for not meeting it. 48

49 Design Reference Missions Description of canonical mission(s) for use in design processes Could take the form of a narrative, storyboard, pictogram, timeline, or combination thereof Greater degree of detail where needed (e.g., surface operations) Created by eventual users of the system ( stakeholders ) very early in development cycle 49

50 Concept of Operations Description of how the proposed system will accomplish the design reference mission(s) Will appear to be similar to DRM, but is a product of the design, rather than a driving requirement Frequently referred to as CONOPS, showing DOD origins 50

51 Space Systems Architecture Description of physical hardware, processes, and operations to perform DRM Term is used widely (e.g., software architecture, mission architecture, planning architecture ), but refers to basic configuration decisions Generally result of significant trade studies to compare options 51

52 ESAS Final Architecture/CONOPS 52

53 Earned Value Management Consider a simple program with four two-month tasks that are expected to cost various amounts $4 M $10 M $6 M $8 M $2M $7M $8M $7M $4M Planned monthly costs Months 53

54 Program Cost Accounting Traditionally monitored by burn rate - cumulative expenditures with time 25 Costs ($M) Cumulative Months 54

55 Earned Value Management - Month 1 In the first month, you complete 60% of task 1 and 10% of task 2 Actual costs for month 1 = $3 M EV=$3.4 M $4 M EV(1)=0.6*4=$2.4 M $10 M EV(2)=0.1*10=$1 M $6 M $8 M Months 55

56 Earned Value Management - Month 2 In the second month, you complete 100% of task 1 and 60% of task 2 Actual costs for month 2 = $10 M EV=$10 M $4 M EV(1)=1.0*4=$4 M $10 M EV(2)=0.6*10=$6 M $6 M $8 M Months 56

57 Earned Value Management - Month 3 In the third month, you complete 100% of task 1, 80% of task 2, and 40% of task 3 Actual costs for month 3 = $16 M EV=$14.4 M $4 M EV(1)=1.0*4=$4 M $10 M EV(2)=0.8*10=$8 M $6 M EV(3)=0.4*6=$2.4 M $8 M Months 57

58 Program Cost Accounting - Tracking Plotting actual costs vs. time shows how money is spent, but doesn t tell anything about how much work has been accomplished Costs ($M) Cumulative Actual Months 58

59 Program Cost Accounting - Tracking Earned value tracks accomplishments against their planned costs Variation shows schedule performance Costs ($M) Cumulative Earned Value Months 59

60 Program Cost Accounting - Tracking Comparing earned value to actual costs shows apples to apples comparison of money spent and value achieved Costs ($M) Cumulative Earned Value Actual Months 60

61 Decision Analysis Tools A number of different approaches exist, e.g. Pugh Matrices Quality Function Deployment Analytic Hierarchy Process Generally provide a way to make decisions where no single clear analytical metric exists - quantifying opinions Allows use of subjective rankings between criteria to create numerical weightings Not a substitute for rigorous analysis! 61

62 Analytical Hierarchy Process Considering a range of options, e.g., ice cream Vanilla (V) Peach (P) Strawberry (S) Chocolate (C) Could ask for a rank ordering, e.g. (1) vanilla, (2) strawberry, (3) peach, (4) chocolate - but that doesn t give any information on how firm the rankings are Use pairwise comparisons to get numerical evaluation of the degree of preference 62

63 Pairwise Comparisons Ideally, do exhaustive combinations Vanilla >> chocolate (strongly agree) Vanilla >> peach (agree) Vanilla >> strawberry (agree) Peach >> chocolate (strongly agree) Peach >> strawberry (disagree) Strawberry >> chocolate (strongly agree) Number of required pairings out of N options is (N)(N-1)/2 - e.g., N=20 requires 190 pairings! Can use hierarchies of subgroupings to keep it manageable 63

64 Evaluation Metric Create a numerical scaling function, e.g. strongly agree = 9 agree = 3 neither agree nor disagree = 1 disagree = 1/3 strongly disagree = 1/9 Numerical rankings are arbitrary, but often follow geometric progressions 9, 3, 1, 1/3, 1/9 8, 4, 2, 1, 1/2, 1/4, 1/8 64

65 Evaluation Matrix Fill out matrix preferring rows over columns C S P V C S 9 P 9 1/3 V

66 Evaluation Matrix Fill out matrix preferring rows over columns Fill opposite diagonal with reciprocals C S P V C S P V C S 9 P 9 1/3 V C 1/9 1/9 1/9 S 9 3 1/3 P 9 1/3 1/3 V 9 3 3

67 Normalization of Matrix Elements Normalize columns by column sums C S P V C 1/9 1/9 1/9 S 9 3 1/3 P 9 1/3 1/3 V C S P V C S P V

68 Evaluation of Hierarchy Among Options Average across the populated row elements C S P V C S P V Top ranking 68

69 Risk Tracking There are two elements of risk How likely is it to happen? ( Likelihood ) How bad is it if it happens? ( Consequences ) Each issue can be evaluated and tracked on these orthogonal scales This is not an alternative to probabilistic risk analysis (PRA) discussed in a later lecture 69

70 Likelihood Rating Categories 1. Improbable (P<10-6 ) 2. Unlikely to occur (10-3 >P>10-6 ) 3. May occur in time (10-2 >P>10-3 ) 4. Probably will occur in time (10-1 >P>10-2 ) 5. Likely to occur soon (P>10-1 ) 70

71 Consequence Rating Categories 1. Minimal or no impact 2. Additional effort required, no schedule impact, <5% system budget impact 3. Substantial effort required, <1 month schedule slip, >2% program budget impact 4. Major effort required, critical path (>1 month slip), >5% program budget impact 5. No known mitigation approaches, breakthrough required to resume schedule, >10% program budget impact 71

72 Risk Matrix 72

73 References (Available on Web Site) NASA Systems Engineering Handbook - SP June, 1995 [2.3 Mb, 164 pgs.] (Obsolete, but nice description of NASA's systems engineering approach) NASA Systems Engineering Processes and Requirements - NPR A - March 26, 2007 [3.6 Mb, 97 pgs.] (Current version - pages are almost impossible to read without a magnifying glass) NASA Space Flight Program and Project Management Requirements - NPR D - March 6, 2007 [2.7 Mb, 50 pgs.] (Current version - pages are almost impossible to read without a magnifying glass) NASA Program and Project Management Processes and Requirements - NPR C - March 22, 2005 [1.9 Mb, 174 pgs.] (Older, superceded version, but includes more figures and is readable by mere mortals) NASA Goddard Space Flight Center Procedures and Guidelines: Systems Engineering - GPG B [1.7 Mb, 31 pgs.] NASA Goddard Space Flight Center Mission Design Processes (The "Green Book") [860 Kb, 54 pgs.] NASA Systems Engineering Toolbox for Design-Oriented Engineers - NASA RP-1538, December 1994 [9.1 Mb, 306 pgs] 73

74 Akin s Laws of Spacecraft Design - #38 Capabilities drive requirements, regardless of what the systems engineering textbooks say. 74

75 System Project Teams Team A1: Shallcross, Michael Kunnath, Sarin Schaffer, Michael Mittra, Atin Team A2: Zittle, Kyle Weber, Kristy Downes, Alexander Kunnath, Sahin Team A3: Ortiz, Oliver Adamson, Colin Phillips, Brandyn Kumar, Rubbel Team A4: Klein, Douglas Schneider, Mark Kantzer, Michael Adams, Matthew Team A5: King, Jennifer Levine, Edward Ouyang, William Gonter, Kurt Team A6: Ferguson, Kevin Toothaker, Cody Patel, Mihir Raghu, Nitin Team A7: Feeney, Matthew Cloutier, Kyle Gregorich, Donald Todaro, Daniel Team A8: Du Toit, Charl Horowitz, Matthew Muller, Brooks Pashai, Pegah Team A9: Kittur, Chandan Chattopadhyay, Rajarshi Brassard, Brianna Wallace, Mazi Team A10: Moran, Ryan Garcia, Irving Bhattarai, Ashok Garay, Samuel Mellman, Benjamin Team A11(G): Borillo Llorca, Irene Carlsen, Chris Rodriguez, Jon 75

76 SDR Agenda (goals for Systems task) 1. Identify Team Members 2. Review Vision, Mission, Goal and Objectives of Project 3. Review System Architecture (includes system definition, concept and layout) 4. Review Level 1 Requirements 5. Review traceability of requirements flow down 6. Review Work Breakdown Structure (WBS) 7. Review preferred system solution definition including major trades and options. CAD model of physical components of system if available. 8. Review preliminary functional baseline 9. Review draft concept of operations 10. Review preliminary system software functional requirements 11. Review risk assessment and mitigations approach 12. Review analysis tools to be used 13. Review cost and schedule data 14. Review software test plan (approach) 15. U Review N I V E hardware R S I T Y test O F plan (approach) 76

77 Today s Tools You should understand and be able to create and use Project scheduling (PERT and Gantt charts, critical path determination) Requirements definition and flow-down Work breakdown structures Risk definition charts Design reference missions Concept of operations (Earned value management) (Analytical hierarchy process) 77