Space Systems Engineering

Transcription

1 Lecture #02 September 5, 2011 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 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 2

3 NASA Lifecycle Overview 3

4 NASA Formulation Stage Overview 4

5 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 5

6 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 6

7 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) 7

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

9 Implementation Stage Overview 9

10 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 10

11 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 11

12 NASA Project Life Cycle - Milestones from NASA SP rev. 1, NASA Systems Engineering Handbook 12

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

14 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 14

15 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. 15

16 Exo-SPHERES Mission Statements MS-1 To develop, test, and demonstrate a protoflight vehicle capable of internal and external operations on the International Space Station (ISS) MS-2 deleted MS-3 To develop a system concept capable of adaptation to other human and robotic space missions, such as exploration of a near-earth object MS-4 To maximize involvement of students in all aspects of space hardware design, development, testing, and qualification 16

17 Exo-SPHERES Mission Requirements M-1 Exo-SPHERES shall be capable of safe and controlled operations internal and external to ISS (MS-1) M-2 Exo-SPHERES shall be capable of visual inspection of ISS and visiting vehicles (MS-1) M-3 Exo-SPHERES shall incorporate modular interfaces for mission-specific instrument and payload packages (MS-3) M-4 Exo-SPHERES shall egress and ingress through the Kibo scientific airlock (MS-1) M-5 Exo-SPHERES shall be capable of teleoperated and autonomous operations (MS-1) M-6 Exo-SPHERES shall be designed in accordance with all established ISS requirements for visiting vehicles (MS-1) M-7 Exo-SPHERES shall be designed to launch on planned logistics carriers (e.g., Progress, ATV, HTV, Dragon, Cygnus) (MS-1) M-8 Exo-SPHERES shall be capable of autonomous docking, recharge, and deployment from the Kibo support system without repressurization (MS-1) M-9 Exo-SPHERES shall be designed for a nominal sortie duration of 8 hours (MS-1, MS-3) M-10 Exo-SPHERES shall be restricted to materials suited to development in a student environment (MS-4) M-11 Exo-SPHERES test beds shall be developed to validate designs and procedures, and to maximize opportunities for student involvement (MS-1, MS-3, MS-4) 17

18 Exo-SPHERES Systems Requirements 1 S-1 Exo-SPHERES shall be capable of safe controlled flight no less than 1 meter away from ISS structure or systems (except during docking) during external operations (M-1) S-2 Exo-SPHERES shall accommodate the operational restrictions of the Kibo airlock (M-4, M-9) S-3 Exo-SPHERES flight control and associated systems shall be two-fault tolerant (M-1, M-6) S-4 Exo-SPHERES shall be capable of monitoring and controlling position and velocity in all three axes (M-1, M-2, M-6) S-5 Exo-SPHERES shall be three-axis stabilized (M-1, M-2, M-8) S-6 Exo-SPHERES shall be capable of return to Kibo and autonomous redocking to its support fixture (M-4, M-5, M-9) S-7 Exo-SPHERES shall have sufficient computational power to meet teleoperated and autonomous flight requirements (M-5) S-8 Exo-SPHERES propellants shall be non-toxic and compatible with ISS life support systems (M-1, M-11, M-12) S-9 Exo-SPHERES shall be capable of performing a collision avoidance maneuver at any time (M-1, M-6) 18

19 Exo-SPHERES Systems Requirements 2 S-10 Exo-SPHERES shall provide security for command data links (M-1, M-6) S-11 Exo-SPHERES shall nominally be controlled from a dedicated control station located inside ISS, with growth option for control from the ISS Robotic Work Station (M-5) S-12 Exo-SPHERES shall be designed to accommodate on-orbit fault diagnosis, repair, maintenance, and servicing (M-2) S-13 Exo-SPHERES shall provide a standardized interface (structural, quick disconnects, etc) for Advanced Mission Packages (AMPs) (M-3) S-14 Exo-SPHERES shall be capable of reaching a safe state following communications or system failure (M-1, M-2, M-8) S-15 Exo-SPHERES shall meet launch requirements for any likely launch vehicle (M-7) S-16 Exo-SPHERES shall have sufficient power for an 8 hour sortie mission (M-10) S-17 Exo-SPHERES shall be in communication regardless of orientation to send status and science data to ISS (M-1, M-3) 19

20 Structures and Mechanisms Requirements S2-1 Exo-SPHERES and docking system external envelope shall not exceed 576 x 830 x 800 mm (S-2) S2-2 Exo-SPHERES shall withstand all launch loads (S-15) S2-3 STRM shall provide launch restraints to ensure survival (S-15) S2-4 Exo-SPHERES shall exclude any sharp protrusion and accommodate the use of cushioning surface treatments (S-1) S2-5 STRM shall provide an interface between Exo-SPHERES and the Kibo airlock (S-2, S-6) S2-6 STRM shall provide access panels for on station repair, maintenance and servicing (S-12) S2-7 STRM shall provide a structural attachment for AMPs (S-13) S2-8 STRM materials shall meet all outgassing and stress corrosion cracking requirements (M-1, S-15) 20

21 Exo-SPHERES Rqmts Verification Matrix 21

22 Requirements Verification Matrix 2 22

23 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 ) 23

24 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) 24

25 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)! 25

26 Exo-SPHERES RCS Block Diagram 26

27 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. 27

28 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,... 28

29 NASA Standard WBS Levels 1 & 2 29

30 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

31 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 31

32 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

33 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 33

34 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. 34

35 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 35

36 PERT* Charts Task Title Task Duration Slack Time Earliest Starting Date Earliest Completion Date *Program Evaluation and Review Technique 36

37 The Critical Path and Slack Time 37

38 The Critical Path and Slack Time 38

39 Cascading Slack Time 39

40 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

41 Some Pitfalls of Project Management 41

42 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. 42

43 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 43

44 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 44

45 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 45

46 ESAS Final Architecture/CONOPS 46

47 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 47

48 Program Cost Accounting Traditionally monitored by burn rate - cumulative expenditures with time 25 Costs ($M) Cumulative Months 48

49 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 49

50 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 50

51 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 51

52 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 52

53 Program Cost Accounting - Tracking Earned value tracks accomplishments against their planned costs Variation shows schedule performance Costs ($M) Cumulative Earned Value Months 53

54 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 54

55 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! 55

56 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 56

57 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 57

58 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 58

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

60 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

61 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

62 Evaluation of Hierarchy Among Options Average across the populated row elements C S P V C S P V Top ranking 62

63 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 Lecture 07 63

64 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 ) 64

65 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 65

66 Risk Matrix 66

67 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] 67

68 Akin s Laws of Spacecraft Design - #38 Capabilities drive requirements, regardless of what the systems engineering textbooks say. 68

69 Don t Forget... Log onto elms.umd.edu and go to the ENAE D site TODAY Take the test to list your preferences and relevant experience If you don t do this by the end of the day, you will be assigned to any random project and group needing people - and subsequent complaints will fall on deaf ears! 69