NASA TECHNICAL NOTE NASA TN D-7990 0 o* z c 4 m 4 z CASE FILE COPY APOLLO EXPERIENCE REPORT - GUIDANCE AND CONTROL SYSTEMS: LUNAR MODULE ABORT GUIDANCE SYSTEM Put Me Kzlrten Lyndon B. Johnson Space Center Houston, Texas 77058 NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON, D. C. JULY 1975 1. Report No. I 2. Government Accession No. I 3. Recipient's Cataloq No. NASA TN D-7990 4. Title and Subtitle 5. Report Date APOLLO EXPERIENCE REPORT July 1975 GUIDANCE AND CONTROL SYSTEMS: 6. Performing Organization Code LUNAR MODULE ABORT GUIDANCE SYSTEM JSC- 08589 7. Author(s) 8. Performing Organization Report No. Pat M. Kurten JSC S-424 10. Work Unit No. 9. Performing Organization Name and Address 9 76- 10-4 1-0 1- 72 Lyndon B. Johnson Space Center 11. Contract or Grant No. Houston, Texas 77058 13. Type of Report and Period Covered 2. Sponsoring Agency Name and Address Technical Note National Aeronautics and Space Administration 14. Sponsoring Agency Code Washington, D. C. 20546 1 5. Supplementary Notes The history of a unique development program that produced an operational fixed guidance system of inertial quality is presented in this report. Each phase of development, beginning with requirement definition and concluding with qualification and testing, is addressed, and develop- mental problems are emphasized. Software generation and mission operations are described, and specifications for the inertial reference unit are included, as are flight performance results. Significant program observations are noted. 7. Key Words (Suggerted by Author(s)) 18. Distribution Statement - Display Devices .Monte Carlo Method STAR Subject Category: - Hardware - Software (Computers) 12 (Astronautics, General) Mission Trajectory t Lunar Landing - Short Circuit Accelerometers ^. u; n..__ 19. Security Classif. (of this report) ZU. Security Ciassii. ioi this pagei 41. 22. Price' Unclassified Unclassified 73 $4.25 CONTENTS Section Page SUMMARY ..................................... 1 INTRODUCTION .................................. 1 ACRONYMS .................................... 2 DISCUSSION .................................... 4 Preliminary LM Abort Concepts ........................ 4 Program Redefinition .............................. 6 System De scr iption ............................... 7 Test Program .................................. 14 Software Development ............................. 19 Abort Guidance System Mission Revisions ................... 25 Mission Operation ............................... 26 Abort Sensor Assembly Development Problems ................ 28 Abort Electronics Assembly Development Problems ............. 35 Data Entry and Display Assembly Development Problems .......... 40 Abort Guidance System Software Development Problems ........... 42 Capability Estimate ............................... 45 Flight Performance and Anomalies ...................... 50 PROGRAM OBSERVATIONS ........................... 58 Schedule ..................................... 58 Thermal-Vacuum Acceptance ......................... 59 Compatibility Testing .............................. 59 Dual Source Procurement ........................... 59 A sst: iilbiy Eeiia’uiXy .............................. 55 iii . Section Page Transient Protection .............................. 59 Software Development ............................. 60 Memory Functions ............................... 60 Scale .Factor Asymmetry ............................ 60 Electroluminescent Display .......................... 60 Pushbuttons ................................... 60 Pushbutton Switches .............................. 60 Environmental Testing ............................. 61 Ground-Support -Equipment Heaters ...................... 61 Abort Sensor Assembly Mission Acceptance .................. 61 Abort Sensor Assembly ............................. 61 Gyro Fluid ................................... 61 Gyro Resonant Frequency ........................... 62 Engineering Mode 1 ............................... 62 Assembly Cabling ................................ 62 Vibration Transmissibility ........................... 62 Split-Pin Wire Wrapping ............................ 62 Program Incentives ............................... 62 Capability Retention .............................. 62 Subcontractor Test Participation ........................ 63 Program Control ................................ 63 Earth-Orbit Software Programs ........................ 63 Test Programs ................................. 63 Mission Performance Analysis ......................... 63 Gyro Rundown Time ............................... 64 iv Section Page Program Evaluation Reporting Technique ................... 64 Inertial Package Alinement ........................... 64 Backup Guidance Definition ........................... 64 Nailhead Bond Capacitors ............................ 64 Flight Connector Integrity ............................ 65 Work Packages ................................. 65 Elapsed-Time Indicators and "G" Balls .................... 65 Checkout Meetings ............................... 65 Computer Startup Sequence ........................... 65 Operator Error Lights ............................. 66 CONCLUDINGREMARKS .............................. 66 V TABLES Table Page I ABORT SENSOR ASSEMBLY SPECIFICATION VALUES ......... 10 I1 ABORT SENSOR ASSEMBLY TIME-STABILITY LIMITS * * * 11 III ABORT SENSOR ASSEMBLY REPEATABILITY LIMITS ......... 12 IV EARTH PRELAUNCH CALIBRATION TIME-STABILITY LIMITS .... 13 V DESIGN VERIFICATION TESTING ENVIRONMENTS FORTHEAGS.. ............................ 15 VI ACCEPTANCE TESTS PERFORMED ON THE AGS ........... 18 VI1 ABORT GUIDANCE SYSTEM ERROR MODEL I CAPABILITY ESTIMATE ........................ 46 VIII ABORT GUIDANCE SYSTEM ERROR MODEL I1 CAPABILITY ESTIMATE ........................ 47 M ABORT GUIDANCE SYSTEM ERROR MODEL III CAPABILITY ESTIMATE ........................ 48 X ABORT GUIDANCE SYSTEM ERROR MODEL IV CAPABILITY ESTIMATE ........................ 49 XI FINAL PIC, FINAL EPC, AND IFC DATA OF THE AGS ........ 50 XI1 IN-FLIGHT DETERMINATION OF GYRO AND ACCELEROMETER BIAS IN FREE FLIGHT ......................... 51 XI11 ALINEMENT ACCURACIES OF THE PGNCS DURING THE APOLLO 9 MISSION. .......................... 51 XIV A COMPARISON OF THE VG MAGNITUDES FOR ALL BURNS .... 52 XV A COMPARISON OF THE RENDEZVOUS MANEUVER VELOCITIES AS COMPUTED BY THE AGS AND THE GROUND ........... 52 XVI ALINEMENT ACCURACIES OF THE PGNCS DURING THE APOLLO 10 MISSION .......................... 53 XVII GYRO AND ACCELEROMETER CALIBRATIONS ............ 54 XVIII A COMPARISON OF AGS AND PGNCS BURN RESIDUALS ........ 54 I vi Table Page XIX ALINEMENT ACCURACIES OF THE PGNCS DURING THE APOLLO 11 MISSION .......................... 55 XX GYRO-DRIFT PERFORMANCE DATA .................. 56 XXI ACCELEROMETER BIAS IN FREE FLIGHT ............... 57 XXII A COMPARISON OF BURN RESIDUALS ................. 58 FIGURES Figure Page 1 Abort guidance system components (a) Data entry and display assembly .................. 7 (b) Abort sensor assembly ....................... 7 (c) Abort electronics assembly ..................... 7 2 Abort sensor assembly asymmetry requirements ........... 11 3 Coelliptic rendezvous flight profile ................... 26 4 Gyro bias history ............................ 56 5 Accelerometer bias history ....................... 57 vii APOLLO EXPERIENCE REPORT GU I DANCE AND CONTROL SYSTEMS: LUNAR MODULE ABORT GUIDANCE SYSTEM By Pat M. Kurten Lyndon B. Johnson Space Center SUMMARY With respect to the lunar module abort guidance system, the Apollo Program experience included the full range of program development from requirements through design, development, and production and culminated with successful flight. As a result of preliminary lunar-abort concepts, a strapped-down inertial-sensor package for attitude reference and an open-loop programer were selected to provide ascent steering for lunar-orbit insertion. A clear pericynthion orbit could be obtained by postinsertion burns, and rendezvous was to be accomplished by means of external information. A program redefinition in 1964 added the requirement for a clear peri- cynthion orbit from the initial abort burn and the requirement for a rendezvous within the lunar module fuel budget without information from sources outside the lunar module. The required accuracy of the strapped-down package was therefore increased, and a general-purpose digital computer containing 4096 words of memory replaced the open-loop programer. A display and keyboard device was added for crew communica- tions with the computer. INTRODUCTION The lunar module (LM) abort guidance system (AGS) represents the first opera- tional usage of a strapped-down guidance system. The AGS was designed and developed specifically for application in the Apollo LM. The AGS is composed of a strapped-down (or fixed) inertial-sensor package, the abort sensor assembly (ASA); a general-purpose digital computer with specialized input/output, the abort electronics assembly (AEA); and a display and keyboard device for crew communication with the computer, the data entry and display assembly (DEDA). The AGS forms the digital portion of a hybrid digital/analog guidance and control system and is configured to provide automatic con- trol for mission abort resulting from a primary guidance system (PGS) malfunction. The AGS was supplied by the LM prime contractor under NASA cognizance at the NASA Lyndon B. Johnson Space Center (JSC) (formerly the Manned Spacecraft Center (MSC)). The E~C~PII?respnnsihilit-y