Nasa Space Vehicle Design Criteria [Environment)
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NASA NASA SP-8111 SPACE VEHICLE DESIGN CRITERIA [ENVIRONMENT) C ASSESSMENT AND CONTROL OF ELECTROSTATIC CHARGES MAY 1914 FOREWORD NASA experience has indicated a need for uniform design criteria for space vehicles. Accordingly, criteria are being developed in the following areas of technology: Environment Structures Guidance and Control Chemical Propulsion Individual topics are issued as separate monographs as soon as they are completed. A list of monographs published in this series can be found on the last page. These monographs are to be regarded as guides to design and not as NASA requirements except as may be specified in formai project specifications. it is expected, however, that the monographs will be used to develop requirements for specific projects and be cited as the applicable documents in mission studies, or in contracts for the design and development of space vehicle systems. This monograph was prepared under the cognizance of the NASA Goddard Space Flight Center (GSFC) by Matthew Barrett of Analytic Products Inc., Bethesda, Md. Scott Mills of GSFC was the program coordinator. Daniel Dembrow of GSFC served as the chairman of the Advisory Panel which provided guidance for the monograph’s scope and technical content. Other members of the Advisory Panel were : Larry Brace GSFC Kenneth Carpenter East Tennessee State University Elliott DeGraff Ambionics Inc. Dominick Gignoux Columbia Research Inc. John E. Jackson GSFC Joseph Nanevicz Stanford Research Institute John Robb Lightning & Transients Research Institute John Sutton GSFC Comments concerning the technical content of these monographs will be welcomed by the National Aeronautics and Space Administration, Goddard Space Flight Center, Systems Reliability Directorate, Greenbelt, Maryland 2077 1. May 1974 i For sale by the National Technical Information Service Springfield, Virginia 221 5 1 Price - $3.75 CONTENTS INTRODUCTION ..................................................... 1 STATE OF THE ART ................................................. 2 2.1 Design and Operational Experience .................................... 2 2.1.1 Rangerstudies .............................................. 2 2.1.2 Delta ..................................................... 3 2.1.3 Minuteman ................................................ 3 2.1.4 Titan111 .................................................. 3 2.1.5 Apollo 12 .................................................. 3 2.1.6 Applications Technology Satellite (ATS-5) ........................ 5 2.2 On-board Sources of Electrostatic Charges .............................. 5 2.2.1 Friction ................................................... 5 2.2.2 Rocket Exhaust Effects ....................................... 6 2.2.3 FluidFlow ................................................. 6 2.3 External Sources of Electrostatic Effects ................................ 7 2.3.1 Lightning .................................................. 7 2.3.2 Triboelectric Charging ........................................ 9 2.3.3 Atmospheric Field ........................................... 9 2.3.4 Ionosphere and Space ........................................ 11 2.3.4.1 Ionospheric Parameters ................................ 11 2.3.4.2 Effect of Ionospheric Parameters on Spacecraft Potential ...... 11 2.3.4.3 Effects of Radiation Flux .............................. 12 2.4 Electrostatic Discharge .............................................. 13 2.4.1 Corona Discharge ............................................ 19 2.4.2 ArcDischarge ............................................... 19 2.4.3 Surface Streamers ........................................... 19 2.5 Hazards from Electrostatic Charges .................................... 20 2.5.1 Electro-Explosive Devices ..................................... 20 2.5.1.1 Resistive Bridgewire ................................... 21 2.5.1.2 Exploding Bridgewire .................................. 21 2.5.1.3 Capacitive Discharge .................................. 21 2.5.2 Combustible Gases ........................................... 21 2.5.3 Electronics ................................................. 22 2.5.4 Communications ............................................ 22 2.5.5 Persons .................................................... 22 iii 2.6 Methods for Limiting Electrostatic Charge Problems .................24 2.6.1 Prelaunch Operations ............................... 24 2.6.2 On-board Sources ................................. 24 2.6.2.1 Control of Charge Accumulation .................... 24 2.6.2.2 Reduction of Discharge Effects .................... 25 2.6.3 Lightning Protection ............................... 25 2.6.3.1 Weather Watch .............................. 25 2.6.3.2 Vehicle Design .............................. 25 3. CRITERIA ........................................... 27 3.1 Assessment of Electrostatic Effects ........................... 27 3.2 Control Objectives .................................... 27 3.2.1 Fabrication and Test ............................... 27 3.2.2 Flight ........................................ 28 3.3 Management for Electrostatic Charge Control ..................... 29 4 . RECOMMENDED PRACTICES ............................... 29 4.1 Design ........................................... 29 4.1.1 Grounding Objectives ............................... 29 4.1.2 Shielding by the Vehicle Shell .......................... 29 4.1.3 High Voltage Electronics ............................. 30 4.1.4 Low Voltage Electronics ............................. 30 4.1.5 Dielectrics ..................................... 31 4.1.6 Electro-Explosive Devices ............................ 31 4.1.7 Installation of Ordnance Devices ........................ 32 4.2 Testing ........................................... 32 4.3 Operations ......................................... 33 REFERENCES ........................................... 35 APPENDIX A .ELECTROSTATIC SYMBOLS AND COMMON UNITS ......... 39 APPENDIX B .SOME USEFUL FORMULAS FOR ELECTROSTATIC CALCULATIONS ................................ 41 APPENDIX C .CHARGING AND DISCHARGING EQUATIONS ............. 43 NASA SPACE VEHICLE DESIGN CRITERIA MONOGRAPHS ..............45 iv ASSESSMENT AND CONTROL OF ELECTROSTATIC CHARGES 1. INTRODUCTION Adverse effects of electrostatic charges on space vehicle design, development, test, and operations sometimes have been serious. Such effects include inadvertent ignition of electro- explosive devices, spurious triggering of electronics, and damage to insulating materials. The I ignition by eiectrostatic charge of the final stage solid rocket motor of the Delta launch , vehicle for the Orbiting Solar Observatory spacecraft during test operations killed three men in 1964. Electrostatic charges previously had ignited a similar motor without loss of life. In addition, failures of several vehicles after launch have been attributed to electrostatic charges. Electrostatic charges in the atmosphere can have adverse effects on launch operations. NASA SP-8084, revision of June 1974, gives lightning models that should be applied to electrostatic problems. The lightning strikes on Apollo 12, shortly after liftoff, caused major disturbances to on-board electrical systems. Fortunately, most of the effects in this case were of a temporary nature and the mission was able to continue. Later, during lunar surface operations of the same mission, lunar dust was found to cover many of the experi- ment packages and space suits, thus causing them to overheat. The attraction of the dust particles to the thermal control surfaces may be partially attributable to electrostatic charges. Electrostatic charges have been of concern in the design of scientific satellites because of the need to account for electrostatic effects on sensitive instruments in the ionosphere and space. Hazards to space vehicles can arise from electrostatic charges that are generated on board, externally, or by interaction between the space vehicle and its environment. Damage gener- ally occurs during the sudden breakdown of matter in the field between accumulated charges of opposite polarities. This results in a current surge which is characterized by a very fast rise time and a high intensity for a very short period. Techniques for minimizing the foregoing hazards are available, but hazardous situations are not always recognized. The problem of electrostatic charges sometimes is confused with problems of electro- magnetic interference (EMI). A program to control EM1 is not closely related to require- ments for preventing damaging electrostatic charges. (EM1 is treated in a separate design criteria monograph, NASA SP-8092.) 1 To be effective, a program to minimize the hazards of electrostatic charges must be insti- tuted early in the design phase and must consider all aspects of the design, test, launch, and operations of the launch vehicle, spacecraft, and experiments. This monograph is intended (1) to alert the designers of space vehicles and experiments to problems associated with electrostatic charges, (2) to provide methods for assessing these problems, and (3) to show means for handling them. For more detailed treatment of particular aspects, the reader is directed to the references cited. Section 2 of this monograph describes experience of NASA and DOD with electrostatic problems, generation mechanisms, types of electrostatic hazards, and current methods for handling electrostatic problems. Section 3 gives guidelines for judging the possible effects of electrostatic charges on a