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NASA/TM--2000-210131 ./iv-- .,S Analysis and Assessment of Peak Lightning Current Probabilities at the NASA Kennedy Space Center D.L. Johnson Marshall Space Flight Center, Marshall Space Flight Center, Alabama W. W. Vaughan University of Alabama in Huntsville, Huntsville, Alabama May 1999

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The NASA STI Program Office...in Profile Since its founding, NASA has been dedicated to the advancement of aeronautics and space science. The NASA Scientific and Technical Information (STI) Program Office plays a key part in helping NASA maintain this important role. The NASA STI Program Office'is operated by Langley Research Center, the lead center for NASA's scientific and technical information. The NASA STI Program Office prdvides access to the NASA STI Database, the largest collection of aeronautical and space science STI in the world. The Program Office is also NASA's institutional mechanism for disseminating the results of its research and development activities. These results are published by NASA in the NASA STI Report Series, which includes the following report types: TECHNICAL PUBLICATION. Reports of completed research or a major significant phase of research that present the results of NASA programs and include extensive data or theoretical analysis. Includes compilations of significant scientific and technical data and information deemed to be of continuing reference value. NASA's counterpart of peer-reviewed formal professional papers but has less stringent limitations on manuscript length and extent of graphic presentations. TECHNICAL MEMORANDUM. Scientific and technical findings that are preliminary or of specialized interest, e.g., quick release reports, working papers, and bibliographies that contain minimal annotation. Does not contain extensive analysis. CONTRACTOR REPORT. Scientific and technical findings by NASA-sponsored contractors and grantees. • CONFERENCE PUBLICATION. Collected papers from scientific and technical conferences, _ _symposia, seminars, or other meetings sponsored or cosponsored by NASA. • SPECIAL PUBLICATION. Scientific, technical, or iaistorical _nformation from NASA programs, prdjects, and mission, often concemed with subjects having substantial public interest. • TECHNICAL TRANSLATION. English-language translations of foreign scientific and technical material pertinent to NASA's mission. Specialized services that complement the STI Program Office's diverse offerings include creating custom thesauri, building customized databases, organizing and publishing research results...even providing videos. For more information about the NASA STI Program Office, see the following: • Access the NASA STI Program Home Page at http://www.sti.nasa.gov • E-mail your question via the Internet to help@sti.nasa.gov • Fax your question to the NASA Access Help Desk at (301) 621-0134 • Telephone the NASA Access Help Desk at (301) 621-0390 Write to: NASA Access Help Desk NASA Center for AeroSpace Information 7121 Standard Drive Hanover, MD 21076-1320

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NASA/TM--2000-210131 Analysis and Assessment of Peak Lightning Current Probabilities at the NASA Kennedy D.L. Johnson Space Center Marshall Space Flight Center, Marshall Space Flight Center, Alabama W. W. Vaughan University of Alabama in Huntsville, Huntsville, National Aeronautics and Space Administration Marshall Space Flight Center • MSFC, Alabama May 1999 Alabama 35812

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Acknowledgments We acknowledge Hugh Christian, Douglas Mach, William Koshak, Dennis Boccippio, and their MSFC Global Hydrology and Climate Center colleagues for advice, references, inputs, and reviews of the lightning probability section of this report. Also appreciated are inputs and comments by Dawn Trout, Carolyn Goodloe, Tony Clark, Steve Pearson, O.E. Smith, and Stanley Adelfang of the MSFC Electromagnetics and Aerospace Environments Branch (EL23). Thanks go to our NASA Kennedy Space Center (KSC) colleague, John Madura at the KSC Weather Office, Michael Maier of Computer Sciences Raytheon at Patrick Air Force Base, Wayne Ordway at NASA Johnson Space Center, and Mark Stanley at New Mexico Institute of Technology, Socorro, NM, for their comments, encouragement, and help. Special thanks to Margaret Alexander/EL23 for editing the draft and to Belinda Hardin, Member of Technical Staff (Associate, CSC) for processing the manuscript. Credit Page ix: National Aeronautics and Space Administration photograph: Powerful electrical storm near NASA Kennedy Space Center launch complex 39A prior to launch of STS-8, August 30, 1983. Available from: NASA Center for AeroSpace Information 7121 Standard Drive Hanover, MD 21076-1320 (301) 62 i-0390 National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 (703) 487-4650 ii

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PREFACE This report presents a summary of lightning characteristics and lightning criteria for the protection of aerospace vehicles and probability estimates for certain lightning strikes (peak currents of 200, 100, and 50 kA) applicable to three operational phases of the Space Transportation System (STS) vehicle at the NASA Kennedy Space Center, Florida. Presented are results of an extensive literature search to compile information others developed for this area in order to answer key lightning current questions posed by the Space Shuttle Program Office at the Johnson Space Center. Vehicle-triggered lightning probability estimates for the various lightning current however, provides some insight on this subject. iii categories are still being worked. Section 4.5,

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TABLE OF CONTENTS 1• INTRODUCTION . ....... ° * °°. ° °. ° °. °...° ° .. ,.. ° ° ° ° °°. °° ° .°°. ° °° °° ° ° °. ** ° ° ° .°°. ° ° °° °°... °. ° °° ° °. ,. ° ° ° °° ° °. ° °°..°° ° °° .°° .° ° °°°.. • l 2. LIGHTNING STRIKE PROBABILITY QUESTIONS ........................................................ 3 3. RESPONSE ............. • ° .... .°°, ..... , ..... °° ...... ,°°,,,°°°°°°,°°°°°°°,°,°,°°°,°°°.. .... °°°.°°° .... °°°.°,,°°,,.,,°°.°°°°,°,°°, 4. RATIONALE 4 ....... '°' °°..**°,°°°°°°,.,,°°..,°°°°H°.° .... ,°°° .... ,°,°°°°,,,°°°°,°° ..... °..°.°.,°°°°°°,°°°°.°°°°*°6° 5 4.1 Background ............... • °,°,..,,, ..... ,°°.°,.°°°°,°°,,.°°,,.°°°, ...... ,°°°,°,°°°°°°°..,° ..... °° .... °,.,°..,°,° .... ,,°,°,,,, 5 4.2 KSC Area and Pad Lightning .......................................................................................... 5 4.3 Probability forA >200, >100, and >50 kA Current Strike ............................................. 7 4.4 STS Vehicle Rollout Risk ................................................................................................ 9 4.5 STS Vehicle-Triggered Lightning ................................................................................... 10 5. CONCLUSIONS ............ •""'"'........... .... ................................. .... .................................. .... ...... 12 APPENDIX A--Literature Search ........ °, .... ,,,.,,.,,.,°,,°°°... 13 ...... ,,°.,°°°.,, ..... ,,°°°.°.°.°,,°°°°,°.,,°,.,,,,°°°,°,,°°° A. 1 Lightning and Current Statistics ..................................................................................... 13 A.2 Positive Lightning ........................................................................................................... 13 A.3 Positive Superstrokes ...................................................................................................... 14 A.4 NLDN Statistics ....................................................................................................... 14 A.5 Sprites From Positive Flashes ......................................................................................... 14 A.6 Sprites Observed Over KSC ........................................................................................... 16 APPENDIX B--Space Shuttle Lightning Launch Commit Criteria ................................................ 18 REFERENCES ...... ,,,,,,,.°.. .... , ...... ,.,°...,., ............. . .... ,°° ..... °,,...,°, ..... , ....... ,,.,°,.** ...... ,° ..... ,, ....... ,, ..... , .... 25 BIBLIOGRAPHY ............. °°.,..,, ..... , ............... ..°..,, ...... ,, ...... ,,, ..... ,, ............. ,,,, .... ,°. ..... ***,°°,,., ...... °,,,°° V 29

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LIST OF FIGURES 1. Distribution of peak currents for first return stroke and subsequent strokes ......................... 6 LIST OF TABLES ° Probability estimates for natural CG lightning to strike STS vehicle during launch ............. 7 2. Estimated CPF's from figure 1 of <200, <100, and <50 kA peak lightning 8 current occurrences ................................................................................................................ vi

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ACRONYMS AFB Air Force Base CC continuing current; cloud to cloud CG cloud to ground CGLSS cloud-to-ground lightning surveillance system CPF cumulative percentage frequency CSC Computer Sciences Corporation EDT eastern daylight time EL23 Electromagnetics and Aerospace Environments Branch ENE East Northeast ET external tank GBFM ground-based field mills IC in-cloud JSC Johnson Space Center KSC Kennedy Space Center LCC launch commit criteria LPC large peak currents LPS Lightning Protection System LST local standard time MCS mesoscale convective systems MLP mobile launch platform MSFC Marshall Space Flight Center NASA National Aeronautics and Space Administration NLDN National Lightning Detection Network NSTS National Space Transportation System OTV operational television RP return period (mean) RSS rotating service structure SAE Society of Automotive Engineers SD standard deviation SLC space launch complex SRB solid rocket booster STS Space Transportation System TBD to be determined TBP to be published TL triggered lightning TM technical memorandum U.S. United States UTC coordinated universal time VAB vehicle assembly building vii

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SYMBOLS AND ABBREVIATIONS approximately A Area Av vulnerability area av average elev elevation forfD flash density ft feet h hour K Kelvin kA kilo amp km kilometer m meter M mega min minute nm nautical mile P, PROB probability direct strike Pd Pn nearby strike S second str lightning strike t exposure time V/m volts per meter wk week Y, yr year viii

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PowerfulelectricalstormnearNASA KennedySpaceCenterlaunchcomplex39A prior to launchof STS-8,August30, 1983. ix

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TECHNICAL MEMORANDUM ANAINSIS AND ASSESSMENT OF PEAK LIGHTNING CURRENT PROBABILITIES AT THE NASA KENNEDY SPACE CENTER 1. INTRODUCTION On a cloudless day the electrical potential gradient in the atmosphere near the surface of the Earth is relatively low (<300 V/m); but when clouds develop, this gradient increases. If the clouds become large enough to have water droplets of sufficient size to produce rain, the atmospheric potential gradient may result in a lightning discharge. A variety of charge separation processes occurs at microphysical and cloud-size scales.I These processes vary in importance depending on the developmental stage of convective clouds. It has been suggested, however, that both induction and interface charging are the primary electrification mechanisms in convective clouds. 2 Inductive charging involves bouncing collisions between particles in the external field. The amount of charge transferred between the polarized drops at the moment of collision depends on the time of contact, contact angle (no charge transferred at grazing collisions), charge relaxation time, and net charge on particles. Interface charging involves the transfer of charge due to contact or freezing potentials during collisions between rimming precipitation particles and ice crystals. Sign and magnitude of the charge transfer depend on the temperature, liquid water content, and ice crystal size and impact velocity. The Earth-ionospheric system can be considered a large capacitor with the surface of the Earth the negatively charged plate, the ionosphere the positively charged plate, and the atmosphere the dielectric. When a cloud develops into the cumulonimbus state, lightning discharges result. For a discharge to occur the potential gradient at a location reaches a value equal to the critical breakdown value of air at that location. Laboratory data indicate a value as high as ! M V/m at standard sea level atmospheric pressure. Electrical fields measured at the surface of the Earth during lightning discharges are much lower than 1M V/re. Reasons include the following: 1. Most clouds have centers of both polarities at the surface. that tend to neutralize values measured 2. Each charge in the atmosphere and its image within the Earth resembles an electrical dipole. The intensity of the electrical field decreases with the cube of the distance from the dipole.

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1. The atmosphericelectricfield measuredoverlandat the surfaceof the Earth is limited by dischargecurrentswhich arisefrom groundedpointssuchasgrass,trees,andotherstructures thationizethe air aroundthe pointsandproducescreenspacecharges. Lightning,a secondaryeffectof electrificationwithin a thunderstormcloud system,is a giant electricalsparkthatcanhavea peakcurrentflow >200000A duringa few microseconds. Thunderresultsfrom suddenheatingof theair to =20000K by the flow of currentalonga narrowchannel.This flow of currentcanbe fromcloud to ground(CG) asseveralindividualstrokes separatedby a tenthof a second.It canbefrom cloud to cloud (CC) in strokesnot readilyvisible from the groundbut which diffusely illuminatethe cloud.The flow canalsobe from cloud throughan aircraft or aerospacevehicleoperatingin the vicinity. About 1800thunderstormsareactiveoverthe surfaceof the Earthatanygiven time.Lightning strikestheEarth --100timesper second. Whenlightning strikesa protectedor unprotectedobjectsuchasan aerospacevehicleon a launchpad,thecurrentflows througha pathto true ground.The voltagedrop alongthis pathmaybe greatenoughovera shortdistanceto bedangerousto peopleandequipment.While standingundera treestruckby lightning,cattle andhumanshavebeenelectrocutedby the currentflow throughthe groundandthe voltagepotentialbetweentheir feet. A staticchargemay accumulateon anobjectsuchasanaerospacevehiclefrom its motion throughanatmospherecontainingraindrops,iceparticles,or dust.A stationaryobject,if not grounded, canaccumulatea chargefrom windborneparticles(often invisiblenuclei), rain, or snowparticles strikingthe object.This chargecanbuild until the local electricfield at thepoint of sharpestcurvature exceedsthebreakdownfield andtriggersa lightning discharge.The quantityof maximumcharge dependson the sizeandshapeof the object(especiallysharppointson the structure). If a chargebuildson a structure not grounded, discharges could ignite explosive gases or fuels, interfere with radio cornmunications or telemetry, or cause severe shocks to people. Static electrical charges occur most frequently during periods of low humidity in any geographical area. Lightning protection assessment and design considerations are critical and important functions in the development and design of an aerospace vehicle. The project lighting protection engineer must be involved iq preliminary design and remain an integral ,nember of the design and development team until construction of the vehicle is completed and all verification tests are accomplished. A National Aeronautics and Space Administration (NASA) technical memorandum (TM) provides guidelines and an overview of considerations for an adequate lightning protection design. 3 This TM presents a summary of the probability of peak lightning strike currents to the NASA Space Shuttle during rollout, on-pad, and boost/launch phases at the Kennedy Space Center (KSC). 2

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1. LIGHTNING STRIKE PROBABILITY QUESTIONS The NASA Johnson Space Center (JSC) Shuttle Systems Integration Office requested the Electromagnetics and Aerospace Environments Branch (EL23) of the Marshall Space Flight Center (MSFC) to provide probabilities for three peak lightning strike currents (i.e., 200, 100, and 50 kA) which could occur if the Space Transportation System (STS) vehicle is hit by a lightning CG return stroke during rollout, while on-pad, and for triggered lightning on ascent. This is referred to as question A. The answer to this question is needed in order to provide lightning criteria applicable to a new STS avionics box. Question B asked if all lightning launch commit criteria (LCC) rules are followed, what is the probability of a 200, 100, and 50 kA peak current lightning strike while the STS vehicle is in the boost/ launch phase. The response given in this technical memorandum provides estimates for these questions. Annual probabilities are expressed in percent and mean return period (RP) in years. Currents are expressed in kiloamps (kA). The launch site is KSC space launch complex 39 (SLC 39).

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1. RESPONSE Question A: Rollout to pad (evening hours, no forecasting Lightning Peak Current >200 kA Point Probability Prob % _ considered) >50 kA >100 kA Prob.__% Prob % RPy£ 0.011 500 8696 Worst Case 0.002 180 45 963 0.005 90 16 934 01004 040 24 749 KSC SLC 40 0.000 037 2 681 000 0.000 31 322 000 On-pad (STS vehicle protected by pad Lightning Protection System (LPS) Lightning Peak Current >200 kA Point Probability Prob % _ Worst Case 0.002 260 44 220 KSC SLC 40 0.000 390 258 000 >50 kA > 100 kA Prob % Prob..% 0.119 53 837 0.061 38 1 629 0.042 00 2 381 0.003 23 30954 Launch (lightning triggered by vehicle) (see sec. 4.5 STS Vehicle-Triggered Lightning) Lightning Peak Current >200 kA Point Probability Prob % _ Worst Case TBD KSC SLC 40 TBD Question B: >i00 kA >50 kA Pr__ob% RP_E Prob% TBD TBD TBD TBD Launch (STS protected by LCC storm distance rule only) Lightning Peak Current >200 kA Point Probability Prob % _ >50 kA >100 kA .Prob % .Prob % 0.001 610 62 274 KSC SLC 40 0.000 304 329 000 0.008 250 121 000 4

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1. RATIONAL 4.1 Background Lightning statistics and procedures from five published reports dealing with lightning probabilities and the Florida/KSC/pad area are presented in this report. 4-8 Two key general references were consulted regarding extreme lightning peak current cumulative percentage frequencies (CPF). 9,1° A technical summary using three key KSC references (Stahman, Mach, and Chai) is given in section 4.2. 5-7 Appendix A presents additional information from the literature on CG lightning stroke peak current characteristics and statistics. 4.2 KSC Area and Pad Lightning Since 1979 the Lightning Protection System (LPS) on SLC 39A at KSC was struck by lightning an average of three times per year. 5 Stahmann's theoretical probability calculations for lightning striking the 122-m (400-ft) tower are two strokes per year and produce an average peak current amplitude of 122 kA. 5 All calculations were based on a pad stroke density of 20 strokes/km2/yr. Six years (1990 to 1995) of CG lightning surveillance system (CGLSS) measurements for Cape Canaveral SLC 40 were analyzed and published by Chai. 7 His paper presents a summary of = 6 200 CG events at or near (within 5 nmi) SLC 40. The absolute maximum peak current measured was -284 kA (negative); the positive current peak was 144 kA. The 5-year total mean current peak was =30.5 kA (standard deviation (SD) value =14.5 kA). The associated negative mean peak current was -30.9 kA; tiae positive was 23.3 kA. A plot of the lightning peak current CPF for SLC 40 is shown in figure I (200 kA peak current =99.9 percentile). Of the 6 186 flashes, 94.5 percent were negative and 5.5 percent positive. Also, 91 percent of the flashes occurred from June through September and 9 percent from October through May. Only three SLC 40 the flashes carried current >200 kA (i.e., -284, -281, and -203 kA). These strikes ranged from 1.9 to 4.9 nmi from SLC 40. The probability for natural lightning current >200 kA to occur within 5 nmi of SLC 40 per year is estimated to be 0.051 30 percent (l event in =! 950 yr). 7 This is an "area" probability and not a "point" probability. A paper entitled "Shuttle Lightning Threat Analysis" by Mach gave lightning probability estimates for various Space Shuttle operational phases. 6 Mach emphasized all his probabilities are estimates and could be in error by more than an order of magnitude. In addition, his estimates do not account for all possible pathways for lightning to damage the STS systems. 6 The three operational phases in his paper of main interest in this report are rollout, on-pad, and launch. During rollout, high current (200 kA) damage current (CC) to the external tank (ET) are the greatest to the solid rocket booster (SRB) and continuing possibilities for major Space Shuttle damage. 6 The probability for lightning damage to the SRB is I in 3 20000 yr (or 3.1×[0 -7) and to the ET, I in 55 000 yr (or 1.9x10-5).

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99.99 99.9 99 98 95 90 80 70 60 50 40 30 20 10 5 2 1 0.1 0.01 1000 100 , ¢D p. tJ ,Jl¢ O Q. 10 1000 FirstReturnStroke 100 2OkA 10 "_ . _ Uman "_ -., ,.. 3.1-- k_,"-__ 1st(-) SubsequentReturn 10kA "_, KSC1st Strokes 1 "% "% ,% Uman "- 2nd (-) 3.1 kA 1.5 kA 1 0.01 O.i 1 2 5 10 20 3040506070 80 90 95 98 99 99.9 99.99 % > Ordinate Figure 1. Distribution of peak currents for first return stroke and subsequent strokes. 7'9'12 While on-pad, it is estimated the LPS catenary wire shields the STS from =97.2 percent of all pad area strikes, with =2.8 percent not diverted. 6 Mach calculated if there are = 1.8 pad str/year and each STS spends =2 weeks on-pad, the probability for SRB damage from lightning is 9.5x 10-5 (RP=I 1 000 yr) and for ET damage is 5.6x10 -3 (RP=I78 yr). Therefore, the maximum probability of a lightning strike of "any" current magnitude hitting the STS directly, while protected on the pad, is 0.028 (2.8 percent) per year. Mike Maier of Patrick Air Force Base (AFB)/Computer Sciences Raytheon stated: "Since 1990, the NASA operational television (OTV) has two documented direct strikes to the pad structure which bypassed the catenary wire LPS. Neither event resulted in a strike to the vehicle; one struck the gaseous oxygen vent ann and the other the far corner of the partially retracted rotating service structure (RSS)." In the boost phase of launch the probability of the STS vehicle and exhaust intercepting a "natural" (not triggered) lightning flash from a nearby storm was calculated assuming a low flash rate (l/rain) to a high flash rate (60/rain), distance from the storm edge of 2, 5, and 10 nrni standoffs, ascent time =50 s, and eight launches per year. Mach's resulting probability estimates are presented in table 1. 6 If Space Shuttle LCC regarding natural lightning are followed during countdown and launch, the estimated probability of the STS being struck by "any" magnitude lightning is 1 in 23 000 (0.004 30 percent). The only LCC rule applied here is the 5- and 10-nmi limit to thunderstorms. ]1 Not included here are triggered lightning from anvils, cloud thickness and ceiling, and other LCC rules. See appendix B for lightning LCC rules. 6

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Table 1. Probability estimates for natural CG lightning to strike STS vehicle during launch* ExposureTime StandoffFrom StormSeverity Probability Probability t(sec) StormEdge(nmi) FlashRate(min-1) PerYear(%) RP(yr) 50 2 50 5 (LCC) 50 10 (LCC) 50 10 (LCC) *Assuming eight STS launches per year (Mach) 6 High = 60 0.62500 160 Avg = 6 0.00434 23 000 Low = 1 0.00007 1300 000 High =60 0.00434 23 000 4.3 Probability for A >200, >100, and >50 kA Current Strike Question A: The three references mentioned in section 4.1 provided the main statistics to develop the conclusions in this section. 5-7 To estimate the probability for "any" peak current strike to the STS, use the higher probability of lightning intercepting the STS (either on-pad 2.8 percent or in-flight 0.004 30 percent). Since the on-pad STS strike probability is higher, multiply the average strikes to pad per year (3) by the probability of lightning striking the STS (0.028) by the 2-week pad exposure (0.038 46 yr). Results are 3xO.O28xO.03846 = 0.00323 str/yr or (0.323 percent and RP=310 yr) (]) This estimated probability includes "all" possible strike magnitude currents. To estimate the probability of a >200, >100, or >50 kA strike, the proper (most representative) peak current CPF is used. The probability of strong CG negative lightning and stronger CG positive lightning currents was applied (but not the lower current-triggered lightning current probabilities). In the 1990 "Lightning Protection of Aircraft," Fisher used the old 1972 Cianos peak current plot (fig. I) and gave 140 kA current at the 98 percentile. 10,12 Lightning peak currents fit a log-normal probability distribution well. 10,13 Uman's peak current summary curves of first return stroke peak current CPF for both negative and positive flashes and Chai's SLC 40 peak current CPF are also shown in figure I. 7,9 Much disagreement exists as to which lightning peak current probability curve to use. 9 Uman's first return stroke peak current has a range of 20 to 40 kA with median value of =30 kA for negative flashes and =35 kA for positive flashes and <200 kA occurring at the =99 percentile level. The Uman 95 percentile negative first stroke peak current is <80 kA and the positive first stroke is <250 kA. 9 With exception of Uman's positive stroke curve, the more recent CPF current plots seem to parallel each other and slope differently from the standard 1972 Cianos plots. 12 Table 2 presents the various extreme probabilities for a <200, <100, and <50 kA peak return stroke CG lightning current by the various investigators. For the KSC area, use any of the first return stroke peak current CPF curves in figure 1 for negative (and the higher magnitude positive) strokes. This partially answers question A. The Chai CGLSS/SLC pad 40 lightning current statistics, however, may be more applicable and realistic for the SLC 39 area. 7

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Table 2. Estimated CPF's from figure 1 of <200, <100, and <50 kA peak lightning current occurrences Uman879 Cianos7212 Uman879 Chai977 Peak Current 1st Positive 1st Return 1st Negative 1st Return <200kA 93.0% 99.35% 99.98% 99.88% <100kA 81.0% 95.6% 98.2% 99.0% <50 kA 63.0% 84.0% 80.0% 87.0% i (Worst Case) (Standard) (KSC) Mike Maier made these statements regarding this unique database: "The CGLSS has been very carefully calibrated using both rocket-triggered lightning (from the former NASA experiment) and direct strikes to SLC 39A and SLC 39B. NASA has both shuttle pads instrumented to measure the peak currents, and these data (once its calibration was fixed) have helped corroborate the triggered lightning calibration. This is an absolute unique data set which can be used to provide the most accurate frequency distributions of peak currents for KSC. This data set is also more accurate than the National Lightning Detection Network (NLDN) data since NLDN has performance problems in this area and has undergone major changes over the years, resulting in changes to the distributions. The CGLSS distributions are probably more accurate and the sample sizes are big. Our median values are below the NLDN, but this is because of the historic NLDN detection efficiency biases against the smaller weak flashes." Maier also compared the lightning climatology at SLC 40 to SLC 39. He stated: "The situation around 39A and 39B is almost the same. We have found the two shuttle pads are exposed to slightly higher flash densities than the Titan pads, since they are a bit farther north and closer to the mean "storm track" which extends ENE from the local lightning frequency maximum west of KSC. However, the peak current distributions don't seem to have any significant (at least within our area) spatial variations so the Cape area distribution would apply." In using the Chai lightning current statistics at SLC 40 to represent the SLC 39 area, we assume a <200 kA return stroke peak current at the 99.88 percent level (table 2). Multiply the equation (1) value by 0.001 20 (0.12 percent is the probability of >200 kA) to calculate a probability of 0.000 388 percent (or RP=258 000 yr). This probability of the STS being hit by a lightning strike of >200 kA current also responds to question A. However, the worst-case situation could arise if a strong, positive current lightning strike (associated with a sprite) occurs at KSC (a rare event) and generates much higher currents. If the Uman positive stroke curve applies to the KSC area, the table 2 worst-case probability of 93 percent for a <200 kA peak current is used with equation (1). Then the result is a worst-case probability of 0.002 26 percent (or RP=44 220 yr) for a >200 kA current event. This is the more conservative answer to question A (with a greater built-in safety factor). Probabilities for occurrence of peak lightning stroke currents >100 and >50 kA are similarly computed Question B: (sec. 3). To answer question B, the Mach report probabilities (table 1) were applied directly to the worstcase CPF values. 6 Lightning LCC rules applicable 8 to the 5- and 10-nmi storm distances are used and

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only naturalCG (not triggered)lightning is assumed.ObservingLCC stormdistancerulesto calculate the pointprobability that the STSwould bestruck"naturally" on ascentby a >200kA lightning-induced peakcurrent,multiply the table1 probability (0.00434) for "any" currentby the worst-caseprobability (0.07)to computea resultantvehicle-hitprobabilityof 0.0003038 percent(or RP=I in 329 164yr). 4.4 STS Vehicle Rollout Risk To calculate the probability of a 200-kA current lightning strike to the STS during rollout, the following assumptions were used. The height of the Space Shuttle atop the mobile launch platform (MLP) and crawler is ---235 feet (72 m) above ground level. The horizontal dimensions of the MLP are 135 feet by i 60 feet for an =21 600 feet 2 (2 007 m 2) strike area. The terrain is assumed flat and level for the =6-hr trip over the 4.2-mi distance from the vehicle assembly building (VAB) to pad 39B. To determine the probability of "any" magnitude lightning strike (str) to "any" square area (A) on the ground (between the VAB and pad 39) of 2 007 m 2, use the KSC annual flash density (f) of 20 strikes/km2/yr. Assuming a Poisson distribution as indicated by Santis, 8 the probability any flat surface will be hit by any magnitude lightning in a certain number of years is Y (yr) = I/(Axj') (2) Hence, = 0.04014 str/yr (4.01%) (3) Y = 24.91 yr/str or Py,. To calculate the probability of a 200-kA current strike at KSC, apply the table 2 worst-case probability (0.070) with other key parameters (elevated vehicle, diurnal time to roll out). worst month, 6-hour exposure period, and best For an object 235 feet tall, Viemeister 14 presents a chart (fig. 50) indicating an isolated tower or object up to 600 feet (on level terrain) located in a moderate (30 thunderstorm days/yr) lightning environment has the probability of lightning strikcs directly related to height (i.e., an object 235 ft tall will be hit twice as often as a ! 17-feet object). Viemeister's strike value for 235-fl height is I lightning strike per year. Since the KSC area has more thunderstorm days (76) than Viemeister (30), this strike value of I is multiplied by 2.533 (76/30) for 2.533 strikes per year. This figure is close to reality because elevated pad 39 is hit directly by lightning approximately two or three times per year. 5 Therefore, = 0. I0 ! 67 str/yr (or P (yr elcv) = l 0.17%) (4) P(yr clev) = (0.04014 str/yr) x (2.533) Since monthly analysis is needed, this yearly probability is converted to a monthly (any month) probability by dividing by 12 to obtain (or P(mo elcv) = 0.847%) (5) P(mo clcv)= 0.008473 f_ \

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Remaining terms are applied to this probability value as follows: 1. To obtain a 200 kA current for the worst case (table 2), use 0.070. 2. Apply this resultant to "any" 6-hour exposure period during a month for an exposure period of 6/720 or 0.008 333 month. . The rollout vehicle could be exposed during the peak lightning season (July for KSC). Since the average monthly KSC thunderstorm days is =6.333 and KSC July averages =16, apply the factor 16/6.33 or 2.53 for July. 15 . Assume the Space Shuttle is rolled out during the 6-hr timeframe when thunderstorm activity is minimal; i.e., between 0200 and 0900 LST when the probability of July KSC thunderstorm occurrence is = 1 percent. 16 The July KSC probability peaks at =23 percent at 1600 LST. The average KSC July hourly thunderstorm probability is =6.9 percent. Therefore, the factor, I/6.9 or 0.145, is applied during early morning hours for conservative rollout purposes. The "final" resultant probability which combines all four of the above procedures is P(mo etev) = 0.008473 × 0.07 × 0.008333 (6) × 2.53 × 0.145 or 0.000001813 str/mo Convening this probability to an annual value results in a yearly probability and return period of 0.002176% P{yr elev) = and RP = 45 963 yr/str (7) Computed lightning current probability values associated with STS rollout for 200, 100, and 50 kA using table 2 worst-case and SLC 40 conditions are presented in table i. If Space Shuttle rollout is not during evening hours but is during peak July afternoon hours, the resultant nominal probabilities for 200 and 50 kA lightning Strikes are respectively 0.04 percent (RP=2 508 yr) and 0.21 percent (RP=475 yr); i.e., it does matter "when" the Shuttle is rolled out. 4.5 STS Vehicle-Triggered Lightning If the STS vehicle is launched under LCC storm distance rules, Mach gives a "nontriggered," natural CG lightning hit probability of 0.004 34 (RP=23 000 yr). 6 The peak stroke current measurement from the KSC rocket-triggered program is 99 kA, which follows the subsequent peak current curve for return strokes (i.e., half the value of an initial return stroke current). 17 Therefore, using the Cianos subsequent stroke curve in figure 1 to estimate the <200, <100, and <50 kA triggered current CPF, the respective probabilities are approxirnately 99.94, 9935' and 96.2 percent. This implies a 0.06-percent risk must be applied (multiplied by) to the probability of a rising vehicle triggering a >200 kA stroke at KSC. This ascent-triggered probability is undetermined. However, some information concerning ascent vehicle-triggered lightning follows. 10

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Gabrielsondeterminedthatanascentvehicle-triggeredlightning probability canbe implied.4 He calculateda probability for anylightning strike to directly hit a standing10-mtall vehicleon the ground undermoderatestormandlightning conditionsby Pd = 2"9x10-9 and RP = 3.45x108 yr (8) He based his probability estimate of either a direct strike, Pd, or a nearby strike, Pn' on thunderstorm day data only. The probability is estimated using three independent parameters: flash density, fD, vulnerability area, Av, and exposure time, t. Hence, Pd =fD x A,. x t. Gabrielson neglected exposure time in calculating Pd" Gabrielson then calculated the probability of any nearby (within 10 km of the spacecraft) vehicle-triggered lightning strike during flight, resulting in either a cloud-to-cloud or cloud-to-ground discharge. In this second case, Gabrielson kept all inputs the same except he assumed the presence of exhaust gases after launch, extending the effective height of the vehicle 10 times and, thereby, affecting the vulnerability area. Gabrielson stated, "As the vehicle rises, the surface area increases significantly causing a large change in the probability prediction. ''4 Gabrieison also included an additional five percent to the calculated flash density to account for discharges (intercloud) triggered on nonstormy days. Vehicle exposure time during ascent is assumed to be 50 seconds. The nearby strike threat estimate (probability) for this vehicle ascent case is P,t = 4.06×10 -4 and RP=2 463 yr (9) This resultant probability value is still a very conservative, small probability of occurrence when compared to reality at KSC with two major vehicle-triggered strikes (Apollo 12 and Atlas-Centaur) within =20 yr. From these two calculated probabilities, a nearby triggered lightning estimate, Pn, for "any" magnitude current strike is =140 000 times greater than the direct hit to a vehicle on the ground estimate, Pd' indicating that vehicle-triggered lightning is indeed a launch consideration. Another consideration is that test rocket-triggered lightning discharges measured during summer campaigns generally indicate large currents (> 100 kA) at discharge are extremely rare compared to natural CG lightning discharge currents. 11

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1. CONCLUSIONS Estimates for the JSC questions concerning KSC SLC 39 "worst-case" lightning probabilities for the STS vehicle are determined. Section 3 also presents KSC SLC 40 results. The answer to JSC question A is the probability of a >200 kA peak lightning current strike to the STS vehicle while protected on-pad is 0.002 26 percent with an RP of I in 44 220 yr. The answer to JSC question B is the probability of a >200 kA peak natural lightning current occurring on or near the launched STS while following the lightning LCC distance to storm rule only is 0.000 303 8 percent with an RP of 1 in 329 000 yr. Other lightning LCC rules such as anvil, thick cloud, ceiling, etc. were not applied. The answer to the JSC question regarding rollout is the probability of a >200 kA peak lightning current strike to the STS during the 6-hour rollout in the worst KSC lightning month (July) and most lightning inactive time of day (night hours) is 0.002 18 percent with an RP of 1 in 45 963 yr. Man forecasting is not considered here; but at KSC a weather forecast always precedes STS rollout. However, the best condition, real-time forecast still allows for an = 10 percent chance of any lightning strike. The answer to the JSC question regarding launch-triggered lightning is that the probability of a >200 kA lightning strike current occurring is undetermined. However, a "triggering" factor of = 140 000 increase in probability and RP has been determined from one special case in the literature and will be investigated to see if it applies to this question. Lightning strike possibilities to the STS also exist during space shuttle exposure at locations other than KSC, i.e., on the Edwards AFB runway for up to a week atop the Boeing 747 aircraft during the return trip (no clouds or adverse weather present) report. to KSC. These operations are not included in this A reminder by the authors and Mach is the concluding probabilities in this report are estimates only and can be greatly in error. 6 To quote Gabrielson, "It is difficult, if not impossible, to establish a probability for lightning strikes with a high level of confidence. ''4 12

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APPENDIX A Literature Search This appendix presents a summary of key information from the literature on recent CG lightning stroke peak current statistics and its application to this analysis for the STS vehicle at KSC. A.1 Lightning and Current Statistics Most lightning discharges produced by summer thunderstorms at KSC originate in the cloud and lower (carry) negative charge to Earth in CG flashes. In-cloud (IC) lightning generally accounts for --60 percent of all lightning occurrences with =40 percent as CG. 18 However, Boccippio believes that this IC:CG ratio of 3:2 should be lowered. He states, "3:1 to 5:1 ratios are more in line with what the lightning community tends to quote and have been confirmed by recent results from the NASA OTV sensor." Peak currents generated in the first return CG stroke typically are 30 kA and range to a maximum of 250 kA. 9'12'19 Subsequent return strokes are typically one-half (=15 kA) the initial return stroke. Negative flashes to ground account for =90 percent of the total CG's with positive flashes accounting for --10 percent. Orville gives values <10 percent positive in summer storms compared to >50 percent positive in winter for an entire year of data over the eastern U.S. 20,21 Fuquay reported only =3 percent positive flashes (summertime, Rocky Mountains) and Reap --4 percent positive flashes (summer season, entire U.S.). 21 However, a fraction of the positive lightning flashes can involve the highest measured peak currents, more than generated from negative flashes. 10,19,22,23 A.2 Positive Lightning Natural CG positive lightning occurrences are responsible for the largest recorded lightning peak currents in the 200 to 300 kA range. 9 Positive lightning can be initiated from tall buildings and towers by an upward-moving leader with no first return stroke of the type associated with downward (CG) initiated flashes. 9"19 Winter thunderstorms, dissipating storms, and rocket-initiated triggered lightning generally bring a higher percentage occurrence of positive charge to ground. 19,21 The occurrence frequency of the positive flashes apparently increases with increasing latitude and elevation or from a low-level cloud base. 19 From available measurements, there is no difference between the currents to towers and those to ground. 9 An interesting conclusion from the 1983 to 1986 Florida triggered lightning studies was all flashes triggered were of the classic type which lowered negative charge. 9 The Florida triggered lightning study in 1990 and in Alabama in 1991 lowered negative charge also and reported a 38 kA peak current measurement. 24 The fact that positive flashes are less common at KSC latitudes is evidenced by Mach's analysis of 130 KSC strokes in 1986. Of these, 86 were negative CG natural, 4 ! negative triggered, 1 positive triggered, and 2 positive CG natural strokes (97.7 percent negative and 2.3 percent positive). The 86 negative CG strokes had a peak current of 84 kA while the two positive CG strokes had peak current values of 125 kA and 150 kA. 2-s Hence, peak positive currents should still be considered. Rocket-triggered flash currents peaked at 60 kA (mean 15 kA) from 1985 to 1987. 26 The entire 1984 to 1991 summer rocket-triggered lightning program at KSC produced only one peak return stroke current of magnitude 99 kA. [7 Artificially triggered lightning strokes are very similar to the subsequent strokes of natural lightning. 24,27 Triggered lightning current strikes to instrumented aircraft have generally been of lower amplitude than natural CG lightning measured at ground level. 9,1° 13

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A.3 PositiveSuperstrokes Rare superstrokes do occur. 28 They were measured mainly in winter thunderstorms in Japan with flashes approximately 56 to 94 percent negative.I°,22,23,29,3° Peak current values >250 kA in positive flashes are documented (>270 kA23; and 280, 320, and 340 kA29; 322 kA with three other observations >300 kA and four observations between 250 and 300 kA3°). The NLDN data indicated <5 percent of all observations were positive in summer and >50 percent in winter with peak values of positive flash current between 300 and 400 kA from the 1984 to 1985 Northeast U.S. network. 2° The 150-meter meteorological tower at KSC was hit July 19, 1976 by a three-return stroke lightning flash that produced large peak currents. The first stroke of the flash yielded a current between 150 and 640 kA (210 kA calculated). The peak current of the second return stroke was between 200 and 870 kA and the third between 66 and 280 kA. 31 A.4 NLDN Statistics Examination of summarized continental U.S. NLDN total (and positive) CG lightning events by Orville, et al. from 1989 through 1995 revealed that the maximum flash density occurs in central Florida and the Midwest. 32'33 Also, the positive CG flash density yearly maximum can occur in central Florida but tends to peak in the Midwest. The annual continental mean percentage of positive CG flashes range from 3.1 to 9.5 percent (average =5.1 percent). The summer months exhibit low continental percentages (3 percent in August); winter months show monthly positive CG percentages (to 25 percent in December). The climatology of peak current CG flashes of both polarities was prepared from 14 summer months of NLDN data. The positives were strongly clustered in the High Plains and Upper Midwest. The large negative CG flashes were concentrated in southeast U.S., especially over the waters of the Gulf/Atlantic, including the KSC area. 34 The annual percentage of positive flashes is also <2 percent at the latitude of Florida but near or greater than 25 percent at latitudes of the Upper Midwest, Maine, and along the West Coast. Orville indicated from the NLDN 1988 eastern database that the first stroke mean peak current is a function of latitude. The peak current varies by almost a factor of 2, from 25 kA in New England to 40 to 45 kA in northern Florida. 35 Since the NLDN upgrade in 1994, the mean peak currents of CG flashes decreased (from a preupgrade mean of 37.5 kA over 1989 to 1993 to a 1995 value of 30.2 kA) and the percentage of positive flashes increased. The positive peak current decreased from 54.4 to 31.6 kA. 36 Recently some controversy exists over the NLDN upgrade and resulting statistics. The NLDN database for the entire U.S. and Florida now extends from 1986 through 1995. 33.37 It is interesting that the location of maximum positive CG flash density in thc Midwest is geographically in agreement with the reported locations of sprite discharges between cloud tops and the ionosphere. 33 Large positive CG peak current values measured by the NLDN arise from extrapolated calibration curves (network initially calibrated to ---80 kA). Therefore, numerical values of these peak currents associated with large positive CG flashes should bc treated with extreme caution. A.5 Sprites From Positive Flashes In 1995, red sprites were studied in detail. 38"39 Sprites are infrequent, illuminosity features that shoot upward from the top of mature or dissipating midlatitude mesoscale convective systems (MCS). Many times they appeared from anvil up to the ionosphere and wcre observed from an altitude of =40 to 14

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95 km.40The MCS regionsproducednegativeCG strokesandpositives(with largepeakreturnstroke currents)from thestratiformprecipitationregions.In 1994Boccippiocomparedthe NLDN observations with two daysof spriteoccurrencesin the Midwest.For thesestormsystems,---85percentof all sprite eventscoincidedwith positiveCG eventsandexhibitedhigherpeak(>400kA) CGcurrent.This is two timesgreaterthanthe subsetof positiveCG strokeswith no sprites.41The spritepeakcurrentswere asmuchasthreetimeslargerthanthe mediannegativeCGpeakcurrentobservedduringthis same period. Spritesoccurin thunderstormareacomplexeswherethe ratio of positiveto negativeCG lightning is higherthanusual.42Otherground-based(1993to 1997)andaircraft researchwasdonein ColoradoandoverKansas,Nebraska,Minnesota,the Southeast, etc. 34,40,41 The relationship between sprites, Q-bursts, and positive CG strokes was confirmed and preference established to occur in decaying portions of thunderstorms. 40,42-44 Lyons says the possibility exists that sprite flashes may be hazardous to spacecraft and aircraft. 45 Sprites, however, appear weak compared to the CG strikes, despite being directly related. The best places in the U.S. to observe sprites are above the northern High Plains and Upper Midwest in a broad belt from Colorado to North Dakota, to Minnesota, and down to Texas. Sprites can occur above strong storms worldwide. 41 Using the CG NLDN climatology, an estimate was made of the chance of the Space Shuttle encountering a sprite (or elve) during descent to KSC. The probability is =1 in 100 (higher than the chance of a direct strike by conventional lightning during conditions conducive to thunderstorm activity). 34 All lightning does not produce sprites. Approximately 40 percent of lightning is CG. Only 5 to 10 percent of CG flashes are positives. Of the positive strokes only =10 percent create sprites. 18 Sprites are mentioned in this paper because the strongest currents generated from CG lightning strikes appear to be associated with sprite occurrences to the ionosphere. As state-ofthe-art sprite research continues, peak CG lightning current extremes and probability of occurrence will be understood better. Lyons recently presented some interesting U.S. NLDN CG statistics derived from =60M CG flashes over 14 summer months (June through September) from 1991 through 1995. 46 CG polarity, diurnal features, multiplicity, and LPC >75, _>200, and _>400 kA are presented for the entire U.S. and for the central U.S. which coincides with the heart of the sprite belt from 30 to 50 °N latitude and 88 to 110 °W longitude. Lyons concluded the following: The average positive (+) CG peak current for the entire U.S. is 35.5 kA (with a peak occurrence of 580 kA); the average negative (-) CG peak current is 30.4 kA (with a peak occurrence of 957 kA). For the entire U.S. =95 percent of all CG flashes are negative in polarity with -_87 percent LPC -CG's, i.e., CG's _>75kA. This indicates that the vast majority of "LPC" strokes nationally are negative in polarity. However, for the central U.S. =70 percent of all LPC CG's are negative (about 30 percent positive). These positive CG's in the central U.S. constitute ---67 percent of all national NLDN LPC +CG's. This makes the region one of high positive CG count where sprites occur most frequently. In the central U.S. the occurrence of positive and negative LPC CG's, as a percent of all LPC CG's, is _9 and 22 percent, respectively. 15

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In contrast,negativeLPC CG's preferentiallyoccuroverthe coastalwatersof theGulf of Mexico andthroughoutthe southernU.S.Of the=1.46M LPC CG'soccurringoverthe southernU.S., including the Atlantic andtheGulf, =86 percentarenegativewith =14 percentpositive.This nationalpeakregion for maximumnegativeLPC CG activity includestheKSC area. The largepeakcurrentstatisticsof Lyonsstill offer a smallprobability of occurrence.On a nationalbasis,theLPC -CG's (>75kA) constitute2.23percentof all negatives.However,the LPC +CG's(>75 kA) represent7.37percentof all positives.ForLPC CG's >200 kA and >400 kA, the percentages fall, but LPC +CG's still represent a greater percentage than LPC -CG's. Positive CG's >200 kA represent =0.08 percent of all LPC +CG's; while negative CG's >200 kA represent =0.02 percent of all LPC -CG's. For LPC CG's >400 kA the probabilities fall to 0.000 44 percent and 0.000 09 percent for positive and negative. The overall U.S. probability of occurrence of CG's (+ or -) >75, >200, and >400 kA is respectively =2.46, 0.018, and 0.000 1 percent. Keep in mind these overall probabilities involve only the statistics of lightning strike occurrences, i.e., not the true probability of a lightning stroke with a certain peak current hitting an object. In order to calculate that true probability, additional derivations are necessary. A.6 Sprites Observed Over KSC Sprites have been observed over the KSC area. During the 1997 summer field season at KSC, Dr. Mark Stanley of the New Mexico Institute of Technology captured at least four days of sprite data. Dr. Stanley remarked about his measurements: "I was surprised by how many positive CG's I detected during my KSC field program last summer (mid-May to mid-July). However, the ratio of negative CG's to positive CG's was probably still quite high due to the very large numbers of the former." Even Maier indicated: "In the KSC area our data show the largest peak currents are from negative flashes, not positive. However, the frequency distributions for positive flashes show a higher percentage of positives having big currents relative to negatives." According to Maier, positive flashes account for only two to four percent of CG strokes at KSC. A conclusion from this is if the sprite occurrence and positive CG correlation do exist, sprite occurrence should be less in Florida than in the Midwest. Dr. Stanley also stated: "Most of the sprites that I detected while at KSC were associated with positive CG's, though there may have been at least one which was caused by just an IC. In two years of research I have never detected a sprite which could clearly be associated with a negative CG. As for the magnitude of the positive CG's, I do not have the NLDN data yet. The static electric field change data that I obtained at KSC indicate that positive CG's associated with sprites on June 22 had rangenormalized step field changes significantly larger than those of average negative CG's from the same stonn. However, the differences were not spectacular, probably all <!00 kA. However, I can say something follow positive CG's and sometimes negative CG's. clearly indicate that positive CG's are considerably which seems to indicate that these positives were about the continuing currents (CC's) which often My electrostatic field change measurements of CG's more violent (by at least an order of magnitude) on average than negatives in regard to CC current magnitude. This is, in my opinion, the reason why positive CG's cause sprites and negatives don't. The peak current does not seem to be relevant to whether a particular positive CG will initiate a sprite." 16

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Boccippiousedall May throughOctober1995NLDN CG datawithin I 000km of KSC to computediurnal cyclesfor "positive" CGcurrents>50, >100,and>200kA. Datacountsweretalliedfor eachhour.Forpositiveflashes>50 and>100kA, the peakcount (>2000 and>400,respectively)occurs at 0000UTC (2000EDT). The minimumcount(about940and 165,respectively)occursat0600UTC (0200EDT). This indicatesdiurnalamplitudemodulationis a factorof =two for positive strokesnear KSC.The diurnalcyclefor peakpositiveCGcurrents>200kA waslessdiscernibledueto thesmall samplesize(countbetween7 and32 over24 hours). DiurnalpositiveCG KSC resultsby Boccippiodiffer with the diurnalresultsof Santis.8 However,Santisusedthetotal NLDN database(positivesandnegatives)for the entire U.S. between June 12, 1996, and October 9, 1996. Uniform diurnal cycle of CG strikes by Santis peaked at 1700 EDT (= 13 percent) with a minimum at 1000 EDT (<2 percent). 17

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APPENDIX B Space Shuttle Lightning Launch Commit Criteria Figure 9.8 in NASA TM 4511 depicts the SAE 1987 current test waveforms for severe direct lightning strikes to the NASA Space Shuttle. 47 NSTS 16007 LAUNCH COMMIT CRITERIA 4.5 Natural and Triggered Lightning Constraints AND BACKGROUND SSID: WEA-01 NOTICE: ANY CHANGES TO THIS SECTION WILL REQUIRE COORDINATION WITH THE 3OTH AND 45TH SPACE WING RANGE SAFETY OFFICES. Even when constraints are not violated, if any other hazardous conditions exist, the Launch Weather Officer will report the threat to the Launch Director. on the instability of the weather. The Launch Director may HOLD at any time based The Launch Weather Officer must have clear and convincing evidence the following constraints are not violated: A° Do not launch if any type of lightning is detected within I0 nautical miles (nmi) of the flight path within 30 minutes prior to launch, unless the meteorological condition that produced the lightning has moved more than 10 nmi away from the flight path. NATURAL LIGHTNING IS AN OBVIOUS HAZARD (COMPARED TO VEHICLE TRIGGERED LIGHTNING) AND IS ALSO THE MOST DIRECT EVIDENCE ELEC- TRIC FIELDS ARE PRESENT WITH SUFFICIENT INTENSITY TO CAUSE TRIG- GERED LIGHTNING. THE MEASURED FREQUENCY DISTRIBUTION OF THE DISTANCE BETWEEN SUCCESSIVE FLASHES TO GROUND APPROACHES ZERO NEAR 6 NMI; THUS 10 NMI PROVIDES A SAFETY FACTOR. THE 30-MINUTE TIME PERIOD WITHOUT LIGHTNING INDICATES THE STORM HAS DISSIPATED OR MOVED AWAY. HOWEVER, FORECASTERS MUST STILL REMAIN ALERT FOR REDEVELOPMENT OR FORMATION OF A NEW CELL. B. Do not launch if the flight path will carry the vehicle: (1) Through a cumulus cloud with its top between the +5.0 °C and -5.0 °C levels unless: (a) The cloud is not producing precipitation; AND 18

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(b) The horizontaldistancefrom thefurthestedgeof thecloud top to at leastone working field mill is lessthanthe altitudeof the-5.0 °C level or 3 nmi, whichever is smaller. AND (c) All field mill readings within 5 nmi of the flight path are between -100 V/m and + 1,000 V/m for the preceding 15 minutes. (2) Through cumulus clouds with tops higher than the -5.0 °C level. (3) Through or within 5 nmi (horizontal with tops higher than the -10.0 °C level. (4) Through or within 10 nmi (horizontal or vertical) of the nearest edge of cumulus clouds or vertical) of the nearest edge of any cumulonimbus or thunderstorm cloud, including nontransparent parts of its anvil. (5) Through or within i 0 nmi (horizontal or vertical) of the nearest edge of a nontransparent detached anvil for the first hour after detachment from the parent thunderstorm or cumulonimbus cloud. NOTE: Cumulus does not include altocumulus or stratocumulus. B(1) CUMULUS (CONVECTIVE) CLOUDS CAN DEVELOP AND PRODUCE ELECTRIC CHARGE VERY RAPIDLY. THE FREEZING LEVEL. HOWEVER, NORMALLY THIS OCCURS WELL ABOVE THE +5.0 °C LEVEL WAS SPECIFIED BECAUSE ELECTRIC CHARGE HAS BEEN SPECULATED TO OCCUR IN SOME "WARM" CLOUDS IN THE TROPICS AND BECAUSE CUMULUS CLOUDS CAN BUILD VERY RAPIDLY. CHARGE SUFFICIENT TO TRIGGER LICHTNING IS NORMALLY NOT DETECTED UNTIL THE CLOUD REACHES WELL ABOVE THE -10.0 °C LEVEL. THUS, IF THE CLOUD IS NOT PRODUCING PRECIPITATION (PRECIPITATION IS BELIEVED TO BE A NECESSARY CONDITION FOR CLOUD ELECTRIFICATION) AND THE GROUND-BASED FIELD MILLS ARE NOT MEASURING ELEVATED ELECTRIC FIELDS ASSOCIATED WITH THE ONSET OF CUMULUS CLOUD ELECTRIFICATION, THEN LAUNCH MAY BE PERMITTED THROUGH CLOUDS BELOW THE -5.0 °C LEVEL. B(2) AS CLOUD TOPS APPROACH-10.0 °C, CHARGE MAY DEVELOP VERY RAPIDLY. THUS, NO LAUNCH IS PERMITTED THROUGH CLOUDS WITH TOPS AT OR ABOVE -5.0 °C. B(3) CLOUDS WITH TOPS ABOVE -10.0 °C CAN CREATE ELECTRIC FIELDS OUTSIDE THE CLOUD WITH SUFFICIENT STRENGTH TO TRIGGER LIGHTNING. THUS, NO FLIGHT PATH IS PERMITTED WITHIN 5 NMI, HORIZONTALLY OR VERTICALLY, OF CLOUDS FROM -10.0 °C TO -20.0 °C. 19

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B(4) THE MOST DANGEROUS CLOUD IS THE CUMULONIMBUS WHICH TYPI- CALLY PRODUCES NATURAL LIGHTNING. THUS, THE DISTANCE CRITERION (10 NMI) IS THE SAME AS FOR NATURAL LIGHTNING IN RULE A. DANGEROUS ELECTRIC CHARGE CAN ALSO BE ADVECTED INTO THE HIGH LEVEL ANVIL PRODUCED BY A CUMULONIMBUS CLOUD, THUS THE FLIGHT PATH MUST REMAIN 10 NMI HORIZONTALLY AND VERTICALLY, FROM THE ANVIL. B(5) SIGNIFICANT CHARGE CAN REMAIN IN AN ANVIL FOR UP TO 1 HOUR AFTER IT DETACHESFROM ITS PARENT SOURCE CLOUD. THUS, THE SAME 10 NMI DISTANCE CRITERION APPLIES AS IN RULE B(4). AFTER 1 HOUR THE DETACHED CLOUD IS TREATED PER RULE F. C° Do not launch if, for Ranges equipped with a working surface electric field mill network, at any time during the 15 minutes prior to launch time the absolute value of any electric field intensity measurement at the ground is >1,000 V/m within 5 nmi of the flight path unless: (1) There are no clouds within 10 nmi of the flight path except (a) Transparent clouds OR (b) Clouds with tops below the +5.0 °C level that have not been associated with convective clouds with tops above the -10.0 °C level within the last 3 hours; AND (2) A known source of electric field (such as ground fog) that is occurring near the sensor, and that has been previously determined and documented to be benign, is clearly causing the elevated readings. (Documents dated April 3, 1997, defining benign ground fog, smoke, and sunrise effect, and the criteria to evaluate their presence, are located in the 45th Space Wing's Range Weather Operation Instruction 15-3, entitled "Launch Weather Procedures.") Constraint Monitoring, Evaluation, and Reporting •NOTE: For confirmed failure of the surface field mill system, the countdown and launch may continue, since the other lightning conditions. LCC completely describe unsafe meteorological GROUND-BASED FIELD MILLS (GBFM) JUST MEASURE THE ELECTRIC POTENTIAL AT THE EARTH'S SURFACE. THEY CAN ONLY INFER THE ELECTRIC FIELD IN AND NEAR CLOUDS ALOFT (WHICH PERHAPS DECREASE WITH THE HORIZONTAL DISTANCE CUBED AND THE CHARGE HEIGHT SQUARED); AND THEIR READINGS CAN BE MASKED BY INTERVENING LAYERS OF SPACE CHARGE BETWEEN THE MILLS AND THE CLOUD. 20

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MEASUREMENTSOF CHARGEALOFT USINGAIRCRAFT EQUIPPEDWITH FIELD MILLS, AND EXPERIMENTSWITH ROCKETSFIRED INTO CLOUDSTO TRIGGERLIGHTNING, INDICATE GBFM MEASUREMENTS>1,000V/M CAN BE INDICATIVE OF ELECTRICFIELDSALOFT SUFFICIENTLY HIGH TO TRIGGER LIGHTNING. THERE ARE OTHERNEAR-SURFACESOURCESOF ELECTRIC CHARGE NOT RELATEDTO CHARGEALOFT; FOR INSTANCEGROUNDFOG, SMOKE, POWER LINES, SEASPRAY,ETC. IF THERE IS NO POSSIBLESOURCEOF CHARGE ALOFT AND THERE IS A CONFIRMED,DOCUMENTED SOURCEOF NEAR- SURFACECHARGE,THEN THIS RULE IS NOT VIOLATED. NOTE: DOCUMENTEDMEANS SUFFICIENTDATA HAS BEEN GATHEREDON THE PHENOMENATO PROPERLYSTUDY IT, AND CIRCUMSTANCESCAUSING IT TO BE PRESENTARE UNDERSTOODAND WRITTEI_IN A TECHNICAL REPORT. D. Do not launch if the flight path is through a vertically continuous layer of clouds with an overall depth of 4,500 feet or greater where any part of the clouds is located between the 0.0 °C and the -20.0 °C levels. THIS RULE COVERS STRATIFORM CLOUDS. ELECTRIFICATION PROCESSES PRIMARILY OCCUR WITHIN CLOUDS BETWEEN -0.0 AND -20.0 °C, AND INCREASE WITH INCREASING CLOUD THICKNESS. IF CLOUD LAYERS ARE CONNECTED BY TURRETS, THE CLOUD LAYER DEPTH IS DETERMINED BY MEASURING FROM THE BASE OF THE LOWER CLOUD LAYER TO THE TOP OF THE HIGHER CLOUD LAYER. THE TURRETS INDICATE POSSIBLE CHARGE- PRODUCING CONVECTION, AND THE CHARGE MAY BE ADVECTED INTO THE INDIVIDUAL LAYERS. THUS, AN INDIVIDUAL CLOUD LAYER MAY NOT BE 4,500 FEET THICK BUT THE RULE MAY BE VIOLATED IF TWO LAYERS ARE CONNECTED AND THEIR LAYERS SUM TO 4,500 FEET OR GREATER. E. Do not launch if the flight path is through any clouds that (1) Extend to altitudes at or above the 0.0 °C level AND (2) Are associated with disturbed weather that is producing moderate (29 dBz) or greater precipitation within 5 nmi of the flight path. CLOUDS EXTENDING ABOVE THE FREEZING LEVEL AND SUFFICIENTLY ACTIVE TO PRODUCE MODERATE OR GREATER PRECIPITATION CAN ALSO CREATE ELECTRIC CHARGE. THIS CHARGE CAN BE ADVECTED INTO ASSOCI- ATED CLOUDS AND CAN CREATE ELECTRIC FIELDS AT A DISTANCE. THUS, IF THE PRECIPITATION IS WITHIN 5 NMI, THIS RULE IS VIOLATED. 21

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F. Do not launchif the flight pathwill carry thevehicle: (1) Throughanynontransparentthunderstormor cumulonimbusdebriscloudduring the first 3 hoursafterthe debriscloud formedfrom the parentcloud. (2) Within 5 nmi (horizontalor vertical)of the nearestedgeof a nontransparentthunderstormor cumulonimbusdebriscloud duringthe first 3 hoursafterthe debriscloud formedfrom a parentcloud,UNLESS (a) Thereis at leastone working field mill within 5 nmi of the debris cloud; AND (b) All electric field intensity measurements at the ground are between +1,000 V/m and -1,000 V/m within 5 nmi of the flight path during the 15 minutes preceding the launch time; AND (c) The maximum radar return from the entire debris cloud is <10 dBz during the 15 minutes preceeding launch time. (3) The start of the 3-hour period is reckoned as follows: (a) Detachment--if the cloud detaches from the parent cloud: The 3-hour period begins at the time when cloud detachment is observed or at the time of the last detected lightning discharge (if any) from the detached debris cloud, whichever is later. (b) Decay or detachment uncertain--if it is not known whether the cloud is detached or the debris cloud forms from the decay of the parent cloud: The 3-hour period begins at the time when the parent cloud top decays to below the altitude of the -10.0 °C level, or at the time of the last detected lightning discharge (if any) from the parent cloud or debris cloud, whichever is later. CLOUDS PRODUCED BY CUMULONIMBUS AND THUNDERSTORMS CAN RETAIN THEIR CHARGE EVEN AFTER THE PARENT STORM HAS DECAYED AND STOPPED PRODUCING CHARGE, OR AFTER THE CLOUD HAS BROKEN AWAY FROM THE CHARGE SOURCE. AIRBORNE FIELD MILL MEASUREMENTS SUGGEST MOST OF THE CHARGE HAS DECAYED WITHIN 90 MINUTES. HOW- EVER, THE CRITERION WAS SET AT 3 HOURS DUE TO THE UNCERTAINTY REGARDING THE START OF THE CLOUD DECAY OR CLOUD BREAKOFF TIME, AND THE POSSIBILITY OF BRIEF INTERNAL CHARGE GENERATION WITHIN THE CLOUD EVEN AFTER BREAKING OFF FROM THE PARENT CLOUD. 22

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SINCE NEGLIGIBLE RADAR RETURNSAND BENIGN GBFM READINGS INDICATE THE CLOUD IS NOT PRODUCINGCHARGE,AND ANY RESIDUAL CHARGE HAS DECAYEDSUBSTANTIALLY,THEN THE 5 NMI STANDOFFCAN BE REDUCEDTO JUSTA "FLIGHT THROUGH" PROHIBITION.NOTE BENIGN GBFM VALUES CANNOT BE USEDBY THEMSELVESTO CONCLUDETHE CLOUD CAN BE SAFELYPENETRATED,SINCE SHIELDING LAYERS CAN MASK SIGNIFICANT FIELDS (AND CHARGE)INSIDE THE CLOUDSFROM THE GBFM NETWORK. TRANSPARENTDEBRISCLOUDSARE NOT CONSIDEREDCAPABLE OF CARRY- ING SUFFICIENTCHARGETO BE DANGEROUS. G. Definitions/Explanations (1) Anvil stratiformor fibrouscloudproducedby the upperleveloutflow or blow-off from thunderstormsor convectiveclouds. (2) Cloudedge--Thevisible cloudedgeis preferred.If this is not possible,thenthe 10dBz radarcloud edgeis acceptable. (3) Cloudlayer--An arrayof clouds,not necessarilyall of the sametype,whosebasesare approximatelyat thesamelevel.Also, multiple arraysof cloudsat differentaltitudes thatareconnectedvertically by cloud elements;e.g.,turretsfrom onecloud arrayto another.Convectiveclouds(e.g.,cloudsfalling underRule B) areexcludedfrom this definition unlesstheyareimbeddedwith othercloud types. (4) Cloudtop--The visible cloud top is preferred.If this is not possible,thenthe 13dBz radarcloud top is acceptable. (5) Cumulonimbuscloud--Any convectivecloud with anypart abovethe-20.0 °C temperaturelevel. (6) Debriscloud--Any nontransparentcloud thathasbecomedetachedfrom a parent cumulonimbuscloudor thunderstorm,or resultsfrom the decayof a parentcumulonimbuscloudor thunderstorm. (7) Documentedwith respectto rule C(2),"documented"meanssufficientdatahasbeen gatheredon the benignphenomenato both understandit andto developprocedures to evaluateit, andthesupportingdataandevaluationhavebeenreportedinatechnical report,journal article,or equivalentpublication.Forlaunchesat the EasternRange, copiesof the documentationshall bemaintainedby the 45thWeatherSquadronandthe KSC WeatherProjectsOffice.The proceduresusedto assessthe phenomenaduring launchcountdownsshallbe documentedandimplementedby the45thWeather Squadron. 23

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(8) Electric field (for surface-based electric field mill measurements)--The l-minute arithmetic average of the vertical electric field (Ez) at the ground, such as measured by a ground-based field mill. The polarity of the electric field is the same as that of the potential gradient; that is, the polarity of the field at the ground is the same as that of the charge overhead. (9) Flight path--The planned flight trajectory including its uncertainties ("error bounds"). (lO) Precipitating cloud--Any cloud containing precipitation, producing virga, or having radar reflectivity greater than 13 dBz. (11) Thunderstorm--Any cloud that produces lightning. (12) Transparent synonymous with visually transparent--Sky cover through which higher clouds, blue sky, stars, etc., may be clearly observed from below. Also, sky cover through which terrain, buildings, etc., may be clearly observed from above. Sky cover through which forms are blurred, indistinct, or obscured is not transparent. 24 -'

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REFERENCES I. Beard, K.; and Ochs, H.: "Cloud Electrification," pp. 984-992, 1983. Rev. in Geophys. Space Phys., Vol. 21, 2. Leteinturier, C.; et al.: "Current and Electric Field Derivatives in Triggered Lightning Return Strokes," .l. Geophys. Res., Voi. 95, pp. 818-828, 1990. 3. Goodloe, C.: "Lightning Protection Guidelines 209734, May 1999. For Aerospace Vehicles," NASA/TM--1999- 4. Gabrielson, B.: The Aerospace Engineer's Handbook of Lightning Protection, Interference Control Technologies, Inc., 1988. 5. Stahmann, J.: "Launch Pad Lightning Protection Effectiveness," 1991 International Aerospace and Ground Conference on Lightning and Static Electricity, Cocoa Beach, FL, pp. 3 I-1 through 31- 12, April 16-19, 1991. 6. Mach, D." "Shuttle Lightning Threat Analysls, AMS Third International Conference On Aviation Weather Systems, Anaheim, CA, pp. 92-95, January 30-February 3, 1989. 7. Chai, J.; et al.: "Survey of CGLSS/SLC40 Lightning Data and Retest Criteria," IEEE 1997 International Symposium on Electromagnetic Compatibility, Austin, TX, pp. 391-396, August ! 8-22, 1997. 8. Santis, L.: "The Calculated Risk of Experiencing ISEE Proceedings of tile 14th Annual Symposium Orleans, LA, pp. 107-119, February 8-11, 1998. a Lightning Caused Unplanned Detonation," o11 E.vplosives and Blasting Research, New 9. Uman, M.: "The Lightning Discharge," Int. Geophys. Set, Vol. 39, Academic Press, Inc., 1987. 10. Fisher, E; ct al.: "Lightning Protection of Aircraft," Chapter 2, Lightning Technologies, Inc., Pittsfield, MA, 1990. 1 I. "Launch Commit Criteria and Background," NSTS 16007, Revision F, Change No. 99, Section 4.5, "Natural and Triggered Lightning Constraints." 12. Cianos, N.; and Pierce, E.T.: "A Ground-Lightning Environment For Engineering Usage," Stanford Research Institute, Technical Report I, SRI Project 1834, August 1972. 13. Galeja, J.: Terrestrial Propagation of Long Electromagnetic Waves, Pergamon Press, 1972. 25

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1. Viemeister,E: The Lightning Book," MIT Press, 1972. 15. Mailander, J.: "Climate of the Kennedy Space Center and Vicinity," NASA TM-103498, June 1990. 16. Golde, R.: Lightning--Volume 2---Lightning Protection, Academic Press, Inc., 1977. 17, Jafferis, W.: "Rocket Triggered Lightning--Kennedy Space Center and Beyond," 1995 International Aerospace and Ground Conference On Lightning and Static Electricity, p. 57-1, September 26-28, 1995. 18. Marshall, L.: "Capturing Sprites and Elves From Afar," Penn. State and AGU Release, December 16, 1996. 19. Volland, H. (Editor): Handbook of Atmospheric Electrodynamics, CRC Press, Chapter 4, "Lightning Currents," T. Ogawa, pp. 93-136, 1995. 20. Orville, R.; et al.: "Cloud-to-Ground Lightning Flash Characteristics from June 1984 Through May 1985," J. Geophys. Res., Vol. 92, pp. 5640-5644, May 20, 1987. 21. Stolzenburg, M.: "Observations of High Ground Flash Densities of Positive Lightning in Summertime Thunderstorms," Monthly Weather Rev., Vol. 122, p. 1740, August 1994. 22. Ishif, M.; and Hojo, J.: "On The Statistics of Field Waveforms Associated With Lightning Return Strokes," 1988 International Aerospace and Ground Conference On Lightning and Static Electricity, Oklahoma City, OK, April 19-22, 1988. 23. Narita, K.; et al.: "Bipolar Lightning in Winter at Maki, Japan," J. Geophys. Res., Vol. 94, No. D11, pp. 13191-13195, September 30, 1989. 24. Fisher, R.; et al.: "'Parameters of Triggered-Lightning Flashes in Florida and Alabama," J. Geophys. Res., Vol. 98, No. DI2, pp. 22887-2902, December 20, 1993. 25. Mach, D.; and Rust, D.: "Photoelectric Return-Stroke Velocity and Peak Current Estimates in Natural and Triggered Lightning," J. Geophys. Res., Vol. 94, No. DI 1, pp. 13237-13247, September 20, 1989. 26. Bankson, N.: "Lightning Current Rate of Rise in the New Lightning Flash Model for the Space Shuttle Program," 1991 International Aerospace & Ground Conference on Lightning and Static Electricity, Cocoa Beach, FL, Vol. !, pp. 5-1 through 5-14,April 16-19, 1991. 27. Depasse, P.: "Statistics on Artificially Triggered Lightning," J. Geophys. Res., Vol. 99, No. D9, pp. 18515-18522, September 20, 1994. 28. Turman, B.: "Detection of Lightning Superbolts," J. Geophys. Res., Vol. 83, p. 2566, 1977. 26

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1. Goto,Y.; andNarita, K.: "ElectricalCharacteristicsof Winter Lightning," J. Atmospheric and Terrest. Phys., Vol. 57, No. 5, pp. 449-458, April l, 1995. 30. Sawada, S.; et al.: "Current Measurement of Lightning Superbolt at the Japan Sea Coast," NOAA International Aerospace and Ground Conference April 1, 1988. on Lightning and Static Electricity, pp. 103-111, 31. Uman, M.; et al.: "An Unusual Lightning Flash at Kennedy Space Center," Science, Vol. 201, No. 4350, July 7, 1978. 32. Orville, R.; et al." "Cloud-to-Ground Lightning Flash Characteristics in the Contiguous United States: 1989-1991," J. Geophys. Res., Vol. 99, pp. 10833-10841, May 20, 1994. 33. Orville, R.; and Silver, A.C.: "Annual Summary-Lightning Ground Flash Density in the Contiguous United States: 1992-95," Monthly Weather Rev., Vol. 125, pp. 631--638, April 1997. 34. Lyons, W.: "Final Report--Sensor System to Monitor Cloud-to-Stratosphere Electrical Discharges," submitted to NASA/KSC under NASA SBIR Phase II, Contract NAS 10-12113, April 25, 1996. 35. Orville, R.: "Peak-Current Variations of Lightning Nature, Vol. 343, pp. 149-151, January 11, 1990. Return Strokes as a Function of Latitude," 36. Wacker, R.: "Changes in Measured Lightning Return Stroke Peak Current After the 1994 National Detection Network Upgrade," M.S. thesis, Texas A&M University, May 1997. 37. Hodanish, S.; and Sharp, D.: "A 10-Yr. Monthly Lightning Climatology of Florida: 1986-1995," Weather & Forecasting, Vol. 12, pp. 439-448, September 1997. 38. Boccippio, D.; et al.: "Sprites, ELF Transients, and Positive Ground Strokes," Science, Vol. 269, pp. 1088-1091, August 25, 1995. 39. Winckler, J.: "Further Observations of Cloud-Ionosphere Electrical Discharge Above Thunderstorms," J. Geophys. Res., Vol. 100, pp. 14335-14345, 1995. 40. Sentman, D.; et al.: "Preliminary Results From the Sprites 94 Aircraft Campaign: Red Sprites," Geophys. Res. Letters, Vol. 22, No.10, pp. 1205-1208, May 15, 1995. 41. Lyons, W.: "Sprites, Elves, and Blue Jets," Weatherwise, August-September 1997. 42. Fullekrug, M.; et al.: "On the Accuracy of Arrival Azimuth Determination of Sprite-Associated Lightning Flashes by Earth-Ionosphere Cavity Resonances," Geophys. Res. Letters, Vol. 23, No. 25, pp. 3691-3694, December 15, 1996. 43. Inan, U.; et al.: "VLF Signatures of Ionospheric Disturbances Associated with Sprites," Geophys. Res. Letters, Vol. 22, No. 24, pp. 3461-3464, December 15, 1995. 27

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1. Staff: GeographyInstitute,Universityof Alaska,"Red SpritesandBlue Jets,"internethomepage, http://elf.gi.alaska.edu/sprites.html,1997. 45. Wakefield,J.: "High-Altitude FlashesMystify Scientists,"Eos AGU, Vol. 75, No. 51, pp. 601-602, December 20, 1994. 46. Lyons, W.; et.al.: "Large Peak Current Cloud-to-Ground Lightning Flashes during the Summer Months in the Contiguous United States," Monthly Weather Rev., Vol. 126, pp. 2217-2233, August 1998. 47. Johnson, D.L.: "Terrestrial Environment (Climatic) Criteria Guidelines for Use in Aerospace Vehicle Development, 1993 Revision, Section IX Atmospheric Electricity," NASA TM-4511, August 1993. 28

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BIBLIOGRAPHY Boccippio, D.: Marshall Space Flight Center, Hydrology January 1998. Maier, M.: Patrick AFB, Computer Sciences Raytheon, Research Office, personal communications, persona! communications, February 1998. Stanley, M.: New Mexico Institute of Technology, personal communications, February 1998. 29

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REPORT DOCUMENTATION Form Approved PAGE OMBNo.0704-0188 Public reporting burden for this collection of information is estimated to average t hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information, Send comments regarding this burden estimate or any other aspect of Ibis coi]ect_onof information, including suggestions for reducing this burden, to Washington Headquarlers Services. Directorate for Information Operation and Reports, 12t 5 Jefferson Davis Highway. Suite t204. Arlington. VA 22202-4302, and to the Office of Management and Budget. Paperwork Reduction Project (0704-0188), Washington, DC 20503 1. AGENCY USE ONLY (Leave B/ank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED May 1999 Technical Memorandum TITLE AND SUBTITLE 5. FUNDING NUMBERS Analysis and Assessment of Peak Lightning Current Probabilities at the NASA Kennedy Space Center AUTHORS D.L. Johnson and W.W. Vaughan* ADDRESS(ES) B. PERFORMING ORGANIZATION PERFORMINGORGANIZATIONNAMES(S)AND George C. Marshall Space Flight Center Marshall Space Flight Center, Alabama 35812 REPORT NUMBER M-977 ADDRESS(ES) 10. SPONSORING/MONITORING 9. SPONSORING/MONITORINGAGENCYNAME(S)AND AGENCY REPORT NUMBER National Aeronautics and Space Administration NASA/TM--1999-21013 ! Washington, DC 20546-0001 11. SUPPLEMENTARY NOTES Prepared by Electromagnetics and Aerospace Environments Branch, Systems Engineering Division, Systems Analysis and Integration Laboratory, Science and Engineering Directorate *University of Alabama in Huntsville 12a. DISTRIBUTION/AVAILABILITY STATEMENT Unclassified-Unlimited Subject Category 18 Nonstandard Distribution 13. ABSTRACT (Maximum 200 words) 12b. DISTRIBUTION CODE This technical memorandum presents a summary by the Electrornagnetics and Aerospace Environments Branch at the Marshall Space Flight Center of lightning characteristics and lightning criteria for the protection of aerospace vehicles. Probability estimates are included for certain lightning strikes (.peak currents of 200, 100, and 50 kA) applicable to the National Aeronautics and Space Administration Space Shuttle at the Kennedy Space Center, Florida. during rollout, on-pad, and boost/launch phases. Results of an extensive literature search to compile information on this subject are presented in order to answer key questions posed by the Space Shuttle Program Office at the Johnson Space Center concerning peak lightning current probabilities if a vehicle is hit by a lightning cloud-to-ground stroke. Vehicle-triggered lightning probability estimates for the aforementioned peak currents are still being worked. Section 4.5. however, does provide some insight on estimating these same peaks. 14. SUBJECT TERMS lighting characteristics and criteria, aerospace peak current probabilities, vehicle-triggered 15. NUMBER OF PAGES vehicle lightning protection, 40 16. PRICE CODE lightning A03 17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20.LIMITATIONOFABSTRACT OF REPORT OF THIS PAGE Unclassified Unclassified NSN 7540 01-280-5500 OF ABSTRACT Unclassified Unlimited Standard Form 298 (Rev 2-89) Pres<:ribedbyANSI SId 239 lS 298 102

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ERRATA NASA TECHNICALMEMORANDUM NASA/TM-2000-210131 ANALYSIS AND ASSESSMENT OF PEAK LIGHTNING CURRENT PROBABILITIES AT THE NASA KENNEDY SPACE CENTER By D.L. Johnson May 1999 Page 30, Block 10, Sponsoring/Monitoring and W.W. Vaughan Agency Report Number, change report number from NASA/TM- 1999-210131 to NASA/TM-2000-210131.

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