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SPA CE OPERATIONS

P.O. Box 707, Br/gham City, UT 84302-0707 (801) 863-351 t

_f(NASA-C_.-134109) RSRM TOP HAT COVf_ N01-22303 _2---SIMULAT_ LIGHTNING TEST,

Repart (Tniokol Corp.)

V_LUME 1 Findl

31 p CSCL 22B

UnclesG3/1B 0333_49

I

mm

https://ntrs.nasa.gov/search.jsp?R=19910012990 2018-07-20T09:21:27+00:00Z

"__ CORPORATION

SPACE OPERATIONS

RSRM Top Hat Cover Simulator Lightning Test

Final Test Report

TWR-60834

Volume I

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Prepared by:

" Test l_Im'In-ingand _eports

Systems Engineer

Approved by:

iTest Planning and Reports

Supervisor

Design En(gineer

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ECS No. SS4156

_7__--_ CORPORATION

SPACE OPERATIONS

ABSTRACT

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The test sequence was to measure electric and magnetic fields induced inside a

redesigned solid rocket motor case when a simulated lightning discharge strikes an

exposed top hat cover simulator. The test sequence was conducted between 21 June

and 17 July 1990. The Lest sequence was performed at the Thiokol Corporation

Lightning Test Complex in Wendover, Utah.

Thirty-six high rate-of-rise Marx generator discharges and eight high current

bank discharges were injected onto three different test article configurations. Attach

points included three locations on the top hat cover simulator and two locations on

the mounting bolts.

Top hal cover simulator and mounting bolt damage (surface pitting and melting)

and grain cover damage (fiberglass Lop was damaged and frayed at arc attachment

point) was observed. Overall electric field levels were well below 30 kilovolts/meter.

Electric field levels ranged from 184.7 to 345.9 volts/meter and magnetic field levels

were calculated from 6.921 to 39.73 amperes/meter.

It is recommended that the redesigned solid rocket motor top hat cover be used

in Configuration No. 1 or Configuration No. 2 as an interim lightning protection

device until a lightweight cover can be developed.

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CONTENTS

Volume I

Section

1

2

3

4

5

6

7

INTRODUCTION ...................................

1.1 TEST ARTICLE DESCRIPTION ................

OBJECTIVES ......................................

EXECUTIVE SUMMARY .............................

3.1 SUMMARY ................................

3.2 CONCLUSIONS ............................

3.3 RECOMMENDATIONS .......................

INSTRUMENTATION ...............................

PHOTOGRAPHY ...................................

RESULTS AND DISCUSSION .........................

6.1 TEST ARTICLE ASSEMBLY ...................

6.2 SIMULATED LIGHTNING TEST ...............

6.3 TEST ARTICLE INSPECTION AND RESULTS .....

APPLICABLE DOCUMENTS ..........................

Appendix

A

B

Volume II

Resistance Measurements .............................

Lightning Test Data Plots .............................

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FIGURES

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RSRM Top Hat Cover Simulator Test Article ...............

Worst-Case Model of Lightning Discharge .................

Top Hat Cover Simulator Mounted Onto Test Article ........

Lightning Detector Mounted Onto Test Article .............

Gap Thickness Between Top Hat Cover Simulator

and the Handling Ring ................................

Attach Point Diagram ................................

Surface Pitting Caused by HCB Discharge to Mounting

Bolts and Top Hat Cover Simulator ......................

Surface Pitting Inflicted Upon Top Hat Cover Simulator ......

Carbon Spot on Grain Cover Proving Unwanted

Arcing Occurred ....................................

Damage to Grain Cover After Subjection to

Marx Discharge ....................................

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Tabl_____e

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TABLES

Total Discharges ....................................

Configuration Test Sequence ..........................

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1

INTRODUCTION

This report documents the procedures, performance, and results obtained from the

evaluation of simulated lightning discharges to an RSRM test article. The test

sequence was conducted following WTP-0245, Rev A. There were three purposes of

this test.

a. Measure the electric field levels inside the redesigned solid rocket motor (RSRM)

case when a simulated lightning discharge is injected onto the top of the test

article. The fields should not exceed 30 kilovolts per meter (kV/m) (1/10 the

dielectric breakdown of the propellant) inside the case.

b. Determine if any arcing occurs between the case, handling ring, grain cover,

segmented ring, or top hat cover simulator.

c. Evaluate methods of detecting a lightning attachment to a segment while in the

vertical transportation mode at Kennedy Space Center (KSC).

This test sequence was accomplished by injecting simulated lightning discharges

onto a top hat cover simulator, mounting bolts, and a grain cover, and then evaluating

the measured electric fields and calculated magnetic fields inside the empty RSRM

case.

The test article was placed between two horizontal grids of a peaking capacitor

(Figure 1). The peaking capacitor has a 9-m distance between two parallel grids. The

two parallel 2,500-m 2 wire grids (upper and lower) make up two plates of a 2.5-nano-

farad (nF) capacitor.

The Marx generator discharges were by direct arc attachment to the top hat

cover simulator, the mounting bolts, and the grain cover. The Marx discharges

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simulated the fast rise in current with respect to time of a worst-case lightning

discharge to unprotected flight hardware on the ground (Figure 2, points A - B), as

defined in NSTS 07636, Rev D.

The high current bank (HCB) simulated lightning discharges were by direct arc

attachment to the top hat cover simulator and the mounting bolts. The HCB

simulated the peak current of a worst-case lightning discharge to unprotected flight

hardware on the ground (Figure 2, points B - C), as defined in NSTS 07636, Rev D.

The test sequence was completed on 17 July 1990. Simulated lightning

discharge testing was performed at the Thiokol Corporation Lightning Test Complex

in Wendover, Utah. Testing complied with JSC 20007 and NSTS 07636, Rev D. This

test was part of an ongoing lightning test program to evaluate the effects of lightning

strikes on the complete RSRM and Space Transportation System.

1.1 TEST ARTICLE DESCRIPTION

All hardware components used in the test article configurations are included in this

test article description except those that had no effect on the results. Deviations

from the configurations listed in WTP-0245, Rev A, were approved by the Integration

Engineer and Program Manager. Three test article configurations were tested using

the Marx generator and the HCB. Table 1 indicates the number of discharges per

configuration and the total number of discharges for each current bank.

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Table I. Total Discharges

Number of Discharges

Configuration No. Marx Current Bank High Current Bank

2 26 3

43 6

4 4

36Total

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Configuration No. 1 listed in WTP-0245, Rev A, was not used because of warping

during the manufacturing of the top hat simulator. This warping prevented the top

hat simulator from making complete contact with the handling ring when all of the

bolts were installed. Configurations No. 2 and 3 were considered worst-case situations.

The rationale was that if the worst-case configuration could survive the test, then the

nominal configuration could survive the test. The fourth configuration listed in this

document was not listed in WTP-0245, Rev A, but was added to the test sequence for

evaluation purposes.

1.1.1 Configuration No. 2

Test article Configuration No. 2 consisted of a test stand placed on the lower capacitor

grid with an empty RSRM case segment (1U50715-02) mounted vertically. Installed

around the top edge of the case was a handling ring (8U50943-03), grain cover

(8U75816-01), and segmented ring (8U50929-03). Mounted above the grain cover onto

the handling ring was a top hat cover simulator (Figure 3). WTP-0245 Configuration

No. 2 calls for 0.25-in. shims to be placed between the top hat simulator and the

handling ring, which was intended to simulate warping of the cover. During the

manufacturing process the top hat simulator warped making the use of shims

unnecessary.

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Four lightning detectors (8U76447) were mounted to the case (Figure 4) using a

piece of polystyrene foam and olive drab waterproof tape (Permacel No. P672, Thiokol

Corporation Stock No. 57-742061). Two of the detectors had sensitivities less than

500 amperes per meter (A/m), and the other two detectors had sensitivities greater

than 500 A/m. The detectors were installed for detection 500 A/m during a Marx

discharge to the test article.


The next test article configuration consisted of a test stand placed on the lower

capacitor grid with an empty RSRM case segment (1U50715-02) mounted vertically.

Installed around the top edge of the case was a handling ring (8U50943-03) and

segmented ring (8U50929-03). Mounted onto the handling ring was a top hat cover

simulator. Non-conductive shims (0.25-in. thick) were to be installed between the

handling ring and the top hat cover simulator. However, due to warping during the

top hat simulator manufacturing process, shims were not needed or installed. The

grain cover was not used.

1.1.3 Configuration No, 4

This test article configuration consisted of a test stand placed on the lower capacitor

grid with an empty RSRM case segment (1U50715-02) mounted vertically. Installed

around the top edge of the case was a handling ring (8U50943-03), grain cover

(8U75816-01), and segmented ring (8U50929-03). The top hat cover simulator was not

installed; only the grain cover was used.

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2

OBJECTIVES

The objectives of Test Plan WTP-0245 were:

A. Verify that the induced electromagnetic field levels are less than 30 kV/m when

the test article is subjected to a simulated lightning discharge.

B° Verify that no arcing occurs between the case, handling ring, grain cover, or top

hat cover simulator when subjected to a simulated lightning discharge.

C. Evaluate methods of detecting a lightning discharge to the RSRM.

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3

EXECUTIVE SUMMARY

3.1 SUMMARY

Additional information and details can be found in Section 6 (Results and Discussion).

A total of 36 Marx generator discharges were conducted. A total of eight HCB

discharges were conducted. A total of 44 lightning current discharges were made

during this test sequence.

The HCB was charged to approximately 36,000 V for each discharge, which

resulted in peak currents of approximately 1.75 x 105 amperes (A). The Marx

generator was charged to approximately 20,000 V for each discharge, which resulted in

peak rise rates of approximately 1.4 x 1011 amperes per second (A/s). The highest

rise rate for the Marx generator was 3.9 x 10 zz A/s.

None of the discharges resulted in an electric field larger than 345.9 V/m. The

largest magnetic field calculated from the surface current data was 39.73 A/m. The

data indicates that the electric field levels measured inside the test article are below

the limit of 30 kV/m in all configurations. The measured electric field levels were not

strong enough to cause dielectric breakdown of the propellant.

The photographic documentation indicates that Configuration No. 2 provides

the necessary arcing protection between the test article hardware components.

Configurations No. 3 and 4 showed evidence of arcing. Top hat cover simulator and

mounting bolt damage (surface pitting and melting) and grain cover damage (fiberglass

top damaged and frayed at arc attachment point) was observed.

Two lightning detectors with sensitivities less than 500 A/m detected induced

current on the case from a Marx discharge. Two lightning detectors with sensitivities

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greater than 500 A/m did not detect the simulated lightning currents from the Marx

discharge. The lightning detector performance indicates that the more-sensitive

lightning detectors are adequate to detect surface currents induced by the fast rising

current portion of the worst-case lightning discharge.

3.2 CONCLUSIONS

The following is a list of conclusions as they relate specifically to the objectives.

Additional information about the conclusions can be found in Section (Results and

Discussion).

Obj ectives Conclusions

A° Verify that the induced

electromagnetic field levels are

less than 30 kV/m when the test

article is subjected to a simulated

lightning discharge.

Verified. The electric field levels and

magnetic field levels were well below

the limit. The largest measured

electric field being 345.9 V.

So Verify that no arcing occurs

between the case, the handling

ring, the grain cover, or the top

hat cover simulator when

subjected to a simulated lightning

discharge.

Partially Verified. No arcing was

detected between any of the hardware

components in Configuration No. 2.

Photographic documentation was used

to verify this conclusion.

In Configuration No. 2 no arcing was

detected between the top hat cover

simulator and the handling ring

during the Marx attachments.

During the HCB attachments, arcing

was detected between the handling

ring and the top hat cover simulator.

Arcing was detected between the

grain cover and handling ring in

Configuration No. 4. Photographic

documentation was used to verifythese conclusions.

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C.

Objectives

Evaluate methods of detecting a

lightning discharge to the RSRM.

Conclusions

Evaluated. Two detectors with

sensitivities less than 500 A/m

detected the simulated lightning

discharge indicating that thesedetectors can detect the case surface

currents induced from the Marx

generator.

Two lightning detectors with

sensitivities greater than 500 A/m did

not detect the case surface currents

induced by the Marx generator.

3.3 RECOMMENDATIONS

3.3.1 Electromagnetic Fields

No further testing is recommended to determine electric field levels induced within

the test article. The levels measured were 1/100 the objective limit (1/1000 of the

dielectric breakdown point of the RSRM propellant).

3.3.2

Additional testing, to determine if arcing between hardware components occurs, is not

recommended. Test article Configuration No. 2 survived 26 Marx discharges and four

HCB discharges with no arcing. This indicates that this configuration provides

adequate arcing protection between hardware components.

3.3.3 Lightning Detectors

The lightning detectors presently being used to monitor railcar shipments are

adequate for the detection of a lightning strike to a segment and should be used for

this purpose. However, additional testing with a goal to develop a more practical

method of detecting a lightning strike should continue.

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INSTRUMENTATION

Instrumentation used during this test was a Nanofast Electric Field Sensor (model No.

EFS1) and two magnetic flux density derivative sensors, EG&G model MGLS5A (B dot

sensors). The electric field sensor was calibrated by the manufacturer on 29 June

1990. The B dot sensor was calibrated by the manufacturer before being purchased in

1987, and did not require any new calibrations.

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PHOTOGRAPHY

Still color photographs were taken of the test article assembly and during the

simulated lightning discharges. Copies of the photographs (Series 118336, 118337,

118338, 118339, 118340, and 118476) are available from the Thiokol Photographic

Services department.

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RESULTS AND DISCUSSION

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6.1 TEST ARTICLE ASSEMBLY

The test article was configured three different ways. Each configuration is detailed in

the following sections.


The RSRM top hat cover simulator test article was assembled per WTP-0245, Rev A.

This configuration consisted of a test stand placed on the lower parallel peaking

capacitor grid, an empty RSRM segment mounted vertically on the test stand, a

segmented ring, a handling ring, a grain cover, and a top hat cover simulator. Due to

warping there was a gap in excess of 0.25 in., so the nonconductive shims were not

used.


This configuration consisted of a test stand placed on the lower parallel peaking


segmented ring, a handling ring and a top hat cover simulator. This configuration did

not include the grain cover. The 0.25-in. shims were not installed between the top

hat cover simulator and the handling ring. The shims were not installed because the

gap between the top hat cover simulator and the handling ring was a minimum of

0.25 in. at several locations around the circumference of the test article (Figure 5).


This configuration consisted of a test stand placed on the lower parallel plate peaking


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segmented ring,a handling ring,and a grain cover.

the top hat cover simulator.

This configuration did not include

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6.2 SIMULATED LIGHTNING TEST

6.2.1 Discharge Locations/Modes

The discharge down-conductor was positioned on the top of each test article

configuration in the following five locations (Figure 6).

Location No. 1: At 1-ft radial distance in from the RSRM case edge

Location No. 2: On the mounting bolt at 0 deg

Location No. 3: At 2-ft radial distance from the centerline of the RSRM case

Location No. 4: At the RSRM case centerline position

Location No. 5: On the mounting bolt at 180 deg

A total of 36 Marx generator discharges were conducted. A total of eight HCB

discharges were conducted. A total of 44 electrical current discharges were conducted

during this test sequence.

The discharge down-conductor was positioned on the top hat cover simulator,

the mounting bolts, and the grain cover (Figure 6). The Marx generator was charged

to approximately 26,000 V for each discharge, which resulted in peak current rise

rates of 2 x 1011 A/s.

The discharge down-conductor was positioned on the top hat cover simulator,

the mounting bolts, and the grain cover (Figure 6). The HCB was charged to 36,000

V (for most shots) and 45,000 V (for one shot) for each discharge, resulting in peak

currents of approximately 175,000 to 200,000 A. Action integrals of the discharges

were approximately 2 x 106 (A2).

6.2.2 Test Sequence

Table 2 identifies each set of discharges with respect to each configuration.

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Figure 6. Attach Point Diagram

LocationNo. 4

LocationNo. 3

0 deg

LocationNo. 1

LocationNo. 2

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Table 2. Configuration Test Sequence

Discharge Set No.

Configuration No. Marx Current Bank High Current Bank

2 26 3

4 0 1

3 6 2

4 4 0

3 0 2

There were 26 Marx discharges and three HCB discharges injected onto the test

article in Configuration No. 2 for a total of 29 discharges. The simulated lightning

injection waveform and the interior electric field were measured. The interior

magnetic field was calculated.

Following the testing in Configuration No. 2, the test article was configured

with only the handling rings and grain cover installed. This was to allow the testing

of the present handling configuration, which had never been done. Two shots were

attempted, but only the first was successful. Since the field sensor had been dropped

and damaged previously, only the magnetic field data were collected on this shot.

After the discharges were completed for Configuration No. 4, the test article

was assembled to Configuration No. 3. In this configuration six Marx discharges and

two HCB discharges were injected onto the test article before the HCB was damaged.

The test article was assembled to Configuration No. 4. A total of four Marx

discharges were injected onto the test article in this configuration and one HCB.

The test article was reassembled to Configuration No. 3. When the test article

and the HCB were ready for testing, two HCB discharges were injected onto the test

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The test article was reassembled to Configuration No. 3. When the test article

and the HCB were ready for testing, two HCB discharges were injected onto the test

article completing the RSRM top hat cover simulator lightning test.

6.2.2 Data Recovery

Data plots of the injected waveforms, the derivative of the injected waveforms (Marx

attachments only), the interior electric fields, and the interior magnetic fields were

made, following each strike (Volume II).

Of the 44 electrical current discharges conducted, the electric field

measurements during the first eight discharges failed because the fiber optic data

transmission line was disconnected to the data acquisition system. During discharges

No. 15 through No. 29 an analog integrator was installed on the B dot sensor fiber

optic transmission line. It was discovered after looking at the data that the integrator

was faulty. The data were unrecoverable and cannot be used for analysis.

6.3 TEST ARTICLE INSPECTION AND RESULTS

6.3.1 Electromagnetic Fields

None of the discharges resulted in electric fields exceeding the 30 kV/m objective.

The electric field levels were approximately 1,000 times lower than the dielectric

breakdown level of th.e RSRM propellant and approximately 100 times lower than the

30-kV/m objective level specified in WTP-0245, Rev A_ Magnetic field levels were 10

times lower than the electric field levels.

6.3.2 Arcin_

Arcing was observed between hardware components in Configurations No. 2 and No. 3.

Arcing was observed between the handling ring and top hat cover simulator in

Configuration No. 3 during the last two HCB discharges. Top hat cover simulator and

mounting bolt damage (surface scorching, pitting, and melting) was observed

(Figures 7 and 8).

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SPA CE OPERATIONS

Arcing was observed between the grain cover and the handling ring during the

HCB discharges injected onto the test article in Configuration No. 4 (Figure 9).

Damage to the grain cover is shown in Figure 10. During HCB discharges injected

directly to the grain cover, the fiberglass top was damaged and frayed at the arc

attachment point.

6.3.3 Li_htnin_ Detectors

Two detectors with sensitivities less than 500 A/m detected the simulated lightning

discharge indicating that these detectors can detect the case surface currents induced

from the Marx generator.

Two lightning detectors with sensitivities greater than 500 A/m did not detect

the case surface currents induced by the Marx generator.

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Document No.

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APPLICABLE DOCUMENTS

Titl...___e

Lightning Protection Criteria Document

Lightning Protection Verification Document

RSRM Top Hat Cover Simulator Lightning Test Plan

Marking Methods, Identification

D

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8U76447

8U5O943

8U5O929

1U5O715

8U5O816

Sensor--Magnetic Field, Passive

Handling Ring--Solid Rocket Motor

Ring, Segmented, Clevis Joint, Rocket Motor

Case Segment, Stiffener--Lightweight

Tie-Down Assembly, Cover Assembly--Railcar, Heavy Duty

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DocNo TWR-60834 j vo,

sec I PAGe 26

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._-'ne

R. Danforth

N. Black

B. Whidden

J. Griffin

P. St Jean

J. Godfrey

L. Abrahamson

K. Sanofsky

R. Larsen

F. Duersch

R. Papasian

M. Fisher

Print Crib

Data Management

Distribution List

L71

L71

L62A

L62A

L62A

E06

E80

851

851

851

E05

K68 (USBI)

Q51B1

L74B

No. Copies

1

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1

1

1

45

5

5

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ooc No TWR-60834 I voL

SEC [ PAGE

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