Reducing/Eliminating ESD Hazards During PYRO Operations

https://ntrs.nasa.gov/search.jsp?R=20010056602 2017-11-10T13:28:06+00:00Z

NASA

TM-2001-210256

Reducing/Eliminating PYRO Operations J. Francisco

National John

June

ESD Hazards

Soriano

Aeronautics

F. Kennedy

2001

Space

and

Space

Center,

Administration Kennedy

Space

Center,

Florida

32899-0001

During

REDUCING/ELIMINATING PYRO

ESD HAZARDS OPERATIONS

J. Francisco 1 Aerospace Systems

Engineer

Division,

Engineering,

and McNair

ET/SRB

NASA

John

Soriano

Scholar,

& Launch

1

now at the Space

Accessories

F. Kennedy

Space

DURING

Branch,

Center,

Shuttle

Mechanical

Pyrotechnics

Systems

Florida.

ABSTRACT Several

safety

OPF area the

concerns

based

safety

have

occurred

on the increase

of personnel,

during

pyro

of electrostatic

flight

hardware

operations

discharge

and

at 30%

(ESD).

ground

or lower

These

support

equipment

proposed methods considered to control ESDs during pyro operations RH are 1) the use of an ionizer blower and 2) to increase the moisture to demonstrate

that

experimental

runs

the

ionizer

were

is effective

conducted

in

Operations & Checkout (O&C) Building PYRO Systems Engineering representative Dr. Rupert was

Lee from

in charge

effectiveness metal

of the ionizer

plate

and angle

NASA

KSC

of performing

from

initial

of attack.

Failure

Analysis

the experiment blower

1000

A full factorial

volts.

situations

would

into the charged be the

most

increasing OPF ECS currently

be to position

beneficial

This

during

the moisture content current configuration not planned

the ionizer

scenario pyro

based

operations

upon

variables

distance that the

blower

resulted

Two

or lower In order

a series

located

Testing

in

the time were

NASA KSC assistant to

Laboratory

who

conducted.

The

lapse

studied:

of the

of a charged distance,

Since

RH,

we did not

SAS available, calculations were done (ANalyis of VAriances), but R 2 (fitness of

obtained. As conjectured, Therefore, we concluded plate.

charge,

KSC. I served as the as a laboratory research

(2 3 = 8) was

as

(GSE).

#: KSC-MSL-0331-2000-00-00).

These

experiment

targeted

at 30% content.

Laboratory

and Physical

(Job

was evaluated

to 400

static

Electrostatics

at NASA as well

have a statistical analysis program, such manually based on the method of "ANOVA" curve) was not influencialvariable.

in neutralizing

the

RH in the

concerns

was best

as close

in the quickest below

30%

found to be the major possible combination of

as possible discharge RH.

The

and facing rate, second

directly

which

would

method

of

in the work environment through a modification of the appeared to be dependent on budget constraints and

to be modified.

Finally,

some

recommendations

as to test the ionizer in an actual field experiment with technician with all the NASA KSC Safety-compliant effectiveness of the ionizer blower.

are discussed

such

a mockup pyro connector and a PPE to assess the realistic

GENERAL

ORDNANCE

OPERATIONS

Mechanical Operation The term "mechanical" refers to all operations where the pyro devices are hand-held, installed/removed as a single unit device or as part of an assembly where

no electrical

involving MLG/NLG

connections/disconnections

mechanical Uplock

installation Release

are

Thruster,

assemblies,

are performed. the

Avionics

MPM

devices

Bay

Some Firex,

guillotine/jettison,

guillotine/jettison

pyro

with

Faraday

during installation, location assembly

and separation nuts (8 installed and 2 located in the Aft structural

Caps

of the pyro

NLG Ku

on and

devices

Strut

Thruster,

Band

Antenna

are not removed

on each SRB/MLP hold down post attachments between the Orbiter &

ET). Electrical

Operation

connections/disconnections performed

during open

The

term

"electrical"

are performed pin (exposed

refers

to all

on pyro devices.

pin to the environment)

operations These

where

operations

electrical are usually

during mating/demating

pyro connectors. The pyro system is intimately related to the electrical system of all the wiring, cabling, interconnects, power supply, and additional interfaces.

of

consisting electrical

NASA STANDARD INITIATOR (NSI) The NASA

Standard

(EED)

in the STS Program.

used

the only approved

Initiator

EEDs

They

electricity

and

emergency

escape

NSIs

contain

are

are

used

types

Shuttle.

NSIs

of Electro-Explosive

Docking

System

are category

Devices

(ODS)

designed

for

a minimum

for

all pyro

probability

system

pyros

"A" explosive

is that which by expenditure of its own of events, causes injury or death to people

in Orbiters

of

initiation

devices. energy, or or damage

initiation except

are

for

by

static

the

crew

systems.

2 electrical

contacts,

The bridgewire of 0.95

of two

This and the Orbiter

device reaction

grams of granular mixture transforms electrical energy characteristics: 1)

is one

for the Space

A category "A" explosive because it initiates a chain to equipment.

(NSI)

which

lead to a bridgewire

of Zirconium into explosive

is a 0.002"

by 0.114

Potassium Perchlorate (ZrKC104). An NSI energy. Specifically, they have the following

diameter

to 1.15 _2. The bridge

that is surrounded

stainless

distance

steel

of 0.118"

(304 Nilstain) results

with a resistance

in a circuit

resistance

of

1.05 + 0.10 _. 2)

An electrical

current

of 3.5 to 5 amps

will heat the bridgewire

to 600 °F and cause

ignition. 3) 4)

Output pressure of 650 + 125 psi in a 10cc closed Will not fire if subjected to 1 amp for 5 minutes.

5)

Can auto-ignite

6)

An airtight shrapnel

if subjected

thin stainless

when

(LSC),

they

closure

in excess welded

of 400 °F.

to the cartridge

will contribute

the NSI detonates.

Although NSIs are used as NSI Detonators, NSI Charges

to temperatures steel end

Volume.

have

mainly Booster enough

for initiating Cartridges, power

other secondary/high explosive pyros such NSI Pressure Cartridges, and Linear Shape

to be used

alone

in some

other

Orbiter

systems

suchas in the Crew ModuleFirex System,MPM Guillotine, and Aft Gas Samplers. An expendedNSI will havea hole in the endwheretheexplosivechargewaslocated,andan unexpendedNSI will havea smoothendcapwith no visible hole. NSI

Detonator

An NSI Detonator

NSI threaded into a detonator acts on the detonator's Lead detonator's produce end.

boosters,

Protection

era called

block.

is not present

and NSI pressure

Electrostatic Apollo

Trinitramine

in a steel

This protrusion

An unexpended

all have

in NSIs

The

Standard

NSI

used

Initiator.

explosive.

detonator

Detonators

has

a protrusion

One

will on its

NSI detonators,

fiats for installation today

of an

mixtures. The NSI in turn acts on the

is expended.

wrench

and consists

explosive which

high

after the detonator

cartridges

Apollo

(RDX)

device,

is based

of the design

NSI

and removal.

on a design

from

the

changes

that the NSI

incorporated was electrostatic protection. Electrostatic safety is achieved The NSI utilizes the spark gap/air gap method, and also the ordnance cavity

in two ways. is electrically

isolated

the

"A" explosive

housing containing additional Azide (PbN6) primer/accelerator,

Cyclotrimethylene a 0.040"-dent

is a category

from ground.

Spark

gaps

are located

in the electrical

connector

cavity

where

arcing

is not dangerous.

The design scheme is to provide as high an internal breakdown voltage in the ordnance area and as low an external spark gap breakdown voltage as possible. Providing a spark gap between the pins and case involves the electrical breakdown of air dielectric. Electrical breakdown in an air gap happens after the onset of voltage on the pins. If voltage order

is applied of Ix-seconds,

to the pins

the spark jumps

The dielectric

strength

200+10

volts

for 60 seconds

current

shall

not exceed

degraded. in place feature.

Isomica

discs

starts

and

a short

for the NSI is that it shall withstand

between

500

process

time

later,

in the

from pin to case.

specification

the case and the pins shorted

Ix-amperes.

are installed

The

initiator

at the top surface

shall

an AC voltage

together.

not ignite

The leakage

nor

of the propellant

of

otherwise

be

and are secured

with an epoxy impregnated washer or sealing tape as an electrically insulating The metal disk welded in place across the output end is for hermetic sealing.

As a design consideration to 1500 volts AC can compromise reliability

dielectric compromise

electrostatic

safety

specifications the design

while

at the

calling for no breakdown pins to case of the external spark gap and thus

same

time

adding

nothing

to functional

over the 500 volts DC specifications.

Electrostatic charged

an ionization

specifications

to 25,000

volts

state

that the EED

is discharged

from

shall not function pins

to case.

when

a 500-pF

A human

on

capacitor

average

is the

equivalent of 300 pF. NSIs are designed with a "no fire current" and "no fire power". That requirement specifies that all NSIs will not fire nor be degraded with 1 amp/1 watt applied Firing appeared

for 5 minutes. System

Compatibility

that the NSI-1

was delivered

According

fast enough.

with

required

to Test

Report

NSI-I's

on

-40

millijoules

TR82-106 Appendage of energy

"Verification 2" dated to fire,

July

provided

of Electrical 22,

1982,

this energy

it

A typical

energy

Capacitance

analysis

of an average

during pyro operations, value 16,000

for a human

of 16,300 volts

known

to have

Failure

mode

human

which

volts

a human

would

ignited

an NSI.

in which

is 300

result

is required

follows: pF.

Maximum

in a calculated

for an average

have

the

an NSI would

same

allowable

energy human

amount

of energy

A manufacturing

defect

with the NSI spark

Static

around

the NSI at a level

3.

Failure

4.

Voltage

5.

Technician

of the wriststat

to dissipate

not measured

in some

way

connecting/disconnecting 6.

Technician spark

current

reaches

is 350 volts A calculated

40 millijoules.

At

that as a minimum

is

fire are:

1.

potential

of 18.3 _t-joules. to produce

2.

generation

voltage

does

gap. >16,000

volts.

static.

with a volt scanner. not

touch

the

connector

backshell

when

NSIs. to the NSI in a way

goes from

pin through

bridge

to touch wire

one

of the pins

then to ground.

and the

SAFETY

PROCEDURES AND REQUIREMENTS ELECTRICAL PYRO OPEERATIONS

NSIs are designed two NSI connector

USED

DURING

to be relatively insensitive to static electricity and RF radiation (the pins may act as antenna to RF energy) as compared to other EEDs,

however they can still be initiated by either of these forms of energy level exists. Incorrect usage of meters or other energy sources may inadvertently safety

initiated.

practices

KHB

Therefore,

and procedures

1710.2

KENNEDY

during

SPACE

design,

CENTER

operations

operations. It is intended to assure manner with maximum efficiency. manual

personnel,

is divided control

use of plastic The

films

remainder

NASA safety

KSC policy

Of specific

areas,

completion

safety,

for pressure interest

the

chapters

and

the

following

tapes contains

eleven

vessels

from

annexes

to Pyro Systems

It outlines

tools,

equipment,

phase

power

firing shoes,

The

personnel

Orbiter

or canisters upon

should handling

arrival

wear

grounding

EEDs

line extension

performed

procedures grounding

Electric among

weather, and

areas.

with OSHA

requirements,

Code,

and

NASA

others.

and Pyro operations,

hoisting

possible

requirements,

Processing

National

for grounding during

safest

there

controls

to avoid

of personnel, of flight

are two main

flight

hardware,

unsafe

hardware, and

three-

connections.

All personnel open grain,

specific

materials,

Kennedy

information,

facilities

dealing

systems,

to the

general

Shuttle/Payload

and pressurized

handbook, which is safety policies and at NASA

task

hazardous

document,

HANDBOOK

activities

annexes: Annex D. KSC Supplement to NFPA 70--National Electric Code This section discusses all sources of static electricity discharges situations.

NASA/KSC

These requirements identify and associated with daily industrial of the

ranging unique

in Space

requirements

applicable

PRACTICES

maintenance

under KSC. and property

operational

of this manual

SAFETY

and

into seven

and adhesive

safety

operations

for safety at NASA/KSC. This 1998, establishes and specifies

Space Center and areas of jurisdiction minimize the hazards to personnel

This

pyro

must be followed.

This is the governing document Revision D dated November requirements

during

if a high enough cause NSIs to be

when

cables should

devices

Faraday

are connected stand

on

Caps

when

handling

or Shorting

to EEDs.

a conductive

When surface.

or working

Plugs

within

are removed,

using

legstats

Resistance

5 ft of

also when

or conductive checks

shall

be

prior to operations. shall

be grounded

containing

and wheels

chocked

explosives

or hazardous

at the facility/handling

mechanism.

fluids

inside

the OPF

platforms.

shall be grounded

to facility

Payloads ground

Pneumatictools usedon hardwarecontaining EEDs, within 10 ft of open grain, or in petroleum/oil/lubricant areas shall be fitted with a conductive air supply hose or connectedto facility ground. All materialsin contactwith open grain shall be grounded. Conductiveplastic sheeting(velostat)shall be groundedto common groundwith railcar prior to installation. Annex F. KSC Supplement Propellants_ and Pyrotechnics This section discusses the

to

NSS-1740.12-NASA

Relative

Humidity

RH shall

be recorded

Safety (RH)

Standard

requirements

for

Explosives,

and

Explosive

requirements. Relative

Humidity

operations.

(RH)

When

personnel should during operations into

the work

segments,

The

RI-I_50%,

be verified and every

area.

and

is not

to start

wearing

RH50%

and should

Environments should

absorb

where

be carefully

surfaces,

should

with the ground Grounding The basic

RH