Testing/Selection of Materials for Manned Payloads

European Space Research & Technology Centre ESTEC

Testing/Selection of Materials for Manned Payloads

M.v. Eesbeek 1, C. Semprimoschnig 1, J. Meehan 2

1 Materials Physics and Chemistry Section 2 ISS Payloads Product Assurance and Safety Office

ESTEC, PO BOX 299, Keplerlaan 1,

NL - 2200 AG Noordwijk, The Netherlands


• 1. Flammability

Materials and hardware to be launched by the STS and other manned spacecraft shall be evaluated for flammability in the worst case oxygen concentration. This includes the s/c and all the payload.

Flammability testing is described in ECSS-Q-70-21A.

• 2. Off-gassing

All products considered for use in the crew compartment of manned spacecraft shall be evaluated for off-gassing. Samples of materials and assembled hardware shall be tested according to ECSS-Q-70-29A.

THE REQUIREMENTS


• Identify potentially flammable materials, their quantities, thickness, exposed surface, exposure environment (% O2 ).

• Identify propagation paths for exposed materials (including housing).

• If flammable materials are housed (container, rack etc.) evaluate the capability to contain an internal fire

• If unacceptable through the configuration assessment, then

Consider use of fire barrier to reduce flammability hazard

Conduct a test to evaluate the configuration

Flammability configuration assessment (1)


YES

ARE THERE ANY FLAMMABLE MATERIALS OR MULTIPLE APPLICATIONS OF FLAMMABLE MATERIALS IN AMOUNTS >0.1 LB OR 10 SQ. INCH IN MANNED COMPARTMENTS

OR >1.0 LB OR 12 LINEAR INCHES IN OTHER COMPARTMENTS?

ACCEPTABLE

ARE EXTERIOR SURFACES AND ANY EXTERNALLY ATTACHED MATERIALS FLAMMABLE?

COULD A FIRE PROPAGATE ON THE SURFACE MORE THAN 6” IN MANNED COMPARTEMENTS OR 12” IN OTHER COMPARTMENTS?

UNACCEPTABLE; MODIFICATION REQUIRED (SEE GUIDELINES)

IS IT A CONTAINER?

WILL THE CONTAINER CONTAIN ANY INTERNAL FIRE? (SEE EXAMPLE CONTAINER CASES)

DOES THE CONTAINER CONTAIN AIR?

ARE INTERNAL IGNITION SOURCES PRECLUDED WHILE THE CONTAINER IS LOCATED IN THE ORBITER?

UNACCEPTABLE; MODIFICATION REQUIRED (SEE GUIDLINES

ACCEPTABLE

ACCEPTABLE YES

ACCEPTABLE NO

ACCEPTABLE

NO

NO

NO

YES

YES

YES

YES

YES

NO

NO

NO

Flammability configuration assessment (2)

NSTS 22648


Flammability : Guidelines

• Flammability control is based on minimizing potential ignition sources and limiting the use of materials that can propagate

flames.

• Ignition sources always assumed to be present in habitable environments.

• Fire extinguishers are always provided on manned spacecraft, but are not considered as part of the flammability control process.


• Replace flammable materials by non-flammable wherever possible.

• Covering of flammable materials with an approved non-flammable barrier

e.g. 1 Betacloth or Nomex for foams 2 An approved conformal coating over commercial PCB’s 3 Aluminium tape over flammable polymers

How to reduce flammability hazards


Upwards Propagation Test (1)ECSS-Q-70-21 (Former ESA PSS-01-721) : Flammability testing for the screening of space materials

Purpose :Determine if a material, when exposed to a standard ignition source, will self-extinguish and not transfer burning debris, which can ignite adjacent materials

Test criteria :Self extinguishing within 15 cmNo transfer of burning debris (no dripping) Burn Propagation time (less than 10 minutes)

Sample dimensions : 300 x 64 mm, worst case thicknessTest atmosphere : depends on application (21% O2 or more…)


Upwards Propagation Test (2)

NiCr

Ignitor

Test Specimen

64 mm

300

mm


Upwards Propagation Test (3)


Wire Flammability test (1)• ECSS-Q-70-21 (Former ESA PSS-01-721) : Flammability testing for the screening of space materials

Purpose:Determine if a wire insulation system, when exposed to an external ignition source, will self-extinguish and not transfer burning debris, which can ignite adjacent materials

Acceptance criteria:Prior to flame application, while heating wire to maximal operation T, no spontaneous combustion, splitting insulation or exposure of the conductor.During ignition and combustion no burning droplets/particlesAfter burner is extinguished, cease burning within 10 s and within a total burn length of 150 mm.

Test atmosphere : depend on application (21% O2 or more…)


Wire Flammability test (2)


Wire Flammability test (3)


ECSS-Q-70-29 (former ESA PSS-01-729) : The determination of off-gassing products from materials and assembled articles to be used in a manned space environment.

Purpose:Determine the identity and quantity of volatile off-gassed products from materials and assembled articles.

Material screening test:

• Quantity of Carbon Monoxide [g/g]• Quantity of total organics (pentane equivalent) [g/g]

General test for materials/assembled articles:

• Identifies and quantifies all contaminants present• Use of T-value for acceptance

Off-gassing test (1)


Off-gassing Test (2)

• Test normally conducted for 72 hours at ambient pressure andtemperature of 50oC with hardware un-powered (h/w exposed to vacuum for 30-40 seconds during preparation for test)

– Provides an adequate margin above maximum cabin temperatures forthermal effects of powering the hardware

– Non-electrical hardware may be tested at lower temperatures if damaged by exposure to 50oC

• Testing should be conducted at nominal operating temperature ifexpected to significantly exceed 50oC (by more than 25oC )


Off-gassing test (3)• Acceptance Limits• Screening test

– Carbon Monoxide : <25 µg/g material– Total Organics : <100 µg/g material (Pentane equivalent)

• General test– No definitive acceptability defined by this test. Data are

evaluated by the Safety Office of the relevant project • for assessment of toxic hazard due to volatile

contamination off-gassed from the item under test

• for assessment of the impacts on the potential toxicity of the total quantity of off-gassed products from all contaminant-generating items for a given mission


Off-gassing test (4)–Following primary acceptance criteria are relevant:

– The quantity of each individual off-gassed product shall result in a predicted Spacecraft concentration below the SMAC value

– Toxic Hazard Index (T) shall not exceed 0.5. T is determined by calculating the ratio of the projected concentration of each off-gassed product to its SMAC value and summing up these ratios for all off-gassed products

• T = C1/SMAC1 + C2/SMAC2 ..... + Cn/SMACn

•C1…n is the concentration in μg/m3 i.e Projected Spacecraft Concentration (PSC) of each trace contaminant off-gassed during the test.

•SMAC1…n is the Spacecraft Maximum Allowable Concentration for the individual trace contaminant.


General test conditions

• Temperature 50 ºC

• Atmosphere : synthetic air or clean/dry air

• Pressure : 1 Atmosphere at 50 ºC

• Duration : 72 hrs

• Mass (material) 5g/liter test volume

Sampling : +/- 250 ml gas on trap after cooling to RT; flow rate sampling is +/- 25 ml/min.

Off-gassing test Procedure (1)


Test chambers Different sizes are available :

Heraeus ovens 128 and 718 l.Vacucell oven 111 l.Glass bottles 1, 2.5 and 5 l.

Analyses:Screening:

TO/CO (total organic/carbon monoxide)GC with Methaniser and Flame Ionisation Detector

General testPre-concentrated samplingDesorption system : Model MW-1A from Rektorik (CH)GC with DB5MS from JW column (60m, diam 0.25mm, film

(0.25m) Mass spectrometer model Profile from Kratos (UK)

Off-gassing test procedure (2)


Off-gassing test procedure (3)


Off-gassing – Testing Sites

• Test capability at ESA Materials and Processes Division and Naval Institute in Toulon

– European facilities are certified by ESA.

• Data from assembled article level testing much easier to evaluate than data from materials-level testing

– Materials-level testing can be used to assess minor late changes

• Testing of flight unit(s) not required – a materially-representative unit is acceptable.


Off-gassing – Lessons Learned

• Test failures at assembled article level unusual if the materials have been adequately screened– Most failures caused by inadequately cured paints, conformal coatings, adhesives and cleaning of the hardware with alcohol in preparation for the test.

– Hardware that fails can usually be brought into compliance by baking (e.g. 48 hours at 50oC at ambient pressure is usually adequate; however vacuum and/or higher temperatures better if acceptable for hardware).

• Although materials-level test data is available in ESA and NASA databases, using such data instead of testing at assembled article level is not recommended unless hardware is very simple.


ESA - NASA Interagency Agreement

• For organizations with reciprocal agreements, the applicable payloadsafety hazard reports must reference the materials certification*provided by the responsible materials and processes organization

* Terminology may vary -- JSC uses a “Materials and Fracture ControlCertification”, MSFC uses a “Certification Materials Usage Agreement”, ESA uses “ESA Materials and Fracture Control Certification”.• No additional documentation/hazard report content is required• Greater than 90% Shuttle payloads are covered by M&P reciprocalagreements (new International Partners in ISS may lower number).

• Reciprocal agreement between NASA and ESA for NASA and ESA-certified payloads


Interagency Agreement/Example


Example of “Packaging Procedure”

Documents

Testing/Selection of Materials for Manned Payloads