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Testing/Selection of Materials for Manned Payloads

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

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Testing/Selection of Materials for Manned Payloads

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  1. 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

  2. THE REQUIREMENTS • 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.

  3. Flammability configuration assessment (1) • 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

  4. Flammability configuration assessment (2) NSTS 22648

  5. 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.

  6. How to reduce flammability hazards • 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

  7. 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 cm No transfer of burning debris (no dripping) Burn Propagation time (less than 10 minutes) Sample dimensions : 300 x 64 mm, worst case thickness Test atmosphere : depends on application (21% O2 or more…)

  8. Upwards Propagation Test (2)

  9. Upwards Propagation Test (3)

  10. 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/particles After 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…)

  11. Wire Flammability test (2)

  12. Wire Flammability test (3)

  13. Off-gassing test (1) • 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 [mg/g] • Quantity of total organics (pentane equivalent) [mg/g] • General test for materials/assembled articles: • Identifies and quantifies all contaminants present • Use of T-value for acceptance

  14. Off-gassing Test (2) • Test normally conducted for 72 hours at ambient pressure and temperature 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 for thermal 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 if expected to significantly exceed 50oC (by more than 25oC )

  15. 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

  16. 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.

  17. Off-gassing test Procedure (1) • 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.

  18. Off-gassing test procedure (2) 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 test Pre-concentrated sampling Desorption system : Model MW-1A from Rektorik (CH) GC with DB5MS from JW column (60m, diam 0.25mm, film (0.25mm) Mass spectrometer model Profile from Kratos (UK)

  19. Off-gassing test procedure (3)

  20. 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.

  21. 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.

  22. ESA - NASA Interagency Agreement • For organizations with reciprocal agreements, the applicable payload safety hazard reports must reference the materials certification* provided by the responsible materials and processes organization * Terminology may vary -- JSC uses a “Materials and Fracture Control Certification”, 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 reciprocal agreements (new International Partners in ISS may lower number). • Reciprocal agreement between NASA and ESA for NASA and ESA-certified payloads Acrobat Document

  23. Interagency Agreement/Example

  24. Example of “Packaging Procedure”

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