SLA-561V (super lightweight ablator) SLA-561V

spore: profile
id: sla-561v
spore_version: 0.2
family: silicones
name: SLA-561V (super lightweight ablator)
abbreviation: SLA-561V
role: Silicone-based filled-cork ablator for Mars entry backshell and heat shield thermal protection
category: thermal-protection
type: ablators
summary: |
  SLA-561V is a super light-weight ablator made by Lockheed Martin. The NASA Ames TPSX database lists a virgin emissivity of 0.7, and the Mars 2020 TPS sizing paper gives a nominal flight thickness of 1.27 cm. The MEDLI2 slides name SLA-561V as the backshell thermal protection system on Mars 2020. Its predecessor SLA-561, a filled cork, had a bulk density of 0.222 to 0.233 g/cm3 and a thermal conductivity of about 0.059 W/m-K at 340 K in a 1971 NASA report, but that report does not cover SLA-561V.
best_for: Backshell and heat shield ablation on Mars entry vehicles where the heat flux stays below about 110 W/cm2 (Wikipedia summary)
weakest_at: Glass melt flow at high surface temperature (about 1800 degC in an Ames turbulent flow duct test) and failure above 300 W/cm2 (Wikipedia summary)
identity:
  formula: 'Silicone-based filled-cork ablator: cork particles, fibres and microspheres in a silicone binder (constituents from the SLA-561 predecessor, per the 1971 report; the -561V recipe is not printed in any source read)'
  designations:
    - system: Trade name
      code: SLA-561V
      source: tpsx-sla561v
      where: Page title, SLA-561V [virgin]
  source: wiki-atmospheric
  where: 'Super light-weight ablator section: ''SLA in SLA-561V stands for super light-weight ablator'' and made by Lockheed Martin'
tags:
  environments:
    - re-entry
  stresses:
    - aerothermal-heating
  applications:
    - heat-shields
properties:
  - benchmark: emissivity
    label: Emissivity, SLA-561V virgin (TPSX)
    value: 0.7
    unit: '-'
    scope: material
    conditions:
      state: virgin, unablated
      wavelength_and_temperature: not printed on the page
    method: Value on the NASA Ames TPSX database page
    status: ground
    note: Name not in property-canon.yaml. The cells beside the row read 'N/A, unknown, assumed/assumed, 2006-01-05'.
    source: tpsx-sla561v
    where: Properties at Standard Conditions table, Emissivity row
  - benchmark: density
    label: Bulk density, SLA-561 filled cork (1971 predecessor report, not -561V)
    value: 0.222
    value_high: 0.233
    bound: range
    unit: g/cm3
    scope: material
    conditions:
      material: SLA-561, filled cork (predecessor, not SLA-561V)
      form: virgin bulk density, four disks
      method_as_printed: ASTM C177 guarded hot plate apparatus
    method: Range from the four disk values in Table 4 and the report text
    status: ground
    source: smyly-1971
    where: Materials and Cutting Plans section (density range text) and Table 4, Bulk Density of SLA-561, Filled Cork
  - benchmark: thermal_conductivity
    label: Thermal conductivity, SLA-561 filled cork at 340 K (1971 predecessor report)
    value: 0.059
    unit: W/m-K
    scope: material
    conditions:
      material: SLA-561, filled cork (predecessor, not SLA-561V)
      temperature: 340 K
      method_as_printed: ASTM C177 guarded hot plate (per the report table titles)
    method: Value from the report summary, which says about 0.059 W/m-K at 340 K and calls it the lowest of the four materials. The detailed conductivity tables were not used because their scan is unreadable.
    status: ground
    note: The summary says about 0.059, so the value is approximate.
    source: smyly-1971
    where: Summary, paragraph on thermal conductivity at 340 K
  - benchmark: specific_heat
    label: Specific heat, SLA-561 filled cork at 340 K (1971 predecessor report)
    value: 1290
    unit: J/kg-K
    scope: material
    conditions:
      material: SLA-561, filled cork (predecessor, not SLA-561V)
      temperature: 340 K
    method: Value from the report summary, printed as 1290 J/Kg-K for the filled cork
    status: ground
    source: smyly-1971
    where: Summary, paragraph on heat capacity at 340 K
  - benchmark: charring_temperature
    label: Temperature at which SLA fully chars (MEDLI2 slides)
    value: 600
    unit: degC
    scope: material
    conditions:
      material: SLA as named on the slide
      heating: heating rate and atmosphere not printed
    method: Slide note under the emissivity panel, printed as 'SLA Fully Chars at 600oC'
    status: ground
    note: Name not in property-canon.yaml. The slide names SLA, not SLA-561V specifically.
    source: medli2-2019
    where: Slide 'Optical properties', emissivity panel note
  - benchmark: ablation_onset_heat_flux
    label: Heat flux at the start of significant ablation, SLA-561V (Wikipedia)
    value: 110
    unit: W/cm2
    scope: material
    conditions:
      basis: stated as approximately 110 W/cm2
      test_method: not given in the article
    method: Secondary statement in the Wikipedia article; no primary source is cited in the text read
    status: ground
    note: Name not in property-canon.yaml. Secondary source only.
    source: wiki-atmospheric
    where: Super light-weight ablator section
  - benchmark: ablation_failure_heat_flux
    label: Heat flux above which SLA-561V fails (Wikipedia)
    value: 300
    bound: lower
    unit: W/cm2
    scope: material
    conditions:
      basis: stated as heat fluxes greater than 300 W/cm2
      test_method: not given in the article
    method: Secondary statement in the Wikipedia article
    status: ground
    note: Name not in property-canon.yaml. Secondary source only.
    source: wiki-atmospheric
    where: Super light-weight ablator section
  - benchmark: nominal_thickness
    label: Nominal uniform SLA-561V thickness on the Mars 2020 backshell
    value: 1.27
    unit: cm
    scope: material
    conditions:
      location: Mars 2020 backshell acreage, packed into the Flexcore honeycomb
      basis: nominal flight design thickness, the same as for MSL
    method: Printed nominal value in the Mars 2020 TPS sizing paper; the MEDLI2 material response paper also prints 1.27cm (0.5") for its SLA-561V stackup
    status: flight
    note: Name not in property-canon.yaml.
    source: tps-m2020
    where: Backshell description paragraph after Fig. 4, sentence 'The nominal uniform thickness of SLA-561V for Mars 2020 was 1.27 cm (0.5 inch)'
  - benchmark: test_heat_flux
    label: Panel Test Facility high condition for SLA-561V flight-lot panels (Mars 2020)
    value: 13.5
    unit: W/cm2
    scope: material
    conditions:
      facility: Panel Test Facility (PTF), arc jet
      condition: high, representative of predicted Mars 2020 backshell environments
      test_series: PTF 163, SLA-561V flight-lot panels
    method: Target heat flux printed in the Mars 2020 TPS sizing paper
    status: ground
    note: Name not in property-canon.yaml.
    source: tps-m2020
    where: 'Paragraph ''SLA-561V flight lot testing'' (PTF 163), sentence ''Two conditions that were representative of the predicted backshell environments were targeted: 13.5 W/cm2 (high) and 5.2 W/cm2 (low)'''
  - benchmark: test_heat_flux
    label: Panel Test Facility low condition for SLA-561V flight-lot panels (Mars 2020)
    value: 5.2
    unit: W/cm2
    scope: material
    conditions:
      facility: Panel Test Facility (PTF), arc jet
      condition: low, representative of predicted Mars 2020 backshell environments
      test_series: PTF 163, SLA-561V flight-lot panels
    method: Target heat flux printed in the Mars 2020 TPS sizing paper
    status: ground
    note: Name not in property-canon.yaml.
    source: tps-m2020
    where: Paragraph 'SLA-561V flight lot testing' (PTF 163), same sentence as the 13.5 W/cm2 high condition
  - benchmark: test_heat_flux
    label: Cold-wall heat flux target, PTF162 MEDLI2 SLA-561V flight-lot acceptance test, condition (a)
    value: 5.4
    unit: W/cm2
    scope: material
    conditions:
      facility: Panel Test Facility (PTF)
      test_series: PTF162, MEDLI2 SLA-561V flight-lot acceptance panel (a different test from PTF 163)
      condition: (a), cold-wall heat flux target, pressure about 0.2 kPa, table up exposure 63 s
    method: Figure 6 caption of the MEDLI2 material response paper
    status: ground
    note: Name not in property-canon.yaml. This is a different PTF test from the PTF 163 values above.
    source: medli2-flight
    where: Figure 6 caption, condition (a)
  - benchmark: test_surface_temperature
    label: SLA surface temperature in the Ames turbulent flow duct arc-jet test
    value: 1800
    unit: degC
    scope: material
    conditions:
      test: turbulent flow duct with an augmented radiating ceramic wall
      measurement: pyrometer on the SLA surface
      note_as_printed: approximately, printed as ~1800°C
    method: Pyrometer reading printed in the Sepka et al. paper; the paper approximates the charred SLA surface emissivity as one for its radiative estimate
    status: ground
    note: Name not in property-canon.yaml. Approximate value as printed.
    source: sepka-2010
    where: Section C, Pyrometer measurements of SLA surface temperature, sentence 'was ~1800°C during the testing'
  - benchmark: absorptivity
    label: Absorptivity used for SLA-561V in Mars 2020 thermal sizing
    value: 1
    unit: '-'
    scope: material
    conditions:
      basis: assumed maximum possible value, used because reliable data were lacking; not a measured value
    method: Sizing assumption printed in the Mars 2020 TPS sizing paper
    status: calculated
    note: Name not in property-canon.yaml. A sizing assumption, not a measured property.
    source: tps-m2020
    where: Thermal analysis tools paragraph, sentence 'an absorptivity of 1.0 (maximum possible value) is used for SLA-561V due to lack of reliable data'
corrosion:
  - environment: Turbulent flow duct test with an augmented radiating ceramic wall (NASA Ames, MSL heatshield programme)
    headline: In the Ames turbulent flow duct, the SLA-561V surface reached about 1800 degC and glass melted and flowed, but the material did not fail.
    effect: Glass formed, melted and flowed at the SLA-561V/Silfrax interface. The paper calls this the first appearance of such a large amount of glass melt flow in these tests and says further investigation of SLA-561V as a candidate heatshield material would be required. It also says the material did not experience any failure and that the char layer was well behaved.
    conditions:
      stream: arc-heated air, stream Mach 2.5, static pressure about 0.1 atm, enthalpy about 8.8 MJ/kg
      test_model: 2.54 cm thick SLA-561V
      surface_temperature: about 1800 degC by pyrometer during testing
      calorimeter: steady heat flux of about 80 W/cm2 read by a convective-only calorimeter
    rating: moderate
    source: sepka-2010
    where: Sections II, III.A and III.C, and Section VI (Concluding Remarks)
  - environment: Heating to high temperature in MEDLI2 emissivity and reflectance tests
    headline: SLA fully chars at 600 degC, and charring lowers emissivity and reflectance.
    effect: The MEDLI2 slide note says SLA fully chars at 600 degC. The discussion slide says the optical data confirm that charring results in a significant decrease in emissivity and reflectance.
    conditions:
      basis: FTIR and UV-Vis data on virgin and charred SLA, as summarised on the slides
      atmosphere: not printed
    rating: moderate
    source: medli2-2019
    where: Slide 'Optical properties', emissivity note; Discussion of results slide
  - environment: Flight heat flux, secondary summary
    headline: Significant ablation begins near 110 W/cm2 and the material fails above 300 W/cm2.
    effect: The Wikipedia article says SLA-561V begins significant ablation at approximately 110 W/cm2 and will fail for heat fluxes greater than 300 W/cm2. It also says that on Viking 1 the TPS acted as a charred thermal insulator and never experienced significant ablation.
    conditions:
      basis: secondary summary; no test method in the text read
    rating: unknown
    source: wiki-atmospheric
    where: Super light-weight ablator section
risks:
  hazards:
    - text: No safety data sheet or GHS classification for SLA-561V was found in the sources read in this run. The Mars 2020 TPS sizing paper describes the material as RTV silicone resin with granulated cork, silica and phenolic microballoons, and chopped refrasil fibers, and prints no hazard data.
      ghs: []
      source: tps-m2020
      where: Backshell description paragraph (material composition); the paper gives no hazard or SDS data
  failure_risks:
    - mode: Glass melt flow at high surface temperature
      trigger: Turbulent flow duct test with a radiating ceramic wall; surface about 1800 degC by pyrometer
      consequence: Glass formed, melted and flowed at the SLA-561V/Silfrax interface. The paper says the material did not fail and the char layer was well behaved, but further investigation would be required.
      severity: moderate
      source: sepka-2010
      where: Test model and pyrometer sections; Section VI Concluding Remarks
    - mode: Ablation failure at high heat flux
      trigger: Heat flux above 300 W/cm2
      consequence: The Wikipedia article says the material will fail for heat fluxes greater than 300 W/cm2.
      severity: high
      source: wiki-atmospheric
      where: Super light-weight ablator section
  side_effects: []
  handling: []
  mitigations: []
uses:
  - application: heat-shields
    device: Backshell thermal protection on the Mars 2020 entry vehicle, with MEDLI2 instrumentation
    example: The MEDLI2 slide says the backshell TPS is made of SLA-561V, a super lightweight ablative manufactured by Lockheed Martin, and that the SLA also features MEDLI2 instrumentation.
    source: medli2-2019
    where: Background slide, paragraph on the Mars 2020 backshell TPS
  - application: heat-shields
    device: Primary TPS on NASA 70 degree sphere-cone Mars entry vehicles other than MSL
    example: The Wikipedia article says SLA-561V has been used as the primary TPS material on all the 70 degree sphere-cone entry vehicles NASA sent to Mars other than Mars Science Laboratory.
    source: wiki-atmospheric
    where: Super light-weight ablator section
  - application: heat-shields
    device: Viking 1 entry vehicle
    example: The Wikipedia article says that for Viking 1 the TPS acted as a charred thermal insulator and never experienced significant ablation.
    source: wiki-atmospheric
    where: Super light-weight ablator section
  - application: heat-shields
    device: Mars 2020 aeroshell backshell
    example: The Lockheed Martin Mars 2020 fact sheet says the biconic backshell is covered with super light ablator (SLA) 561V, a cork/silicone thermal protection system created by Lockheed Martin that originated with the Viking landers in the 1970s.
    source: lm-fact-sheet
    where: Fact sheet text, backshell paragraph
supply:
  - subject: Manufacturer
    demand: No production or market figure for SLA-561V was read in any source.
    routes: ''
    producers: []
    critical_lists: []
    substitutes: []
    source: medli2-2019
    where: 'Background slide: SLA-561V is manufactured by Lockheed Martin'
  - subject: Constituents of the SLA-561 predecessor (filled cork)
    demand: No production figure was read for these constituents.
    routes: ''
    producers: []
    critical_lists: []
    substitutes: []
    source: smyly-1971
    where: Materials and Cutting Plans section, paragraph on SLA-561 (cork particles, fibres and microspheres in a silicone binder)
documents:
  - title: NASA Ames Thermal Protection Materials database, SLA-561V [virgin] (Material id 39)
    type: database
    url: https://tpsx.arc.nasa.gov/Material?id=39
  - title: Cole, Feldman and Gasch, Characterization of Thermal Protection Systems (MEDLI2 support material), NTRS 20190029000
    type: report
    url: https://ntrs.nasa.gov/api/citations/20190029000/downloads/20190029000.pdf
  - title: Smyly and Pears, Thermal Properties of Some Filled and Foamed Low-Density Ablators, NTRS 19710018270
    type: report
    url: https://ntrs.nasa.gov/api/citations/19710018270/downloads/19710018270.pdf
  - title: Sepka, Kornienko and Radbourne, Testing of SLA-561V in NASA-Ames Turbulent Flow Duct With Augmented Radiative Heating, NTRS 20100033684
    type: paper
    url: https://ntrs.nasa.gov/api/citations/20100033684/downloads/20100033684.pdf
  - title: Mahzari, Beck, Hwang, Monk and Morgan, Development and Sizing of the Mars 2020 Thermal Protection System, AIAA Aviation 2022, NTRS 20220006688
    type: paper
    url: https://ntrs.nasa.gov/api/citations/20220006688/downloads/Development%20and%20Sizing%20of%20the%20Mars%202020%20Thermal%20Protection%20System_AIAA%20Aviation%202022.pdf
  - title: 'Monk, Feldman, Mahzari, Santos, White, Prabhu and Alpert, MEDLI2 Material Response Model: Development and Validation, NTRS 20210024735'
    type: paper
    url: https://ntrs.nasa.gov/api/citations/20210024735/downloads/AIAA_2022_Monk.pdf
  - title: Lockheed Martin, Mars 2020 Aeroshell Fact Sheet
    type: datasheet
    url: https://www.lockheedmartin.com/content/dam/lockheed-martin/space/documents/space/Mars-2020-Aeroshell-Fact-Sheet.pdf
sources:
  tpsx-sla561v:
    title: NASA Ames Thermal Protection Materials database, SLA-561V [virgin] (Material id 39)
    id: TPSX Material id 39, category Silicon-Based Ablators, last modified 1996-08-01
    url: https://tpsx.arc.nasa.gov/Material?id=39
    year: 1996
    kind: database
    license: NASA public database, linked not reproduced
  medli2-2019:
    title: Cole, Feldman and Gasch, Characterization of Thermal Protection Systems (MEDLI2 support slides), Clemson University and NASA Ames
    id: NTRS 20190029000
    url: https://ntrs.nasa.gov/api/citations/20190029000/downloads/20190029000.pdf
    year: 2019
    kind: report
    license: NASA public document
  smyly-1971:
    title: Smyly and Pears, Thermal Properties of Some Filled and Foamed Low-Density Ablators, Southern Research Institute for NASA Langley
    id: NTRS 19710018270; Volume I, Properties of Ablation and Insulation Materials
    url: https://ntrs.nasa.gov/api/citations/19710018270/downloads/19710018270.pdf
    year: 1971
    kind: report
    license: NASA public document
  sepka-2010:
    title: Sepka, Kornienko and Radbourne, Testing of SLA-561V in NASA-Ames Turbulent Flow Duct With Augmented Radiative Heating, AIAA extended abstract
    id: NTRS 20100033684; 10th AIAA/ASME Joint Thermophysics and Heat Transfer Conferences, June 2010
    url: https://ntrs.nasa.gov/api/citations/20100033684/downloads/20100033684.pdf
    year: 2010
    kind: paper
    license: NASA public document
  wiki-atmospheric:
    title: Atmospheric entry, Wikipedia (section Super light-weight ablator)
    id: Wikipedia article, read 2026-11-01
    url: https://en.wikipedia.org/wiki/Atmospheric_entry
    year: 2026
    kind: web
    license: CC BY-SA 4.0, linked not reproduced
  tps-m2020:
    title: Mahzari, Beck, Hwang, Monk and Morgan, Development and Sizing of the Mars 2020 Thermal Protection System, NASA Ames
    id: NTRS 20220006688; AIAA Aviation 2022
    url: https://ntrs.nasa.gov/api/citations/20220006688/downloads/Development%20and%20Sizing%20of%20the%20Mars%202020%20Thermal%20Protection%20System_AIAA%20Aviation%202022.pdf
    year: 2022
    kind: paper
    license: NASA public document
  medli2-flight:
    title: 'Monk, Feldman, Mahzari, Santos, White, Prabhu and Alpert, MEDLI2 Material Response Model: Development and Validation, NASA Ames'
    id: NTRS 20210024735; AIAA 2022 (file AIAA_2022_Monk.pdf)
    url: https://ntrs.nasa.gov/api/citations/20210024735/downloads/AIAA_2022_Monk.pdf
    year: 2022
    kind: paper
    license: NASA public document
  lm-fact-sheet:
    title: Lockheed Martin, Mars 2020 Aeroshell Fact Sheet
    id: Lockheed Martin space documents, Mars 2020 Aeroshell Fact Sheet (PDF)
    url: https://www.lockheedmartin.com/content/dam/lockheed-martin/space/documents/space/Mars-2020-Aeroshell-Fact-Sheet.pdf
    kind: datasheet
    license: manufacturer document
gaps:
  - 'Flight history: the Mars 2020 TPS sizing paper lists SLA-561V on Viking, Pathfinder, MER, MSL, Genesis and Stardust, and the Lockheed fact sheet says it originated with the Viking landers. Mars 2020 is confirmed by the sizing paper, the MEDLI2 paper and the MEDLI2 slides. Wikipedia says SLA-561V was the primary TPS on NASA 70 degree sphere-cone Mars vehicles other than MSL, and says SIRCA was used on the Pathfinder and MER backshell interface plate. Per-mission SLA-561V thickness and lot data for Pathfinder, MER and Viking were not read.'
  - 'Operating temperature range of SLA-561V: not printed in any fetched page.'
  - 'SLA-561V composition: shares and binder chemistry are not printed. The cork, fibre and microsphere constituents come from the 1971 report on the SLA-561 predecessor.'
  - 'TPSX values: the emissivity (0.7) is the only TPSX value recorded. The TPSX virgin density (2.64e+02 kg/m^3), thermal conductivity (5.92e-02 W/m-K), specific heat (1.16e+03 J/kg-K) and effective heat of ablation (5.41e+07 J/kg) are printed in exponent form, so the brief leaves them out. The TPSX temperature and test method are not printed, and several TPSX cells are marked assumed or unknown.'
  - 'Thermal conductivity and specific heat of SLA-561V against temperature: the 2019 MEDLI2 slides show plots only, with no readable numbers.'
  - The 1971 report detailed conductivity and heat capacity tables (Tables 7 and 8, and the enthalpy tables) have unreadable OCR, so only the summary values at 340 K are recorded. The 1971 report covers SLA-561, not SLA-561V.
  - 'Hazards, GHS classification and safety data sheet for SLA-561V: a web search found no SDS for SLA-561V, and PubChem could not be reached in this run (captcha page and HTTP 400), so no GHS data is recorded. The hazards entry only states that the Mars 2020 TPS sizing paper prints no hazard data.'
  - 'Handling, storage, bonding and mitigation steps for SLA-561V: none read.'
  - 'Supply, producers, country shares and critical-mineral status: not found. Only the manufacturer (Lockheed Martin) is recorded.'
  - 'Corrosion or ageing in air, humidity, UV, or of aged char: not found.'
  - 'Numeric emissivity and reflectance of virgin and charred SLA: not readable from the MEDLI2 slides, so only the charring temperature note is recorded.'
  - 'Names not in spores/property-canon.yaml: emissivity, charring_temperature, ablation_onset_heat_flux, ablation_failure_heat_flux, nominal_thickness, test_heat_flux (three rows), test_surface_temperature and absorptivity. Short snake_case names are used.'
  - The 110 and 300 W/cm2 heat-flux values come from the Wikipedia article only. No primary source was read for them.
  - 'Coverage: 13 properties and 8 sources. The lithium-standard target of 15 properties is not reached: the TPSX density, conductivity, specific heat and heat of ablation are printed in exponent form and are left out. The SLA-561V rows of the MEDLI2 model conductivity and density table are not readable as text in the fetched PDF (the PICA rows are readable but are not used).'
  - The TPSX values were read through a fetch summary of the page, not from the raw HTML. Re-check them against the page before publishing.
license: CC-BY-4.0
updated: '2026-11-02'
review:
  status: draft
  method: assistant
  checked_values: 13
  unreachable: 1
  caveats: 5
  note: Values were read by an AI assistant on 2026-11-01 from the pages named in each entry. TPSX values come from a fetch summary of the page. The 1971 values are summary text from a report on the predecessor SLA-561 (not SLA-561V). The 110 and 300 W/cm2 values are from Wikipedia only. The MEDLI2 slide numbers are a single note (600 degC), since the other slide values are plots.
story:
  recipe:
    line: SLA-561V is a silicone-based filled-cork ablator made by Lockheed Martin. Per Wikipedia, the ablative material is packed into a honeycomb core that is pre-bonded to the aeroshell structure. Its predecessor SLA-561 was cork particles, fibres and microspheres in a silicone binder, per the 1971 report. The -561V composition is not printed in any source read, so no shares are recorded.
    parts:
      - name: Silicone binder
        role: Binder that holds the filler together, per the 1971 report on the SLA-561 predecessor
        share_note: not printed in any source read
      - name: Cork particles
        role: Filler, per the 1971 report on the SLA-561 predecessor
        share_note: not printed in any source read
      - name: Fibres and microspheres
        role: Filler, per the 1971 report on the SLA-561 predecessor
        share_note: not printed in any source read
  risk_groups:
    - title: For people
      lead: No hazard or safety data sheet for SLA-561V was read in this run, so no hazard level is recorded.
      verdict: Not recorded
      points:
        - label: Hazard data
          line: The safety data sheet and GHS classification were not read. Check the manufacturer's data before handling.
    - title: If it fails
      lead: The failure routes in these sources are glass melt flow at high surface temperature and ablation past a heat flux limit.
      points:
        - label: Glass melt flow
          line: In the Ames turbulent flow duct test with a surface near 1800 degC, glass formed and melted at the SLA-561V/Silfrax interface. The paper says the material did not fail.
        - label: Heat flux limit
          line: The Wikipedia article gives a failure heat flux above 300 W/cm2 for SLA-561V.
  why: SLA-561V is a Lockheed Martin ablator for Mars entry backshell thermal protection. The MEDLI2 slides name it as the backshell TPS on Mars 2020, and the Wikipedia article says it was the primary TPS on NASA's 70 degree sphere-cone Mars entry vehicles other than MSL. The Mars 2020 TPS sizing paper gives a nominal flight thickness of 1.27 cm (0.5 inch).
  can_do:
    - label: Ablate and protect
      value: Significant ablation from about 110 W/cm2
      benchmark: ablation_onset_heat_flux
      line: Per the Wikipedia article, SLA-561V begins significant ablation at approximately 110 W/cm2 and fails above 300 W/cm2. The article gives no test method.
    - label: Flight thickness
      value: 1.27 cm nominal thickness
      benchmark: nominal_thickness
      line: The Mars 2020 TPS sizing paper gives a nominal uniform SLA-561V thickness of 1.27 cm (0.5 inch) on the backshell, the same as for MSL. The TPSX conductivity is printed in exponent form, so no conductivity is quoted here.
    - label: Char
      value: Full char at 600 degC
      benchmark: charring_temperature
      line: The MEDLI2 slide note says SLA fully chars at 600 degC.
  compare: The 1971 report on the SLA-561 predecessor gives a bulk density of 0.222 to 0.233 g/cm3 and, at 340 K, a thermal conductivity of about 0.059 W/m-K and a specific heat of 1290 J/kg-K. The TPSX row for SLA-561V virgin density and conductivity is printed in exponent form, so no value is compared here. The 1971 values are for the predecessor SLA-561 under different test methods, so no ranking is made.
  compare_rows:
    - scope: material
      label: Density
      benchmark: density
    - scope: material
      label: Thermal conductivity
      benchmark: thermal_conductivity
    - scope: material
      label: Ablation onset heat flux
      benchmark: ablation_onset_heat_flux
  handling:
    - No handling or safety data sheet for SLA-561V was read in this run.
    - Use the 1971 density range only for the predecessor SLA-561. The TPSX density is for the SLA-561V virgin material.
  good_for:
    - Mars entry backshell thermal protection, the flight role the MEDLI2 slides describe for Mars 2020.
    - Ablative heat shields where the heat flux stays below about 110 W/cm2, per the Wikipedia summary.
  watch_out:
    - Glass melt flow above about 1800 degC at the test surface, seen in the Ames turbulent flow duct test.
    - Full char at 600 degC. Per the MEDLI2 discussion slide, charring lowers emissivity and reflectance.
    - The 1971 report covers SLA-561, not SLA-561V, so its numbers are for the predecessor.
  verdict: SLA-561V is a Lockheed Martin silicone-based filled-cork ablator used for Mars entry backshell thermal protection. The Mars 2020 TPS sizing paper gives a nominal flight thickness of 1.27 cm. The Wikipedia summary gives ablation onset near 110 W/cm2 and failure above 300 W/cm2. Flight history beyond Mars 2020 for SLA-561V, the -561V composition, and test-method details are not verified in this run.