spore: profile
id: carbon-dioxide-two-phase-coolant
spore_version: 0.2
family: carbon-dioxide
name: Carbon dioxide (two-phase pumped-loop coolant)
abbreviation: CO2
role: coolant
category: thermal-protection
type: multi-layer-insulation
summary: |
  Carbon dioxide (CO2) is one carbon atom bonded to two oxygen atoms. NIST's reference data put its triple point at 216.58 K and 5.185 bar, and its critical point at 304.18 K and 73.80 bar, so liquid CO2 exists only above the triple-point pressure. NASA used liquid carbon dioxide as the coolant in the pumped loop that cools the silicon tracker of the Alpha Magnetic Spectrometer (AMS-02) on the International Space Station.
best_for: Pumped cooling loops on a space instrument where the coolant can be refilled on orbit, as NASA planned for the AMS-02 tracker
weakest_at: 'Narrow margins: the liquid exists only above the 5.185 bar triple-point pressure, and the AMS-02 pumps are the documented failure point'
identity:
  formula: CO2
  cas: 124-38-9
  source: nist-phase
  where: 'NIST WebBook compound page header: CAS Registry Number 124-38-9 and molecular weight 44.0095'
tags:
  applications:
    - thermal-control
properties:
  - benchmark: critical_temperature
    label: Critical temperature
    value: 304.18
    unit: K
    scope: material
    conditions:
      phase: critical point, liquid and vapour
      reference_row: Suehiro, Nakajima, et al., 1996
    method: Critical temperature as tabulated by NIST; NIST assigns an uncertainty of 0.04 K (TRC). Other rows in the same table give 304.1 K to 304.35 K.
    status: ground
    source: nist-phase
    where: Phase change data table, Tc row (Suehiro, Nakajima, et al., 1996)
  - benchmark: critical_pressure
    label: Critical pressure
    value: 73.8
    unit: bar
    scope: material
    conditions:
      phase: critical point
      reference_row: Suehiro, Nakajima, et al., 1996
    method: Critical pressure as tabulated by NIST; NIST assigns an uncertainty of 0.15 bar (TRC).
    status: ground
    source: nist-phase
    where: Phase change data table, Pc row (Suehiro, Nakajima, et al., 1996)
  - benchmark: critical_density
    label: Critical density
    value: 10.6
    unit: mol/l
    scope: material
    conditions:
      phase: critical point
      reference_row: Suehiro, Nakajima, et al., 1996
    method: Critical density as tabulated by NIST; NIST assigns an uncertainty of 0.05 mol/l (TRC). Angus et al. 1976 gives 10.590 mol/l.
    status: ground
    source: nist-phase
    where: Phase change data table, rho c row (Suehiro, Nakajima, et al., 1996)
  - benchmark: critical_volume
    label: Critical volume
    value: 0.0919
    unit: l/mol
    scope: material
    conditions:
      phase: critical point
    method: Critical volume as tabulated by NIST (uncertainty 0.001 l/mol, TRC).
    status: ground
    source: nist-phase
    where: Phase change data table, Vc row (Li and Kiran, 1988)
  - benchmark: triple_point_temperature
    label: Triple point temperature
    value: 216.58
    unit: K
    scope: material
    conditions:
      basis: solid, liquid and vapour in equilibrium
      reference_row: Marsh, 1987
    method: Triple-point temperature as tabulated by NIST; NIST assigns an uncertainty of 0.008 K (TRC) and recommends it as a thermometry fixed point. Angus et al. 1976 gives the same 216.58 K.
    status: ground
    source: nist-phase
    where: Phase change data table, Ttriple row (Marsh, 1987)
  - benchmark: triple_point_pressure
    label: Triple point pressure
    value: 5.185
    unit: bar
    scope: material
    conditions:
      basis: solid, liquid and vapour in equilibrium
      reference_row: Angus, Armstrong, et al., 1976
    method: Triple-point pressure as tabulated by NIST; NIST assigns an uncertainty of 0.005 bar (TRC).
    status: ground
    source: nist-phase
    where: Phase change data table, Ptriple row (Angus, Armstrong, et al., 1976)
  - benchmark: molar_mass
    label: Molecular weight
    value: 44.0095
    unit: amu
    scope: material
    conditions:
      basis: molecular weight of CO2 as printed by NIST
    method: Molecular weight as printed on the NIST WebBook compound page (IUPAC Gold Book link).
    status: ground
    source: nist-phase
    where: Molecular weight line on the NIST WebBook page header
  - benchmark: enthalpy_of_vaporization
    label: Enthalpy of vaporization
    value: 16.7
    unit: kJ/mol
    scope: material
    conditions:
      temperature: 288 K
      basis: liquid to vapour transition
    method: Enthalpy of vaporization as tabulated by NIST from Stephenson and Malanowski, 1987, based on data from 273 K to 304 K.
    status: ground
    source: nist-phase
    where: Enthalpy of vaporization table, first row (Stephenson and Malanowski, 1987)
  - benchmark: enthalpy_of_vaporization
    label: Enthalpy of vaporization
    value: 16.4
    unit: kJ/mol
    scope: material
    conditions:
      temperature: 258 K
      basis: liquid to vapour transition
    method: Enthalpy of vaporization as tabulated by NIST from Stephenson and Malanowski, 1987, based on data from 216 K to 273 K.
    status: ground
    source: nist-phase
    where: Enthalpy of vaporization table, second row (Stephenson and Malanowski, 1987)
  - benchmark: enthalpy_of_vaporization
    label: Enthalpy of vaporization
    value: 16.5
    unit: kJ/mol
    scope: material
    conditions:
      temperature: 282 K
      basis: liquid to vapour transition
    method: Enthalpy of vaporization as tabulated by NIST from Boublik and Aim, 1972, based on data from 267 K to 303 K.
    status: ground
    source: nist-phase
    where: Enthalpy of vaporization table, third row (Boublik and Aim, 1972)
  - benchmark: enthalpy_of_sublimation
    label: Enthalpy of sublimation
    value: 26.1
    unit: kJ/mol
    scope: material
    conditions:
      temperature: 207 K
      basis: solid to vapour transition
    method: Enthalpy of sublimation as tabulated by NIST from Stephenson and Malanowski, 1987, based on data from 198 K to 216 K.
    status: ground
    source: nist-phase
    where: Enthalpy of sublimation table, first row (Stephenson and Malanowski, 1987)
  - benchmark: enthalpy_of_sublimation
    label: Enthalpy of sublimation
    value: 26.3
    unit: kJ/mol
    scope: material
    conditions:
      temperature: 167 K
      basis: solid to vapour transition
    method: Enthalpy of sublimation as tabulated by NIST from Stull, 1947, based on data from 139 K to 195 K.
    status: ground
    source: nist-phase
    where: Enthalpy of sublimation table (Stull, 1947)
  - benchmark: enthalpy_of_sublimation
    label: Enthalpy of sublimation
    value: 25.2
    unit: kJ/mol
    scope: material
    conditions:
      temperature: 195 K
      basis: solid to vapour transition
    method: Enthalpy of sublimation as tabulated by NIST from Giauque and Egan, 1937, based on data from 154 K to 196 K.
    status: ground
    source: nist-phase
    where: Enthalpy of sublimation table (Giauque and Egan, 1937)
  - benchmark: enthalpy_of_formation_gas
    label: Standard enthalpy of formation, gas
    value: -393.51
    unit: kJ/mol
    scope: material
    conditions:
      state: gas at standard conditions
      uncertainty: plus or minus 0.13 kJ/mol as printed
    method: CODATA review value as printed by NIST (Cox, Wagman, et al., 1984). Chase, 1998 gives -393.52 kJ/mol.
    status: ground
    source: nist-thermo
    where: Gas phase thermochemistry data, delta-f H gas row (Cox, Wagman, et al., 1984)
  - benchmark: entropy_gas_standard
    label: Standard entropy, gas at 1 bar
    value: 213.785
    unit: J/mol*K
    scope: material
    conditions:
      state: gas at 1 bar standard pressure
      uncertainty: plus or minus 0.010 J/mol*K as printed
    method: CODATA review value as printed by NIST (Cox, Wagman, et al., 1984). Chase, 1998 gives 213.79 J/mol*K.
    status: ground
    source: nist-thermo
    where: Gas phase thermochemistry data, S gas row (Cox, Wagman, et al., 1984)
risks:
  hazards:
    - text: 'PubChem''s GHS entry for carbon dioxide gives H280: contains gas under pressure; may explode if heated. The signal word is Warning, and the pictogram is the compressed-gas symbol.'
      ghs:
        - H280
      source: pubchem-ghs
      where: GHS Classification section, Hazard Statements (ECHA C&L entries, CID 280)
    - text: 'PubChem also lists H281 for carbon dioxide: contains refrigerated gas; may cause cryogenic burns or injury. This applies to the cold liquid or refrigerated form.'
      ghs:
        - H281
      source: pubchem-ghs
      where: GHS Classification section, Hazard Statements (ECHA C&L entries, CID 280)
  failure_risks:
    - mode: Coolant pump wear-out in the AMS-02 tracker loop
      trigger: Pumps run far beyond their original design life on orbit
      consequence: NASA reported that most of the coolant pumps had stopped, and the last one ran only intermittently under good sunlight conditions, so the cooling system was close to stopping altogether.
      severity: high
      source: spaceflightnow-2019
      where: Article paragraphs on the four coolant pumps and the expected loss of cooling
    - mode: Leak in a cooling line after the loop is rebuilt
      trigger: Fluid-line work during spacewalks
      consequence: Leak checks are a required step before the loop is trusted. The 2020 spacewalk completed leak checks and opened a valve to begin pressurizing the system.
      severity: moderate
      source: nasa-2020-01-25
      where: Spacewalk summary paragraph, leak checks and pressurization
  handling:
    - text: Keep containers closed and away from heat. The gas is under pressure and may explode if heated (PubChem H280).
      source: pubchem-ghs
      where: GHS Classification section, H280 hazard statement
    - text: Protect skin and eyes from refrigerated or liquid carbon dioxide, which can cause cryogenic burns (PubChem H281).
      source: pubchem-ghs
      where: GHS Classification section, H281 hazard statement
    - text: Before cutting lines on orbit, the crew vented the carbon dioxide that remained in the old cooling pump.
      source: nasa-2019-11-22
      where: Summary paragraph on tube cutting and venting
    - text: After leak checks, ground teams filled the new AMS thermal control system with carbon dioxide and then powered the pumps.
      source: nasa-2020-01-25
      where: Spacewalk summary paragraph, fill and pump power-on
uses:
  - application: thermal-control
    device: AMS-02 silicon tracker coolant loop on the International Space Station (flight, original pumped system)
    example: NASA's spacewalk reporting describes the AMS tracker coolant as liquid carbon dioxide, which the astronauts would replenish during the repair spacewalks.
    source: spaceflightnow-2019
    where: Article paragraph on carbon dioxide coolant and replenishment
  - application: thermal-control
    device: Upgraded tracker thermal pump system on the International Space Station (flight, installed during spacewalks)
    example: The crew installed the upgraded tracker thermal pump system and connected all the AMS cooling lines to the new system by swaging, a metalworking connection.
    source: nasa-2019-12-02
    where: Spacewalk summary paragraph on the upgraded tracker thermal pump system
supply:
  - subject: Carbon dioxide (industrial supply)
    producers: []
    critical_lists: []
    recycling: Not stated in the source used.
    substitutes: []
    source: wiki-co2
    where: 'Industrial and geological sources section: byproduct of hydrogen production by steam reforming and of ammonia production, and from natural gas processing. No country production shares are given.'
story:
  recipe:
    line: Carbon dioxide has one carbon atom bonded to two oxygen atoms. Industrially it is recovered as a byproduct of hydrogen production by steam reforming and of ammonia production, and from natural gas processing.
    parts:
      - name: Carbon
        symbol: C
        role: The central atom. Each carbon atom is bonded to two oxygen atoms in the molecule.
      - name: Oxygen
        symbol: O
        role: The two outer atoms. Together with the carbon they make a molecule of molar mass 44.0095 amu.
  risk_groups:
    - title: For people
      level: 1
      verdict: Compressed gas; cold liquid can cause burns
      lead: PubChem lists the compressed-gas hazard (H280) and the cold-burn hazard (H281) for carbon dioxide.
      points:
        - label: Pressure
          line: The gas is under pressure and may explode if heated. Keep containers away from heat.
        - label: Cold
          line: Refrigerated or liquid carbon dioxide can cause cryogenic burns or injury.
    - title: If a pumped loop fails
      lead: The AMS-02 record shows how coolant-loop trouble appeared on orbit.
      points:
        - label: Pumps
          line: Most of the coolant pumps had stopped, and the last one ran only intermittently under good sunlight conditions.
        - label: Repair
          line: The repair installed a new loop on spacewalks, followed by leak checks and a refill with carbon dioxide.
    - title: Handling and storage
      points:
        - label: Storage
          line: Keep containers closed and away from heat, since the gas may explode when heated.
        - label: Venting
          line: The crew vented the carbon dioxide left in the old pump before cutting its lines.
  why: Carbon dioxide is a coolant that stays liquid only under pressure. NASA's tracker cooling on the International Space Station circulated liquid carbon dioxide through a pumped loop, which is why its phase data matter for the design. The triple point and critical point set the pressure and temperature window in which the liquid can be held.
  uses:
    - where: AMS-02 tracker on the International Space Station
      line: NASA's spacewalk reports describe liquid carbon dioxide as the coolant of the AMS-02 silicon tracker. The crew replenished the instrument with it during the repair spacewalks.
    - where: Upgraded tracker thermal pump system
      line: The upgraded system was installed on a later spacewalk and connected to the existing AMS cooling lines, with the new loop filled with carbon dioxide after leak checks.
  can_do:
    - label: Strength
      line: Carry heat away in a pumped liquid loop on a space instrument, as the AMS-02 tracker did.
    - label: Strength
      line: Be refilled on orbit during spacewalks, which NASA planned for the AMS-02 tracker.
    - label: Strength
      line: Stay liquid only above its triple-point pressure of 5.185 bar, at its triple-point temperature of 216.58 K and above.
  compare: NIST's reference data for carbon dioxide give a critical point at 304.18 K and 73.80 bar, a triple point at 216.58 K and 5.185 bar, and an enthalpy of vaporization of 16.7 kJ/mol at 288 K. The table below lists three of these values. No other cooling fluid is compared, because the sources read for this profile give no same-basis values for one.
  compare_rows:
    - label: Critical temperature
      benchmark: critical_temperature
    - label: Triple point temperature
      benchmark: triple_point_temperature
    - label: Enthalpy of vaporization
      benchmark: enthalpy_of_vaporization
  handling:
    - Keep the container closed and away from heat. The gas is under pressure and may explode if heated.
    - Protect skin and eyes from refrigerated or liquid carbon dioxide, which can cause cryogenic burns.
    - On orbit, refill the loop only after leak checks, as the NASA crew and ground teams did.
  good_for:
    - Pumped cooling loops on space instruments, where NASA used liquid carbon dioxide on the AMS-02 tracker.
    - 'Reference thermodynamic data: NIST gives the triple point and critical point with stated uncertainties.'
  watch_out:
    - 'Pumps: the AMS-02 record shows coolant pumps that wore out well past their design life.'
    - 'Pressure: the liquid exists only above the triple-point pressure of 5.185 bar.'
    - 'Heat: the gas is under pressure and may explode when heated (PubChem H280).'
  verdict: Carbon dioxide has well-measured phase data for a pumped loop. On the AMS-02 record, the pumps failed before the fluid did, and the repair was a refill and replacement of the loop.
sources:
  nist-phase:
    title: 'NIST Chemistry WebBook: carbon dioxide, phase change data (NIST SRD 69)'
    id: CAS 124-38-9
    url: https://webbook.nist.gov/cgi/cbook.cgi?Mask=4&ID=C124389
    year: 2026
    kind: database
    license: NIST Standard Reference Data (cited, not reproduced)
  nist-thermo:
    title: 'NIST Chemistry WebBook: carbon dioxide, gas phase thermochemistry data (NIST SRD 69)'
    id: CAS 124-38-9
    url: https://webbook.nist.gov/cgi/cbook.cgi?ID=C124389&Mask=1
    year: 2026
    kind: database
    license: NIST Standard Reference Data (cited, not reproduced)
  pubchem-ghs:
    title: PubChem compound record, Carbon dioxide (CID 280), GHS classification
    id: CID 280
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/280/JSON?heading=GHS+Classification
    year: 2026
    kind: database
    license: public domain (NCBI)
  nasa-2019-11-22:
    title: Astronauts Complete Intricate Tasks During Second Cosmic Repair Spacewalk (NASA blog)
    id: NASA Space Station blog, 22 November 2019
    url: https://www.nasa.gov/blogs/spacestation/2019/11/22/astronauts-complete-intricate-tasks-during-second-cosmic-repair-spacewalk/
    year: 2019
    kind: web
    license: public domain (NASA)
  nasa-2019-12-02:
    title: Astronauts Wrap Up Third Spacewalk for Cosmic Particle Detector Repairs (NASA blog)
    id: NASA Space Station blog, 2 December 2019
    url: https://www.nasa.gov/blogs/spacestation/2019/12/02/astronauts-wrap-up-third-spacewalk-for-cosmic-particle-detector-repairs/
    year: 2019
    kind: web
    license: public domain (NASA)
  nasa-2020-01-25:
    title: Astronauts Wrap Up Spacewalk Repair Job on Cosmic Ray Detector (NASA blog)
    id: NASA Space Station blog, 25 January 2020
    url: https://www.nasa.gov/blogs/spacestation/2020/01/25/astronauts-wrap-up-spacewalk-repair-job-on-cosmic-ray-detector/
    year: 2020
    kind: web
    license: public domain (NASA)
  spaceflightnow-2019:
    title: Repair equipment for particle physics experiment aboard next station cargo launch (Spaceflight Now)
    id: Spaceflight Now, 1 November 2019
    url: https://spaceflightnow.com/2019/11/01/repair-equipment-for-particle-physics-experiment-aboard-next-station-cargo-launch/
    year: 2019
    kind: web
    license: news article, linked not reproduced
  wiki-co2:
    title: Carbon dioxide (Wikipedia), sections on industrial sources and refrigerant use
    id: Wikipedia article, Carbon dioxide
    url: https://en.wikipedia.org/wiki/Carbon_dioxide
    year: 2026
    kind: web
    license: CC BY-SA 4.0 (linked, not reproduced)
documents:
  - title: 'NIST WebBook: carbon dioxide phase change data (CAS 124-38-9)'
    type: database
    url: https://webbook.nist.gov/cgi/cbook.cgi?Mask=4&ID=C124389
    year: 2026
  - title: 'NIST WebBook: carbon dioxide gas phase thermochemistry'
    type: database
    url: https://webbook.nist.gov/cgi/cbook.cgi?ID=C124389&Mask=1
    year: 2026
  - title: 'PubChem: Carbon dioxide (CID 280), GHS classification'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/280
    year: 2026
  - title: 'NASA Space Station blog: second cosmic repair spacewalk'
    type: report
    url: https://www.nasa.gov/blogs/spacestation/2019/11/22/astronauts-complete-intricate-tasks-during-second-cosmic-repair-spacewalk/
    year: 2019
gaps:
  - No flight or space-environment test data for the fluid's own properties in any source fetched; the only space source is the AMS-02 operations record.
  - Corrosion or material-compatibility data for carbon dioxide in cooling-line materials were not found in any source opened, so the corrosion section is left out.
  - 'Two-phase operation: the planner''s name says two-phase, but none of the fetched sources calls the AMS-02 loop two-phase. They describe liquid carbon dioxide in a pumped loop. The name is kept as the planner gave it and is not verified.'
  - No country production shares for carbon dioxide were found; the supply section is qualitative and cites the Wikipedia sources section.
  - No USGS or EU critical-minerals entry was checked for carbon dioxide, so critical_lists is left empty.
  - 'Property names are not in spores/property-canon.yaml and were not invented to match it: critical_temperature, critical_pressure, critical_density, critical_volume, triple_point_temperature, triple_point_pressure, molar_mass, enthalpy_of_vaporization, enthalpy_of_sublimation, enthalpy_of_formation_gas and entropy_gas_standard.'
  - NIST gives several critical-point rows from different references (for example 304.1 K to 304.35 K). Only one row is recorded per quantity; the others are named in the method text.
  - No safety data sheet for carbon dioxide was opened. PubChem's ECHA-derived GHS entry was read through its REST view, because the HTML page showed a bot check.
  - NIST fit coefficients (Antoine and Shomate) were not recorded as properties.
  - Spaceflight Now blocks automated access, so its statements were read through WebFetch in this run and are not checked by the value script.
  - Carbon dioxide's loop temperature and pressure operating ranges were not found in any source opened.
  - No thermal-protection type fits a coolant. The type is set to multi-layer-insulation, the same as the methanol heat-pipe fluid profile, because the schema requires a type; a coolant type would need a taxonomy change.
license: CC-BY-4.0
updated: '2026-11-01'
review:
  status: draft
  method: assistant
  checked_values: 15
  unreachable: 0
  caveats: 1
  note: Written by an AI assistant on 2026-11-01. NIST and PubChem values were checked against the raw pages in this run.