Artemis II Environmental Impact Report: Why ‘Clean’ Spaceflight Starts on the Ground

Where Do Artemis II Emissions Come From?

Emissions associated with an SLS launch can be divided into three categories:

• Component
• Fuel Type
• Primary Output
• Environmental Concern
• Core Stage
• LH₂ / LOX
• Water vapour (H₂O)
• High-altitude radiative forcing
• Solid Rocket Boosters
• Composite solid (PBAN - Polybutadiene acrylonitrile)
• Alumina, HCl
• Ozone chemistry, aerosols
• Upstream H₂ Production
• Natural gas (SMR - Steam Methane Reformation)
• CO₂
• Global warming

Note: Upstream figures focus on Hydrogen due to high data availability; Solid Rocket Booster manufacturing impacts are excluded from headline totals due to lack of verified public LCA data.

Direct Emissions at Launch

Water Vapour Production (Core Stage)

The SLS core stage burns approximately 143.8 tonnes of liquid hydrogen. Through combustion:

Using standard molar mass ratios, this produces:

• ≈ 1,285 tonnes of water vapour

Important clarification: This water is produced during ascent, but it should not be described as entirely injected into the stratosphere. The exact altitude distribution depends on flight profile and atmospheric dynamics, which are not fully resolved in public data.

Solid Rocket Boosters (Context Only)

The two solid rocket boosters burn over 1,250 tonnes of propellant combined.

They produce:

• Aluminum oxide (alumina)
• Hydrogen chloride (HCl)
• Trace CO₂ and other gases

These emissions are environmentally relevant, particularly for ozone chemistry. However, publicly available data does not provide a fully verified exhaust breakdown for Artemis II, so they are not included in our headline carbon figures.

Upstream Lifecycle Emissions (The Hidden Carbon)

The Hydrogen Production Pathway

Although hydrogen combustion produces no CO₂ at launch, the majority of industrial hydrogen today is produced via Steam Methane Reforming (SMR).

This process:

• Uses natural gas (primarily CH₄ - 70 to 90%)
• Releases CO₂ during hydrogen extraction
• Requires significant energy for liquefaction (−253°C)

A Transparent Emissions Range

Rather than relying on a single lifecycle estimate, this report uses a range-based approach derived from:

• International Energy Agency (IEA): hydrogen production emissions
• U.S. Department of Energy (DOE): liquefaction energy requirements
• EPA grid intensity: electricity emissions

Inputs:

• Hydrogen mass: 143.8 tonnes
• Production emissions: 10.6 kg CO₂e per kg H₂ (Source: EcoInvent, geography = US, excluding liquefaction)
• Liquefaction energy: 10–13 kWh per kg LH₂
• Grid factor: 0.438 kg CO₂e per kWh (Source: eGRID US average)

Calculation Results

• Scenario
• Emission Factor
• Total CO₂e
• Low (10 kWh liquefaction)
• ~14.98 kg CO₂e/kg
• 2,154 t CO₂e
• Midpoint (11.5 kWh liquefaction)
• ~15.64 kg CO₂e/kg
• 2,249 t CO₂e
• High (13 kWh liquefaction)
• ~16.29 kg CO₂e/kg
• 2,343 t CO₂e

This figure accounts for the fact that hydrogen liquefaction in the U.S. is powered by electricity, the footprint of which is determined by the specific carbon intensity of the regional or national power grid.

Historical Comparison: Apollo 8

To contextualise this result, we compare Artemis II with a kerosene-era lunar mission.

Apollo 8 (Saturn V First Stage)

• Fuel: RP-1 (kerosene)
• Consumption: ~203,000 gallons
• Emissions factor: ~9.75 kg CO₂ per gallon

Result:

• ≈ 1,979 tonnes of CO₂ (direct combustion only)

Comparison

• Mission Component
• CO₂ / CO₂e
• Artemis II (LH₂ upstream only)
• 2,154–2,343 t CO₂e
• Apollo 8 (RP-1 combustion only)
• ~1,979 t CO₂

Interpretation:

• Artemis II produces no CO₂ at launch
• But its upstream hydrogen footprint is of similar magnitude to Apollo-era direct emissions

Data Note on Lifecycle Equivalence: While Apollo 8 also had upstream refining emissions, they arelikely to be lower in intensity than the cryogenic processing required for Artemis II’s hydrogen. Even when accounting for Apollo’s full lifecycle, the "Hydrogen Paradox" remains: modern hydrogen missions carry a front-loaded carbon debt that rivals the total impact of 1960s kerosene-based launches.

Key Insight: The Hydrogen Paradox

Hydrogen-powered rockets present a clear contrast:

• At the launch pad: No CO₂ emissions, only water vapour
• Across the lifecycle: Significant carbon emissions from fuel production

This leads to a central conclusion:

Under current industrial conditions (grey hydrogen), the upstream footprint of LH₂ can match or exceed the direct emissions of kerosene-based systems.

What This Report Does Not Include

To maintain scientific defensibility, the following are excluded from headline figures:

• Full mission lifecycle CO₂ (no verified booster LCA)
• Ground infrastructure emissions
• Hardware manufacturing impacts
• Quantified climate forcing from water vapour, alumina, or chlorine species

These areas require further research or more detailed public datasets.

Conclusion

The Artemis II mission demonstrates both the promise and the limitations of hydrogen as a “clean” fuel.

• The rocket itself emits no CO₂ at launch
• Yet producing its fuel likely generated between roughly 2,154 to 2,343 t CO₂e of CO₂e upstream

This places Artemis II’s hidden carbon cost in the same order of magnitude as historic lunar missions, despite fundamentally different propulsion chemistry.

The implication is clear: Decarbonising hydrogen production - not just using hydrogen - is essential to reducing the climate impact of spaceflight.

Sources:

Why it is used

NASA Artemis II Launch Day Updates - Launch date and timing.

NASA Artemis II Press Kit - Mission profile; Orion service module translunar injection wording.

NASA SLS Solid Rocket Booster Fact Sheet - Current booster role and heritage facts.

DOE Program Record 9013 - Hydrogen liquefaction electricity range.

IEA Global Hydrogen Review 2024 - Grey-hydrogen production emissions factor.

EPA eGRID 2023 summary data - U.S. grid CO2e factor for the liquefaction add-on.

NASA NTRS S-IC Stage of Saturn V - Apollo 8 / Saturn V RP-1 volume.

EPA GHG Emission Factors Hub 2025 - Kerosene combustion factor used as the RP-1 proxy.

More detail:

Mission specifications (rocket + fuel mass)

• NASA Artemis II Press Kit
• NASA SLS Reference Guide / Boeing SLS specs

Used for:

• LH₂ mass (~143.8 tonnes)
• LOX mass and propellant ratios
• Overall vehicle configuration

Hydrogen combustion and water production

• Standard chemical stoichiometry (H₂ + O₂ → H₂O)

Used for:

• 8.94× mass conversion ratio
• Total water output (~1,285 tonnes)

Hydrogen production emissions (SMR)

• IEA Global Hydrogen Review (2024)

Used for:

• 10–12 kg CO₂e per kg H₂ range

Hydrogen liquefaction energy

• DOE Hydrogen Program Record 9013

Used for:

• 10–13 kWh per kg LH₂ energy requirement

Electricity emissions factor

• EPA eGRID (2023)

Used for:

• ~0.438 kg CO₂e per kWh

Combined hydrogen lifecycle emissions

Derived from:

• IEA (production emissions)
• DOE (liquefaction energy)
• EPA (electricity intensity)

Used for:

• Final range: 2,154–2,343 t CO2e.

Solid Rocket Boosters (context only)

• NASA SLS Solid Rocket Booster Fact Sheet
• Supporting PBAN composition references

Used for:

• Qualitative statements only
• Not used in headline carbon figures

Apollo 8 comparison (kerosene baseline)

• NASA NTRS Saturn V S-IC documentation

Used for:

• RP-1 fuel volume (~203,000 gallons)

Kerosene emissions factor

• EPA GHG Emission Factors Hub (2025)

Used for:

• ~9.75 kg CO₂ per gallon
• Total: ~1,979 t CO₂