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Artemis II Environmental Impact Report: Why ‘Clean’ Spaceflight Starts on the Ground
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By Kara Anderson, UK Copywriter, on 02/06/2026
Methodology Disclaimer
Methodology Disclaimer: This analysis is based on publicly available NASA mission specifications alongside recognised industrial emission factors from the IEA, US DOE, and EcoInvent. These figures provide a data-driven snapshot of the relative scale of the mission’s carbon footprint and are not intended as exhaustive measurements.
The results rely on a range of calculated assumptions, including average US electricity grid intensity and standard industrial production methods for liquid hydrogen. Real-world emissions may vary based on specific supply chain logistics and evolving energy grid mixes. While the exact numbers will shift as aerospace and energy systems decarbonise, this report offers a robust comparison based on the best available data at the time of publication.
The Artemis II mission, launched on 1 April 2026, marked NASA’s first crewed mission beyond low-Earth orbit since Apollo 17. Powered by the Space Launch System (SLS), the rocket’s core stage burns liquid hydrogen (LH₂) and liquid oxygen (LOX), producing only water vapour at the point of combustion.
This has led to a widely cited claim: that Artemis represents a “clean” form of spaceflight. However, this claim applies only at the launch site. The broader environmental picture requires examining the full lifecycle of the fuel.
This report focuses on the most robust, publicly defensible data available. Rather than presenting a single total mission footprint, it isolates the most scientifically supported component: the upstream carbon cost of liquid hydrogen.
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:
2H₂ + O₂ → 2H₂O
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.
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:
Cleaner at the point of use does not mean carbon-free overall.
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
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