Environmental and Moral Implications of Human Space Travel Reading

Authors: Michael Carbajales-Dale (Clemson University) and Thomas W. Murphy (UC San Diego)
HIGHLIGHTS:
- First investigation of environmental impacts of human space travel across its entire timeline.
- Reports global warming impacts measured in global citizen equivalents (GCE).
- Identifies hourly global warming impact of sustaining humans in space, estimated between 1500-3500 kg CO2-eq per hour.
- Asserts space travelers have global warming impacts of 2000-4600 GCE per hour.
- Discusses moral implications of disparities in access to space travel due to large environmental impacts.
Keywords: Life cycle assessment, Environmental impact, Climate change, Sustainability, Space travel.

Humans have historically aspired to travel in space. In light of increased commercial spaceflight, this paper evaluates both past and present environmental impacts associated with human space travel.
The analysis highlights that this activity places a significant environmental burden on Earth, which the majority of the global population, unlikely to partake in space travel, must bear.
Contrary to alleviating Earth's resource constraints, human space travel considerably burdens planetary resources due to its limited beneficiaries.
Methodology: Life cycle assessment structure was utilized; data on launch vehicles and propellants were sourced publicly. Emissions were calculated using specialized software and analyzed in connection with life cycle inventory databases.

The desire for space travel dates back to Yuri Gagarin's historic flight, with many envisioning future explorations of planets beyond Earth, exemplified in cultural references (e.g., films).
The recent missions by commercial entities (like Blue Origin) have blurred the lines between fiction and reality in space travel.
There is a debate around potential off-world colonization as a solution to Earth's unsustainable practices, with proponents arguing for the necessity of space colonization as a future pathway. This viewpoint is echoed by leading voices like Jeff Bezos.
Current Context: Current human spaceflight must contend with the nutritional and restocking limits of the International Space Station (ISS); potential Mars missions would require indefinite crew sustenance, raising significant operational challenges.

Discussion on the environmental ethics of space exploration dates back to the Earth’s perspective showcased in the iconic ‘pale blue dot’ image.
Key Ethical Concerns Discussed:
- Does space possess intrinsic value warranting ethical consideration?
- Could space exploration alleviate Earth environmental impacts?
- Risks of contamination of extraterrestrial worlds and vice versa.
Notable critiques include notions that space exploration could detract from addressing terrestrial environmental issues.
Research on environmental impacts of space activities is limited, despite accumulating evidence of the ecological footprint, including the production analysis of hydrazine propellant versus greener alternatives.

The analysis employed life cycle assessment per ISO 14040 standards, involving multiple phases:
1. Goal and Scope Definition
2. Inventory Analysis
3. Impact Assessment
Goal: Raise awareness about human space travel's environmental toll; intended audiences include policymakers and the general public.
Scope: Focused on processes necessary for human space launches above the Kármán line (100 km altitude) and excluded missions below that height.
Impacts Defined: Evaluation focused on manufacturing and combustion of propellants as well as construction materials for launch vehicles.
Functional Unit: The duration humans have spent in space was quantified, totaling over 60,000 person-days or 1.42 million person-hours (p-h).

An uptick in human presence in space has been observed, with varying times spent depending on the space agencies involved. For instance, NASA’s astronauts alone have spent approximately 12,000 person-days in space.
Findings underscore that each crewed launch and associated supply chain activities have significant environmental impacts, especially during propellant production and combustion.
Environmental Impact Quantification: The paper identified that:
- The global warming impact of human space travel ranges between 2000-4600 times higher than average citizens, depending on the launch mission.
- For every hour spent in space, there is a fossil fuel and greenhouse gas emission equivalent significantly outpacing terrestrial averages.

Impacts from human space activities raise critical sustainability and ethical considerations regarding resource allocation and responsibility for ecological harm.
The authors argue that with access to space limited to wealthier strata of the population, the costs of exploring space must be justified by clear benefits to global citizens, extending beyond just the participants.
Concerns about the disproportionate impact of space endeavors on vulnerable populations (e.g., communities near launch sites) are raised, emphasizing environmental justice issues.

The paper draws a stark conclusion regarding the unsustainable nature of current human space travel from an environmental and moral perspective. The disparity between rich and poor in accessing space travel is highlighted as being ethically significant.
Recommendations for further detailed research on environmental impacts in policy planning for future missions, including potential bases on the Moon or Mars, are called for, emphasizing the need for transparency and robust impact assessment in future endeavors.

Aerosene-50 (A50): A type of propellant.
Global Citizen Equivalent (GCE): A measure of emissions corresponding to the average annual greenhouse emissions of a global citizen.
Life Cycle Assessment (LCA): A methodology to evaluate environmental impacts throughout a product’s life cycle.
International Space Station (ISS): A habitable artificial satellite in low Earth orbit.
Launch Vehicle (LV): A vehicle designed to transport payloads into space.