Source G

Introduction

The growth in Low Earth Orbit (LEO) satellite broadband constellations involves plans to launch tens of thousands of new satellites into space to provide global broadband coverage. LEO constellations are a key reason why the quantity of rocket launches to space has rapidly increased, from fewer than 250 launches annually in the 1970s (below 2,900 per decade), to now exceeding 1,300 launches annually (~16,000 in a single decade), marking a more than 400% increase.

This increasing number of launches raises emerging questions regarding the negative environmental externalities of these satellite megaconstellations. The environmental sustainability aspects of this approach, particularly given the increasing commercialization of space activities (from tourism to earth observation), warrant scrutiny. The shift towards ultra-dense satellite megaconstellations raises new environmental sustainability questions, with evidence-based studies indicating that projected trends are likely to produce adverse impacts, drawing the attention of regulatory authorities.

Therefore, it is imperative for governments to carefully balance the growth of the space sector and the associated benefits in progressing the Sustainable Development Goals (SDGs) against environmental sustainability issues. This creates a strong research motivation for assessing the sustainability implications associated with launching large numbers of planned LEO satellites in key megaconstellations. This is crucial as the rapid growth of the space sector raises concerns among those beyond the space community. Evidence is urgently needed to understand negative environmental impacts and to guide mitigation strategies.

Given this context, the paper develops an integrated model capable of assessing the environmental impacts associated with rocket launches for specific phase 1 LEO constellations, which includes metrics on provided capacity, the Social Cost of Carbon (SCC), and associated costs of delivery. Phase 1 of each LEO constellation refers to the filing information submitted to the US Federal Communications Commission (FCC), such as for Amazon's Kuiper (3,236 satellites), Eutelsat Group's OneWeb (648 satellites), and SpaceX's Starlink (4,425 satellites).

Additionally, a representative Geostationary Earth Orbit (GEO) constellation is assessed for comparison. The GEO satellite industry features several major operators including Intelsat (52 satellites), Eutelsat (35 satellites), Inmarsat (14 satellites), Arabsat (8 satellites), ViaSat (4 satellites), and Avanti (4 satellites). In the paper, a representative GEO operator is treated as having 19 satellites, which represents the mean quantity across these operators.

Policy makers must consider a key trade-off regarding the SDGs. The delivery of broadband services to unconnected communities is recognized to progress the SDGs, yet the results of this research reveal that the rapid growth in the satellite sector presents substantial sustainability implications for the environment. This situation creates a 'space sustainability paradox,' necessitating decision-makers to balance the economic, social, and environmental benefits of improved broadband connectivity against the growing environmental footprint of the satellite sector. The method and evidence produced from this paper can be used to:

  1. Inform future space sustainability metrics, such as the Space Sustainability Rating (SSR) system.

  2. Support strategic future choices regarding rocket design and fuel options.

Current and Proposed LEO Satellite Broadband Constellations

In very remote areas where terrestrial broadband infrastructure is not economically viable due to low population density and/or low adoption, LEO satellites provide high-capacity, low-latency broadband connectivity to hard-to-reach communities. Importantly, there are key differences when LEO satellites are compared to traditional GEO constellations. LEO satellites are designed to be smaller, have shorter lifespans (e.g., 5 years), and are therefore less costly to produce. However, their proximity to Earth means many more satellites are required to achieve global coverage. This has led satellite operators to file for a very large number of satellites in their proposed constellation designs, with the expectation that each constellation will need continuous replenishment as older satellites end their operational life.

For instance, in 2022, there were approximately 6,300 satellites in operation, while the total number of proposed satellites over the next decade in new constellations is expected to be as high as ~320,000.

Technical Details of Major LEO Constellations

1. Kuiper

  • Operator: Amazon

  • Satellites: 3,236

  • Earth Radius: 6,378 km

  • Orbital Altitude: 610 km

  • Orbital Radius: 6,988 km

  • Path Distance: 982 km

  • Satellite Centric Angle: 48.4 degrees

  • Earth Centric Angle: 6.61 degrees

  • Mean Satellites per Launch: 36

  • Satellites in Orbit (phase 1): 0

2. OneWeb

  • Operator: Eutelsat

  • Satellites: 648

  • Earth Radius: 6,378 km

  • Orbital Altitude: 1,200 km

  • Orbital Radius: 7,578 km

  • Path Distance: 1,580 km

  • Satellite Centric Angle: 36.5 degrees

  • Earth Centric Angle: 8.48 degrees

  • Mean Satellites per Launch: 36

  • Satellites in Orbit (phase 1): >630

3. Starlink

  • Operator: SpaceX

  • Satellites: 4,425

  • Earth Radius: 6,378 km

  • Orbital Altitude: 550 km

  • Orbital Radius: 6,928 km

  • Path Distance: 1,123 km

  • Satellite Centric Angle: 56.5 degrees

  • Earth Centric Angle: 8.45 degrees

  • Mean Satellites per Launch: 23

  • Satellites in Orbit (phase 1): 4,425

Summary of Operational Status (December, 2023)

  • Amazon's Kuiper is in a testing phase having launched only two prototype satellites (KuiperSat-1 and KuiperSat-2) and has not yet launched any of the planned 3,236 phase 1 satellites.

  • OneWeb has deployed 98% of the 648 phase 1 satellites.

  • SpaceX Starlink has launched 100% of the 4,425 phase 1 satellites.

Life Cycle Assessment of Satellite Constellations

Emissions produced during the launching of satellites depend on the rocket vehicles used. Most operators planning or launching LEO broadband satellites have used (or intend to use) SpaceX's Falcon-9 or Falcon-Heavy, the European Space Agency's (ESA's) Ariane, or Russia's Soyuz-FG rocket launch systems. The analysis focuses predominantly on the emissions produced by rocket and propellant manufacturing, transportation, rocket testing, and finally launching carried satellite payloads into LEO, to be compared to a hypothetical GEO system.

Emissions of Rocket Vehicles

Rocket Vehicle Specifications:
1. Falcon-9

  • Dry Mass: 22 tonnes

  • Operator: SpaceX

  • Payload to LEO: 23 tonnes

  • Height: 70 m

  • Price Per Launch: US$ 62 Million

  • Propellant Mass: 488 tonnes (Kerosene - Rocket Propellant-1)

2. Falcon-Heavy

  • Dry Mass: 66 tonnes

  • Operator: SpaceX

  • Payload to LEO: 64 tonnes

  • Height: 70 m

  • Price Per Launch: US$ 90 Million

  • Propellant Mass: 1,397 tonnes (Hydrocarbon)

3. Soyuz-FG

  • Dry Mass: 14 tonnes

  • Operator: Progress Rocket Space Center

  • Payload to LEO: 8 tonnes

  • Height: 46 m

  • Price Per Launch: US$ 80 Million

  • Propellant Mass: 256 tonnes (Kerosene and Hypergolic)

4. Ariane-5

  • Dry Mass: 53 tonnes

  • Operator: European Space Agency

  • Payload to LEO: 20 tonnes

  • Height: 46-52 m

  • Price Per Launch: US$ 149-198 Million

  • Propellant Mass: 7,645 tonnes (Hydrogen)

Quantifying the emissions from these rocket launches is complex and not well understood; extensive work has been conducted on approximating the emissions per mass of the fuel burned for the four common propellants used (known as the "mass fraction"). Additional studies have explored the role of black carbon due to its impact on climate change.

Environmental Emissions Assessment

LEO constellations have significant and growing environmental impacts. Different rocket combinations have been or will be used to launch upcoming satellite constellations, as depicted in diagrams shown in the supplemental materials. Currently, Starlink has completed 127 launches to place all its 4,425 satellites in orbit using the Falcon-9, a hydrocarbon (HYC) fuel-based rocket. OneWeb has placed 96 of its satellites using three launches with Falcon-9; the remaining satellites were launched via different rockets (Indian LVM3 and Russian Soyuz-FG).
Amazon Kuiper has announced a majority of future launches using different rockets, including United Launch Alliance's Vulcan Centaur, Arianespace's Ariane-6, and Blue Origin's New Glenn, in combination with Falcon-9 launches.

The resulting annual emissions per subscriber (in kg CO₂eq) indicate that LEO constellations have substantial environmental footprints. These impacts are broken down into five categories:

  1. Global Warming Potential (GWP): Defined as the radiative forcing in carbon dioxide equivalents (CO₂eq.) over a 100-year horizon by the Intergovernmental Panel on Climate Change (IPCC).

  2. Ozone Depletion Potential (ODP): Defined by the World Meteorological Organization (WMO) as the steady-state depletion potential in chlorofluorocarbon-11 equivalents (CFC-11eq).

  3. Mineral & Metal Resource Depletion Potential: Recommended by ESA Life Cycle Assessment (LCA) Handbook, defined as the abiotic resource depletion in antimony (Sb) equivalents.

  4. Freshwater Aquatic Ecotoxicity Potential: Measured in Comparative Toxic Units for ecosystems (CTU) based on potentially affected fraction of species per m³ per day (PAF.m³.day).

  5. Human Toxicity Potential: Comparative Toxic Units for humans (CTUh), implemented in USEtox as the estimated increase in morbidity (cases).

Two emissions scenarios are presented for the launch event in terms of the GWP and ODP categories: a baseline scenario and a worst-case option. The baseline option classifies the exhaust products based on models applied, while the worst-case scenario also includes the potential influence of black carbon, aluminum oxide, and water vapor exhaust particles termed Non-normally Included Emissions (NIES).

Given the complexities and high uncertainty regarding these exhaust products, they are often excluded from traditional impact assessment models, yet it is hypothesized that these could be some of the most influential particles from the launch event. Emissions per subscriber must be assessed to account for the substantial growth over the coming years and inform mitigation strategies effectively.

Environmental Impact Summary

The annual environmental impacts from emissions, per subscriber from a lifecycle perspective, which illustrates significant sustainability implications associated with LEO constellations. These emissions vary greatly depending on the rocket launch vehicles used and quantity, but exhibit alarming rates of increase with projected launches over the next decade.

Base Emissions Scenario Comparisons

The analysis evaluates the emissions averaged per subscriber across different constellations, highlighting that LEO constellations exhibit emissions that exceed traditional GEO systems. Furthermore, subscriber emissions from LEO constellations are quantified, with notable measurements revealing they average more than 12 times higher emissions than a representative GEO operator. This comparative analysis captures the Environmental Sustainability Implications between these contrasting systems.

The Social Cost of Carbon (SCC)

The SCC measures the monetary value of damages resulting from emitting an incremental ton of CO₂ or its equivalents over the unit's lifetime in the atmosphere. This approach is utilized in conducting cost-benefit analyses of policies which may have sustainability impacts, often mandated by regulatory agencies.

SCC Estimations by Constellation Type

  1. Social Cost Estimates in Baseline Scenario:

  • Kuiper: $621 million

  • OneWeb: $179 million

  • Starlink: $526 million

  • GEO Operator: $127 million

  1. Social Cost Estimates in Worst-Case Scenario:

  • Kuiper: $1.3 billion

  • OneWeb: $273 million

  • Starlink: $1.1 billion

  • GEO Operator: $341 million

  1. Annualized SCC per Subscriber:

  • Baseline estimates show Kuiper at $50, OneWeb at $45, Starlink at $30, and GEO at $3.

  • In the worst-case emissions scenario, Kuiper's estimated annual social cost per subscriber is projected at $101, OneWeb at $68, Starlink at $65, and GEO at $9.

Environmental Policy Implications

The findings reveal that phase 1 LEO constellations currently being deployed will yield significant sustainability implications that are likely to escalate with the sector’s move towards larger constellations over the next decade. Regulatory frameworks will need to adapt as launch volume and operational intensity are forecasted to increase.

This analysis indicates the acceleration of megaconstellations will create a substantial annual operational environmental footprint, equivalent to the energy usage from thousands of homes or gasoline-powered vehicles. In the worst-case scenario for LEO emissions, the operational impact becomes comparable to significant environmental burdens recorded in terrestrial mobile broadband networks, necessitating reevaluation of the social costs involved.

Significantly, alongside addressing the increasing emissions, careful policy guidance will be required to balance the social benefits of broadband access against the environmental consequences. Further research information on the lifecycle environmental consequences of satellite constellations is essential for sustainable policymaking and understanding international agreements on environmental impacts.

Utilizing integrated modeling frameworks (as outlined here) is one way to approach these complexities effectively, while keeping in mind the wide-ranging socio-economic benefits of broadband connectivity.