Space Debris Is Crashing Into Earth. Should You Worry? | WSJ

Key Concepts

• Space debris: Defunct satellites, spent rocket stages, and fragments of space hardware orbiting Earth.
• Uncontrolled reentry: The process of space debris falling back to Earth without a predetermined landing location.
• Controlled reentry: The process of guiding space debris to a specific, safe location (usually the ocean) during reentry.
• Demise: The complete burning up of an object during reentry into the Earth's atmosphere.
• Low-Earth orbit (LEO): An orbit around Earth at an altitude of approximately 2,000 km (1,200 mi) or less.
• Active debris removal: Technologies and missions designed to capture and deorbit existing space debris.
• Mitigation measures: Strategies and technologies aimed at reducing the creation of new space debris.

Space Debris: A Growing Threat

• Space debris is falling to Earth in increasing amounts due to heightened space-launch activity.
• While most debris burns up during reentry, some survives and reaches the ground.
• The European Space Agency (ESA) estimates that up to 200 tons of space hardware reenters the Earth's atmosphere uncontrollably each year.
• While the chance of debris striking a human is statistically low, the risk is increasing with more launches.
• Darren McKnight (LeoLabs) and Andrew Monham (EUMETSAT) co-authored a study highlighting the growing ground hazards from space debris reentry.
• Analysis suggests a nearly 3% annual chance of someone on Earth being injured by reentering debris.

Recent Incidents and Close Calls

• February 19th: A SpaceX Falcon 9 rocket upper stage experienced an uncontrolled reentry over Europe, scattering debris.
• 2024: A piece of debris from the International Space Station (ISS) crashed through a home's roof in Naples, Florida. This debris was part of a 5,800-pound cargo pallet containing batteries that was expected to fully burn up on reentry.
• These incidents highlight the need for improved reentry models and mitigation strategies.

Factors Affecting Reentry and Survival

• Material Composition: Low-melting-point materials like aluminum tend to demise during reentry, while heat-resistant materials like titanium, stainless steel, and beryllium are more likely to survive.
• Object Size and Mass: Larger and more massive objects have a higher probability of surviving reentry.
• SpaceX Dragon Trunk: Instances of Dragon trunk parts surviving reentry and crashing in Canada, Australia, and elsewhere led SpaceX to move splashdown locations and implement material changes to improve demise probability.

Rocket Bodies: A Major Source of Debris

• Rocket stages left in orbit since the beginning of the space age are a significant source of space debris.
• These are often the largest and most massive objects in orbit.
• Monham estimates that 32 rocket bodies will reenter the atmosphere in the next year, and 270 in the next 50 years.
• These bodies can weigh several tons, with a significant portion surviving reentry and scattering over a large area.

Uncontrolled Reentries and International Concerns

• Uncontrolled reentries of Chinese Long March 5B rocket stages have drawn international criticism.
• In 2022, a Long March 5B rocket broke up, with debris landing near the Philippines.
• Another Long March 5B reentry prompted Spain to close a large section of its airspace, delaying flights.
• These events highlight the need for better preparedness and international cooperation in managing space debris.
• NASA Administrator Bill Nelson stated that the debris posed a significant risk of loss of life and property.

Mitigation Efforts and Future Solutions

• Controlled reentries outnumbered uncontrolled ones for the first time last year, driven by increased awareness and mitigation measures.
• Active debris removal is a proposed solution, with the ESA's ClearSpace-1 mission planned for launch in 2028 to capture and deorbit a derelict object.
• Active removal could also lead to in-space servicing capabilities like refueling and repair, potentially reducing the need for new launches.

Conclusion

The increasing amount of space debris poses a growing risk to people and property on Earth. While the statistical probability of individual harm remains low, recent incidents and uncontrolled reentries highlight the need for improved reentry models, mitigation strategies, and international cooperation. Active debris removal and advancements in spacecraft design are promising solutions, but their development must keep pace with the increasing risks posed by a crowded orbit. The legacy of past space activities, particularly the accumulation of rocket bodies in orbit, continues to contribute to the problem, requiring a collective effort to address the challenges of space debris.