🛰️Space Debris Mitigation Unit 1 – Introduction to Space Debris

What's Space Debris?

• Space debris, also known as space junk or orbital debris, refers to the collection of defunct human-made objects in orbit around Earth
• Includes non-functional spacecraft, abandoned launch vehicle stages, mission-related debris, and fragmentation debris from the breakup of derelict rocket bodies and spacecraft
• Ranges in size from tiny flecks of paint to entire satellites and spent rocket stages
• As of January 2022, the United States Space Surveillance Network tracked more than 27,000 pieces of orbital debris
  • Only includes objects larger than about 5 cm (2 inches) in low Earth orbit and 1 meter (3 feet) at geostationary altitudes
• Estimated over 100 million pieces of space junk smaller than 1 cm exist in Earth's orbit
• Space debris orbits at speeds up to 28,000 km/h (17,500 mph), fast enough for even relatively small pieces to damage a satellite or spacecraft
• Most orbital debris resides in low Earth orbit (LEO), where the space station and many weather, communication, and Earth observation satellites operate

How Did We Get Here?

• The accumulation of space debris is a consequence of more than 60 years of space activities
• The launch of Sputnik 1, the first artificial satellite, in 1957 marked the beginning of humanity's presence in space
• Early space exploration and the Cold War space race led to a rapid increase in the number of objects launched into orbit
  • Many early satellites and rocket stages were left in orbit after their missions ended
• Anti-satellite weapons testing has significantly contributed to the space debris problem
  • China's 2007 anti-satellite test created over 3,000 trackable debris fragments
• Accidental collisions between orbiting objects have also generated significant amounts of debris
  • The 2009 collision between the active Iridium 33 and the derelict Kosmos-2251 satellites created over 2,000 trackable fragments
• Explosions of spent rocket stages and defunct satellites, often due to residual fuel or failed batteries, have added to the debris population
• The increasing commercialization of space has led to a surge in satellite launches, particularly large constellations like SpaceX's Starlink, further exacerbating the issue

Types of Space Junk

• Inactive satellites that have reached the end of their operational life but remain in orbit
  • Example: Envisat, an 8-ton Earth observation satellite that failed in 2012
• Spent rocket stages that were used to launch payloads into orbit but were not designed to deorbit or be recovered
  • Upper stages from rockets like the Russian Proton and the European Ariane 4
• Mission-related debris, such as lens covers, payload shrouds, and separation bolts, released during spacecraft deployment and operations
• Fragmentation debris resulting from the breakup of satellites and rocket stages due to explosions or collisions
  • Includes pieces ranging from large fragments to tiny particles of paint and metal
• Solid rocket motor slag, which are aluminum oxide particles ejected during the burning of solid rocket propellants
• Sodium-potassium (NaK) coolant droplets released from nuclear-powered satellites like the Soviet RORSAT series
• Debris from the erosion and degradation of spacecraft surfaces, such as paint flakes and insulation fragments

Tracking the Mess

• Space debris is tracked using a combination of ground-based and space-based sensors
• The United States Space Surveillance Network (SSN) is the most comprehensive tracking system, using a global network of radars and telescopes
  • Includes the Space Fence radar system, which can detect objects as small as 1 cm in LEO
• The European Space Agency (ESA) operates its own Space Debris Office and contributes to debris tracking through its Space Situational Awareness (SSA) program
• Tracking data is used to maintain catalogs of known space objects and their orbits
  • These catalogs help predict potential collisions and support collision avoidance maneuvers for active satellites
• Optical telescopes are used to observe debris in higher orbits, such as geostationary orbit (GEO)
  • Example: The ESA's 1-meter telescope in Tenerife, Spain
• Radar systems are more effective for tracking debris in lower orbits, as they can detect smaller objects and are not affected by weather or daylight
• In-situ measurements, using impact sensors on spacecraft like the ISS, provide data on the small debris population that cannot be tracked from the ground

Why It's a Big Deal

• Space debris poses a significant threat to active satellites and spacecraft, including the International Space Station (ISS)
  • Even small debris can cause critical damage due to the high orbital velocities
• Collisions between space objects can create more debris, leading to a self-sustaining cascade of collisions known as the Kessler Syndrome
  • This could render certain orbital regions unusable for generations
• The increasing debris population makes it more difficult and costly to operate satellites and conduct space missions safely
  • Satellite operators must constantly monitor for potential collisions and perform avoidance maneuvers
• Debris can also pose a risk to Earth's environment and human safety when it reenters the atmosphere
  • While most debris burns up during reentry, larger objects can survive and reach the ground
• The growing space industry and the deployment of large satellite constellations (Starlink, OneWeb) further increase the risk of collisions and debris generation
• Debris in popular orbits, such as sun-synchronous orbit (SSO), can limit the availability of these valuable resources for future missions

Current Cleanup Efforts

• Active debris removal (ADR) technologies are being developed to remove existing debris from orbit
  • Examples include robotic arms, nets, harpoons, and lasers to capture and deorbit debris
• The RemoveDEBRIS mission, led by the University of Surrey, successfully demonstrated key ADR technologies in 2018-2019
  • Tested a net capture system, a harpoon capture system, and a drag sail for deorbiting
• ESA's ClearSpace-1 mission, planned for 2025, aims to rendezvous with and capture a Vespa upper stage in LEO for deorbiting
• The ELSA-d (End-of-Life Services by Astroscale) mission, launched in 2021, is testing magnetic capture and deorbiting technologies
• International guidelines and standards have been established to mitigate the creation of new debris
  • The Inter-Agency Space Debris Coordination Committee (IADC) provides guidelines for debris mitigation
  • The ISO 24113 standard defines requirements for space debris mitigation in spacecraft design and operation
• Improved spacecraft design, such as the use of shielding and redundant systems, can help protect against debris impacts
• Post-mission disposal strategies, such as controlled reentry or moving satellites to graveyard orbits, help reduce the long-term debris population

Future Challenges

• Developing cost-effective and reliable ADR technologies that can remove debris of various sizes and types
  • Current ADR demonstrations have focused on large, intact objects, but small debris pose a significant threat as well
• Establishing a legal and regulatory framework for ADR activities, addressing issues such as ownership, liability, and consent for debris removal
  • The Outer Space Treaty does not explicitly address space debris or ADR
• Securing funding and international cooperation for large-scale debris removal efforts
  • The cost of removing all large debris objects is estimated to be in the billions of dollars
• Improving the accuracy and completeness of debris tracking and cataloging, particularly for small debris
  • Better data is needed to assess the risk posed by debris and to plan mitigation strategies
• Encouraging responsible behavior and debris mitigation practices among all space actors, including private companies and emerging spacefaring nations
  • Ensuring that the growth of the space industry does not outpace efforts to control the debris population
• Developing new materials and technologies that can better withstand debris impacts and reduce the generation of new debris
  • Examples include self-healing materials and spacecraft with improved shielding
• Raising public awareness about the importance of preserving the space environment and the risks posed by space debris
  • Debris is an invisible but critical issue that affects all of humanity's activities in space

Key Takeaways

• Space debris is a growing threat to the safety and sustainability of space activities
• The debris population has been increasing since the beginning of the space age due to human activities such as satellite launches, anti-satellite tests, and accidental collisions
• Debris ranges in size from tiny flecks of paint to entire defunct satellites and rocket stages
• Tracking debris is essential for collision avoidance and planning debris removal efforts
  • Ground-based radars, telescopes, and space-based sensors are used to monitor the debris population
• Collisions between debris and active satellites can create more debris, potentially leading to a catastrophic cascade effect (Kessler Syndrome)
• Active debris removal technologies, such as nets, harpoons, and lasers, are being developed to remove existing debris from orbit
• International guidelines and standards have been established to mitigate the creation of new debris through improved spacecraft design and operation
• Future challenges include developing cost-effective ADR technologies, establishing a legal framework for debris removal, and encouraging responsible behavior among all space actors
• Addressing the space debris issue is critical for ensuring the long-term sustainability of space activities and preserving the space environment for future generations