Overview of the Space Environment
The space environment around Earth has become increasingly congested over the past six decades. Since the launch of Sputnik 1 in 1957, the number of catalogued objects in Earth orbit has grown to over 34,000 as of January 2023. This includes operational satellites as well as rocket bodies, mission-related debris, and fragmentation debris from explosions, collisions, and other breakup events. In addition, models estimate there are over 128 million untracked debris fragments between 1 mm and 1 cm in size.
Three key metrics are used to characterize the space environment: object count, mass, and area. The total count of catalogued objects in orbit has risen steadily to over 30,000. Total mass has reached over 8,000 metric tons, while total area is approaching 120,000 m2. Low Earth orbit (LEO) below 2000 km is by far the most populated region, accounting for over 60% of objects. Geosynchronous orbit (GEO) has over 2500 objects, while other orbital regimes have on the order of hundreds to low thousands of objects.
This article reviews the current status the space environment based upon data from the 2022 ESA's Annual Space Environment Report.
A protected region in the context of space debris mitigation refers to key orbital zones that are prioritized for protection from debris congestion and interference. The two main protected regions are:
- Low Earth Orbit (LEO) protected region – Defined as the spherical shell region from the Earth's surface up to an altitude of 2000 km. This encompasses the most heavily used orbits for Earth observation, communications, and human spaceflight.
- Geosynchronous Orbit (GEO) protected region – A segment of the GEO belt spanning ±200 km in altitude around 35,786 km, the altitude where satellites have a 24 hour orbital period synchronized with Earth's rotation. This region is critical for communications, weather monitoring, and other services.
These protected orbital zones were established through space debris mitigation guidelines from the UN, NASA, and other space agencies. The goal is to preserve these regions by limiting debris generation and removing non-functional objects. Specific mitigation practices include:
- Post-mission disposal of satellites and rocket bodies to clear out the protected orbital zones when operational lifetime is complete. This is done by deorbiting (LEO) or moving to graveyard orbits (GEO).
- Avoiding intentional destruction and minimizing accidental explosion/collision risks.
- Designing spacecraft to withstand debris impacts and minimize breakup potential.
- Adopting best practices in operations, maintenance, and propellant passivation.
While not completely protected, the intent is to prioritize conservation of these key orbital areas to ensure safe and sustainable use of space long-term. However, debris congestion in LEO and GEO continues to pose challenges.
Evolution of LEO Environment
LEO has seen the most growth in object population over the space age. The number of catalogued objects rose from just a handful in 1957 to over 20,000 by early 2023. More than 5000 tons of material now resides in LEO. A large fraction of objects in LEO originate from or pass through the LEO protected region between 0-2000 km altitude. This includes over 15,000 objects equivalent to permanently residing in the protected zone.
Several trends have driven the increase in LEO congestion:
- Rise of large constellations for telecommunications and Earth observation, comprising hundreds to thousands of satellites. From 2019-2022, over 3000 satellites were launched into LEO constellations.
- Increased prevalence of small satellites, especially Cubesats. Over 2000 satellites under 50 kg were launched in the 2010s.
- On average 11 fragmentations per year from explosions, collisions, and other breakups.
- Only partial success in post-mission disposal. Between 20-85% of payloads and 30-80% of rocket bodies are successfully disposed of after completion.
Evolution of GEO Environment
The GEO belt around 35,786 km altitude is the other protected region critical for space sustainability. The number of objects in GEO has climbed to over 2500, though growth has been far slower than in LEO. Equivalent objects penetrating the GEO protected zone number around 3500.
Total mass in GEO is approximately 3500 tons, while total area exceeds 30,000 m2. Trends in GEO include:
- Steady launch rate of communication satellites, typically 5-35 per year. Mass to GEO peaked in the late 1990s and has since declined.
- Improved disposal compliance, with 60-90% of GEO satellites moving to disposal orbits after completion.
- GEO is still threatened by rocket bodies in highly elliptical orbits crossing the zone. Over 100 such objects exist and this number continues to grow.
Global Launch Traffic
The global launch rate provides insight into sources of growth in the space environment. The annual launch rate into LEO has risen from less than 50 in the 2000s to over 175 in 2022. Launches into GEO, historically 25-35 per year, dropped below 10 in 2022.
China has dominated launch traffic in recent years, accounting for over 40% of orbital deployments. SpaceX represents over 60% of commercial launches, recovering and reusing many first stage boosters. Launch vehicle diversity continues to expand, with new versions introduced by Blue Origin, RocketLab, Firefly, and others.
An emerging trend is the rise in rideshare launches, with over 100 small satellites deployed on a single rocket. Identification and tracking of rideshare payloads is an increasing challenge, with 10% identified within 0-2 months after launch and 90% within 2-12 months.
Compliance with Mitigation Guidelines
International guidelines and standards have been developed to mitigate space debris, centered around the UN Space Debris Mitigation Guidelines and the ISO Space Systems Standard. Key guidelines include:
- Avoiding intentional destruction and minimizing mission-related debris
- Passivating systems and depleting fluids at end-of-life
- Disposing of payloads and rocket bodies after completion by deorbiting (LEO) or moving to graveyard orbit (GEO)
- Limiting debris during operations and minimizing potential for breakup
Overall compliance remains low but improving gradually. About 60-70% of LEO payloads and 40-50% of GEO payloads meet post-mission disposal guidelines. For rocket bodies, 40-60% comply in LEO and 40-50% comply in GEO. Fragmentation rates have remained steady at 10-15 per year.
Earth's orbital environment continues to grow more congested and complex. LEO faces the greatest challenges, with growing launch traffic and only partial success mitigating debris. Steps like enhancing post-mission compliance, limiting fragmentation, and instituting traffic management will be key to preserving space for future generations.
The 2022 ESA Space Environment Report provides a comprehensive reference to understand the evolution of the space environment and progress in debris mitigation efforts.