1.1 Definition and historical context of space debris

Space debris is a growing problem in Earth's orbit. From tiny paint flecks to entire defunct satellites, these human-made objects pose risks to operational spacecraft and future missions. The issue has roots in early space exploration and continues to worsen.

As debris accumulates, it increases collision risks and could trigger a cascade effect called Kessler Syndrome. This scenario could make certain orbits unusable, impacting vital satellite services we rely on daily. Understanding space debris is crucial for ensuring sustainable space activities.

Definition of Space Debris

Terminology

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• Space debris refers to any non-functional, human-made objects orbiting Earth or any other celestial body
• Orbital debris is another term for space debris, emphasizing its location in Earth's orbit
• Space junk is a colloquial term for space debris, often used in media and public discourse to describe the growing problem of accumulating non-functional objects in space

Composition and Size

• Space debris can range in size from tiny paint flecks and metal fragments to entire defunct satellites and rocket stages
• Debris smaller than 1 cm (millimeter-sized debris) is the most numerous but difficult to track and poses a significant threat to spacecraft due to high impact velocities
• Larger debris, such as derelict satellites and spent rocket stages, are less numerous but can cause catastrophic damage in the event of a collision

Potential Consequences

Kessler Syndrome

• Kessler syndrome is a theoretical scenario in which the density of objects in low Earth orbit (LEO) becomes high enough that collisions between objects could cause a cascade effect
• In this scenario, each collision generates more debris, increasing the likelihood of further collisions and potentially rendering certain orbital regions unusable for space activities
• The cascading effect could make it difficult or impossible to launch new satellites or conduct space missions, severely impacting modern technology and infrastructure that relies on satellite services (communication, navigation, Earth observation)

Threat to Operational Spacecraft

• Space debris poses a significant threat to operational spacecraft, including satellites and manned missions (International Space Station)
• Even small debris particles can cause damage to solar panels, optics, and other sensitive components due to high impact velocities in orbit
• Larger debris can lead to catastrophic collisions, resulting in the loss of expensive space assets and potentially endangering human lives in the case of manned missions

Historical Context

Early Space Exploration

• The Space Age began with the launch of Sputnik 1, the first artificial satellite, by the Soviet Union in 1957
• Vanguard 1, launched by the United States in 1958, became the oldest piece of space debris still in orbit, highlighting the long-term nature of the space debris problem
• As space exploration and satellite launches increased during the Cold War era, the amount of space debris in Earth's orbit began to grow

Growth of Space Debris

• The number of space debris objects has increased significantly since the early days of the Space Age due to the proliferation of satellite launches, space missions, and occasional intentional destruction of satellites (anti-satellite weapon tests)
• Major debris-generating events, such as the Chinese anti-satellite test in 2007 and the collision between Iridium 33 and Cosmos 2251 satellites in 2009, have greatly contributed to the current space debris population
• As of 2021, the United States Space Surveillance Network is tracking more than 27,000 pieces of orbital debris, with many more smaller objects believed to exist

Orbital Regions Affected

Low Earth Orbit (LEO)

• Low Earth Orbit (LEO) is the region of space closest to Earth's surface, extending up to an altitude of about 2,000 km
• LEO is the most congested orbital region, with the highest concentration of space debris due to its popularity for satellite placement (Earth observation, communication, and scientific missions)
• The high density of objects in LEO increases the risk of collisions and makes it the primary focus of space debris mitigation efforts

Geosynchronous Earth Orbit (GEO)

• Geosynchronous Earth Orbit (GEO) is a high-altitude orbit (approximately 35,786 km above Earth's surface) where satellites have an orbital period equal to Earth's rotational period
• GEO is a valuable orbital region for communication and weather satellites because they appear stationary relative to a point on Earth's surface
• Although less congested than LEO, GEO is still affected by space debris, primarily due to the presence of defunct satellites and upper stages of launch vehicles
• The limited number of available slots in GEO and the importance of the satellites placed there make it crucial to manage and mitigate space debris in this region