Space debris: overview
Space debris by apogee (1957-March 6th, 2022)
Satellites can follow a circular or elliptical orbit: the apogee is the point of highest
altitude from Earth (when they are most distant).
As we produce junk on Earth, we leave multiple traces of our passage also in space.
Space junk is composed of human-made objects in space that are no longer functional. The
category includes derelict spacecraft, abandoned launch vehicles, and fragmentation debris caused by collisions,
erosion, unburned particles, or solidified liquids expelled from spacecraft. Since 1957, tonnes of rockets,
spacecraft, and instruments have been launched into space. Initially, there was no plan for what to do with them
at the end of their lives. But numbers have continued to increase: explosions and collisions in space
have created hundreds of thousands of shards of dangerous fragments.
Space junk represents an enormous risk for current and future missions in space, as much for the security of
human lives on Earth. Million of debris objects are smaller than 1 cm; most are even smaller micrometer-sized
debris, while only a few thousands are larger than a softball. The greater part of the debris is currently
orbiting in Low Earth orbit and can reach the speed of almost 30,000km per hour. LEO is also the orbit where
most satellites are positioned: therefore, it is essential to keep track of these fragments to avoid impacts.
• European Space Agency: The current state of space debris
• NASA: Orbital debris
As of March 6th, 2022, a total of 51,688 items have been registered as space objects on the satellite catalog. Of this amount, satellite debris accounts for 64%, while payloads (the actual satellites) are less than one quarter. Rocket bodies (launch vehicles to send satellites in space) and TBA (objects To Be Assigned, identified with just a letter) compose the remaining 13%.
39,716 objects have been cataloged as debris. More than half is already decayed and disintegrated by entering the atmosphere. The rest is still orbiting above our heads. Even if it is unlikely that large objects can make it to the Earth's surface, one person has been already hit by a piece of Delta II rocket debris in 1997.
17,319 space junk objects are currently orbiting Earth. 14,734 are satellite debris; 2,282 are fragments that belonged to launch vehicles while the remaining 303 items are TBA objects, still unidentified. However, there are many fragments of less than 1 cm are non-trackable: even if so small, they can cause damage to solar panels, optics, and windows. Small-size fragments constitute the highest mission-ending risk to most robotic spacecraft operating in low Earth orbit.
• ABC News: Space Junk survivor
• Satellite catalogue boxscore
Who is going to clean up the space?
The Kessler Syndrome is a phenomenon in which the amount of junk in orbit around Earth reaches a point where it just creates more and more space debris. Named after former NASA scientist Donald Kessler, the scenario described in his 1978 paper is likely already started. Debris-creating events have become more and more common: by today, the main cause is related to propulsion and anomalies during the many stages of launch and separation, followed by accidental, electrical, aerodynamical, and unknown cases. However, collisions between debris and working satellites are predicted to overtake explosions as the dominant source of debris.
Space debris by country and organization (1957-March 6th, 2022)
The Commonwealth of Independent States is an
organization formed following the dissolution
of the Soviet Union in 1991. It is composed by Armenia, Azerbaijan, Belarus, Kazakhstan, Kyrgyzstan,
Moldova, Russia, Tajikistan, Uzbekistan.
The higher the altitude, the longer the orbital debris will remain in Earth's
orbit. Debris located below 600 km normally fall back to Earth within several years. At altitudes of 800 km,
the
time for orbital decay is often measured in decades. Above 1,000 km, orbital debris normally will continue
circling our planet for a century or more.
The main action to undertake is to prevent the creation of more orbital debris. Countries like the United
States, Russia, China, Japan, France and the European Space Agency have issued guidelines to mitigate the risk
of collision. Mathematical models have also been implemented to assess the direction and speed of debris, as
well
as tracking re-entering objects. Furthermore, several startups are studying and developing new technologies
to
retrieve debris such as the ELSA-d (End-of-Life Services by Astroscale Demonstration), developed by a
Japan-based satellite services company. It consists of two satellites, a “servicer” satellite designed to
remove
debris from orbit and a “client” that captures them: the debris and service satellite will return to the
Earth’s
atmosphere together, burning up on re-entry.
Finding ways to remove the space junk should be a global priority, especially considering that Low Earth
orbit is on the verge of becoming too crowded. Most of the recent commercial satellite constellations
(SpaceX’s
Starlink, OneWeb and the upcoming Amazon’s Project Kuiper) are located there, and they are all composed of
thousands satellites.
• Scientific American: Space Junk Removal Is Not Going Smoothly