Orbital debris in brief:
Our dependency on vital satellite services is growing. There are already over 4,000 operational satellites in orbit and over the next decade that number will more than double. Orbital debris, which poses a serious threat to satellites and humankind’s access to space, is also accumulating in Earth orbits. Some pieces of debris are large objects, such as spent rocket stages, while most are small fragments that have resulted from fragmentation events, some of which are from the intentional destruction of satellites and on-orbit collisions. With significant numbers of orbital debris already present and the satellite population growing rapidly, the potential for satellite-debris and satellite-satellite collisions is significant. The nature of on-orbit collisions presents a unique problem; they occur at relative speeds of up to 58,000km/h. This means even small objects can cause serious fragmentation events, each of which greatly increases the collisional cross section of material, and thus the probability of on-orbit collisions per time. Of biggest concern is a potential scenario wherein debris-debris and debris-satellite collisions generate so much debris that large sections of LEO become unusable, at least as we know it.
Technological solutions and international cooperation help mitigate some aspects of orbital debris creation and on-orbit collisions. However, due to the sheer growth in space activity, most of which now comes from private sector developments, many additional measures are needed to ensure the sustainability of Earth’s orbital environment. Mitigating debris is not just a technical challenge.
Satellite mega-constellations, which consist of hundreds to tens of thousands of satellites, are actively being constructed. Private companies such as SpaceX, OneWeb, Telesat and Amazon are intending to use these constellations to provide a range of global services. The sheer number of satellites that will be added to Earth orbits by mega-constellations is creating new challenges for the prevention and mitigation of space debris. Many additional concerns are well documented in a recent Dark and Quiet Skies for Science and Society report and recommendations.
Ten thousand satellites have been launched since Sputnik in 1957. They support many vital activities, including weather forecasting, global positioning systems, communications, financial services, agriculture, forestry, fisheries, climate change science, search and rescue, and disaster relief. Our dependency on space is only increasing, and new technologies such as small satellites, reusable rockets and artificial intelligence, as well as the growing involvement of commercial actors, are reducing the cost of developing and launching satellites. The number of objects launched into Earth orbits is rapidly increasing every year as a result. For a current snapshot of space traffic, see AstriaGraph. Frequently updated statistics concerning the increase of space objects over time are available at ESA Space Environment Statistics and CelesTrak.
Space debris is the legacy of 6,020 orbital-rocket (i.e. satellite) launches since 1957. There are roughly 128 million pieces of debris in orbit, with 900,000 of them being larger than one centimeter. Some pieces are dysfunctional satellites; others are discarded rocket stages. Most are the result of satellite fragmentation due to accidental on-board explosions. Deliberate destruction has also occurred. However, some anomalous fragmentation events are thought to result from collisions between satellites and debris — at relative speeds of up to 58,000 kilometers per hour. Of greatest concern, each fragmentation increases the effective collisional cross section of material, which increases the probability of another collision per time. At a certain point, the dominant debris-generating mechanism will be debris-debris and debris-satellite collisions, initiating runaway orbital debris. This process, called the ‘Kessler Syndrome’, threatens a global economy which increasingly relies on satellites, as well as humanity’s long-term access to space and other celestial bodies. Concern of this process is only elevated as the number of satellites and objects in space increases rapidly over the next decade.
As more objects are added to Earth orbits there is a growing potential for debris-debris, debris-satellite and satellite-satellite collisions. Close approaches between space objects are already a frequent occurrence — see, Conjunction Streaming Service Demo. In April of 2021, a SpaceX Starlink satellite passed within 190 feet of an oncoming OneWeb satellite. In a similar event in 2019, a Starlink satellite came close to colliding with an ESA satellite. Close approaches between operators are uncertain events due to imprecise orbital knowledge. The absence of space traffic management norms confounds the decision making process — operators rely on archaic means of communication to determine how they should manoeuvre their satellites in relation to one another so that a collision is avoided.
Fortunately, orbital debris can be addressed through international cooperation and technological innovation. Space-faring countries are already cooperating on this issue: over 28,000 pieces of orbital debris have been detected, tracked and catalogued using Earth-based radar and telescopes. This information is widely shared, since advance warning of collisions can provide time for endangered satellites to be moved to safer orbits using on-board thrusters. National space agencies are also researching ways to remove derelict satellites from orbit, and perhaps most important, militaries are refraining from testing kinetic anti-satellite weapons in ways that could create long-lasting orbital debris. But this is not enough, particularly with the greatly expanding use of space. Overall, we need to have a major shift in our concept of space – an environment that is worth preserving.
What low Earth orbit and geo-orbital slots are needed to accommodate increased space use while minimizing risk to Earth’s growing satellite population, and can these be regulated more effectively than the current International Telecommunications Union regime? How can space traffic management norms for operating in space be better developed and diffused globally? Can recent guidelines on satellite design, ensuring the ability to de-orbit at the end of the equipment’s operational lifetime, be made binding under international law? Will the high frequency of space objects re-entering Earth’s atmosphere pose safety and environmental risks on Earth?
In January of 2020, The Outer Space Institute held an international, transdisciplinary workshop that addressed many questions concerning the issues of orbital debris. The consensus “Salt Spring Recommendations” reached by the participants encourage sustainable on-orbit operations, and comprehensive governance and licensing regimes that reflect developments in the ‘NewSpace’ era. The Recommendations serve as an instrument to guide national and international policy makers to adopt solutions that encourage the long-term sustainability of space.