A piece of orbital debris recently hit Canadarm2, the nearly 18-meter-long robotic arm on the International Space Station that helps with maintenance tasks and “catches” visiting spacecraft. Thankfully, the functioning of the robotic arm is unaffected.
According to Canadian Space Agency (CSA), a routine inspection on May 12 discovered the damage. While utmost precautions are taken to reduce the potential for collisions with the space stations — objects softball-size and bigger are monitored for potential collision with the ISS in orbit — this apparently came from a piece of debris that was too small to be tracked.
This is a significant and worrying development which comes on the back of three emergency maneuvers by the space station last year — the latest being on Sept. 22, 2020 — to avoid potential collision with unidentified objects.
As orbits around Earth get more and more crowded, this again opens up for debate around what we are doing about orbital debris and space traffic management.
How many satellites orbit Earth?
According to the Union of Concerned Scientists, there are a total of 3,372 operational satellites currently orbiting Earth. This data was last updated January 1, 2021. After that as many as 48 launches have taken place till May, most of them carrying more than one payload. In May 2021, SpaceX alone launched 172 Starlink satellites in just three launches making their constellation over 1,600.
Additionally, roughly the same number are defunct or have been out of operation. Then there are various stages of rockets, nuts and bolts left behind by astronauts, and millions of harder-to-track objects such as bits of paint and plastic. More than 27,000 pieces of orbital debris, or “space junk,” are tracked by the Department of Defense’s global Space Surveillance Network (SSN) sensors. Most of the cataloged objects are larger than a softball (approximately 10 centimeters).
However, according to estimates by ESA’s Space Debris Office at ESOC, Darmstadt, Germany, while the number of debris objects regularly tracked by Space Surveillance Networks and maintained in their catalog is about 28,600, total number of debris objects of size greater than 10 cm is around 34,000. And this is where it gets more interesting — there are 900,000 objects from greater than 1 cm to 10 cm and 128 million objects from greater than 1 mm to 1 cm.
Why is space debris a growing concern?
With the increasing number of satellite launches, experts have been warning about the increasing number of objects, especially the upper stages of rockets, in the Earth’s lower orbits, leading to collision risks.
Like the damage to the Canadarm2 reveal, any of these objects, including the tiny flecks which largely go untracked, can impair an operational spacecraft.
That CSA announced that the robotic arm is still operational and the damage not significant is just pure coincidence and luck. On September 22 last year, ISS maneuvered to raise its orbit out of the path of the debris, which was trackable and was estimated to come within 1.39 km of the station. As a safety measure, the three crew members moved to the Russian segment of the station to be closer to their Soyuz MS-16 spacecraft.
According to ESA, a collision with a 10-cm object would entail a catastrophic fragmentation of a typical satellite. A 1-cm object would most likely disable a spacecraft and penetrate the ISS shields, and a 1-mm object could destroy subsystems on board a spacecraft.
“As the potential for orbital collisions rises with increasing congestion, it is important to recognize that risks to astronauts, critical national security capabilities and global space commerce are also on the rise, to the extent that the use of some orbital regimes may become impractical due to debris density,” the report states.
Are we creating more debris in orbit?
On an average, the past two decades have seen as many 12 accidental “fragmentations” per year, a trend found to be unfortunately increasing, according to ESA. Fragmentations are typically described as events that lead to debris creation due to collisions, explosions, electrical problems and even just the detachment of objects due to the harsh conditions in space.
“The biggest contributor to the current space debris problem is explosions in orbit, caused by leftover energy — fuel and batteries — onboard spacecraft and rockets. Despite measures being in place for years to prevent this, we see no decline in the number of such events. Trends toward end-of-mission disposal are improving, but at a slow pace,” Holger Krag, head of the Space Safety Program, said in a statement in October last year.
In its 2020 annual report NASA’s Aerospace Safety Advisory Panel cited space debris as “a major safety issue”, identifying it as two of the top three safety risks for the International Space Station. It found that the number of objects being tracked in Earth’s orbit has seen a steep increase in the past decade.
ESA also predicts that collisions between debris and working satellites is predicted to overtake explosions as the dominant source of debris.
The risk of collisions with debris generating further debris ultimately could lead to a catastrophic phenomenon called the Kessler Syndrome.
What is the Kessler Syndrome?
The Kessler Syndrome — named after Donald Kessler, the man who first proposed the theory — is a theoretical scenario in which the density of objects in LEO due to space debris is so high that collisions between objects could cause a cascade, each collision generating further debris that increases the likelihood of further collisions. NASA became concerned about this cascade of collisions the first time in the 1970s when derelict Delta rockets left in orbit began to explode creating shrapnel clouds.
Kessler demonstrated that once the amount of debris in a particular orbit reaches critical mass, collision cascading begins even if no more objects are launched into the orbit.
While Kessler had proposed it would take 30 to 40 years for such a threshold to be reached, a US National Research Council report in 2011 predicted that this could take place within the next two decades. A 2016 NASA report worried that we could already have arrived at that critical mass in LEO at about 900 to 1,000 kilometers.
It has been five years since 2016 and the number of launches and satellites going up in space, accompanied by the usual small, untrackable objects, have gone up exponentially in the last five years, due to growing institutional uses and commercialization of space activities and thanks to technological innovations like smaller and smaller satellites and rideshare options.
This evolution is expected to continue and accelerate with the deployment of megaconstellations for satellite broadband, some comprising several thousand satellites. An OECD report, Space Sustainability The Economics Of Space Debris In Perspective, which came out in April last year, said “the real game changer would be the full deployment of one or several of the broadband megaconstellations that are under preparation.” That was in April. Since then SpaceX has been on a launch spree while several others, including Amazon and OneWeb have announced mega comsat constellation plans.
The Kessler Syndrome, if it leads to that, according to OECD, could be “an ecological tipping point that may render certain orbits unusable”, severely impacting weather forecasting, climate monitoring, Earth sciences and space-based communications.
Individual exceptional events (anti-satellite tests, collisions) can have disastrous consequences. The 2007 destruction of the FengYun-1C satellite doubled the amount of debris at 800 km altitude and led to a 30% increase in the total orbital debris population.
As for the cost in dollars, though no readily available data is available, OECD estimates that such a damage to a satellite in geostationary orbit could amount to an estimated 5-10% of the total mission costs, which could be hundreds of millions of dollars. In LEO, the relative costs per mission could be even higher than 5-10%.
There exist certain international guidelines and standards for sustainable use of space. ESA lists the following:
- Avoid intentional generation of debris (including anti-satellite tests)
- Minimize potential for accidental explosions
- A 25-year deorbit rule for missions in low-Earth orbit
- Missions in geostationary orbit should be sent to a higher ‘graveyard orbit’ at the end of their lives, keeping out of the way of functioning satellites
- Collision avoidance should take place when feasible, as well as minimizing the risk of casualties on the ground due to re-entries.
According to ESA’s latest Space Debris Environment Report, while most operators of satellites in geostationary orbit comply with these guidelines, less than 60% of those flying in low-Earth orbit adhere (and only 20% in orbits above 650 km). Add to that countries increasingly conducting anti-satellite tests, space sustainability surely needs a greater, more concerted effort by a global independent authority.
Anusuya Datta is a journalist based in Canada. She previously worked for Geospatial World, where she wrote on Earth observation and space technology. She also writes for Global Investigative Journalism Network on the use of satellite technologies for journalism.