Space is not as peaceful as you might expect. Look a little closer - typically with the help of ground-based radars, RF sensors, and optical telescopes - and you’ll notice there are tens of thousands of objects orbiting Earth.
The vast majority of them are present because of our endeavors in space to date. Since 1957, decommissioned satellites, spent rocket bodies, and all manner of space junk have accumulated. A dynamic system of debris now envelops our planet.
From 9,000 kg satellites to nanosats that weigh less than 10 kg to Elon Musk’s Tesla Roadster, there are thousands of tracked items. Most of those are traveling at speeds faster than 17,000 mph within Low Earth Orbit (LEO), which is less than 2,000 km above ground level. The vast majority of satellites are >300 km because of the thrust required to overcome drag below that.
In short, there’s a lot going on up there. The situation is continually evolving as new missions are launched and governments around the world carry out operations that exacerbate the problem, increasing the risk of objects colliding.
One of the main contributors to the specter of space junk is anti-satellite (ASAT) experiments. Since the Cold War, weapons testing and displays of force made their way into orbit. In 1968, the Soviets launched a series of ASAT experiments, adding thousands of extra pieces of debris to LEO in the process. Similar operations were conducted by the United States, China, and India.
A database of items greater than 10 cm in diameter is maintained by 18 SPCS. The U.S. government public catalog includes some 23,000 actively tracked objects. Among that figure are around 8,000 satellites - both abandoned and operational.
In terms of debris that’s too small to easily track but large enough to cause significant damage - fragments between one and ten centimeters - NASA suggests there are 500,000 such objects. The latest estimates from the European Space Agency (ESA) suggest the figure is closer to 900,000.
In fact, the ESA estimates that there are more than 8,000 metric tons of material orbiting Earth.
The threat of space junk
Even small fragments of space debris can cause a huge amount of damage because of how fast they travel. Remember the equation for kinetic energy from high school physics class?
In other words, the single biggest factor determining the energy of a collision is the velocity of the objects involved.
To provide some perspective, a 10-centimeter sphere of aluminum traveling in LEO at around 17,000 mph has energy on par with seven kilograms of TNT.
In February 2009, two satellites (Iridium 33 and defunct COSMOS 2251) collided for the first time, causing thousands of pieces of debris to scatter into orbit and make their way into the public catalog, maintained by 18 SPCS. Many still pose a threat to future missions and current satellite operations.
Increasingly populated with debris from new satellite launches, space missions, and collisions, NASA scientist Donald Kessler famously hypothesized that left unchecked, the LEO environment will become a dangerous maelstrom of smaller, more uniform fragments, smothering Earth like a sandstorm.
The Kessler Syndrome could, in theory, cause the environment around Earth to be too precarious for us to use. In the not too distant future, our planet could have rings like Saturn consisting of garbage - not quite as aesthetically pleasing as shattered asteroids.
What does this mean for our ambitions in space?
Should Kessler’s prediction play out, the debris left in orbit will cause huge disruptions to the satellite technology we rely on and a significant barrier to future space exploration.
In the short term, object tracking and an accurate awareness of space traffic are critically important. For communications companies, weather forecasters, and government agencies, space debris can leave live satellites with millions of dollars’ worth of damage or put them out of action completely. The only viable solution is to track the many objects and make avoidance maneuvers in time to avoid them.
The same goes for larger-scale structures like the International Space Station (ISS). The ISS has conducted 26 debris avoidance maneuvers since 1999 and the frequency of these will increase as more debris enters LEO. The most recent occurred on September 22, when the three astronauts on board were forced to wait in the Soyuz capsule in case critical damage was caused to the ISS and an evacuation was needed. The object was an initially unknown piece of space debris which was determined to be a piece of a 2018 Japanese rocket that broke up into 77 different pieces last year. Again, without accurate object tracking, the ISS could have been caught by surprise.
Making space sustainable
The question facing governments, telecom companies, researchers, scientists, and would-be colonizers of other worlds is clear: how can we adapt operations in Earth’s orbit to make them sustainable?
In part, the answer lies in international policy efforts. The United Nations has guidelines in place that require countries and organizations to clear up any mess they make in space. But these are voluntary for member states. Sadly, it may take a serious incident to generate the political will required to enforce accountability in Earth’s orbit.
As recently as 2019, India conducted an ASAT test, destroying the 1,630-pound Microsat-R probe and producing thousands of debris fragments in the process. The relatively low altitude of the strike meant relatively fewer remnants (compared to a Chinese ASAT test in 2007, for example). Many of the remnants have burned up upon reentering the atmosphere but hundreds of fragments remain.
Looking beyond an international shift toward sustainable space use, the challenge is dealing with objects that have been orbiting the Earth for years already.
Collecting items floating in space is a huge technical challenge. But considering the number of active satellites is expected to increase dramatically to deliver the full-coverage, low-latency telecom and monitoring services of the future, it’s an entirely necessary one.
The most promising developments in the field of space cleanup have come from Europe. RemoveDEBRIS, an experimental project led by the University of Surrey, England, launched into orbit in 2018 and trialled a number of ways to capture space junk. The methods included nets, a harpoon, and attaching a ‘dragsail’ to redundant satellites to bring them out of orbit faster.
At the end of 2019, the European Space Agency (ESA) announced ClearSpace-1, an ambitious 5-year plan led by Swiss startup ClearSpace. It will culminate in a 2025 mission to remove a 100 kg payload left behind by an ESA rocket in 2013.
The aim is twofold. First, to develop and test methods of space clean-up. And second, to establish a market for in-orbit services and debris removal operations.
Change must also come from those with a vested commercial interest in keeping space free of junk. In October 2020, SpaceX launched 60 more Starlink satellites, taking the total to 775. It’s just one of many ambitious LEO programs underway. The company has taken several interesting steps that highlight the role corporate responsibility has to play in keeping space sustainable.
Starlink satellites operate lower than conventional satellites, are designed to de-orbit one to five years after their missions are completed, and link to the DoD’s debris tracking system to autonomously adjust their flight paths in response to threats. Another example of a company taking responsible, safe actions is Iridium who replaced their entire constellation, de-orbiting all their old satellites and replacing them with newer ones while keeping comms going.
Smarter space traffic management
Whatever the outcome of the ESA’s bold cleanup initiative and whatever steps companies take to make their space operations sustainable, all stakeholders know what’s coming: an increasingly congested LEO with heightened risk to critical operations.
For many years, NASA and the DoD have worked together to assess threats in LEO. The U.S. Space Surveillance Network (SSN) tracks thousands of objects and keeps a close eye on their trajectories to identify and flag potential encounters.
It’s run by the 18th Space Control Squadron at Vandenberg Air Force Base in California and relies on a large network of radar installations and optical sensors.
Earlier in 2020, the U.S. Space Force announced the launch of a new Space Fence radar system based in the Marshall Islands. Using observation technology developed by Lockheed Martin, the program plans to extend the reach and precision of the SSN’s work and track much smaller objects hurtling through LEO.
Gathering granular data on the thousands of objects in Earth’s orbit is one challenge. Aggregating information from multiple sources in a way that improves awareness and makes space safer is another.
Advances in AI, predictive analytics, and data management are therefore just as important as policy progresses and technology moves forward in the fields of radar, laser, RF, and optical telescopes.
These hurdles need to be overcome if we are to make the most of satellite technology, create sustainable space programs, and embark on further adventures in the solar system and beyond.