Space Debris: Understanding the Threat to Our Future Beyond Earth
And how novel research can help us avoid this threat
If you were to ask any space enthusiast which developments would be necessary for the future of space exploration, what are some of the answers you would get? Those with ambitions for Mars exploration would leap to radiation protection so astronauts can travel further into the solar system. More practical minded engineers and economists would suggest improving reusability of spacecraft for cost reduction. Our science fiction fans, might even be tempted to propose things like warp drive for light speed travel.
These are all really exciting ideas (with the sole exception of warp drive as that would probably destroy the fabric of our reality) that improve on our current capabilities. However, there’s a growing issue that demands our attention now, or we risk losing the opportunity to achieve these future advancements altogether: space debris.
Since the dawn of the space age in the 1950s, we have advanced rapidly from the first spacecraft in orbit to astronauts exploring on the moon. Towards the end of the 1970s, there were increasing concerns that the amount of space debris in orbit would grow uncontrollably and funds were dedicated to study the problem. Today, with renewed interest in rocket launches and plans for expansive satellite constellations, there has been a big push towards sustainability in our space environment.
We already have a few safeguards in place to limit overcrowding. For example, companies must outline in their application to the FCC how their mission impacts the space environment and what their plans for limiting the generation of orbital debris are, before they get approval to launch. Additionally, any spacecraft that wants to orbit must have a decommission plan and can only occupy an orbit for a set amount of time. While this is a good start, we still have many policies we need to refine as our understanding of environmental impacts continues to improve. As things stand, our space exploration culture has led to an uncontrollable growth of space debris, and it is threatening our future access to space.
What is Space Debris?
Formally, space debris includes all the non-functioning objects derived from human activity in space and has the potential to cause damage or destroy objects in space through impacts. Currently there are over 170 million pieces of space debris in orbit that are larger than 1mm in size!
Debris is catalogued by source as follows:
Rocket Bodies: Rocket stages left in orbit after getting the payload to its destination. These are large area surfaces that are susceptible to collisions with other objects.
Mission Related Objects: Debris that was once important to the operation of either the rocket or its payload and is intentionally released.
Rocket/Payload Debris: Unintentionally released objects.
Fragmentation Debris: Also unintentionally released but due to some sort of collision/aerodynamic event.
There has been a slight increase in the amount of rocket bodies, but also a concerning growth in payload fragmentation. If you look at the sharp increase occurring in 2010, it correlates strongly with a suspected anti-satellite systems test (ASAT). This is a test where a missile targets an orbiting satellite and destroys it. A handful of countries have these capabilities, and this type of test creates a dangerous type of debris where shrapnel from the explosion orbits our space environment.
Kessler Syndrome: A Growth in Debris From Collisions
Regardless of source, this upward trend is dangerous. In 1978, Kessler predicted that the space environment could reach a point where the population becomes unstable, leading to exponential growth of debris. This is commonly referred to as Kessler Syndrome.
He highlights the danger of fragmentation debris by demonstrating how collisions between objects will become more likely for various population growth rates with a statistical analysis of average the average size of any 2 colliding objects. While the absolute quantity of debris is a problem, a specific dynamic becomes concerning. Leaving rocket bodies in orbit increases the likelihood that they collide with many smaller objects drastically increasing the collision rate. Collisions at orbital speeds (> 7 km/s) are high enough energy to cause significant damage to things currently in space. Even objects a millimeter in diameter impart enough energy to create craters several times their size, as shown by various impact studies.
These impacts are threatening to the operation spacecraft but there is a second order effect in play as well. The material lost in the formation of such large craters joins the orbital debris population too! Kessler went as far as to suggest there could be an orbital debris belt forming around Earth crippling our space exploration capabilities in the future.
Diagnosing the Problem
To prevent this cascade of collisions, we need to be well informed about debris count, size, and orbit. The statistics provided by ESA only include catalogued debris. Meaning if our systems cannot identify the objects, they were not included in the total count.
Our current technology excels at tracking objects greater than 10cm in diameter at all altitudes of concern. The Space Surveillance Networks (SSN) maintains a catalogue of objects for national security reasons. Moving down to object sizes less than 1mm but greater than 10cm, our tracking capabilities span all of LEO but limited to specific orbits. And debris less than 1mm currently can only be estimated by spacecraft bodies at a specific elevation that have been returned and had their impact history analyzed. There is a huge gap in our technology for submillimeter debris tracking, and that is the focus of my research!
Vision for the Future
Though we are at risk of achieving what Kessler predicted with massive satellite constellations being developed and active threats being made to satellites by ASATs, our government agencies are investing in solutions to this problem, with IARPA funding a joint effort under the SINTRA program. Additionally, NASA is funding efforts through the ODPO and seeks to fund detection efforts for lunar exploration efforts.
In order to maintain our space environment, I believe we need to make significant progress the following 2 points:
Creating a map of orbital debris of all sizes will help with collision avoidance techniques that can be implemented in future spacecraft. Keeping spacecraft operational and reducing impact probability is key to limiting the growth of orbital debris. Additionally, we can upgrade the predictive capability of our models and identify which areas of our space environment are most at risk of becoming unstable.
Active debris removal will also become very important in the coming years. One of the studies suggests we need to remove 5 large objects per year from the more densely populated orbital regions to remain at a stable population of orbital debris. By removing larger objects, we reduce the likelihood of collisions, which should slow down the growth rate substantially. Additional efforts will need to be made to keep large bodies out of orbit except when necessary.
I have been heavily involved in making progress on that first point throughout my Ph.D thus far. My research involves developing alternative tracking methods for orbital debris. In the space environment, we expect debris to accumulate charge due to its interaction with the ambient plasma. Instead of directly targeting the object, we can pick up on electrostatic and electromagnetic signals emanating from the charged object and propagating through the space plasma. The signal would have to be a proxy, which carries velocity and size information to enable tracking, so the tricky part is figuring out how to extrapolate that information from the plasma waves. My focus is on understanding the plasma behavior at and around orbital debris to identify features that we might be able to observe with preexisting technology.
With the threat properly assessed through the development of advanced tracking methodology and investment in active debris removal missions, we should start to see movement towards a stable space environment. Our future exploration beyond the stars depends on us taking care of our great home on Earth. 🌎
Enjoy your stargazing! 🌠
Michael
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Very cool, would love to chat more about your space debris research!