Two ideas to help FCC curb orbital debris
By Moriba Jah|July/August 2024
The U.S. Federal Communications Commission, in its licensing role, has begun to take the threat of orbital debris seriously. Lately, the commission seems intrigued by the “100 object-years metric,” which involves adding up the number of years it would take each satellite in a proposed constellation to naturally fall back into the atmosphere if disposal efforts fail. Keeping the figure below 100, some believe, would keep the risks of collisions and explosions at an acceptable level. So far, FCC has made only limited use of this metric in weighing licensing requests, but in May it asked for public comment about whether the metric should be applied “more or less widely” and whether there are alternative ideas.
In my view, while this metric provides some insight, it is fundamentally inadequate for comprehensive risk assessment. It does not account for the relative geometry among satellites, their sizes, maneuverability, trackability or the varying risks posed by orbital neighborhoods or highways. This lack of granularity makes it insufficient for a comprehensive risk assessment.
To address these limitations, I suggest that the FCC Space Bureau should scrap the 100 object-year concept and go with these two other metrics.
Let’s look first at orbital carrying capacity, a term in the space community that refers to the maximum number of satellites and debris that a given orbital region can sustain without hindering meaningful and safe space operations, erring on the side of caution given the inherent uncertainties in our ability to track and predict the motion of these objects. This concept is akin to the ecological carrying capacity in environmental science, which quantifies the maximum population an ecosystem can sustain without degrading. High satellite populations, independently operated in the absence of common norms of behavior, increase the risk of collisions. Orbital carrying capacity should account for the number of active satellites, defunct satellites and debris in a given orbital highway and region, with associated uncertainties, along with the undesirable outcomes of this capacity becoming saturated.
To wit, this metric should also address the real cost and detriment to the space environment, as well as the operational and economic costs to space services and capabilities, due to space activities, events and traffic. Different altitudes have varying carrying capacities. For example, low-Earth orbit, at 100-1,200 kilometers, is more congested and has higher collision risks compared to geosynchronous orbit. Satellites with propulsion systems can avoid collisions more effectively, thus increasing the carrying capacity of an orbit, especially if smart automation is implemented. Also, the effectiveness of post-mission disposal strategies impacts the longevity of satellites. Efficient and intentional deorbiting increases the carrying capacity by reducing long-term debris, versus the status quo of satellite abandonment.
Carrying capacity should be an essential consideration, given that as of mid-June there were just over 10,000 active satellites in orbit, with this number set to skyrocket with the further deployment of megaconstellations by SpaceX, OneWeb, Amazon and others. These constellations comprising thousands of satellites aim to provide global internet coverage, but they also heighten the risk of collisions and additional debris creation. Orbital debris includes defunct satellites, spent rocket stages and fragments from disintegrations, collisions or anti-satellite tests. Even tiny, paint-fleck-sized debris pieces can be perilous due to their high velocities of many times the speed of a bullet. This underscores the urgency of developing robust debris mitigation strategies.
The skyrocketing numbers also underscore the need for my second proposed metric, the space traffic footprint. This composite index, which I first proposed in 2019, would quantify the burden any given anthropogenic space object imposes on the orbital environment, analogous to the carbon footprint used in environmental management. Components of this footprint include the size and mass of a satellite, with larger and heavier satellites posing greater collision risks and generating more debris in case of fragmentation, as an example. Orbital lifetime is another factor, as satellites that remain in orbit longer contribute to long-term congestion. On the flip side, satellites with reliable propulsion systems have a lower footprint due to their ability to avoid collisions. The probability of a satellite colliding with other objects in its orbit should also be factored into its footprint. Finally, launch and deployment strategies that minimize debris creation and ensure timely deorbiting should be rewarded with a lower footprint.
Consider the case of SpaceX’s Starlink constellation, which could grow to 42,000 satellites. While SpaceX has implemented measures to deorbit satellites at the end of their lives and to avoid collisions, the sheer number of satellites poses significant risks to the orbital environment. Imagine, for instance, the LEO region between 500 and 600 km. Current assessments might show that this region can safely support 10,000 active satellites without significantly increasing collision risks. With Starlink and other constellations aiming to deploy thousands of satellites in this altitude range, we risk surpassing the carrying capacity, leading to increased collision risks and potential cascading debris generation.
FCC’s current initiative to update its orbital debris mitigation rules is an excellent opportunity to integrate these new metrics. By collaborating with the space community to develop the orbital carrying capacity metric and implement the space traffic footprint metric, we can establish a more comprehensive and effective regulatory framework. These metrics would enable FCC to make more informed decisions when evaluating satellite licensing permits, balancing the needs of industry growth with the imperative to protect our orbital environment.
Incorporating these metrics would also drive innovation and responsibility in satellite design and operations. Companies would be incentivized to develop technologies and practices that minimize their space traffic footprint and operate within the carrying capacity of their chosen orbits. This proactive approach would help maintain the viability of space activities, ensuring that the benefits of space exploration and utilization continue to be available for future generations. Our actions today will determine the legacy we leave for tomorrow’s explorers.
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