The Building Blocks of Space Sustainability
In October of 2020, the Federal Communications Commission (FCC) ended the collection of formal public comments on its continuing rulemaking for orbital debris. U.S. agencies create new regulations through notice and comment rulemaking: a draft proposed rule is released, the public is first invited to submit Comments, then Replies, and finally the collective input is considered when the agency finalizes new regulations. In the year since Astroscale U.S. filed our comment supporting more holistic risk assessments, the state of the debris environment has worsened.
In March alone, there was a collision between an operational satellite and space debris, while another satellite suffered a large explosion. Both events generated more debris in an already congested region of space. Several other “close call” conjunction events — where one space object passes uncomfortably close to another — sparked considerable anxiety about additional collisions. Even more recently, the uncontrolled descent of a rocket stage in May generated global headlines and widespread public confusion, drawing attention to the need for clear and comprehensive national strategies to address and understand the risks debris poses to both space operations and life on Earth.
With commercial operators already deploying their megaconstellations, and many more requesting market access or operational licenses in the U.S, the world is eagerly waiting to see how the U.S. government will set the bar for responsible behavior in space for its licensees.
In the United States, each operator that applies for a spectrum license through the FCC must present an analysis of the risk its system poses to the orbital environment. As part of serving the public’s best interest, the FCC then conducts a review of this analysis through the evaluation of several variables. One critical variable is a system’s probability of collision (or Pc) with other large objects in orbit, because such collisions create significant amounts of space debris. Operators commonly strive to lower their system Pc by maneuvering to avoid collisions and removing retired satellites from orbit as soon as possible.
Under the current rules, regardless of how many satellites are in an operator’s system, the Pc is only assessed on a per-satellite basis. In other words, showing the probability of collision for any one satellite to be within the regulatory limit is sufficient to demonstrate compliance with FCC policy. This is known as the “single-sat Pc” assessment method.
When considering the many thousands of satellites that form each megaconstellation, it’s clear that assessing the risk of but one satellite per system is grossly insufficient.
The single-sat Pc metric is from an era when megaconstellations did not exist. In those previous decades, it seemed rational to evaluate a satellite based on the risk associated with a single spacecraft because these systems rarely included multiple satellites, let alone hundreds. But in this decade, it would strain credulity to judge the risk a satellite constellation posed to the orbital environment and public welfare based upon the risk of one single satellite without also considering the number of satellites being licensed with said risk. Doing so would wrongly suggest a constellation of 10 satellites would pose the same environmental risk as a constellation of 10,000.
This is not to say larger constellations are inherently bad or dangerous. In fact, having large numbers of satellites with rapid iteration cycles can allow operators to make more frequent improvements to the reliability, safety, and sustainability of their constellations. Using lessons-learned along the way, satellite designs can change after the time of license application and during the launch and operation of the constellation, and this is a good thing.
But we cannot protect our space environment of today with a metric developed for the past. Astroscale U.S. calls for a more accurate, comprehensive measure for when a licensing body evaluates the potential collision risk of a system. This measure is called the “aggregate Pc” method.
Aggregate Pc would calculate a system’s probability of collision based upon the aggregate measure of collision risk for all non-maneuverable satellites across a licensing term. In essence, aggregate Pc would limit the sum of the risk posed by the entire licensed constellation. A specific focus is placed on risk from non-maneuverable (or failed) satellites because these satellites cannot mitigate potential collision risks as they arise. We can only hope for the best as long as these satellites remain in orbit.
As we detail in our FNPRM comment, the Pc measured in the aggregate against trackable objects would form a metric with significant benefit. Importantly, aggregate Pc is performance-based: allowing operators flexibility in risk management as the constellation design evolves, so long as the whole system remains below the aggregate risk threshold.
For example, an operator with a Gen1 constellation that performs substantially below the risk threshold could afford to begin testing higher-risk Gen2 satellite prototypes. As Gen2 technology matures and increases in reliability, and Gen1 risk is retired, the process can then be repeated with Gen3, and so on. In this way, because aggregate Pc is performance-based and not tied to a specific design a priori (single-sat Pc), it would permit operators and regulators to de-risk the orbital environment and incentivize improvements over time to the safety of systems.
So what does this mean in practice?
Astroscale’s global vision is to create a sustainable space environment for future generations. With this goal in mind, we’ve been advocating for the modernization of the policy and regulatory environment — and we’ve seen widespread support among likeminded members of industry. We were pleased to see the FCC take note of sustainability in a modification request granted to SpaceX for their Starlink constellation, which will provide broadband internet access from LEO.
As we’ve seen, it’s critical to accurately measure and track the risks that constellations pose in orbit. We think constellations operate safely when risk is Quantified, Capped, and Monitored, with limits Enforced. These form the core building blocks of sustainable and effective regulatory oversight of system risk.
The SpaceX modification grant for the Starlink system supported this framework in a few ways:
Quantify: The FCC acknowledged that the “single-sat” method of collision risk was insufficient to represent the constellation. Instead, it estimated the risk posed by a failed Starlink satellite, and multiplied that by the expected rate of disposal failures for the system. They acknowledged that risk across an entire system must be measured as a whole and include the risk posed by all expected failures — a key improvement over the current status quo.
Cap: The FCC also identified the number of Starlink failures within a set period (a calendar year) that would “trigger” a reporting requirement, based on reaching an aggregate Pc of 0.005. While this reflects a relaxation from the heritage Pc cap of 0.001, it’s a notable step in the right direction. It also serves as further indication that the FCC is realizing that aggregate risk limits (which, when put into practice, result in de facto “caps” to the number of allowable failures across a system) are the best way to ensure the long-term safety of orbits.
Monitor: The Commission set up a semi-annual monitoring requirement, another positive step. We believe that because the FCC is the main entity taking action to regulate orbital debris, they should enact a licensing regime that facilitates risk monitoring by requiring licensed constellations to submit regular check-ins on constellation health, including the number of failed satellites, which cannot actively mitigate collision risks, still in orbit.
Enforce: Finally, the FCC should not only set, but also enforce, more effective regulations for orbital safety. By showing in the modification grant that it is prepared to materially enforce risk limitations and reporting requirements, the FCC is setting a clear tone of U.S. leadership in the control of space debris — a sorely needed element for long-term space safety.
Together, these four elements are building blocks for regulators globally to begin creating more sustainable and effective orbital debris standards. In the long term, the goal is to foster common behavioral standards for risk interpretation and reduction among all operators, with regulators providing clarity and guiding the industry towards equitable, assured access to space. We believe common methods and metrics of risk measurement are a key first step on that path, delivering effective understanding of actual risk posed. There’s more work to be done in the details, but we’re encouraged by the momentum behind this critical arena for the future of space safety.
