To sustain space, we must manage orbital capacity

Once upon a time, we thought that our actions were insignificant and could not affect something as big as the natural environment. It was impossible for fishermen to deplete fishery resources. Groundwater was abundant and did not need protection. The sky was big enough that the possibility of two man-made objects colliding in space could be Negligible, not to mention threatening our ability to exploit orbit. Today we know better. But there is still a long way to go from recognizing that resources are limited to managing them in a sustainable way.

As researchers on the topic of orbital capacity, we regularly engage with stakeholders: government representatives, satellite operators and NGOs, among others. We recognize and are increasingly concerned that an increasingly crowded low-Earth orbit (LEO) environment may exceed natural capacity and cause serious environmental harm. At the same time, we also found that it was unclear how to translate this awareness into policy-level discussions and actions regarding track use and coordination. We believe that successful track management requires the explicit incorporation of environmental models into track use decisions.

For about 20 years, the standard approach to managing the impact of man-made objects on the orbital debris environment has been largely rooted in requirements for each satellite or mission license and indirectly informed by sporadic technical research. This makes sense if your main goal is to avoid grossly irresponsible behavior and the number of new spacecraft is predictable and well below the system’s capacity. However, in an era where active satellites are increasing by orders of magnitude, fixed rules alone are no longer sufficient to ensure space sustainability. We also need to explicitly manage capacity if we want to ensure that use of low Earth orbit remains within the capacity of natural systems.

What is track capacity?

Orbital capacity is not the number of satellites, but a set of bounds on where, how and how intensively satellites can utilize the orbital volume. Multiple factors, not simply the number of satellites, limit orbital use and paint a range of possible futures and permissible consequences.

What are these limitations? When it comes to physical collision risks, there are at least three: long-term sustainability, operational risks and orbital volume coordination. Long-term sustainability looks at the evolution of the space environment over decades or centuries and asks whether the amount or quality of debris will continue to increase. Operational risk involves the likelihood that a given spacecraft will be destroyed or disabled by debris during its service life, as well as the operational burden of avoiding collisions. What is the difference between the first two constraints? Even if no debris grows causing long-term sustainability issues, certain areas may become too cluttered, posing unacceptable operational risks to operators. Even if the number of landmines does not increase, minefields are dangerous.

The third limitation involves coordinating orbital volumes between large constellations. We agree with those calling for uncoordinated large constellations to avoid overlapping parking orbits. However, this restriction limits the number of satellites that can be placed in a specific volume of space, especially if the constellation claims an overextended exclusive operating volume to the exclusion of other satellites.

Orbital capacity is not the number of satellites, but a set of bounds on where, how, and how many satellites utilize the orbital volume.

In addition to the physical collision risk, there are many other factors that may limit orbital use: the degree of risk posed by material re-entering the Earth’s atmosphere to people on the ground, the impact on ground-based optical and radio astronomy, access to communications spectrum, which is important for satellites The potential environmental impact of large amounts of aluminum and other materials evaporating in the upper atmosphere during re-entry, and the impact of the aerospace industry on ground sustainability.

Some have suggested using simplified metrics to roughly quantify overall environmental constraints and allocate resource usage to specific constellations. Simplicity can lead to insight. However, this approach also implies an often imperfect connection between these indicators and the underlying constraints they seek to reflect. This indirection is not necessarily a problem, but should be done with caution. As Goodhart’s Law warns, measures that become targets often cease to be useful measures. Likewise, attempts to directly limit or allocate the allowable capacity of a single system would short-circuit many of the prerequisite steps necessary for stakeholders to deem such management to be legitimate, making progress more difficult.

Sustainable Management of Earth’s Orbit

We know you’re still wondering: how many satellites are appropriate to share the sky with? The frustrating answer is: it depends. Different factors will limit capacity at different altitudes or under different assumptions, such as which satellites will be launched, how operators behave responsibly in orbit, and even how effectively we combat climate change. A feasible solution is defined by considering a set of constraints and assumptions that are feasible.

Defining these constraints and selecting important ones is a mixed problem of science, stakeholder goals, technology, and policy, the solution of which must balance the competing values ​​and priorities of a broad and representative group of stakeholders. How much operational risk should businesses accept? What do you do when they always disagree? How do you weigh the economic benefits of enhanced satellite connectivity against the realization that such deployments could have significant impacts on ground-based astronomy, even with mitigation measures in place? Given our limited understanding of the effects of atmospheric chemistry and climate processes, do you take some precautions regarding atmospheric satellite disposal? There are no easy answers to these questions, but the resulting value-laden constraints define the limits of the system and distinguish good futures from bad ones. Choosing among these solutions is a collective action and resource management problem faced simultaneously by operators and regulators from dozens of countries.

So how do we use the concept of orbital capacity to make progress? We believe that four steps must be taken to realize a future of capacity-aware usage of LEO:

1. Build consensus around technical definitions of spatial sustainability and reasonable modeling assumptions.

We need to build broad consensus on what limits on track capacity meet the needs of stakeholders. The level of discourse needs to go beyond avoiding Kessler Syndrome to a level of technical specifications sufficient to clearly assess various futures. Different operators have different views on acceptable operational risk levels and collision avoidance burdens. Regulators have different policy goals. They want to benefit from space services, but they also know that even without future launches, the amount of debris at certain altitudes will continue to increase in the coming years. Experts can help translate these perspectives into concrete technical constraints, but these constraints must be supported by stakeholders to be meaningful.

2. Mature communities have confidence in open source, accessible environment modeling tools and the ability to use them.

Some industry players have expressed concern that track capacity, once defined, could be cynically used by competitors as a tool of market exclusion or as an arbitrary black-box veto by regulators. Solving these problems requires models that are accessible to the entire community, transparent, and accessible to people with varying training. This openness should be a powerful antidote to malicious attempts to use sustainability issues to stoke fear, uncertainty and doubt. Consensus constraints and models enable apples-to-apples comparisons and delineate debates on scientific modeling approaches through discussions of sustainability goals, efficiency of orbit usage, and equity in orbit volume acquisition. Data-driven technologies and user-friendly implementations are necessary to move from intuition to evidence-based decision-making and break down difficult and contentious coordination problems into smaller, manageable parts.

3. Incorporate track capacity considerations into the regulatory process.

Satellite and mission-based standards are credible as a means of preventing gross irresponsible behavior, but are not sufficient to ensure that overall traffic levels are actually sustainable. The mission authorization process should include the use of consensus models to understand the contribution of new missions to the evolution of the space environment. Doing so requires establishing regulatory and applicant proficiency in relevant modeling tools. Established space regulators can initiate this process, starting with capacity-related disclosure requirements and safe harbor reviews, and then gradually incorporate these factors into licensing decisions. Over time, market access conditions can help encourage wider adoption of capabilities-based approaches. Crucially, transparent models and decision criteria increase regulatory certainty for applicants by explaining exactly how their system’s capacity usage is assessed.

4. Committed to adaptive management and adaptive governance.

Natural resource management is often characterized by significant uncertainty in both system inputs and responses. Progress has been made in the field of terrestrial resource management, thanks to adaptive management strategies that use models to develop iteratively customized management strategies based on observations of how the environment responds to user behavior, and to engage with stakeholders over time. needs to maintain a consistent adaptive governance strategy. Together they offer a better alternative to fixed rules and adversarial legal processes for natural resource management regimes. In many cases, voluntary consensus structures can enhance or eliminate mandatory governance systems. We should adapt and apply these mechanisms to manage and coordinate track usage.

Defining and developing strategies around track capacity provides a critical missing link, directly linking sustainability goals to operator and regulatory decisions. As the number of spacecraft proposed for use in low Earth orbit continues to increase, clear capacity management will be an important step in ensuring that sustainability goals are actually achieved. Achieving this goal requires buy-in, good faith and hard work from operators, regulators and stakeholders across the aerospace community. We think it will be well worth it. We hope you agree.

Miles Lifson is a doctoral student in the MIT Department of Aeronautics and Astronautics and a research assistant in the Astrodynamics, Space Robotics, and Control Laboratory (ARCLab). Richard Linares is an associate professor in the Department of Aeronautics and Astronautics and director of ARCLab at MIT.

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