- Email: [email protected]
A practical perspective on Space Traffic Management
The Journal of Space Safety Engineering 6 (2019) 101–107
Contents lists available at ScienceDirect
The Journal of Space Safety Engineering journal homepage: www.elsevier.com/locate/jsse
A practical perspective on Space Traffic Management Darren McKnight
T
Integrity Applications, 15020 Conference Center Drive, Chantilly, VA, United States
ARTICLE INFO Keywords: Orbital debris Space safety Space Traffic Management Debris remediation Debris mitigation
Space Traffic Management (STM) is a critical topic for the space community as the number of operational satellites may potentially grow by an order of magnitude over the next decade [1]. However, the term STM is jumbled with other issues and terms such as Space Situational Awareness (SSA), constellations, smallsats, the globalization of space, etc. Before the community starts to “develop a STM solution” it is imperative to understand the “problems” that need to be solved. The first step of this process is to agree on terminology to ensure that stakeholders do not “talk past each other.” A proposed structure to enable cooperation and collaboration has three major components. First, Space Environment Management (SEM) describes how to reduce debris growth, largely by preventing collisions between non-operational objects especially clustered massive derelicts [2,3]. This component drives the population monitored by Space Situational Awareness (SSA) assets and it also provides direct insight to the space operators executing Space Traffic Management (STM). SSA characterizes the space object population that is critical context for STM. STM enables reliable satellite operations for all satellites with a focus on the potentially large constellations that are slated to be deployed in the near future. The vantage point of operational satellites, in turn, provides a potential feedback loop to the SEM domain through recording of satellite anomalies/failures and even direct feeds from in situ sensors. Each of these three areas are normally run by different people with different skills yet the final positive outcome depends on all three of the domains’ contributions. The term, Space Operations Assurance (SOA), is proposed as the overarching domain (encompassing SEM, SSA, and STM) as shown in Fig. 1.
1. Introduction Space Traffic Management (STM) is a relevant topic as the community examines how to deal with the potential constellations slated for deployment to Low Earth orbit (LEO) in the next five years [4–6]. At a high level, the following guiding principles are key to moving the dialogue forward on this critical issue: - We need to agree on terminology that provides a clear framework that enables cooperation and collaboration. A three-pillared framework of Space Operations Assurance (SAO) is proposed within which STM is the ultimate objective. - The focus should be on activities not on entities. More pointedly, it is critical to examine the evolution of the space environment and constellation resiliency through a sequence of activities first which will then determine the level of entity resolution required within a common catalog of space objects. This is in contrast to focusing on a complete database of all objects as the primary objective; let the resolution of any space catalog be the result of an activity-focused analysis based on SOA thresholds. - It is important to examine the key problems and not just the
“problems du jour.” More specifically, space operations will be assured by addressing the phenomena that will have the greatest effect on constellations (and all satellites) to operate reliably. For example, do not overlook existing on-orbit space safety concerns such as derelict-on-derelict collisions, the lethal nontrackable (LNT) population, attributing spacecraft anomalies, and spacecraft reliability in lieu of fixating solely on collision avoidance and debris mitigation. In summary, the goal should be that the right questions are being asked of the right people in the right order of priority. 2. SOA components Space Operations Assurance (SOA) has three major components, however, at its core, SOA is a risk management process (Fig. 2). Space Traffic Management (STM) is primarily satellite command and control to manage the interactions between space operators and the trackable debris population. STM has immediate, real-time needs (i.e., seconds to days) to include reliability of spacecraft (deployment, mission operations, and retirement), radio frequency interference (RFI) identification/resolution, defining an operating envelope (temporally,
E-mail address: [email protected]. https://doi.org/10.1016/j.jsse.2019.03.001 Received 16 February 2018; Received in revised form 26 January 2019; Accepted 26 March 2019 Available online 05 April 2019 2468-8967/ © 2019 International Association for the Advancement of Space Safety. Published by Elsevier Ltd. All rights reserved.
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spacecraft design/manufacturing guideline creates a capability to collect and then share space environmental effects data so that operators know better what risks are being posed to operational space assets to aid in anomaly attribution, spacecraft design, and space weather characterization. 3. Linear success process (Alternative to risk management) Space Operations Assurance is basically a risk management process; the figure below provides a depiction of a linear success framework as a surrogate for the traditional circular risk management construct [12]. This process is applicable to all three pillars of SOA. The first phase – Prepare – strives to identify, characterize, and predict risks. In this phase it is important to examine the effects, uncertainties, and predictability of potential risks. We must first identify both the barriers to success (i.e., threats which may manifest as risks to assured space operations) and enablers for success (e.g., means to prevent risks from manifesting). There are four general families of barriers to success (i.e., threats):
Fig. 1. Space operations assurance should be the primary objective of debris management.
spatially, etc.), collision avoidance (involving at least one operational satellite), and automated decision support (covering all of the previous activities). The Space Data Association (SDA) is one commercial practitioner in this area; their experience and insights should be considered carefully from the outset [7]. STM is informed primarily by the second major domain, SSA, that discovers, monitors, characterizes, and warns about space objects (with an emphasis on non-operational objects since constellation/satellite operators normally know their locations better than anyone else). The observations gathered by SSA resources produce mid-term insights (minutes to months) such as uncorrelated target processing, discovery of newly created space objects, space catalog maintenance, and deterministic collision risk (for dead-on-dead and dead-on-operational while providing backup for operational-on-operational). SSA may also contain the identification of hazards that are posed “with intent” (i.e., attack). Lessons learned and best practices from diverse entities such as the U.S. Joint Space Operations Center (JSpOC), Space Data Association (SDA), the Russian International Scientific Optical Network (ISON), etc. should be leveraged and not ignored just because none of them have the “total” solution. SSA requirements are driven by debris generation as modulated by Space Environment Management (SEM) activities. This domain focuses on long-term (weeks to decades) issues such as examining tradeoffs between debris remediation options (e.g., active debris removal [ADR], just-in-time collision avoidance [JCA], and Just-in-time ADR [JADR]) [8–10], debris wake modeling, space weather/predictions, debris growth modeling, statistical collision risk, surface erosion, migration of high area-to-mass ratio objects, and spacecraft anomaly/failure attribution analysis. SEM considers all hazards and phenomena that are natural (i.e., without intent). This domain is likely to depend heavily on an organization's funding and executing basic research that can examine fundamental issues related to space object behavior. However, operational and regulatory aspects of evolving debris mitigation efforts and nascent debris remediation work are also part of SEM activities. To enable success in SOA, it is proposed that a public-private partnership called the SOA Consortium (SOAC) be established to help both develop and define the framework outlined within this article and to facilitate deliberate interactions between stakeholders. It is likely best for the SOAC to first be established at a national level and then combined into bilateral and multilateral implementations before trying to execute it globally. The SOAC will help to manage interactions and results from and across these three domains. Some potential implementation approaches to the SOAC are provided later. An interesting recent space system guideline that supports these domains in an integrated fashion is the Secretary of the U.S. Air Force requirement in March 2015 that required all satellite systems’ programs (that have not passed Milestone B in the acquisition process) to incorporate an energetic charged particle (ECP) sensor [11]. This
1 Cognitive features include requirements definition, design, relevancy of testing conditions, operator error, deception (by an adversary), decisionmaking/analysis, and concept of operations. 2 Mechanical features contain material/component reliability/availability and manufacturing/integration quality. 3 Natural phenomena comprise conditions imposed by the space environment. 4 Manmade threats are those activities created by another space operator with the sole purpose of preventing your operational success (i.e., threats with intent) and accidental manmade phenomena (e.g., software coding mistakes, operator command error, etc.). Identifying each of these at an early stage provides an opportunity to compare and contrast these aspects. This will be important later as techniques to enhance operational success are considered and prioritized. Each barrier to success has the following dimensions that can be characterized: - Effects: type, persistence, and rate; - Uncertainty: variability in space and time plus effects due to lack of awareness or limited understanding; and - Predictability: ability to project effects into the future. The last major component of the Prepare phase leverages this last barrier to characterization – predict (or forecast). Unfortunately, it is also the most difficult as many of the phenomena of note have little to no historical precedence or may involve very complex physical models. It is critical to not get overly fixated on 200-yr predictions when monthly and annual effects may be significant on space operations. This resonates with the call to solve the right problems in the right order at the right pace. As a matter of fact, the focus on the long-term cascading effect of debris may have caused many to ignore significant short-term space safety issues that may manifest in the next 1–10 years. This will be addressed at the end of this article in a SOA Action Plan Within the Prepare phase, it is also critical to understand that much of the uncertainty that exists in collision risk analysis and STM may be reduced by better observations and advanced modeling. However, there is some natural variability that may never be eliminated; some ambiguity will persist in almost every dimension of risk assessment related to space operations in areas such as spacecraft reliability, orbit fidelity, probability of collision (both deterministic and statistical), and anomaly/failure attribution. The second phase – Plan – focuses on dissuading, denying, and deterring potential threats (i.e., space environmental hazards, both natural and manmade). This is largely done in design and testing of space systems. Clearly, for threats without intent, deterrence and 102
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Fig. 2. Space Operations Assurance is basically risk management.
dissuasion are irrelevant. However, shielding from particulates or radiation hazards is one way to reduce risk in this phase. All threats cannot be avoided so there must be a plan to react in response to realized threats in the third phase – Act (During) – by interdicting, suppressing, or mitigating risks. Activities here normally include operational procedures, warning technologies, and automated decision support. Even after a hazard has been realized, there are still options – Act (After) – such as remediation, recovery, and reconstitution. Actions here could include activating on-orbit spares, using redundant terrestrial backups, launching new systems, active debris removal, and satellite servicing. It should be noted that for complex risk situations the sequence of countermeasures is often based on ease of implementation rather than a measured return on investment. This is human nature and logical to incorporate easy to implement approaches first. However, as time passes and the risk landscape evolves and is characterized more expensive and challenging risk management activities may be required. All phases of risk management need to be considered from the onset; starting with the bias that all risks must be eliminated will create unrealistic and, potentially, counterproductive behavior. A layered approach, where mechanisms are employed in each area, usually produce the most reliable and efficient final system/architecture performance. In addition, the dynamic of how quickly threats develop and countermeasures act (i.e., response physics) drive the monitoring and warning systems required.
subsystem failures, etc.; and - Retire, reorbit (from high Earth orbit), and deorbit (low Earth orbit, LEO): perform end-of-life operations. This list of activities provides both a source of where risks may arise and also where countermeasures may be employed. 5. Execution of the SOA framework via SOAC With a clear understanding now of what needs to be done, focusing more on exactly how SEM, SSA, and STM pillars will cooperate is essential. In this spirit, it is important to first focus on a balanced perspective between: - Simplicity vs flexibility: do not try to come up with an overly complex solution (whether design, regulatory, or operational) that will not be flexible enough to handle emerging issues over time; - Responsiveness vs accuracy: the constellation deployments may occur quickly or environmental hazards may grow quickly so it is important to create “nimble” policies and processes; - Efficiency vs completeness: risk management depends on realistic assessments of hazards presented to space operations but eliminating risk is not possible; - Current vs future concerns: it is important to not overly focus on long-term risk at the expense of immediate space safety; - One vs many (i.e., constellations): emphasis on the management of constellations may create onerous policies for individual satellites (i.e., create unintended negative consequences).
4. Activity-focused analysis construct Activity-focused analysis will be used to manage the risk from threats by examining the activities that space systems might perform. By focusing on activities that are indicators of the realization of a risk to space operations assurance, resources are applied optimally to manage the risk from these threats. This analysis will then, in turn, drive the level of entity resolution required. For SOA, a list of potential activities includes, but are not limited to, the following:
6. Possible initial SOAC discussions Immediate discussions catalyzed by the SOAC should focus on the following three questions for space-based parts of the constellations: 1 How reliable will your space systems be during deployment, operations, and retirement? Previous satellite and constellation deployments have shown that the time where most satellites are lost is in launch and the first 30 days on orbit. 2 Have you employed viable means to avoid collisional interactions between members of your constellation? The initial focus should be on the potential collision risk that is directly a result of the new deployments. 3 Have you considered and planned for potential interactions from objects and other debilitating phenomena outside of your control (e.g., debris, other constellation members, natural space environmental effects, severe space weather event, prolonged RFI activity, etc.)? History has shown that the suite of risks to satellites is evolving quickly and must be part of any long-term understanding of satellite/constellation operations assurance.
- Design: mission needs are translated into engineering plans; - Manufacture: assemble components and subsystems; - Test: verify proper functioning of components, subsystems, and system; - Mating: space system is integrated into the launch vehicle; - Deploy: space system is launched; - Activate: turn on and checkout systems; - Operate: individually (adjust orbit, change orientation, change size, change stability/tumbling, etc.) and as a constellation (maintain spacing, activate spare, etc.); - Service & repair: recover from system performance degradation; - Emit: emanate energy (e.g., radio frequency, infrared, optical, etc.) or effluents (e.g., outgassing volatiles, leaking propellants, etc.) - Rendezvous and proximity operations (RPO): operate near another space object; - Conjunction or close approach: cross nearby another space object; - Collide: strike another space object; - Create more objects: release objects from routine space operations,
An op-ed in Space News in January 2019 provided a composite assessment of the most appropriate activities by constellation developers with respect to orbital debris and sustainability of space operations. This public statement called for simple, but powerful, efforts: do not let constellations overlap, determine root cause when satellites fail, space operators should be able to control the paths of their satellites, 103
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disposal should be prompt & reliable after mission is completed (5 yr not 25 yr), and minimize risks to people on the ground from reentering spacecraft [13]. The design, architecture, and operations of the supporting ground infrastructure supporting space assets are just as important to the overall assurance of space operations. As a result, two questions might be considered as a starting point for the non-space-based parts of these constellations:
be cataloged (i.e., ∼10 cm in low Earth orbit and ∼1 m in geosynchronous orbit). This is considered a significant part of STM; tasks to improve this capability include data sharing, improving the positional uncertainty of cataloged objects, and the new S-band fence (which will increase the number of cataloged objects in LEO). As noted, improvement in space situational awareness (SSA), such as the new S-band fence, will in essence decrease the LNT risk as more of those previously nontrackable objects will be added to the catalog and, thus, potentially avoided. Debris Mitigation efforts, upper left quadrant of Fig. 3, includes both enhancing compliance to existing guidelines and examining strengthening mitigation thresholds (e.g., reduce the 25-yr rule to a 5-yr rule). It is interesting that tougher guidelines are being considered even as existing guidelines are not universally adhered to by spacefaring entities. Debris mitigation efforts serve to not only reduce debris that might have to be avoided but also prevents the deposition of new intact objects that might require eventual removal. It is the last quadrant, lower left box labeled Active Debris Removal (ADR), that has received the least attention. The removal of massive derelicts from Earth orbit, however, will prevent the most likely and most consequential debris-generating events. To more efficiently execute ADR activities (or other debris remediation options such as just-intime collision avoidance [8–10]) requires both better SSA capabilities and operationalizing ADR solutions. ADR operations will not only reduce the number of targets that have to be avoided by operational satellites but will prevent the highly consequential collisions that would occur if two massive payloads or rocket bodies were to collide. There is a cluster of 36 abandoned rocket bodies and payloads distributed in the 815–865 km altitude range that if any two would collide, the event would likely double the cataloged population and add over 200,000 LNT [14]. An examination of the activities in Fig. 3 can be used to summarize the priorities to assure space operations now and enhance the long-term sustainability of space (Fig. 4).
1 For the ground segment of your business, do you have redundant paths for the telemetry, health maintenance, and service (e.g., imagery, video, data, voice, etc.)? 2 Is there resiliency built into your architecture if the ground segment of your operations is taken off line for a period of time? For how long? Longer term objectives of SOAC would include, but not be limited to, the following (1) establish, communicate, and enforce standards and best practices between and for operators and operations; (2) facilitate communications between global spacefaring entities; (3) monitor progress in SOA; and (4) interface with and leverage industry, academic, and commercial entities. While the focus on constellations is warranted, there is a general baselining of risks for the continued assured operations of space systems in general at the current level of reliability that should also be addressed by the SOAC. Fig. 3 portrays four priorities to be addressed based on community discussions. The activity in the lower right quadrant – Characterize Lethal Nontrackable (LNT) Population – is the anchor for space operations assurance. The other three boxes describe three primary activities that are either actively being pursued or should be. The Collision Avoidance activity in the upper right quadrant comprises the efforts to warn operational satellites of potential collisions with objects large enough to
Fig. 3. Priorities for space operations assurance should be anchored in controlling the lethal nontrackable debris population through debris remediation (e.g., active debris removal, ADR) debris mitigation, and collision avoidance activities. 104
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security, and environmental performance of international shipping as a regulatory framework. The group covers ship design, construction, equipment, manning, operation, and disposal while the operators “selfregulate” by developing agreed-upon best practices for operations. The International Virtual Observatory Alliance (IVOA) http://www. ivoa.net/ is an organization that debates and agrees on technical standards that are needed to make the ubiquitous sharing of astronomical observations worldwide possible. It also acts as a framework for discussing and sharing ideas and technology. DIAS (Data Integration & Analysis System) provides infrastructure for sharing Earth observation data globally http://www.diasjp.net/en/. DIAS was started in 2006 to collect and store earth observation data; to analyze such data in combination with socio-economic data; convert data into information useful for crisis management with respect to global-scale environmental disasters and other threats; and to make this information available within Japan and overseas. Open Geospatial Consortium (OGC) http://www.opengeospatial. org/ is an International, not-for-profit organization committed to making quality open (freely available) standards for the global geospatial community made through a consensus process. It produces standards, best practices, discussion papers, engineering reports, etc. The OGC standards are used in a wide variety of domains including Environment, Defense, Health, Agriculture, Meteorology, Sustainable Development, and many more. Coordination Group for Meteorological Satellites (CGMS) https:// www.cgms-info.org/index_.php/cgms/index consists of 15 organizations and six observers. The proposed Terms of Reference (TOR) for space weather activities includes the reporting on spacecraft anomalies and sharing the results of anomaly resolution and analyses. The International Civil Aviation Organization (ICAO) https://www. icao.int/about-icao/Pages/default.aspx is a specialized agency of the United Nations, established in 1944 to manage the administration and governance of the Convention on International Civil Aviation. There are 192 members states and industry groups that cooperatively develop international civil aviation Standards and Recommended Practices (SARPs) and policies in support of a safe, efficient, secure, economically sustainable and environmentally responsible civil aviation sector. ICAO ensures that local civil aviation operations and regulations conform to global norms, which in turn permits more than 100,000 daily flights in aviation's global network to operate safely and reliably in every region of the world. Consortium For Execution of Rendezvous and Servicing Operations (CONFERS) https://www.darpa.mil/program/consortium-for-executionof-rendezvous-and-servicing-operations is an industry-government consortium to develop technical standards for safe on-orbit rendezvous and servicing operations. The benefits of CONFERS are enhanced on-orbit safety through established “rules of the road”, creation of behavioral norms for transparent international engagements, and streamlining of USG commercial mission authorization with a technical foundation.
Fig. 4. Debris mitigation and collision avoidance are necessary but not sufficient means to assure safe space operations; debris remediation will also have to be employed.
As noted, debris mitigation guidelines have been in force and maturing since ∼1995. Similarly, collision avoidance processes have been actively refined globally since ∼2010. However, there are still no operational capabilities for debris remediation despite the risk of massiveon-massive collisions in LEO. The activities proposed for an initial SOAC discussion have led to Fig. 4 above highlighting the following observations: - Collision avoidance is necessary but the capabilities of operational satellites and the increased collision avoidance support from both government and commercial SSA capabilities makes the probability of a collision between an operational satellite with a trackable object very unlikely. In addition, the consequence would only be moderate as most payloads in LEO are on the order of 100–600 kg. - Debris mitigation guidelines are necessary to limit the future growth of debris; this includes both (1) reducing LNT production from deployment & explosions and (2) removing intact objects within 25 years of end of operational life. The compliance rate for the 25-yr rule globally is between 20–80%, depending how it is calculated [15]. This means that the probability of non-compliance is fairly high but the consequence of such an adverse event is very low (i.e., basically leaving an intact object on orbit longer than 25 yr). - Debris remediation activities, as exemplified by active debris removal, is receiving the least attention currently. Unfortunately, the probability of a massive collision between two derelict objects is on the order of 1000 kg to 8000 kg is fairly high (i.e., ∼0.1%−1%/yr) and the consequences are significant (i.e., ∼4000–17,000 cataloged objects and ∼10,000–2000,000 LNT). As depicted in Fig. 4, debris remediation activities provide the greatest benefit (i.e., risk reduction), however, the cost and complexity (both technical and legal) of debris remediation solutions have impeded their development.
8. Summary - SOA big picture SOA is enabled by the collaborative, joint execution of SEM, SSA, and STM activities. The four major steps of this risk management process nominally have two phases: (1) early in Prepare and Plan steps risks are deterred while (2) later efforts will focus on responding to (i.e., mitigating) specific realized threats to reliable space operations (i.e., Act (During) and Act (After)). In applying a linear operational success framework there are two overarching, and inter-related, issues that are considered in turn: (1) interplay between warning systems & “response physics” and (2) success monitoring & risk/response interactions (as depicted in Fig. 5). Warning systems and “response physics” (i.e., rate at which barriers/enablers to success act and react relative to each other) tie together linear success tasks. Warning systems defined and established during the Prepare and Plan phases may improve the effectiveness of
7. How to start SOAC The SOAC could follow the organizational framework of one of several productive examples of public-private partnerships and industry organizations: The International Maritime Organization (IMO) http://www.imo. org/en/Pages/Default.aspx is a specialized agency of the United Nations (UN) serves as global standard-setting authority for the safety, 105
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Fig. 5. The overall SOA framework leverages many existing processes, personnel, and technologies.
responses to enhance operational success once the risk (e.g., potential direct collision, nearby debris-generating event between derelicts, severe space weather, etc.) has been manifested by providing information on the existence, evolution, and extent of the risk. The ability to leverage warning depends on “response physics”: how quickly do natural, mechanical, and manmade threats act relative to potential countermeasures (i.e., available means to deny, deter, suppress, and mitigate risks) and how quickly can realized risks be identified. Last, there is a need to continually monitor and predict operational success as a measure of effectiveness of the industry's attempt to assure space operational success. This is facilitated by an ongoing set of interactions which include communications (e.g., sharing information on precursors and indicators of threats becoming realized and messaging to stakeholders about countermeasures in place) and transfer of assets from one activity to the next (i.e., resources that transition from planning to interdiction or remediation). One successful manifestation of this activity is the sequence of spacecraft anomalies and failures workshops held globally over the last seven years [16]. The SOAC can be a major unifying mechanism for similar processes. A preliminary exercise of this SOA evaluation identified three activities (debris mitigation, collision avoidance, and debris remediation) as the main enablers to manage the LNT collision risk. This process highlighted that the most impactful response (i.e., debris remediation as exemplified by ADR) is the least mature countermeasure to limiting debris growth. It should be noted that this is not surprising as it is also clearly the most difficult technically and politically. It is hoped that this situation will change soon, possibly catalyzed by a SOAC-like entity, in order to assure safe space operations now and in the future.
References [1] Space Policy Directive-3, National Space Traffic Management Policy, issued by the U.S. Government in June 2018 provided a framework for space traffic management issues, https://www.whitehouse.gov/presidential-actions/space-policy-directive-3national-space-traffic-management-policy/. [2] D. McKnight, F. Di Pentino, S. Knowles, Massive collisions in LEO - a catalyst to initiate ADR, 65th International Astronautical Congress, Toronto, CA, September 2014. [3] D. McKnight, Insights gained from the massive collision monitoring activity, International Association for the Advancement of Space Safety, Toulouse, France, October 2017. [4] Mark Brown, Space traffic management and orbital debris: a path forward to ensure safe and uninterrupted space operations, Space Traffic Management Conference, 15 2018 https://commons.erau.edu/stm/2018/presentations/15. [5] V. Samson, B. Weeden, Possible SSA futures: a report of the 2017 AMOS dialogue, 4th Annual STM Conference, “Seeking Sustainable Solutions”, Daytona Beach, FL, ERAU, Jan. 16, 2018. [6] S. Hunter, J. Detroye, Two perspectives on civil space traffic management implementation, 4th Annual STM Conference, “Seeking Sustainable Solutions”, Daytona Beach, FL, ERAU, Jan. 16, 2018. [7] M. Dickinson, Preparing for Congested Space. An SDA Focus, (May 2017) spacedata.org/sda/. [8] C. Bonnal, D. McKnight, Just-in-time collision avoidance (JCA): a realistic solution for future sustainable space activities, 1st IAA Conference on Space Situational Awareness (ICSSA), Orlando, FL, USA, Nov 2017. [9] C. Phipps, C. Bonnal, Pulsed UV laser system design for re-entering or nudging debris in LEO and re-orbiting GEO debris, Presented at the “Laser Solutions to Orbital Debris” Workshop, Paris, Université Paris Diderot, 2015. [10] D. McKnight, F. Di Pentino, S. Douglass, Developing a tactical adjunct to ADR to insure a sustainable space environment, 65th International Astronautical Congress, Jerusalem, IS, October 2015. [11] In March 2015, the U.S. Secretary of the Air Force required that pre-Milestone B satellite programs had to incorporate energetic charged particle (ECP) sensor to help characterize the space environment, https://spacenews.com/air-force-seeksinfo-on-space-weather-sensor/.
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D. McKnight [12] D. McKnight, Debris remediation examined via an operational success framework, Stardust 2nd Global Virtual Workshop, Southampton, UK, January 2016; 8th IAASS Conference, Melbourne, FL, May 2016; and 4th International Workshop on Space Debris Modelling and Remediation, Paris, France, June 2016 Journal of Space Safety Engineering, Fall 2016. [13] https://spacenews.com/op-ed-responsible-satellite-operations-in-the-era-of-largeconstellations/. [14] D. McKnight, S. Speaks, J. Macdonald, Assessing potential for cross-contaminating breakup events from LEO to GEO, 68th International Astronautical Congress,
Bremen, Germany, October 2018. [15] C. Bonnal, Space debris mitigation & remediation: a general update, 8th JAXA Space Debris Workshop, Chofu, 3 Dec. 2018. [16] The Spacecraft Anomalies and Failures Workshop has been hosted in Chantilly, Virginia, US annually since 2011 and the International Association of the Advancement of Space Safety (IAASS) held the first international Spacecraft Environmental Anomalies and Failures Workshop in 2017 with the second one slated for 2019.
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Contents lists available at ScienceDirect
The Journal of Space Safety Engineering journal homepage: www.elsevier.com/locate/jsse
A practical perspective on Space Traffic Management Darren McKnight
T
Integrity Applications, 15020 Conference Center Drive, Chantilly, VA, United States
ARTICLE INFO Keywords: Orbital debris Space safety Space Traffic Management Debris remediation Debris mitigation
Space Traffic Management (STM) is a critical topic for the space community as the number of operational satellites may potentially grow by an order of magnitude over the next decade [1]. However, the term STM is jumbled with other issues and terms such as Space Situational Awareness (SSA), constellations, smallsats, the globalization of space, etc. Before the community starts to “develop a STM solution” it is imperative to understand the “problems” that need to be solved. The first step of this process is to agree on terminology to ensure that stakeholders do not “talk past each other.” A proposed structure to enable cooperation and collaboration has three major components. First, Space Environment Management (SEM) describes how to reduce debris growth, largely by preventing collisions between non-operational objects especially clustered massive derelicts [2,3]. This component drives the population monitored by Space Situational Awareness (SSA) assets and it also provides direct insight to the space operators executing Space Traffic Management (STM). SSA characterizes the space object population that is critical context for STM. STM enables reliable satellite operations for all satellites with a focus on the potentially large constellations that are slated to be deployed in the near future. The vantage point of operational satellites, in turn, provides a potential feedback loop to the SEM domain through recording of satellite anomalies/failures and even direct feeds from in situ sensors. Each of these three areas are normally run by different people with different skills yet the final positive outcome depends on all three of the domains’ contributions. The term, Space Operations Assurance (SOA), is proposed as the overarching domain (encompassing SEM, SSA, and STM) as shown in Fig. 1.
1. Introduction Space Traffic Management (STM) is a relevant topic as the community examines how to deal with the potential constellations slated for deployment to Low Earth orbit (LEO) in the next five years [4–6]. At a high level, the following guiding principles are key to moving the dialogue forward on this critical issue: - We need to agree on terminology that provides a clear framework that enables cooperation and collaboration. A three-pillared framework of Space Operations Assurance (SAO) is proposed within which STM is the ultimate objective. - The focus should be on activities not on entities. More pointedly, it is critical to examine the evolution of the space environment and constellation resiliency through a sequence of activities first which will then determine the level of entity resolution required within a common catalog of space objects. This is in contrast to focusing on a complete database of all objects as the primary objective; let the resolution of any space catalog be the result of an activity-focused analysis based on SOA thresholds. - It is important to examine the key problems and not just the
“problems du jour.” More specifically, space operations will be assured by addressing the phenomena that will have the greatest effect on constellations (and all satellites) to operate reliably. For example, do not overlook existing on-orbit space safety concerns such as derelict-on-derelict collisions, the lethal nontrackable (LNT) population, attributing spacecraft anomalies, and spacecraft reliability in lieu of fixating solely on collision avoidance and debris mitigation. In summary, the goal should be that the right questions are being asked of the right people in the right order of priority. 2. SOA components Space Operations Assurance (SOA) has three major components, however, at its core, SOA is a risk management process (Fig. 2). Space Traffic Management (STM) is primarily satellite command and control to manage the interactions between space operators and the trackable debris population. STM has immediate, real-time needs (i.e., seconds to days) to include reliability of spacecraft (deployment, mission operations, and retirement), radio frequency interference (RFI) identification/resolution, defining an operating envelope (temporally,
E-mail address: [email protected]. https://doi.org/10.1016/j.jsse.2019.03.001 Received 16 February 2018; Received in revised form 26 January 2019; Accepted 26 March 2019 Available online 05 April 2019 2468-8967/ © 2019 International Association for the Advancement of Space Safety. Published by Elsevier Ltd. All rights reserved.
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spacecraft design/manufacturing guideline creates a capability to collect and then share space environmental effects data so that operators know better what risks are being posed to operational space assets to aid in anomaly attribution, spacecraft design, and space weather characterization. 3. Linear success process (Alternative to risk management) Space Operations Assurance is basically a risk management process; the figure below provides a depiction of a linear success framework as a surrogate for the traditional circular risk management construct [12]. This process is applicable to all three pillars of SOA. The first phase – Prepare – strives to identify, characterize, and predict risks. In this phase it is important to examine the effects, uncertainties, and predictability of potential risks. We must first identify both the barriers to success (i.e., threats which may manifest as risks to assured space operations) and enablers for success (e.g., means to prevent risks from manifesting). There are four general families of barriers to success (i.e., threats):
Fig. 1. Space operations assurance should be the primary objective of debris management.
spatially, etc.), collision avoidance (involving at least one operational satellite), and automated decision support (covering all of the previous activities). The Space Data Association (SDA) is one commercial practitioner in this area; their experience and insights should be considered carefully from the outset [7]. STM is informed primarily by the second major domain, SSA, that discovers, monitors, characterizes, and warns about space objects (with an emphasis on non-operational objects since constellation/satellite operators normally know their locations better than anyone else). The observations gathered by SSA resources produce mid-term insights (minutes to months) such as uncorrelated target processing, discovery of newly created space objects, space catalog maintenance, and deterministic collision risk (for dead-on-dead and dead-on-operational while providing backup for operational-on-operational). SSA may also contain the identification of hazards that are posed “with intent” (i.e., attack). Lessons learned and best practices from diverse entities such as the U.S. Joint Space Operations Center (JSpOC), Space Data Association (SDA), the Russian International Scientific Optical Network (ISON), etc. should be leveraged and not ignored just because none of them have the “total” solution. SSA requirements are driven by debris generation as modulated by Space Environment Management (SEM) activities. This domain focuses on long-term (weeks to decades) issues such as examining tradeoffs between debris remediation options (e.g., active debris removal [ADR], just-in-time collision avoidance [JCA], and Just-in-time ADR [JADR]) [8–10], debris wake modeling, space weather/predictions, debris growth modeling, statistical collision risk, surface erosion, migration of high area-to-mass ratio objects, and spacecraft anomaly/failure attribution analysis. SEM considers all hazards and phenomena that are natural (i.e., without intent). This domain is likely to depend heavily on an organization's funding and executing basic research that can examine fundamental issues related to space object behavior. However, operational and regulatory aspects of evolving debris mitigation efforts and nascent debris remediation work are also part of SEM activities. To enable success in SOA, it is proposed that a public-private partnership called the SOA Consortium (SOAC) be established to help both develop and define the framework outlined within this article and to facilitate deliberate interactions between stakeholders. It is likely best for the SOAC to first be established at a national level and then combined into bilateral and multilateral implementations before trying to execute it globally. The SOAC will help to manage interactions and results from and across these three domains. Some potential implementation approaches to the SOAC are provided later. An interesting recent space system guideline that supports these domains in an integrated fashion is the Secretary of the U.S. Air Force requirement in March 2015 that required all satellite systems’ programs (that have not passed Milestone B in the acquisition process) to incorporate an energetic charged particle (ECP) sensor [11]. This
1 Cognitive features include requirements definition, design, relevancy of testing conditions, operator error, deception (by an adversary), decisionmaking/analysis, and concept of operations. 2 Mechanical features contain material/component reliability/availability and manufacturing/integration quality. 3 Natural phenomena comprise conditions imposed by the space environment. 4 Manmade threats are those activities created by another space operator with the sole purpose of preventing your operational success (i.e., threats with intent) and accidental manmade phenomena (e.g., software coding mistakes, operator command error, etc.). Identifying each of these at an early stage provides an opportunity to compare and contrast these aspects. This will be important later as techniques to enhance operational success are considered and prioritized. Each barrier to success has the following dimensions that can be characterized: - Effects: type, persistence, and rate; - Uncertainty: variability in space and time plus effects due to lack of awareness or limited understanding; and - Predictability: ability to project effects into the future. The last major component of the Prepare phase leverages this last barrier to characterization – predict (or forecast). Unfortunately, it is also the most difficult as many of the phenomena of note have little to no historical precedence or may involve very complex physical models. It is critical to not get overly fixated on 200-yr predictions when monthly and annual effects may be significant on space operations. This resonates with the call to solve the right problems in the right order at the right pace. As a matter of fact, the focus on the long-term cascading effect of debris may have caused many to ignore significant short-term space safety issues that may manifest in the next 1–10 years. This will be addressed at the end of this article in a SOA Action Plan Within the Prepare phase, it is also critical to understand that much of the uncertainty that exists in collision risk analysis and STM may be reduced by better observations and advanced modeling. However, there is some natural variability that may never be eliminated; some ambiguity will persist in almost every dimension of risk assessment related to space operations in areas such as spacecraft reliability, orbit fidelity, probability of collision (both deterministic and statistical), and anomaly/failure attribution. The second phase – Plan – focuses on dissuading, denying, and deterring potential threats (i.e., space environmental hazards, both natural and manmade). This is largely done in design and testing of space systems. Clearly, for threats without intent, deterrence and 102
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Fig. 2. Space Operations Assurance is basically risk management.
dissuasion are irrelevant. However, shielding from particulates or radiation hazards is one way to reduce risk in this phase. All threats cannot be avoided so there must be a plan to react in response to realized threats in the third phase – Act (During) – by interdicting, suppressing, or mitigating risks. Activities here normally include operational procedures, warning technologies, and automated decision support. Even after a hazard has been realized, there are still options – Act (After) – such as remediation, recovery, and reconstitution. Actions here could include activating on-orbit spares, using redundant terrestrial backups, launching new systems, active debris removal, and satellite servicing. It should be noted that for complex risk situations the sequence of countermeasures is often based on ease of implementation rather than a measured return on investment. This is human nature and logical to incorporate easy to implement approaches first. However, as time passes and the risk landscape evolves and is characterized more expensive and challenging risk management activities may be required. All phases of risk management need to be considered from the onset; starting with the bias that all risks must be eliminated will create unrealistic and, potentially, counterproductive behavior. A layered approach, where mechanisms are employed in each area, usually produce the most reliable and efficient final system/architecture performance. In addition, the dynamic of how quickly threats develop and countermeasures act (i.e., response physics) drive the monitoring and warning systems required.
subsystem failures, etc.; and - Retire, reorbit (from high Earth orbit), and deorbit (low Earth orbit, LEO): perform end-of-life operations. This list of activities provides both a source of where risks may arise and also where countermeasures may be employed. 5. Execution of the SOA framework via SOAC With a clear understanding now of what needs to be done, focusing more on exactly how SEM, SSA, and STM pillars will cooperate is essential. In this spirit, it is important to first focus on a balanced perspective between: - Simplicity vs flexibility: do not try to come up with an overly complex solution (whether design, regulatory, or operational) that will not be flexible enough to handle emerging issues over time; - Responsiveness vs accuracy: the constellation deployments may occur quickly or environmental hazards may grow quickly so it is important to create “nimble” policies and processes; - Efficiency vs completeness: risk management depends on realistic assessments of hazards presented to space operations but eliminating risk is not possible; - Current vs future concerns: it is important to not overly focus on long-term risk at the expense of immediate space safety; - One vs many (i.e., constellations): emphasis on the management of constellations may create onerous policies for individual satellites (i.e., create unintended negative consequences).
4. Activity-focused analysis construct Activity-focused analysis will be used to manage the risk from threats by examining the activities that space systems might perform. By focusing on activities that are indicators of the realization of a risk to space operations assurance, resources are applied optimally to manage the risk from these threats. This analysis will then, in turn, drive the level of entity resolution required. For SOA, a list of potential activities includes, but are not limited to, the following:
6. Possible initial SOAC discussions Immediate discussions catalyzed by the SOAC should focus on the following three questions for space-based parts of the constellations: 1 How reliable will your space systems be during deployment, operations, and retirement? Previous satellite and constellation deployments have shown that the time where most satellites are lost is in launch and the first 30 days on orbit. 2 Have you employed viable means to avoid collisional interactions between members of your constellation? The initial focus should be on the potential collision risk that is directly a result of the new deployments. 3 Have you considered and planned for potential interactions from objects and other debilitating phenomena outside of your control (e.g., debris, other constellation members, natural space environmental effects, severe space weather event, prolonged RFI activity, etc.)? History has shown that the suite of risks to satellites is evolving quickly and must be part of any long-term understanding of satellite/constellation operations assurance.
- Design: mission needs are translated into engineering plans; - Manufacture: assemble components and subsystems; - Test: verify proper functioning of components, subsystems, and system; - Mating: space system is integrated into the launch vehicle; - Deploy: space system is launched; - Activate: turn on and checkout systems; - Operate: individually (adjust orbit, change orientation, change size, change stability/tumbling, etc.) and as a constellation (maintain spacing, activate spare, etc.); - Service & repair: recover from system performance degradation; - Emit: emanate energy (e.g., radio frequency, infrared, optical, etc.) or effluents (e.g., outgassing volatiles, leaking propellants, etc.) - Rendezvous and proximity operations (RPO): operate near another space object; - Conjunction or close approach: cross nearby another space object; - Collide: strike another space object; - Create more objects: release objects from routine space operations,
An op-ed in Space News in January 2019 provided a composite assessment of the most appropriate activities by constellation developers with respect to orbital debris and sustainability of space operations. This public statement called for simple, but powerful, efforts: do not let constellations overlap, determine root cause when satellites fail, space operators should be able to control the paths of their satellites, 103
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disposal should be prompt & reliable after mission is completed (5 yr not 25 yr), and minimize risks to people on the ground from reentering spacecraft [13]. The design, architecture, and operations of the supporting ground infrastructure supporting space assets are just as important to the overall assurance of space operations. As a result, two questions might be considered as a starting point for the non-space-based parts of these constellations:
be cataloged (i.e., ∼10 cm in low Earth orbit and ∼1 m in geosynchronous orbit). This is considered a significant part of STM; tasks to improve this capability include data sharing, improving the positional uncertainty of cataloged objects, and the new S-band fence (which will increase the number of cataloged objects in LEO). As noted, improvement in space situational awareness (SSA), such as the new S-band fence, will in essence decrease the LNT risk as more of those previously nontrackable objects will be added to the catalog and, thus, potentially avoided. Debris Mitigation efforts, upper left quadrant of Fig. 3, includes both enhancing compliance to existing guidelines and examining strengthening mitigation thresholds (e.g., reduce the 25-yr rule to a 5-yr rule). It is interesting that tougher guidelines are being considered even as existing guidelines are not universally adhered to by spacefaring entities. Debris mitigation efforts serve to not only reduce debris that might have to be avoided but also prevents the deposition of new intact objects that might require eventual removal. It is the last quadrant, lower left box labeled Active Debris Removal (ADR), that has received the least attention. The removal of massive derelicts from Earth orbit, however, will prevent the most likely and most consequential debris-generating events. To more efficiently execute ADR activities (or other debris remediation options such as just-intime collision avoidance [8–10]) requires both better SSA capabilities and operationalizing ADR solutions. ADR operations will not only reduce the number of targets that have to be avoided by operational satellites but will prevent the highly consequential collisions that would occur if two massive payloads or rocket bodies were to collide. There is a cluster of 36 abandoned rocket bodies and payloads distributed in the 815–865 km altitude range that if any two would collide, the event would likely double the cataloged population and add over 200,000 LNT [14]. An examination of the activities in Fig. 3 can be used to summarize the priorities to assure space operations now and enhance the long-term sustainability of space (Fig. 4).
1 For the ground segment of your business, do you have redundant paths for the telemetry, health maintenance, and service (e.g., imagery, video, data, voice, etc.)? 2 Is there resiliency built into your architecture if the ground segment of your operations is taken off line for a period of time? For how long? Longer term objectives of SOAC would include, but not be limited to, the following (1) establish, communicate, and enforce standards and best practices between and for operators and operations; (2) facilitate communications between global spacefaring entities; (3) monitor progress in SOA; and (4) interface with and leverage industry, academic, and commercial entities. While the focus on constellations is warranted, there is a general baselining of risks for the continued assured operations of space systems in general at the current level of reliability that should also be addressed by the SOAC. Fig. 3 portrays four priorities to be addressed based on community discussions. The activity in the lower right quadrant – Characterize Lethal Nontrackable (LNT) Population – is the anchor for space operations assurance. The other three boxes describe three primary activities that are either actively being pursued or should be. The Collision Avoidance activity in the upper right quadrant comprises the efforts to warn operational satellites of potential collisions with objects large enough to
Fig. 3. Priorities for space operations assurance should be anchored in controlling the lethal nontrackable debris population through debris remediation (e.g., active debris removal, ADR) debris mitigation, and collision avoidance activities. 104
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security, and environmental performance of international shipping as a regulatory framework. The group covers ship design, construction, equipment, manning, operation, and disposal while the operators “selfregulate” by developing agreed-upon best practices for operations. The International Virtual Observatory Alliance (IVOA) http://www. ivoa.net/ is an organization that debates and agrees on technical standards that are needed to make the ubiquitous sharing of astronomical observations worldwide possible. It also acts as a framework for discussing and sharing ideas and technology. DIAS (Data Integration & Analysis System) provides infrastructure for sharing Earth observation data globally http://www.diasjp.net/en/. DIAS was started in 2006 to collect and store earth observation data; to analyze such data in combination with socio-economic data; convert data into information useful for crisis management with respect to global-scale environmental disasters and other threats; and to make this information available within Japan and overseas. Open Geospatial Consortium (OGC) http://www.opengeospatial. org/ is an International, not-for-profit organization committed to making quality open (freely available) standards for the global geospatial community made through a consensus process. It produces standards, best practices, discussion papers, engineering reports, etc. The OGC standards are used in a wide variety of domains including Environment, Defense, Health, Agriculture, Meteorology, Sustainable Development, and many more. Coordination Group for Meteorological Satellites (CGMS) https:// www.cgms-info.org/index_.php/cgms/index consists of 15 organizations and six observers. The proposed Terms of Reference (TOR) for space weather activities includes the reporting on spacecraft anomalies and sharing the results of anomaly resolution and analyses. The International Civil Aviation Organization (ICAO) https://www. icao.int/about-icao/Pages/default.aspx is a specialized agency of the United Nations, established in 1944 to manage the administration and governance of the Convention on International Civil Aviation. There are 192 members states and industry groups that cooperatively develop international civil aviation Standards and Recommended Practices (SARPs) and policies in support of a safe, efficient, secure, economically sustainable and environmentally responsible civil aviation sector. ICAO ensures that local civil aviation operations and regulations conform to global norms, which in turn permits more than 100,000 daily flights in aviation's global network to operate safely and reliably in every region of the world. Consortium For Execution of Rendezvous and Servicing Operations (CONFERS) https://www.darpa.mil/program/consortium-for-executionof-rendezvous-and-servicing-operations is an industry-government consortium to develop technical standards for safe on-orbit rendezvous and servicing operations. The benefits of CONFERS are enhanced on-orbit safety through established “rules of the road”, creation of behavioral norms for transparent international engagements, and streamlining of USG commercial mission authorization with a technical foundation.
Fig. 4. Debris mitigation and collision avoidance are necessary but not sufficient means to assure safe space operations; debris remediation will also have to be employed.
As noted, debris mitigation guidelines have been in force and maturing since ∼1995. Similarly, collision avoidance processes have been actively refined globally since ∼2010. However, there are still no operational capabilities for debris remediation despite the risk of massiveon-massive collisions in LEO. The activities proposed for an initial SOAC discussion have led to Fig. 4 above highlighting the following observations: - Collision avoidance is necessary but the capabilities of operational satellites and the increased collision avoidance support from both government and commercial SSA capabilities makes the probability of a collision between an operational satellite with a trackable object very unlikely. In addition, the consequence would only be moderate as most payloads in LEO are on the order of 100–600 kg. - Debris mitigation guidelines are necessary to limit the future growth of debris; this includes both (1) reducing LNT production from deployment & explosions and (2) removing intact objects within 25 years of end of operational life. The compliance rate for the 25-yr rule globally is between 20–80%, depending how it is calculated [15]. This means that the probability of non-compliance is fairly high but the consequence of such an adverse event is very low (i.e., basically leaving an intact object on orbit longer than 25 yr). - Debris remediation activities, as exemplified by active debris removal, is receiving the least attention currently. Unfortunately, the probability of a massive collision between two derelict objects is on the order of 1000 kg to 8000 kg is fairly high (i.e., ∼0.1%−1%/yr) and the consequences are significant (i.e., ∼4000–17,000 cataloged objects and ∼10,000–2000,000 LNT). As depicted in Fig. 4, debris remediation activities provide the greatest benefit (i.e., risk reduction), however, the cost and complexity (both technical and legal) of debris remediation solutions have impeded their development.
8. Summary - SOA big picture SOA is enabled by the collaborative, joint execution of SEM, SSA, and STM activities. The four major steps of this risk management process nominally have two phases: (1) early in Prepare and Plan steps risks are deterred while (2) later efforts will focus on responding to (i.e., mitigating) specific realized threats to reliable space operations (i.e., Act (During) and Act (After)). In applying a linear operational success framework there are two overarching, and inter-related, issues that are considered in turn: (1) interplay between warning systems & “response physics” and (2) success monitoring & risk/response interactions (as depicted in Fig. 5). Warning systems and “response physics” (i.e., rate at which barriers/enablers to success act and react relative to each other) tie together linear success tasks. Warning systems defined and established during the Prepare and Plan phases may improve the effectiveness of
7. How to start SOAC The SOAC could follow the organizational framework of one of several productive examples of public-private partnerships and industry organizations: The International Maritime Organization (IMO) http://www.imo. org/en/Pages/Default.aspx is a specialized agency of the United Nations (UN) serves as global standard-setting authority for the safety, 105
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Fig. 5. The overall SOA framework leverages many existing processes, personnel, and technologies.
responses to enhance operational success once the risk (e.g., potential direct collision, nearby debris-generating event between derelicts, severe space weather, etc.) has been manifested by providing information on the existence, evolution, and extent of the risk. The ability to leverage warning depends on “response physics”: how quickly do natural, mechanical, and manmade threats act relative to potential countermeasures (i.e., available means to deny, deter, suppress, and mitigate risks) and how quickly can realized risks be identified. Last, there is a need to continually monitor and predict operational success as a measure of effectiveness of the industry's attempt to assure space operational success. This is facilitated by an ongoing set of interactions which include communications (e.g., sharing information on precursors and indicators of threats becoming realized and messaging to stakeholders about countermeasures in place) and transfer of assets from one activity to the next (i.e., resources that transition from planning to interdiction or remediation). One successful manifestation of this activity is the sequence of spacecraft anomalies and failures workshops held globally over the last seven years [16]. The SOAC can be a major unifying mechanism for similar processes. A preliminary exercise of this SOA evaluation identified three activities (debris mitigation, collision avoidance, and debris remediation) as the main enablers to manage the LNT collision risk. This process highlighted that the most impactful response (i.e., debris remediation as exemplified by ADR) is the least mature countermeasure to limiting debris growth. It should be noted that this is not surprising as it is also clearly the most difficult technically and politically. It is hoped that this situation will change soon, possibly catalyzed by a SOAC-like entity, in order to assure safe space operations now and in the future.
References [1] Space Policy Directive-3, National Space Traffic Management Policy, issued by the U.S. Government in June 2018 provided a framework for space traffic management issues, https://www.whitehouse.gov/presidential-actions/space-policy-directive-3national-space-traffic-management-policy/. [2] D. McKnight, F. Di Pentino, S. Knowles, Massive collisions in LEO - a catalyst to initiate ADR, 65th International Astronautical Congress, Toronto, CA, September 2014. [3] D. McKnight, Insights gained from the massive collision monitoring activity, International Association for the Advancement of Space Safety, Toulouse, France, October 2017. [4] Mark Brown, Space traffic management and orbital debris: a path forward to ensure safe and uninterrupted space operations, Space Traffic Management Conference, 15 2018 https://commons.erau.edu/stm/2018/presentations/15. [5] V. Samson, B. Weeden, Possible SSA futures: a report of the 2017 AMOS dialogue, 4th Annual STM Conference, “Seeking Sustainable Solutions”, Daytona Beach, FL, ERAU, Jan. 16, 2018. [6] S. Hunter, J. Detroye, Two perspectives on civil space traffic management implementation, 4th Annual STM Conference, “Seeking Sustainable Solutions”, Daytona Beach, FL, ERAU, Jan. 16, 2018. [7] M. Dickinson, Preparing for Congested Space. An SDA Focus, (May 2017) spacedata.org/sda/. [8] C. Bonnal, D. McKnight, Just-in-time collision avoidance (JCA): a realistic solution for future sustainable space activities, 1st IAA Conference on Space Situational Awareness (ICSSA), Orlando, FL, USA, Nov 2017. [9] C. Phipps, C. Bonnal, Pulsed UV laser system design for re-entering or nudging debris in LEO and re-orbiting GEO debris, Presented at the “Laser Solutions to Orbital Debris” Workshop, Paris, Université Paris Diderot, 2015. [10] D. McKnight, F. Di Pentino, S. Douglass, Developing a tactical adjunct to ADR to insure a sustainable space environment, 65th International Astronautical Congress, Jerusalem, IS, October 2015. [11] In March 2015, the U.S. Secretary of the Air Force required that pre-Milestone B satellite programs had to incorporate energetic charged particle (ECP) sensor to help characterize the space environment, https://spacenews.com/air-force-seeksinfo-on-space-weather-sensor/.
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D. McKnight [12] D. McKnight, Debris remediation examined via an operational success framework, Stardust 2nd Global Virtual Workshop, Southampton, UK, January 2016; 8th IAASS Conference, Melbourne, FL, May 2016; and 4th International Workshop on Space Debris Modelling and Remediation, Paris, France, June 2016 Journal of Space Safety Engineering, Fall 2016. [13] https://spacenews.com/op-ed-responsible-satellite-operations-in-the-era-of-largeconstellations/. [14] D. McKnight, S. Speaks, J. Macdonald, Assessing potential for cross-contaminating breakup events from LEO to GEO, 68th International Astronautical Congress,
Bremen, Germany, October 2018. [15] C. Bonnal, Space debris mitigation & remediation: a general update, 8th JAXA Space Debris Workshop, Chofu, 3 Dec. 2018. [16] The Spacecraft Anomalies and Failures Workshop has been hosted in Chantilly, Virginia, US annually since 2011 and the International Association of the Advancement of Space Safety (IAASS) held the first international Spacecraft Environmental Anomalies and Failures Workshop in 2017 with the second one slated for 2019.
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