In February 2009 the commercial communications satellite Iridium 33 collided with the Russian military communications satellite Cosmos 2251. The collision, which was not the first recorded between two satellites in orbit, but the most recent and alarming, produced thousands of pieces of debris, only a small percentage of which could be tracked by sensors located around the world. In early 2007, China tested a kinetic anti-satellite weapon against one of its own satellites, which also generated substantial amounts of space debris. These collisions highlighted the importance of maintaining accurate knowledge, and the associated uncertainty, of the orbit of each object in space. These data are needed to predict close approaches of space objects and to compute the probability of collision so that owners/operators can decide whether or not to make a collision avoidance maneuver by a spacecraft with such capability. The space object catalog currently contains more than 20,000 objects, and when the planned space fence radar becomes operational this number is expected to exceed 100,000. A key task is to determine if objects might come close to each other, an event known as “conjunction,” and the probability that they might collide.
The U.S. Air Force is the primary U.S. government organization tasked with maintaining the space object catalog and data on all space objects. This is a complicated task, involving collecting data from a multitude of different sensors—many of which were not specifically designed to track orbiting objects—and fusing the tracking data along with other data, such as data from atmospheric models, to provide predictions of where objects will be in the future.
In 2011 Air Force Space Command (AFSPC) asked the National Research Council to:
Assess the astrodynamics standards established by Air Force Space Command (AFSPC) and their effectiveness in meeting mission performance needs, as well as possible alternatives.
Specifically, as part of the assessment, the committee will:
1. Assess the current AFSPC astrodynamics standard orbit determination and prediction models for accuracy, interoperability, and ability to meet JSpOC and user mission requirements. The assessment should include an examination of any unique or undocumented needs (such as sharing the standards with industry, mission partners, allies, etc.).
2. Compare and contrast leading industry, academic, and government alternatives, including benefits and drawbacks, to the current AFSPC astrodynamics standard, as well as assess the potential impacts of employing such an
alternative on existing data acquisition programs (for example, JSpOC Mission System, Space Surveillance Network (SSN) sensors, other users, etc.).
3. Outline options for a strategy of how AFSPC should proceed with using these alternate standards to meet JSpOC and user requirements. The committee’s examination and description of the options should include the following:
a. Near and far term options,
b. A description of each option’s pros and cons,
c. Avenues towards meeting the unique needs identified,
d. If warranted, transition approaches or potential difficulties with transitioning should also be described.
4. Examine broader issues concerning overall cost and risk of the options. In its report, the committee should consider detailing these issues for several of the larger users of the standards (such as SSN sensors).
5. Prepare a report with recommendations regarding the optimal strategy to utilize the assessed options.
In response, the Committee for the Assessment of the U.S. Air Force’s Astrodynamic Standards collected data and heard from numerous people involved in developing and maintaining the current astrodynamics standards for AFSPC, as well as representatives of the user community such as NASA and commercial satellite owners and operators. As the Cosmos/Iridium incident demonstrates, collisions between objects not owned or operated by the U.S. government can have a profound impact on all of the organizations and countries that operate satellites, including impacts on vital U.S. national security assets. Preventing collisions of space objects, regardless of their ownership, is in the national security interests of the United States.
During the course of its deliberations, the committee was encouraged by the study sponsor to look beyond the narrow issue of the currently used algorithms and consider the broader policy issues associated with their development and evolution. Although the committee was tasked with comparing the existing algorithms with other potentially available algorithms, it was unable to do so because the other algorithms are proprietary and will likely be part of future contract competitions as the Air Force modernizes its systems. Accordingly, and because this study’s sponsor encouraged the committee to consider broader issues, the committee sought to address the overall management environment, of which the algorithms are but one aspect.
The use of the term “standard” in the larger term “AFSPC astrodynamics standard” is different from what one might expect. In the usual sense, “standards” are widely accepted specifications to be used for a specific purpose (e.g., IEEE standards for electrical outlets). Standards are normally expressed only in technical documents. AFSPC astrodynamics standards, however, are physical models and astrodynamics algorithms expressed as computer code. Perhaps a more descriptive name would be “standardized astrodynamics algorithms”—the term that is used throughout the rest of this report to describe AFSPC astrodynamics standards.
The committee concluded that AFSPC’s current system for maintaining and developing the standardized astrodynamics algorithms has done an adequate job, but community needs and changes in national space policy are leading to increased demands. The number of objects in space and the number of operators are increasing and so too is the challenge of maintaining accurate ephemerides of these objects, as well as the difficulty of communicating information about the objects.
Accurate ephemerides on all trackable space objects are maintained at the U.S. Strategic Command (USSTRATCOM) Joint Space Operations Center (JSpOC), which it is AFSPC’s responsibility to organize, train personnel for, and equip with computer and communications systems as the major command (MAJCOM) for space. The JSpOC Mission System (JMS) is the Air Force’s current program to modernize the infrastructure used in the JSpOC for maintaining a catalog of objects in space, tasking sensors, assisting decision makers, and informing satellite owners and operators. JMS is being implemented in a series of steps or phases, with the initial phase emphasizing the use of commercially available software mixed with a judicious use of legacy software as needed.
The committee believes that the primary limitation in the current system for objects not experiencing significant drag is not the accuracy of the algorithms, but rather the quantity and the quality of the sensor tracking data. The key system limitations are current sensor coverage, understanding of the quality of the observations, and the challenge of fusing disparate data from different systems and phenomenology. Understanding the quality or statistics of the observations is necessary for obtaining a realistic covariance, which is needed for computing an
accurate probability of collision. For near-Earth orbiting satellites another limitation is understanding and modeling of the atmosphere.
In the JSpOC Mission System, or any other new systems the Air Force may develop, close attention will have to be paid to the architecture—both hardware and software—to handle current needs and unknown future needs, and innovation will have to be encouraged. For the system to be effective it will have to emphasize interoperability—for legacy users, and for more demanding users. However, true interoperability will require the development of international standardized astrodynamics algorithms, because the Air Force will have to interact and communicate with non-U.S. satellite owners and operators to a greater degree than it currently does.
Automation is key to addressing the growing and diverse demands of the user community as well as the limitations of Air Force military and civilian staffing. The architecture of the new system will have to consider the evolving opportunities for automation. All of these issues are addressed throughout this report. But if there is a single message of this study, it is that the Air Force needs to encourage a change in culture to emphasize openness—in the transparency of its algorithms, in the interaction of its people with the user community and the scientific community, and in its providing of a reasonable amount of sensor tracking data to the scientific community for testing algorithms.
Recommendation: While recognizing security issues, Air Force Space Command (AFSPC) should become more open and transparent in the creation and dissemination of its algorithms and products. Specifically:
• The newly created AFSPC Astrodynamics Advisory Committee should be modified to include a balance of internal (e.g., Air Force Research Laboratory, Defense Advanced Research Projects Agency, Missile Defense Agency, etc.) and external subject-matter experts to encourage the introduction of new approaches and new ideas. Examples of external members include representatives from other federal agencies (e.g., the National Aeronautics and Space Administration, the National Oceanic and Atmospheric Administration, the National Reconnaissance Office, etc.), research centers (such as federally funded research and development centers), commercial industry, and academia.
• AFSPC should create a process and an infrastructure to identify and incorporate improvements into the Joint Space Operations Center (JSpOC) and a way to evaluate candidate improvements (e.g., testbeds, benchmarks).
• AFSPC should expand opportunities for astrodynamics and computation specialists to participate in improving the algorithms used in the JSpOC Mission System. This expanded participation should be achieved by advocating for research initiatives and engaging members of the research community to serve as peer reviewers, and by appropriate sharing of data.
• The JSpOC should provide a database containing a reasonable amount of sensor tracking data that would be available to the research community for the development and validation of new algorithms that support space situational awareness.
The modelers and algorithm developers who support the JSpOC mission have developed an internal community that lacks sufficient two-way interaction with the larger research and user community. Their limited contact with the broader astrodynamics research community has resulted in a lack of knowledge of new algorithms whose implementation could potentially provide significant improvement to the current system.
Whereas in the 1980s and 1990s relatively little astrodynamics research was performed, the past 10-15 years have seen developments in nonlinear estimation methods, numerical integration techniques, dynamical systems theory, force modeling, etc., all of which could have a positive impact on astrodynamics and space situational awareness. The Air Force needs to take advantage of such research and continue to have a vibrant research program that will enhance U.S. astrodynamics capabilities. Thus the committee offers the following recommendation:
Recommendation: Air Force Space Command should work with Air Force Materiel Command, the National Aeronautics and Space Administration, the National Oceanic and Atmospheric Administration, and other community members to create and expand research programs in the astrodynamics research and development community through the Air Force Research Laboratory to:
• Measure, model, and forecast conditions in the upper atmosphere;
• Develop and implement improved nongravitational models for solar radiation pressure and atmospheric drag;
• Develop and implement continued improvements to gravitational modeling;
• Investigate new data association methods, especially for breakups in low Earth orbit and geostationary Earth orbit clusters;
• Develop a program to better characterize sensor-level errors including biases to improve the input to orbit determination;
• Improve nonlinear estimation and the representation of uncertainty to ensure realism in estimations of uncertainty (covariance);
• Investigate modern methods of dynamical systems to develop new ways to analyze and handle astrodynamics challenges;
• Continue to develop and improve classical analytical techniques for the efficient description and prediction of satellite motion; and
• Explore new techniques to meet community needs.
The committee determined that the Air Force recognizes its commitment to supporting legacy customers by maintaining current systems’ compatibility as new systems are developed. At the same time, the requirements for increased accuracy that space situational awareness and conjunction assessment demand would benefit from the inclusion of new types of data. In particular, the consideration of orbital object metadata, new sensor data types, and owner/operator ephemerides in the JSpOC’s analyses offer the promise of higher levels of accuracy and insight.
Recommendation: The Air Force should continue with the design and development of the service-oriented architecture-based Joint Space Operations Center Mission System and employ modern, modular, and extensible hardware and software architecture design practices to ensure the following capabilities:
• Insertion of new technologies, capabilities, and algorithm modifications while preserving interoperability with the external community;
• Hardware and software scalability including explicit adaptation to parallel computing;
• Rigorous configuration management practices to ensure backward compatibility, change control, and full documentation; and
• Accommodation and exploitation of nontraditional data types, including object metadata, new sensor data types, and owner/operator ephemerides and operations information.
Because of the strong interdependency between astrodynamics modeling and the accuracy of propagated products, the current systems run by the Air Force and those run by external entities that use JSpOC products are typically coupled. Thus, it is necessary to coordinate any significant changes among all parties.
As previously noted, communication with other satellite owners and operators is very important. Distributing different data products (e.g., ephemerides rather than epoch state vectors or two-line elements) may be more useful and serve to further decouple Air Force systems from those of external customers. At the same time, tracking data, ephemerides, and maneuver planning information supplied by owners/operators are potentially very useful to the JSpOC for conjunction assessment, maneuver detection, and other purposes. However, incorporation of disparate data types and validation of information received from external sources are currently manually intensive.
Recommendation: The Air Force should create an open-architecture, application programming interface to facilitate the bidirectional exchange of a wider array of data, algorithms, and documentation with a growing number of external entities.
The Air Force is moving in the direction of more openness and data sharing, although some users still desire access to more information. Once they have been restricted from distribution, either by classification or International Traffic in Arms Regulations (ITAR), data and algorithms are often difficult to disseminate to the wider community, even after the restriction may no longer be relevant (e.g., the 40+ year old SGP4 model). The committee found no legitimate justification for continued restriction of such algorithms. These restrictions are inhibiting algorithm development and innovation with no apparent benefit to national security.
Recommendation: The Air Force should review its information distribution policies and work with external customers toward the objectives of (1) more freely sharing data products, algorithms, and documentation and (2) ensuring that such information is timely, accurate, useful, and actionable. Items historically restricted because of International Traffic in Arms Regulations, classification, or other national security or liability concerns should be reevaluated. Although the committee recommends a system-wide review, it also recommends consideration of the following specific examples:
• Examination of whether there is a valid justification for restricting the distribution of Simplified General Perturbations 4.
• Distribution of propagated ephemerides, which would provide users with greater insight into pending conjunctions and facilitate the further decoupling of Air Force systems from those of its external customers.
• Publication of collision probability, which would benefit some members of the owner/operator conjunction assessment community.
The Air Force is correctly anticipating a continuation of the increase in its workload. The evolution and expansion of its mission responsibilities and the growth of the orbital population are likely both to continue and to lead to increased demands on AFSPC. Meanwhile, the existing system is manually intensive. The current software architecture, obsolete hardware platforms, and security-driven network isolation (e.g., the Sneaker Net, called that because it requires someone to physically carry the data) are all contributing factors.
Recommendation: The Air Force should automate routine processes to the extent possible to minimize manual intervention, decrease operational workload, and reduce possibilities for error.
Air Force staffing and training shortfalls could threaten the viability and scope of ongoing programs. The JSpOC is understaffed for operating the existing system and has difficulty retaining the necessary expertise to fulfill its mission. Training materials are insufficient, the training process is long, and frequent military reassignments make long-term retention of expertise difficult.
Recommendation: The Air Force should review personnel recruiting, retention, promotion, and training policies and practices so that Department of Defense military, civilian, and contractor staffing levels and expertise are budgeted for and maintained in space situational awareness mission-critical functions including the Joint Space Operations Center.
Recommendation: The Joint Space Operations Center algorithm and model developers should fully communicate the results of their work and their development activities, such as in appropriate peer-reviewed publications and conferences, so that users gain greater insight into and understanding of the underlying assumptions associated with catalog activities.
Finally, the committee concluded that Air Force Space Command and the JSpOC could benefit from a strategic analysis of space situational awareness-related activities, including algorithm and model development and upgrades as well as operations and personnel management. Without such an analysis Air Force Space Command and the JSpOC could end up making budget decisions and model development priorities in an uncoordinated way, rather than according to a coherent, well-thought-out strategy.
Recommendation: The Air Force Space Command should conduct a strategic analysis of its space situational awareness-related activities, particularly as they pertain to the directives of the 2010 National Space Policy.
Recommendation: The Air Force Space Command should further develop the vision for the future of the Joint Space Operations Center Mission System and the system of systems based on the 2010 National Space Policy.
As the space age has matured, our dependence on space systems has increased—for national security, and for civil and commercial uses. Now, more than 50 years into the space age, the most useful orbits are becoming more crowded with active satellites, defunct satellites, and, unfortunately, with debris. Air Force Space Command, USSTRATCOM’s Joint Space Operations Center, and their predecessor organizations have ably served the nation and the international community, but the needs of their wide spectrum of users are increasing even as the space environment is becoming more cluttered. To address these evolving needs, it is essential that AFSPC improve the JSpOC infrastructure, modernize the software, architect the system to incorporate new algorithms and sensor data more easily, and adapt its products to meet the more demanding needs of some customers. Increasing the openness and transparency of its algorithms, research, and processes could have great value for the broader community—and increase user-driven innovation. The Air Force needs to position the JSpOC—and its overall space situational awareness system—to rapidly evaluate, adapt, and adopt evolving technologies to meet community needs more proactively.