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Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
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OCR for page 1
Summary
In February 2009 the commercial communications satellite Iridium 33 collided with the Russian military com -
munications 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 colli -
sion 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 dif -
ferent 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 exami -
nation 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 draw -
backs, to the current AFSPC astrodynamics standard, as well as assess the potential impacts of employing such an
1
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2 CONTINUING KEPLER’S QUEST—ASSESSING AIR FORCE SPACE COMMAND’S ASTRODYNAMICS STANDARDS
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 fol -
lowing:
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 commu -
nicating 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 sig -
nificant 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
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3
SUMMARY
accurate probability of collision. For near-Earth orbiting satellites another limitation is understanding and model -
ing 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 com -
munity 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 prod -
ucts. 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 intro -
duction 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 partici-
pate 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 commu -
nity 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 pro -
gram that will enhance U.S. astrodynamics capabilities. Thus the committee offers the following recommendation:
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4 CONTINUING KEPLER’S QUEST—ASSESSING AIR FORCE SPACE COMMAND’S ASTRODYNAMICS STANDARDS
Recommendation: Air Force Space Command should work with Air Force Materiel Command, the
National Aeronautics and Space Administration, the National Oceanic and Atmospheric Admin -
istration, and other community members to create and expand research programs in the astro-
dynamics 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 follow -
ing 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.
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5
SUMMARY
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 docu -
mentation 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 Inter-
national 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 commit -
tee 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 recom -
mends 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 Simpli -
fied 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 expan -
sion 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 mini -
mize 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.
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6 CONTINUING KEPLER’S QUEST—ASSESSING AIR FORCE SPACE COMMAND’S ASTRODYNAMICS STANDARDS
Finally, the committee concluded that Air Force Space Command and the JSpOC could benefit from a stra -
tegic 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 com -
munity—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.
