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Summary
Over the past 50 years, various NASA communities have contributed significantly to maturing NASA’s mete -
oroid and orbital debris (MMOD)1 programs to their current state. As a result of these community efforts, and to
NASA’s credit, NASA’s MMOD programs and models are now widely used and respected by the providers and
users of both government and commercial satellites, nationally as well as internationally. Satellites have been rede -
signed to protect critical components from MMOD damage by moving critical components from exterior surfaces
to deep inside a satellite’s structure. Orbits are monitored and altered to minimize the risk of collision with tracked
orbital debris. MMOD shielding added to the International Space Station (ISS) protects critical components and
astronauts from potentially catastrophic damage that might result from smaller, untracked debris and meteoroid
impacts. The space shuttle, as it orbited Earth, and whether docked to the ISS or not, was optimally oriented to
protect its fragile thermal protection and thermal radiation systems from MMOD damage. In addition, astronauts
inspected its thermal protection system for MMOD damage before the shuttle reentered Earth’s atmosphere; Orion,
NASA’s capsule to carry astronauts to low Earth orbit, includes designs to mitigate the threat of MMOD damage
and provide increased safety to the crew.
When a handful of reasonable assumptions are used in NASA’s MMOD models, scenarios are uncovered that
conclude that the current orbital debris environment has already reached a “tipping point.” That is, the amount of
debris—in terms of the population of large debris objects, as well as overall mass of debris in orbit—currently
in orbit has reached a threshold where it will continually collide with itself, further increasing the population of
orbital debris. This increase will lead to corresponding increases in spacecraft failures, which will only create more
feedback into the system, increasing the debris population growth rate. The increase thus far has been most rapid
in low Earth orbit (LEO), with geosynchronous Earth orbits (GEOs) potentially suffering the same fate, but over a
much longer time period. The exact timing and pace of this exponential growth are uncertain, but the serious impli -
cations of such a scenario require careful attention because of the strategic importance of U.S. space operations.
The Office of Science and Technology Policy and the Office of Management and Budget contracted with
the National Research Council for a study to perform three tasks: review NASA’s MMOD programs and efforts,
recommend in which of those NASA should increase or decrease its effort or change focus, and determine whether
1 This report uses the word “meteoroid” according to its precise definition, rather than the term “micrometeoroid,” a colloquialism for “small”
meteoroids and an imprecise term that does not cover the full range of sizes of meteoroids. However, to avoid adding a new acronym to the
literature and to minimize confusion, the committee retains use of the acronym “MMOD” (micrometeoroid and orbital debris) as a modifier
(e.g., MMOD programs).
1
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2 LIMITING FUTURE COLLISION RISK TO SPACECRAFT
NASA should pursue work in any new MMOD areas. The official letter requesting the study and the full state -
ment of task for the Committee for the Assessment of NASA’s Orbital Debris Programs are in Appendixes A and
B, respectively.
REVIEW NASA’S MMOD PROGRAMS AND EFFORTS
As indicated in findings presented throughout this report, the committee identified many positive aspects of
NASA’s MMOD programs and efforts. Of particular note are the following findings of the committee regarding
the resources and responsibilities of NASA’s MMOD programs:
Finding: NASA’s meteoroid and orbital debris programs have used their resources responsibly and have
played an increasingly essential role in protecting the safety of both crewed and uncrewed space opera-
tions.
Finding: The increasing responsibilities given to NASA’s meteoroid and orbital debris programs have
put pressure on the programs’ allotted resources. The increasing scope of work, and the complexity and
severity of the debris and meteoroid environment, are outpacing in real dollars the decreasing funding
levels of NASA’s MMOD programs.
RECOMMEND CHANGES IN EFFORT OR FOCUS
In its examination of NASA’s varied MMOD programs and efforts, the committee found numerous areas in
which NASA should consider doing more or different work. Tackling these research areas is likely to enhance the
benefits delivered by NASA’s MMOD efforts, many of which are listed in Box S.1. Examination of the research
needs and management issues listed in Box S.1, along with consideration of the committee’s other findings and
recommendations, leads to a critical question: How is NASA to prioritize and choose among these numerous
research and management areas, given its limited MMOD resources? To address this question, the committee
offers the following key, overarching recommendation:
Recommendation: NASA should develop a formal strategic plan that provides the basis for prioritizing
the allocation of funds and effort over various MMOD program needs. Among the potential research
needs and management issues to be considered is the selection listed in Box S.1. The strategic plan
should consider short- and long-term objectives, a schedule of benchmark achievements to be accom-
plished, and priorities among them. Stakeholders should be engaged to help develop and review this
plan. Finally, the MMOD strategic plan should be revised and updated at regular intervals.
Chapter 12 of this report offers the committee’s view of what the strategic plan should address. Simply put,
the plan must answer four basic questions regarding MMOD: Where are we? Where do we want to go? How are
we to get there? and, How do we measure how we are doing?
The committee did not believe that it should prioritize the various areas in which NASA could expand its
work; doing so could preempt NASA’s following the above recommendation. Given that the committee was told
to assume a constrained budget environment, it felt that NASA management would be better suited to prioritize
the agency’s efforts, in consultation with the broader MMOD scientific community and in response to the com -
mittee’s various findings and recommendations.
NEW MMOD AREAS FOR NASA TO PURSUE
The study of satellite anomalies, mission-degrading or mission-terminating events affecting on-orbit opera -
tional spacecraft, could provide a meaningful data set that would contribute to an increased understanding of the
hazards to spacecraft posed by MMOD relative to other hazards. Such a data set would have to be of sufficient
fidelity to enable identification of a probable cause of the anomaly. The data set would be strengthened by an
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3
SUMMARY
BOX S.1
Research Needs and Management Issues to Be
Considered in the Formulation of an MMOD Strategic Plan
Throughout this report, the committee identifies various areas of potential research and a number of
management actions that would strengthen NASA’s meteoroid and orbital debris (MMOD) programs. Adop-
tion of a strategic plan of the sort envisioned by the committee would require evaluation and prioritization
of these areas and activities, which include the following:
1. Perform radar cross-section calibrations using fragments from a large range of materials used in
modern satellites and rocket bodies, as well as non-fragmentation debris. (Chapter 2)
2. Expand the environment measurement program to include use of in situ sensors to monitor the
flux of debris smaller than a few millimeters. (Chapter 2)
3. Expand efforts to more accurately model sources of debris. (Chapter 3)
4. Develop criteria or a schedule for the regular release of updates to NASA’s orbital debris- and
meteoroid-related models. (Chapter 3)
5. Establish a base effort to evaluate major environmental uncertainties in three areas: (a) meteor-
oid velocity distributions, (b) flux of meteoroids of larger sizes (greater than 100 microns), and (c) impact
plasma effects. (Chapter 4)
6. Adopt a single model of the meteoroid environment for official use. (Chapter 4)
7. Pursue improving the understanding of the hazards posed by interplanetary meteoroids. (Chapter 4)
8. Expand research on meteoroids to include an understanding of the possible link between space-
craft electrical anomalies and major meteor showers. (Chapter 4)
9. Perform a broad integrative analysis of the various risks posed by meteoroids and orbital debris
(whether probabilistic risk analysis or some alternative). (Chapter 5)
10. Identify major areas of uncertainty in current environmental models and risk assessments, and
develop test plans and analyses to reduce that uncertainty. (Chapter 5)
11. Undertake an effort to refine models for predicting impact damage using a statistics-based ap-
proach. (Chapter 6)
12. Undertake an effort to re-derive the ballistic limit equations in the BUMPER code using a statistics-
based approach that would provide information regarding uncertainty bounds and/or confidence intervals.
(Chapter 6)
13. Increase efforts to characterize the damage resulting from impacts of orbital debris of various
particle shapes and densities. (Chapter 6)
14. Expand program plans to include the technology, political, and legal considerations necessary to
increase international cooperation on mitigation and remediation measures to stabilize the orbital debris
environment. (Chapter 7)
15. In regard to reentry risks, re-examine how thresholds for ground injury effects are estimated and
provide confidence bounds and uncertainty assessments. (Chapter 8)
16. Develop a research plan for (a) assessing the impact of the inaccuracy in the uncertainty in com-
puting the probability of collision and in the ensuing risk assessment and (b) improving the accuracy of the
computation of the probability of collision in the presence of these uncertainty errors. (Chapter 9)
17. Initiate an effort to record, analyze, report, and share data on satellite anomalies in order to bet-
ter quantify the risk from orbital debris particulates too small to be cataloged yet large enough to disrupt
space operations. (Chapter 10)
18. Continue to engage the private sector, U.S. federal agencies, and international agencies in de-
veloping cooperation and political will to effectively address issues regarding orbital debris. (Chapter 11)
19. Identify budget requirements and areas of responsibilities, including personnel and a single point
of contact, for maintaining a viable program as budgets and personnel change. (Chapter 12)
20. Schedule periodic technical assessments written for policy makers and stakeholders. (Chapter 12)
21. Continue to emphasize the long-term objectives of the MMOD programs through public discussions
and improved long-term models. (Chapter 13)
22. Monitor and inventory the costs of debris avoidance, mitigation, surveillance, and reporting over
time. (Chapter 13)
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4 LIMITING FUTURE COLLISION RISK TO SPACECRAFT
increased in situ MMOD environment measurements program, similar to that conducted to measure the meteoroid
environment prior to the Apollo program.
Recommendation: NASA should initiate a new effort to record, analyze, report, and share data on space-
craft anomalies in order to better quantify the risk from particulates too small to be cataloged yet large
enough to disrupt spacecraft operations. The results of this effort would provide general insights into
the effects of meteoroids and orbital debris on operational space systems. Eventually, this effort could
provide data to upgrade current MMOD models—the Meteoroid Environment Model, Orbital Debris
Environment Model, and BUMPER.
The committee also recommends expansion of existing efforts in a number of areas to more adequately mea -
sure and model the MMOD environment and effectively minimize the risk to spacecraft and astronauts—both by
designing spacecraft to survive the MMOD environment, and by implementing policies to limit or reverse growth
in the population of orbital debris. The recommendations include both technical and policy issues. Most of the
technical issues can be addressed with existing technology. Although the committee found no lack of technical
capability within NASA’s MMOD community, most of that capability is only “one deep” and could quickly disap -
pear as the MMOD programs age.
Finding: Nearly all of NASA’s MMOD programs are only one person deep in staffing. This shortage of
staffing makes the programs highly vulnerable to budget reductions or changes in personnel. Further
reductions in real budgetary support over the coming years could threaten the viability and scope of
ongoing MMOD programs.
New resources will be required if NASA is to pursue the 2010 National Space Policy goals of “research and
development of technologies and techniques . . . to mitigate and remove on-orbit debris.” 2 Political and legal issues
will also have to be addressed. If the technologies to remove on-orbit debris are developed and implemented, the
management requirements on NASA as an agency may become as significant as those associated with any major
NASA program.
If the United States is to pursue debris removal operations, then extensive international cooperation will be
required, particularly because current international legal principles restrict nations to retrieving or otherwise sal -
vaging only their own objects, and around 30 percent of the objects are attributable to the United States.
Finding: Debris removal activity that involves selecting and removing any given object—debris or other-
wise—from space, crosses crucial national and international legal thresholds.
Recommendation: NASA’s meteoroid and orbital debris programs should engage the NASA General
Counsel’s Office and, through that office, the U.S. State Department regarding the legal requirements
and diplomatic aspects of active debris removal.
It is likely that changes in NASA’s current management structure will be necessary to address MMOD funding
and policy issues if the MMOD programs are to continue to be a national resource and maintain their international
leadership. Such changes will contribute to preserving the existing capabilities of the MMOD programs, and also
will allow them to expand in a more cost-effective approach to minimizing future risk.
National Space Policy of the United States of America, June 28, 2010, p. 7, available at http://www.whitehouse.gov/sites/default/files/
2
national_space_policy_6-28-10.pdf, accessed July 6, 2011.
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SUMMARY
Finding: NASA’s management structure has not kept pace with the expanding responsibilities of its
MMOD programs. Consequently, the MMOD programs do not have a single management and bud-
get point that can efficiently coordinate all of the current and planned activities and establish clear
priorities.
Recommendation: NASA should review the current management structure of its MMOD programs in
order to achieve better coordination, provide improved central decision making, and establish a frame-
work for setting priorities. This framework should include a major interface with Congress, other fed-
eral and state agencies, and the public.
LOOKING TO THE FUTURE
The danger posed by meteoroids and orbital debris is fundamentally a long-term environmental issue and
should be addressed as such. Mitigation alone has proven to be insufficient, with the current environment in LEO
representing an increasing hazard to spacecraft and astronauts there. Although current mitigation practices in other
regions of Earth orbit may limit the MMOD hazard in the short term, a time will eventually come when those
regions will likely become more hazardous as LEO has. Consequently, the sooner NASA acts to ensure effec -
tive long-term mitigation at all altitudes, the less drastic or expensive future actions may be. Such planning will
require an integrated effort involving all levels of management and policy makers, as well as adequate support at
the technical levels.
Recommendation: NASA should lead public discussion of the space debris problem to emphasize debris as
a long-term concern for society that must continue to be addressed today. Necessary steps include improve-
ments in long-term modeling, better measurements, more regular updates of the debris environmental
models, and other actions to better characterize the long-term evolution of the debris environment.
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