NASA’s orbital debris program officially began in 1979. Lacking an official program designation at the time, it was initiated in the Space Sciences Branch at Johnson Space Center (JSC) as a result of research that concluded that impacts from Earth orbital debris had the potential to become a greater hazard to spacecraft than the natural meteoroid environment. At that time, there were no measurements of the debris environment for objects smaller than about 10 cm—the smallest size of an object in the catalog maintained by the North American Aerospace Defense Command (NORAD).1 However, there was much more than sufficient mass in orbit to produce a significant debris population in the less-than-10-cm-size range. The inevitable mechanism for creating such small debris was collisions between the more massive, cataloged objects. In 1978, this mechanism was predicted to become important around the year 2000, depending on the growth in the cataloged debris population. However, other mechanisms (such as explosions in orbit) were also capable of producing a significant uncataloged population of debris, and could have already done so.2
The NASA orbital debris program began at JSC with a very small budget of $70,0003 provided by the NASA Headquarters Advanced Program Office with the initial goals of characterizing the hazard to spacecraft and recommending mitigation standards that would minimize the growth of the orbital debris environment.4 During the program’s first few years it quickly established—by examining returned spacecraft surfaces and using ground telescopes—that the hazard from debris smaller than about 1 cm had already exceeded the meteoroid hazard in some altitudes below 2,000 km. The funding for the program grew as it added the goal of providing support to other NASA programs as well as to other agencies, both national and international, and as it established a debris measurements program using shorter-wavelength radars. Hypervelocity gun facilities were reconstructed, after having been dismantled more than a decade earlier, for the purpose of developing new shielding concepts for the space station. By 1990, the program had established a debris monitoring program, which included sampling the low Earth orbit (LEO) environment for debris of sizes as small as 6 mm using the Haystack X-band ground
1 The North American Aerospace Defense Command (NORAD) no longer maintains the official catalog of meteoroids; it is currently the responsibility of the U.S. Strategic Command.
2 D.J. Kessler and B.G. Cour-Palais, Collision frequency of artificial satellites: The creation of a debris belt, Journal of Geophysical Research 83(A6):2637-2646, 1978.
3 All dollar figures in this report are for then-year dollars.
4 D.S.F. Portree and J.P. Loftus, Orbital Debris: A Chronology, NASA/TP-1999-208856, NASA, Washington, D.C., January 1999.
radar. The examination of all spacecraft surfaces returned from space, including all space shuttles, resulted in the identification of impacts on these surfaces from both meteoroids and orbital debris.5 NASA and the Department of Defense (DOD) established a working group, sharing resources and information,6 and beginning in 1992, NASA worked with DOD to use a series of hypervelocity tests conducted by DOD to characterize the fragments produced from collisions in orbit.7 DOD’s meteoroid and orbital debris (MMOD) efforts and the responsible parties are described in Box 1.1.
In its early stages the NASA program developed education programs and organized workshops in order to share information from other groups. When it became evident that upper-stage rocket explosions were a major debris producer, bilateral meetings began between NASA and the European Space Agency (ESA) in 1987. By 1991, NASA had also met with space agencies in the USSR, Japan, and China, where each major space agency quickly and informally agreed to the concept of operational procedures for minimizing the possibility of future explosions in orbit.8 These multilateral meetings led to the formal establishment of the Inter-Agency Space Debris Coordination Committee (IADC), under which each major space agency reaffirmed its agreement to these operational procedural concepts that minimize the possibility of future explosions in orbit. NASA also participated in national and international scientific conferences such as those sponsored by the Committee on Space Research (COSPAR), the International Astronautical Federation (IAF), the American Institute of Aeronautics and Astronautics (AIAA), and the American Astronautical Society (AAS), which led to sessions at those conferences devoted totally to orbital debris studies.
The orbital debris program became a major contributor to the design of a safer International Space Station (ISS)9 and supported the space shuttle10 program to bring it up to the safety standards of the ISS. NASA also supported DOD operations so that certain tests could be safely conducted in space. By 1995, the NASA program had established a comprehensive set of mitigation guidelines. Although these guidelines applied only to NASA programs, they were shared with other national and international agencies for their consideration.
Since the mid-1990s, those mitigation guidelines have been accepted not only by NASA, but also by other U.S. and international agencies.11 Membership in the IADC increased and has contributed to a major exchange of data when the IADC meets annually. Other countries now have their own environment models, observation programs, and hypervelocity testing programs. At the recommendation of the IADC, the United Nations has now adopted the intent of the NASA guidelines.12
Beginning in the late 1990s, the orbital debris program began to expand into several programs that are today collectively referred to as “NASA’s MMOD programs.” The activities of environment definition and debris mitigation became the Orbital Debris Program Office (ODPO) at JSC. Spacecraft shielding and the examination of returned spacecraft surfaces are organized under what is known as the Hypervelocity Impact Technology Facility (HITF; at JSC). The Meteoroid Environment Office (MEO) was formed at Marshall Space Flight Center (MSFC) in 2004 (see the section “Meteoroids” below). Early work to come up with a probabilistic approach to active avoidance of collision with cataloged debris grew into operational activities for the ISS; that approach has grown into
5 National Research Council, Orbital Debris: A Technical Assessment, National Academy Press, Washington, D.C., 1995.
6 National Science and Technology Council Committee on Transportation Research and Development, Interagency Report on Orbital Debris, Office of Science and Technology Policy, Washington, D.C., November 1995, available at http://orbitaldebris.jsc.nasa.gov/library/IAR_95_Document.pdf, accessed July 6, 2011.
7 D.M. Hogg, T.M Cunningham, and W.M. Isbell, Final Report on the SOCIT Series of Hypervelocity Impact Tests, Report No. WL-TR-93-7025, Wright Laboratory, Armament Directorate, Wright-Patterson Air Force Base, Ohio, July 1993.
8 Inter-Agency Space Debris Coordination Committee, Terms of Reference for the Inter-Agency Space Debris Coordination Committee (IADC), IADC-93-01, October 4, 2006, available at http://www.iadc-online.org/index.cgi?item=torp_pdf, accessed July 6, 2011.
9 National Research Council, Protecting the Space Station from Meteoroids and Orbital Debris, The National Academies Press, Washington, D.C., 1997, available at http://www.nap.edu/catalog.php?record_id=5532.
10 National Research Council, Protecting the Space Station from Meteoroids and Orbital Debris, 1997.
11 Inter-Agency Space Debris Coordination Committee, Space Debris Mitigation Guidelines, IADC-02-01, revision 1, September 2007, available at http://www.iadc-online.org/index.cgi?item=docs_pub.
12 United Nations Office for Outer Space Affairs, Space Debris Mitigation Guidelines of the Committee on the Peaceful Uses of Outer Space, United Nations, New York, N.Y., 2010, available at http://orbitaldebris.jsc.nasa.gov/library/Space%20Debris%20Mitigation%20Guidelines_COPUOS.pdf.
U.S. Government Entities Responsible for Orbital Debris
The Committee for the Assessment of NASA’s Orbital Debris Programs was tasked with evaluating NASA’s meteoroid and orbital debris (MMOD)-related efforts but acknowledges that NASA is not the sole organization involved in addressing the problem of orbital debris and meteoroids. The other primary U.S. government actors working on MMOD issues include numerous Department of Defense (DOD) groups, primarily within the U.S. Strategic Command (USSTRATCOM) and the Air Force Space Command (AFSPC):
• USSTRATCOM: Headquartered at Offutt Air Force Base near Omaha, Nebraska, and one of ten unified commands in the DOD, USSTRATCOM is responsible for the nation’s nuclear command, space operations, global strike, DOD information operations, and global missile defense, among other duties.1
o The Joint Space Operations Center (JSpOC): Within USSTRATCOM, JSpOC is in charge of detecting, tracking, and identifying man-made objects in Earth orbit.2 When an object can be identified with a particular launch but is not a classified military satellite, it appears in the U.S. Space Surveillance Network’s (SSN’s) publicly available catalog (see below), which lists more than 16,000 cataloged objects in Earth orbit.3 However, a total of about 22,000 objects are being tracked routinely and their orbits are being recorded.4
o The U.S. Space Surveillance Network: Operated under the aegis of USSTRATCOM, the SSN consists of a global network of radar and optical sensors belonging to all branches of the U.S. military. The SSN compiles and updates the primary orbital debris catalog used by the federal government.
• AFSPC: A large organization within the Air Force that is spread across 88 locations worldwide, AFSPC is responsible for space launch operations at launch bases on the East and West Coasts, and its many other responsibilities include conducting and maintaining cyberspace operations. AFSPC provides services, facilities, and range safety control for all DOD, NASA, and commercial launches and also integrates and coordinates command and control of all DOD satellites among operators.5
2 U.S. Strategic Command, “USSTRATCOM Space Control and Space Surveillance,” available at http://www.stratcom.mil/factsheets/USSTRATCOM_Space_Control_and_Space_Surveillance, accessed July 21, 2011.
3 As of July 6, 2011, there were 16,094 objects in the Space Surveillance Network’s public catalog. See J.-C. Liou, ed., Satellite box score, Orbital Debris Quarterly News 15(3):10, July 2011, available at http://orbitaldebris.jsc.nasa.gov/newsletter/pdfs/ODQNv15i3.pdf, accessed July 21, 2011.
4 U.S. Strategic Command, “USSTRATCOM Space Control and Space Surveillance,” available at http://www.stratcom.mil/factsheets/USSTRATCOM_Space_Control_and_Space_Surveillance, accessed July 21, 2011.
5 U.S. Air Force, “Fact Sheet: Air Force Space Command,” November 2010, available at http://www.afspc.af.mil/library/factsheets/factsheet_print.asp?fsID=3649&page=1, accessed July 21, 2011.
what is called Conjunction Assessment Risk Analysis (CARA). In 2005, the Goddard Space Flight Center (GSFC) began using CARA to provide collision avoidance information for operational uncrewed spacecraft. Launch Collision Avoidance (COLA), administered at the Kennedy Space Center (KSC), grew out of range safety concerns and screens against possible conjunctions with known objects in orbit, but only during the launch phase of a mission. Although these other meteoroid and orbital debris programs (HITF, MEO, and CARA/COLA) are not officially part of the ODPO, there is close coordination between them.
In 1993, the responsibilities of the ODPO were expanded to include minimizing the hazard on the ground from reentering debris and providing short-term operational support to both crewed and uncrewed spacecraft in the form of warnings that may result in collision avoidance maneuvers or delays in launch in order to avoid
a potential hazard.13 For example, the ODPO provided support for the U.S. presidential decision to destroy the USA-193 satellite in February 2008 by evaluating the potential hazard to civilians on the ground from USA-193’s toxic hydrazine fuel and tank, as well as ensuring that the hazard to operational spacecraft was minimal (see Box 1.2).14 The ODPO now provides warning after any unplanned breakups of spacecraft in orbit using the Satellite Breakup Assessment Model (SBRAM), predicting regions of space to avoid, if possible. Such predictions are essential to the timing of certain DOD operations involving tests that may produce a temporary region of higher risk, for which NASA provides support.
NASA is also now providing CARA for uncrewed spacecraft, whereby spacecraft with the capability to maneuver are warned of the risk of a collision with other cataloged objects and given the option to maneuver. Beginning in 2002, NASA’s research and engineering orbital debris models were reformatted to more easily include the most recent data and to allow for greater flexibility in determining the most efficient mitigation and remedial actions.
As of 1995, key NASA models, measurements, and testing results were combined into a single suite of models (with a graphic user interface) that is publicly available. Known as the Debris Assessment Software (DAS), this application allows any spacecraft designer to determine if a spacecraft is meeting NASA’s current mitigation guidelines, as well as whether critical systems on the spacecraft have a level of protective shielding that is acceptable to the spacecraft designer.
Figure 1.1 illustrates how NASA’s measurements, modeling, and test programs combine to provide a set of customer-user tools and services, as well as research tools used to recommend mitigation and remediation options toward minimizing growth in the orbital debris population. Many of these models have undergone nearly constant upgrades since the beginning of the program, whereas others represent newly developed operational tools. The models and various components of Figure 1.1 are described in more detail in the appropriate chapters of this report.
One of NASA’s major mitigation standards has been that “maneuverable spacecraft that are terminating their operational phases at altitudes of less than 2,000 km above Earth shall be maneuvered to reduce their orbital lifetime, commensurate with 25-year low-Earth orbit lifetime limitations.”15 The reason for this 25-year rule16 was that it has been recognized since the beginning of the program that an increasing accumulation of non-operational spacecraft and upper stages would inevitably lead to increasing collisions involving those objects and would become the major source of small debris. NASA’s goal was to gain both national and international acceptance of the 25-year rule.
Yet although the orbital debris mitigation guidelines developed by NASA were gaining wider acceptance by the space community, an increasing number of studies, both national and international, were coming to the conclusion that even absolute compliance with the 25-year rule would be insufficient to prevent the debris population present below 2,000 km (LEO) from continuing to increase as a result of random collisions involving non-operational intact debris.17 These studies concluded that the rate of collisions had already reached the point that debris would
13 NASA, Process for Limiting Orbital Debris, NASA-STD 8719.14 (Change 4), NASA, Washington, D.C., September 2009, available at http://www.hq.nasa.gov/office/codeq/doctree/871914.pdf.
14 J. Oberg, U.S. satellite shootdown: The inside story, IEEE Spectrum, August 2008, available at http://spectrum.ieee.org/aerospace/satellites/us-satellite-shootdown-the-inside-story.
15 Requirement 56876 of NASA Procedural Requirements 8715.6A. See http://nodis3.gsfc.nasa.gov/displayDir.cfm?Internal_ID=N_PR_8715_006A_&page_name=Chapter3.
16 The “25-year rule” is a guideline adopted by the international Inter-Agency Space Debris Coordination Committee (IADC) in its “IADC Space Debris Mitigation Guidelines” released in 2002 and revised in 2007. The “rule” encourages entities with objects in low Earth orbit to ensure that their spacecraft and/or launch hardware are in an orbit that will decay and cause said object to reenter Earth’s atmosphere within 25 years to mitigate the creation of more orbital debris. See http://www.iadc-online.org/Documents/Docu/IADC_Mitigation_Guidelines_Rev1_Sep07.pdf.
17 D.J. Kessler, Collisional cascading: The limits of population growth in low Earth orbit, Advances in Space Research 11(12):63-66, 1991; S.-Y. Su, On runaway conditions of orbital debris environment, Advances in Space Research 13(8):221-224, 1993; A. Rossi, A. Cordelli, P. Farinella, and L. Anselmo, Collisional evolution of the Earth’s orbital debris cloud, Journal of Geophysical Research—Planets 99(E11):23195-23210, 1994; L. Anselmo, A. Cordelli, P. Farinella, C. Pardini, and A. Rossi, Modelling the Evolution of the Space Debris Population: Recent Research Work in Pisa, ESA SP-393, European Space Operations Centre, European Space Agency, Darmstadt, Germany, 1997, pp. 339-344; D.J. Kessler, Critical Density of Spacecraft in Low Earth Orbit Using Fragmentation Data to Evaluate the Stability of the Orbital Debris Environment, Report LMSEAT-3393, Lockheed Martin, February 2000; P.H. Krisko, J.N. Opiela, and D.J. Kessler, The Critical Density Theory in LEO as Analyzed by EVOLVE 4.0, ESA SP-473, European Space Operations Centre, European Space Agency, Darmstadt, Germany, 2001, pp. 273-278; J.-C. Liou and N.L. Johnson, Risks in space from orbital debris, Science 311:340-341, 2006.
2007 Chinese Anti-Satellite Mission Test and 2008 U.S. Destruction of USA-193
As of December 27, 2006, the U.S. Space Surveillance Network (SSN) was tracking 9,949 cataloged objects larger than 10 cm. On January 11, 2007, China conducted a direct-ascent anti-satellite (ASAT) missile test with its FENGYUN 1C polar-orbiting weather satellite as the target. The destruction of the satellite created more than 3,000 trackable objects and an estimated 150,000 debris particles larger than 1 cm, making it the largest debris-generating event in the history of man-made orbital debris, increasing the known existing orbital debris population in 2007 by more than 15 percent.1,2 For comparison, the previous largest orbital debris-generating event, the explosion of a U.S. Pegasus rocket body in 1996, created 713 trackable pieces of debris. On June 22, 2007, NASA was forced to maneuver its Terra satellite to avoid debris from China’s ASAT test.
Two years after the destruction of China’s satellite, only 50 pieces of debris had decayed from orbit.3 As of May 2011, the SSN had cataloged 3,118 trackable pieces of debris (approximately 10 cm in diameter or larger) still in orbit from China’s ASAT test, constituting nearly 20 percent of the entire debris population of particles 10 cm or larger currently being tracked in the SSN’s public catalog, which was at 16,094 as of July 6, 2011.4,5 Based on models from the Center for Space Standards and Innovation (CSSI), the remnants of FENGYUN 1C will likely remain in orbit for at least a century.
FIGURE 1.2.1 The International Space Station’s orbit (green) and the debris ring (red) from the Chinese ASAT test (December 5, 2007). SOURCE: Courtesy of Dr. T.S. Kelso, CelesTrak.com.
On February 21, 2007, the United States successfully destroyed its National Reconnaissance Office-operated USA-193 satellite, because it posed a serious threat to Earth. The purpose of this missile intercept was to break up the spacecraft and, more specifically, its thick metal fuel tank, which was nearly three-quarters full of toxic hydrazine propellant used for maneuvering the satellite while in orbit.6 Because USA-193 failed shortly after reaching orbit, its fuel would never be depleted through normal operational use.
The Department of Defense and NASA had run tests that determined that the hydrazine tank would survive atmospheric entry intact and thus pose a risk of casualties from dispersal of the deadly hydrazine fuel.
Unlike the Chinese FENGYUN 1C satellite remnants, debris from USA-193 reentered Earth’s atmosphere within 4 months of the satellite’s destruction.7
1 NASA, Orbital Debris Quarterly News, Volume 12, Issue 1, January 2008.
2 NASA, Orbital Debris Quarterly News, Volume 11, Issue 2, April 2007.
5 NASA, Orbital Debris Quarterly News, Volume 15, Issue 3, July 2011, p. 10.
6 G.J. Gilmore, Navy missile likely hit fuel tank on disabled satellite, American Forces Press Service, February 21, 2008, available at http://www.defense.gov/news/newsarticle.aspx?id=49030.
FIGURE 1.1 A depiction of the flow of information between various organizational elements of NASA’s MMOD programs, showing vital aspects of the programs as they relate to both internal and external customers. MMOD models are developed to contribute to studies and analyses that support not only internal missions but also a significant number of interagency deliberations within the United States and meaningful dialogs internationally. Developed by NASA’s Orbital Debris and Program Office, Hypervelocity Impact Test Facility, and Meteoroid Environment Office, the models developed focus on protecting spacecraft, the environment, and people on Earth. Development and use of the models are supported by a robust testing and measurement program that is routinely augmented by external sources of data.
be generated faster than it could be removed by natural forces, mainly atmospheric drag. According to NASA’s most updated long-term model, it would be necessary to remove five large, intact objects per year over the next 100 years in order to prevent this future growth in the orbital debris population, assuming that 90 percent of future launches follow NASA’s current mitigation guidelines, including that no further explosions or other major releases of debris occur. However, the most important guideline is international compliance with the 25-year rule. If these guidelines are not followed, the number of intact objects to be removed could become much higher.18
These conclusions were reinforced by China’s anti-satellite test in January 2007, which involved an intentional collision with its own weather satellite at an altitude of 865 km (see Box 1.2), and then in February 2009 by the accidental collision between the Cosmos 2251 and Iridium 33 satellites at an altitude of 789 km. These two collisions essentially negated the consequences of more than 20 years of international compliance to guidelines that prevented upper rockets from continuing to explode in orbit. As illustrated in Figure 1.2, following these two events, the amount of cataloged fragmentation debris in orbit more than doubled, after having remained nearly constant for more than 20 years.19 In addition, NASA’s Haystack radar observation program measured a significant increase in the 1-cm-debris environment at all altitudes below 1,000 km after China’s 2007 test.20 After the Cosmos–Iridium collision, both the Haystack and Goldstone radars observed a significant increase in the debris population down to sizes as small as 2 mm, consistent with model predictions for collisions involving intact payloads.21
The Cosmos–Iridium conjunction was actually the fourth confirmed accidental collision between cataloged objects, all at altitudes between 680 km and 980 km. The first three occurred between 1991 and 2005, produced less than four cataloged fragments each, and did not draw much attention—so little attention that the 1991 collision was not recognized until 2005. NASA’s findings that if mitigation standards are followed perhaps only five large objects per year might have to be removed from orbit in order to stabilize the orbital debris environment, plus concern over the amount of debris that these two collision events created, have increased interest in strengthening NASA’s mitigation standards and researching the options for remediation.
In 2010, the new National Space Policy expanded NASA’s role in the orbital debris program further with the goal of “improved information collection and sharing for space object collision avoidance; protection of critical space systems and supporting infrastructures, with special attention to the critical interdependence of space and information systems; and strengthening measures to mitigate orbital debris.” The policy also directs NASA and DOD to “pursue research and development of technologies and techniques … to mitigate and remove on-orbit debris, reduce hazards, and increase understanding of the current and future debris environment.”22 Along with these expanded roles comes a need for additional resources, yet funding levels for the programs have not increased commensurate with their increased responsibilities. The ODPO “procurement funding” (no civil servant salaries or travel) has been constant at $3 million per year for the past 15 years, except for the years 2002 and 2003, when it was cut in half; this overall level represents a significant decrease when adjusted for inflation. As a result, capability has been lost and analysis efforts delayed. For example, during 2002 and 2003, the office permanently terminated operations of its Orbital Debris Observatory located in Cloudcroft, New Mexico, shut down the ODPO website for 2 years, and delayed model upgrades that would include debris shape, definition of the debris population at low inclinations, modeling of solid rocket motor aluminum oxide ejecta, and studies to assess the long-term environmental impact of various mitigation measures. Many of these modeling efforts have yet to be accomplished. In addition to these losses and delays, the 2010 National Space Policy’s requirements for increased effort from NASA’s orbital debris program will only stress resources further.
18 J.-C. Liou, N.L. Johnson, and N.M. Hill, Controlling the growth of future LEO debris populations with active debris removal, Acta Astronautica 66(5-6):648-653, 2010.
19 D.J. Kessler, J.-C. Liou, N.L. Johnson, and M. Matney, The Kessler syndrome: Implications to future space operations, Advances in the Astronautical Sciences 137:47-61, 2010.
20 M. Horstman, Q. Juarez, V. Papanyan, E. Stansbery, and C. Stokely, Measurements of the orbital debris environment by the Haystack and HAX radars during fiscal year 2007, Orbital Debris Quarterly News 14(3):3-4, 2010, available at http://orbitaldebris.jsc.nasa.gov/newsletter/pdfs/ODQNv14i3.pdf.
21 M. Matney, Small debris observations from the Iridium33/Cosmos 2251 collision, Orbital Debris Quarterly News 14(2):6-8, 2010, available at http://orbitaldebris.jsc.nasa.gov/newsletter/pdfs/ ODQNv14i2.pdf.
22National Space Policy of the United States of America, June 28, 2010, p. 7, available at http://www.whitehouse.gov/sites/default/files/national_space_policy_6-28-10.pdf.
FIGURE 1.2 Monthly number of objects by type in Earth orbit as officially cataloged by the U.S. Space Network. “Fragmentation debris” includes satellite breakup debris and anomalous-event debris; “mission-related debris” includes all objects dispensed, separated, or released as part of a planned mission. After having been nearly constant since 1987, fragmentation debris jumped from 4,000 objects in 2007 to 9,000 in 2009 as a result of two collisions in LEO. SOURCE: Courtesy of NASA, “Monthly Number of Objects in Earth Orbit by Object Type,” Orbital Debris Quarterly News, Vol. 15, Issue 1, NASA, January 2011, p. 10.
The committee heard from a number of speakers representing other U.S. agencies, as well as commercial space industries and the international community. Without exception, all speakers complimented NASA’s Orbital Debris Program Office for its leadership and working relationship with the community. Some went so far as to say that the program was essential to their operations.
The NASA meteoroid program began with the start of the space program, 50 years ago. At that time, JSC, MSFC, Ames Research Center, GSFC, and Langley Research Center each had its own, nearly independent, meteoroid program.23 The goal of these programs was to characterize the hazard of meteoroids to spacecraft, especially crewed spacecraft. Meteors were measured both from optical cameras and by radar from the ground. A large number of spacecraft experiments were flown during the 1960s to measure the environment, and the surfaces of these returned spacecraft, such as the windows from crewed spacecraft, were examined for impacts.24 Samples of interplanetary dust particles in the stratosphere were also collected to better understand the sources and characteristics of meteoroids. Some of these experiments and samples were misinterpreted as indicating a high meteoroid flux (i.e., the number of objects impacting or passing through a unit area per unit time). However, by 1970 it was
23 D.J. Kessler, “A Partial History of Orbital Debris: A Personal View,” presentation at the Hypervelocity Shielding Workshop, Institute for Advanced Technology, Galveston, Tex., March 8-11, 1998, pp. 81-89.
24 H.A. Zook, R.E. Flaherty, and D.J. Kessler, Meteoroid impacts on the Gemini windows, Planetary and Space Sciences 18(7):953-964, July 1970.
believed that the near-Earth meteoroid hazard was sufficiently understood and benign, and so all of these programs were either significantly reduced or eliminated; this culminated in the issuance of near-Earth25 and interplanetary meteoroid environment26 models that were still being used by NASA and other agencies through most of the 1990s. Some meteoroid studies continued, but studies in the United States had the goal of understanding the history of the evolution of comets, asteroids, and the solar system, and studies with the goal of understanding the hazard to spacecraft mostly shifted to other countries. Some of the NASA meteoroid models still in use today for the design of spacecraft are based entirely on data collected and analysis conducted prior to 1970.27
However, on July 27, 1993, NASA received a wake-up call when a reporter asked how NASA planned to handle the Perseid meteor storm on August 12, 1993, while the space shuttle was in orbit. NASA had been completely unaware of the predicted meteor storm and had no answer. Any predictions that could be obtained in the time available proved to be too uncertain, and so the launch was postponed until after the storm.28 Many uncrewed spacecraft were reoriented to protect their more critical surfaces, the first time operational changes occurred to spacecraft as a direct result of predictions relating to short-term changes in the meteoroid environment. Since this incident in 1993, the meteoroid program has slowly grown, at first to better understand meteor storm predictions (particularly those of the Leonids from 1998 to 2002), and later to understand other areas of uncertainty in the meteoroid environment.
In near-Earth space, the meteoroid hazard is still larger than the orbital debris hazard for any spacecraft operating above an altitude of 2,000 km. Prior to 1970, NASA was also concerned with defining the interplanetary meteoroid environment. However, with very little data to support them, the interplanetary models produced at that time sometimes involved assuming unknown sources and extrapolating the known sources of comets and asteroids over many orders of magnitudes. As a result, those early models had large uncertainties. The situation is not much better today, given that some of those same assumptions are still being used, but NASA has begun planning crewed missions that extend into interplanetary space.
The scientific community outside NASA has been gathering data that can be used to help update meteoroid models:
• Radar observations of meteors have continued to be made outside the United States;
• Meteoroid “dust” was captured both in the stratosphere and in space and returned to Earth for analysis with the purpose of understanding dust from comets;
• Spacecraft surfaces that were examined for orbital debris impacts were also examined for meteoroid impacts; and
• The Max Plank Institute included a cosmic dust detector on the Cassini spacecraft to Saturn, as well as on the Galileo and Ulysses mission, providing data on the dust environment at very small sizes in the outer solar system to complement earlier measurements by Pioneer.29
Of additional importance, at least two spacecraft failures were believed to be associated with high meteor stream activity, even though current meteoroid models predicted no failures during any high meteor stream activity.30 Past measurements of the meteoroid flux in all meteor showers had consistently measured an absence of meteoroids with decreasing size,31 so that the predicted impact rate on satellites during meteor showers was many orders of magnitudes lower than required to be consistent with those two failures.
25 B.G. Cour-Palais, Meteroid Environment Model-1969 (Near Earth to Lunar Surface), NASA SP-8013, March 1969.
26 D.J. Kessler, with assistance of ad hoc committee, Meteoroid Environment Model-1970 (Interplanetary and Planetary), NASA SP-8038, October 1970.
27 “Space Station Program Natural Environment Definition for Design,” SSP 30425 Revision B, 1994, available at http://paso.esa.int/3_Payload_Safety/SSP-30425%20RevB.pdf, accessed July 6, 2011.
28 D.S.F. Portree and J.P. Loftus, Orbital Debris: A Chronology, NASA/TP-1999-208856, NASA, Washington, D.C., January 1999.
29 E. Grün, “Earth Meteoroid Environment,” presentation to the Committee for the Assessment of NASA’s Orbital Debris Programs, March 10, 2011, National Research Council, Washington, D.C.
30 W.J. Cooke, “Overview of NASA’s Meteoroid Program,” presentation to the Committee for the Assessment of NASA’s Orbital Debris Programs, December 13, 2010, National Research Council, Washington, D.C.
31 B.G. Cour-Palais, Meteroid Environment Model—1969 (Near Earth to Lunar Surface), NASA SP-8013, March 1969.
In an attempt to explain the failures, address the uncertainties in the existing meteoroid models, take advantage of data gathered over the past 40 years, and gather new data, NASA’s Office of Safety and Mission Assurance and NASA Headquarters funded the establishment of the MEO at MSFC in 2004, with a budget of about $650,000 per year. MEO was created in part as a response to the Columbia Accident Investigation Board, which noted that NASA lacked means of monitoring meteoroid activity for post-event assessments and that a central office for meteoroid work was required within NASA to reverse loss of expertise and knowledge on the topic within the agency. The MEO is NASA’s technical lead for defining the meteoroid environment using radar and optical measurements, performing data analysis, and developing models that can be used together with test results from the HITF at JSC.
In the past 6 years, the MEO has improved models describing meteor streams and storms and regularly provides forecasts. It monitors meteor activity using a radar located in Ontario, Canada, and a network of all-sky optical cameras. The optical camera images are available online, where a near-instant analysis is performed to determine the orbit of each meteor observed. Although much new information has been obtained—enough to identify necessary updates to existing models—much more can and should be done to safely achieve NASA’s strategic goal to “extend and sustain human activities across the solar system.”32
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 operations.
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.
The programs and activities described above represent NASA’s primary efforts in MMOD research. During the course of its study, the committee became aware of smaller research projects occurring at individual centers (for instance, MMOD support for Project Orion at NASA Ames Research Center33 or, also at NASA Ames, research to improve the accuracy of debris orbit prediction34). The committee did not have the time or resources to conduct a thorough review of these smaller efforts.
32 NASA, 2011 NASA Strategic Plan, Washington, D.C., February 14, 2011, p. ii, available at http://www.americaspace.org/wp-content/uploads/2010/12/NASA_Strategic_Vision_2011.pdf, accessed July 6, 2011.
33 J. Vander Kam, “NASA Ames Micro-Meteoroid and Orbital Debris (MMOD) Support for Project Orion,” presentation to the Committee for the Assessment of NASA’s Orbital Debris Programs, April 22, 2011, National Research Council, Washington, D.C.
34 W. Marshall, “Debris Efforts at Ames,” presentation to the National Research Council Committee for the Assessment of NASA’s Orbital Debris Programs, April 22, 2011, National Research Council, Washington, D.C.