April 7, 2004
Members will hear testimony on strategies for identifying and responding to NEOs. Senator Brownback will preside. Following is a tentative witness list (not necessarily in order of appearance):
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Dr. Wayne Van Citters
Chairman Brownback, Ranking Member Breaux, and distinguished members of the Subcommittee. Thank you for the opportunity to present the position of the National Science Foundation on the important subject of Near Earth Objects. In responding to the questions that the Committee has presented to us, I will present a picture of NSF’s support of research into the nature and origin of these objects, as well as potential important contributions that NSF-supported instrumentation and techniques could make to an expanded discovery and characterization effort. Background and Context The Division of Astronomical Sciences supports basic research in astronomy covering a very wide range of subjects - from studies of objects in our own solar system to investigations of the beginning of the universe, including the very nature of matter and energy. In planning and conducting its programs, the Division benefits from the advice of the scientific community in many ways, including the recently established Astronomy and Astrophysics Advisory Committee (AAAC, jointly advising NSF, NASA, and DOE). The establishment of the AAAC recognizes the value of an integrated strategy to address national efforts to answer questions about our origins and our future. The number and nature of NEOs are clearly fundamental questions about both our origins and our future. In their March 15, 2004 report the AAAC recommended a coordinated implementation effort to ensure timely development of the Large Synoptic Survey Telescope, calling it a key facility for the detection of potentially hazardous earth-intersecting objects as small as 300 meters. Current Activity A number of awardees in our Planetary Astronomy Program are investigating Near Earth Objects (NEOs). The proposals funded by our program are determined by the interest of the research community, as reflected in the number and subject matter of proposals that we receive, and the results of our merit review of these proposals. As one example, Dr. Derek Richardson at the University of Maryland will be modeling the tidal disruption of near Earth asteroids (NEAs) by the Earth’s gravitational field to determine the frequency of binary NEA formation and the typical characteristics of the resulting binary asteroids. The results from this research will give insight into the internal structure of NEAs and may have implications for hazard mitigation strategies. In another effort, Richard Binzel at MIT will measure the near-infrared spectral properties of 40-60 NEOs per year. The observations will balance measurements that push the state-of-the-art limits of the technology for the smallest and faintest objects and measurements that provide sufficient detail for detailed mineralogical analysis. Research in this area also represents a substantial fraction of the use of the Arecibo planetary radar system, characterizing sizes, shapes, rotation rates, and configurations (single or binary, e.g.). The smallest system yet observed (a binary of 120m and ~40 m diameter components) was discovered in 2003. Measurements from a combination of Arecibo and NASA’s Goldstone antenna from 1991 through 2003 demonstrated the existence of the Yarkovsky effect. This effect is an acceleration of the body related to the time delay between the absorption of solar radiation and the re-emission in the infrared. The observations clearly indicated that the acceleration must be included in orbit predictions. We have observed that the number of proposals to investigate NEOs has been increasing annually for the last few years. Of the proposals we receive on this topic, those that do best in our merit review competition are those proposing to characterize the physical properties of the objects. What are they made of? How were they formed and when? I believe NSF is currently playing the role for which it is best suited. It is funding individual investigators to further our understanding of the physical make-up of NEOs. The proposals for these investigations are subject to our normal merit review, thus insuring high quality basic research on these objects. In addition, it provides access to tools such as Arecibo that can enhance the discovery process. Looking to the Future In recent years, there has been an increasing appreciation for the hazards posed by near-Earth objects, those asteroids and periodic comets (both active and inactive) whose motions can bring them into the Earth's neighborhood. In August of 2002, our colleagues at NASA chartered a Science Definition Team to study the feasibility of extending the search for near-Earth objects to smaller limiting diameters. The formation of the team was motivated by the good progress being made toward achieving the Spaceguard goal of discovering 90% of all NEOs with diameters greater than 1 km by the end of 2008. This raised the question of what, if anything, should be done with respect to the much more numerous smaller, but still potentially dangerous, objects. The team was tasked with providing recommendations to NASA as well as the answers to seven specific questions. We believe that the answers to these questions could form a solid basis for the direction of our research efforts and for more detailed studies of the best integrated strategy to carry on at the end of Spaceguard in 2008. What are the smallest objects for which the search should be optimized? The Team recommends that the search system be constructed to produce a catalog that is 90% complete for potentially hazardous objects (PHOs) larger than 140 meters. Should comets be included in any way in the survey? The Team's analysis indicates that the frequency with which long-period comets (of any size) closely approach the Earth is roughly one-hundredth the frequency with which asteroids closely approach the Earth and that the fraction of the total risk represented by comets is approximately 1%. The relatively small risk fraction, combined with the difficulty of generating a catalog of comets, leads the Team to the conclusion that, at least for the next generation of NEO surveys, the limited resources available for near-Earth object searches would be better spent on finding and cataloging Earth-threatening, near-Earth asteroids and short-period comets. A NEO search system would naturally provide an advance warning of at least months for most threatening long-period comets. What is technically possible? Current technology offers asteroid detection and cataloging capabilities several orders of magnitude better than the presently operating systems. This report outlines a variety of search system examples, spanning a factor of about 100 in search discovery rate, all of which are possible using current technology. Some of these systems, when operated over a period of 7-20 years, would generate a catalog that is 90% complete for NEOs larger than 140 meters. How would the expanded search be done? From a cost/benefit point-of-view, the report concludes that there are a number of attractive options for executing an expanded search that would vastly reduce the risk posed by potentially hazardous object impacts. The Team identified a series of specific ground-based, space-based and mixed ground- and space-based systems that could accomplish the next generation search. The choice of specific systems would depend on the time allowed for the search and the resources available. What would it cost? For a search period no longer than 20 years, the Team identified several systems that they felt would eliminate, at varying rates, 90% of the risk for sub-kilometer NEOs, with costs they estimate to range between $236 million and $397 million for both ground and space components. They conclude that all of these systems have risk reduction benefits which greatly exceed the costs of system acquisition and operation. How long would the search take? The Team concludes that a period of 7-20 years is sufficient to generate a catalog 90% complete to 140-meter diameter, which will eliminate 90% of the risk for sub-kilometer NEOs. The specific interval would depend on the choice of search technology and the investment allocated. Is there a transition size above which one catalogs all the objects, and below which the design is simply to provide warning? The Team concluded that, given sufficient time and resources, a search system could be constructed to completely catalog hazardous objects with sizes down to the limit where air blasts would be expected (about 50 meters in diameter). Below this limit, there is relatively little direct damage caused by the object. Over the 7-20 year interval (starting in 2008) during which the next generation search would be undertaken, the Team suggests that cataloging is the preferred approach down to approximately the 140-meter diameter level and that the search systems would naturally provide an impact warning of 60-90% for objects as small as those capable of producing significant air blasts. The path from where we are today to where we should be in 2014 is not defined in the conclusions of the study that NASA sponsored. Clear goals are defined; how one might reach them is wisely left to the scientific and technical community. At the national level, we must now examine these goals in detail, validate the conclusions, and determine how they might best be achieved. NSF Plans for the Future We are considering asking the AAAC to form a subcommittee to advise on the effort that would be appropriate beyond Spaceguard. Broadly based in the scientific and technical community, this subcommittee would consider the conclusions of recent studies, extract necessary research directions that would help us better understand the origin and nature of the objects known to date and help to chart the most productive course into the future. By the very nature of the charge to the AAAC, this would be an integrated look at the ground-based and space-based efforts that would make the most effective scientific advances in this area. Of particular interest to NSF would be the expansion of the individual investigator-driven basic research that we currently support, and a more detailed understanding of how such projects as the Large Synoptic Survey Telescope (LSST) and Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) might best contribute to the discovery and characterization effort in the future. The LSST is a proposed single 8.4meter aperture, very wide field telescope capable of surveying the entire sky visible from one hemisphere every two weeks. It has a variety of science drivers including the characterization of dark matter and dark energy, the discovery of many classes of transient objects such as supernovae and gamma-ray burst counterparts, and NEOs. Pan-STARRS, an Air Force funded project under construction in Hawaii, will be composed of 4 individual telescopes of 1.8meter aperture observing the same region of sky simultaneously. In survey mode, i.e., searching for NEOs, Pan-STARRS will cover 6,000 square degrees per night. The whole available sky as seen from Hawaii will be observed 3 times during the dark time in each lunation. The LSST’s ability to make fast, wide, and faint observations may make it uniquely suited to detecting small NEOs. A model LSST survey covering 9,000 square degrees of sky along the ecliptic, three or four times a month, to a limiting V magnitude of 24.0, achieved a ten-year completeness of about 90% for NEOs larger than 250 m, and about 80% for NEOs down to 140 m as called for by the NASA study. The requirements placed on the telescope, telescope operations, data system and detectors by the NEO detection challenge are considerable. By reaching objects 100 times fainter than those currently observed in the NEO surveys, Pan-STARRS is being designed to help complete the Congressional mandate to find and determine orbits for the 1-km (and larger) threatening NEOs. Further, it should push the detection limit for a complete (99%) sample down to objects as small as 300-meters in diameter. Design studies over the next several years will be needed to determine the strategy for attacking the NEO problem and whether it is best carried out with a single telescope like the LSST or whether an array of smaller telescopes such as Pan-STARRS is more appropriate for this particular problem. NSF’s Division of Astronomical Sciences has begun planning for such studies and we have been actively joined by our colleagues at NASA, who will contribute their knowledge and experience in the handling of large data bases and archives. Conclusion In conclusion, Mr. Chairman, NSF is already pursuing a significant amount of basic research in this important area. We are guided, as always, by the scientific community through our merit review process. We are laying plans for new facilities and expanded research activity that speak to many basic questions about the nature and origin of these objects, and are confident that the body of knowledge so gained will have important application to any eventual risk-mitigation effort. Again I thank you for the opportunity to appear and would be happy to respond to any questions.
Dr. Lindley Johnson
Thank you, Mr. Chairman, for the opportunity to present to the subcommittee information on the important subject of Near Earth Objects. At the request of Congress, NASA conducts the Near Earth Object (NEO) Observation Program to discover the larger sized asteroids (greater than 1 kilometer or 0.62 miles in size) and periodic comets that pass relatively close to the Earth and may one day pose a collision hazard with our planet. Our NEO program has been quite successful in finding these larger objects in the first five years of the effort. BACKGROUND The Earth orbits about the Sun in a cloud of planetary debris still left from the formation of the Solar System. This debris ranges from micron-sized dust particles, to meteoroids at sand grain to a few meters in size, and to asteroids and comets that are tens of meters to several kilometers in dimension. Collision with meter-sized meteoroids is almost a weekly event for the Earth, but the surface is well protected from these common events by its atmosphere, which will cause objects less than about 50 meters in size and of average density to disintegrate harmlessly before reaching the ground. However, even the relatively active surface of the Earth still bears scars of impacts from space, with 168 craters worldwide – some up to 300 kilometers in size – having been identified to date. Though collisions with larger bodies are much less frequent now than in the early stages of planet formation in the Solar System, they do still occur. Very significant events, capable of causing damage at the surface, will happen on scales of a few hundred to a thousand years. But we do not know when the next impact of an object of sufficient size to cause widespread devastation at ground level may occur. At the current state of knowledge, it is about as likely to happen next week as in a randomly selected week a thousand years from now. The Survey In an effort to gain better understanding of this hazard, NASA has been conducting a search of space near the Earth’s orbit to understand the population of objects that could do significant damage to the planet should there be a collision. Commonly referred to as the “Spaceguard Survey”, NASA’s Office of Space Science conducts this research effort on “Near Earth Objects (NEOs)” -- that is, asteroids and comets that come within an astronomically close distance, <50 million kilometers of Earth. The objective of this survey is to detect, within a 10-year period, at least 90% of the NEOs that are greater than 1 kilometer in size and to predict their orbits into the future. The survey officially started in 1998 and to date, over 700 objects of an estimated population of about 1100 have been discovered, so the effort is believed to now be over 70% complete and well on the way to meeting its objective by 2008. A few words of explanation on the parameters and limitations of the survey may be appropriate. The threshold of 1 kilometer in size was accepted for this survey because it is about the size asteroid that current research shows would border on having a devastating worldwide effect should an impact occur. Because of the orbital velocities involved, impact on Earth of an asteroid of this size would instantly release energies calculated to be equivalent to the detonation of almost a 100,000 megaton nuclear device, i.e., more than all the world’s nuclear arsenals detonated at the same time. Not only would the continent or ocean where the impact occurs be utterly devastated, but the effects of the super-heated fragments of Earth’s crust and water vapor thrown into the atmosphere and around the world would adversely affect the global weather for months to years after the event. Such an event could well disrupt human civilization anywhere from decades to a century after an impact. A goal of 90% completeness was adopted as a compromise driven between the level of resources that could be dedicated to this effort and the time period practical to conduct the survey at this level of technical capability. Currently, slightly over $4M per year is budgeted to the NEO Observation Program within the Solar System Exploration Division’s Supporting Research and Analysis Program. This funds modest search efforts, typically using refurbished, ground-based telescopes of about 1-meter aperture and wide-field-of-view, coupled with digital imaging in order to cover significant portions of the sky each month. Presently, five NEO search projects are either wholly or largely funded with this level of resource, along with significant support to central processing of observations, orbit determination and analysis. These five search projects are: PROJECT NAME INSTITUTE PRINCIPAL INVESTIGATOR Lincoln Near Earth Asteroid Research (LINEAR) MIT / Lincoln Laboratory, MA Dr. Grant Stokes Near Earth Asteroid Tracking (NEAT) Jet Propulsion Laboratory, CA Dr.Ray Bambery Lowell Observatory Near Earth Object Search (LONEOS) Lowell Observatory, AZ Dr. Edward Bowell Catalina Sky Survey LPL, University of Arizona Mr. Steve Larson Spacewatch LPL, University of Arizona Dr. Robert McMillan Both the LINEAR and NEAT projects operate using optical telescope facilities owned and supported by research components of the U.S. Air Force. This represents that service’s entire contribution to the search effort, but utilization and direction of these assets must be coordinated with the cognizant Air Force Material Command offices. The Spacewatch Project also receives some modest private funding. Ten years was considered a reasonable amount of time for this level of effort to bring the overall large asteroid population known to 90% completeness. No level of effort could ever be assured of achieving absolute 100% completeness, because of the vast difficulty in searching all possible orbit regimes and sources for generation of new NEOs. It should also be understood that the NEO Observation Program is merely a science survey and does not have the resources to provide a “leak-proof” warning network for impact of any size natural object, large or small. Such a comprehensive network would require an order of magnitude increase in funding and could require the cooperative efforts of several government departments and agencies. PROGRESS OF THE PROGRAM. The NEO Observation Program continues to make steady progress toward the goal of finding at least 90% of the large NEO population. As of the end of March 2004, 513 of the 750 known NEOs (including 49 Earth-approaching comets) determined to be larger than 1 kilometer in size have been found by the program, of an estimated total population of about 1100. In addition, the program found 1862 of 2032 known Near Earth Asteroids (NEAs) of smaller sizes. The MIT/Lincoln Labs-led LINEAR project continues to be the leading search team, having found 40 large NEOs in 2003 along with 196 smaller objects. Significant contributions continue to be made by JPL’s NEAT team (10 large and 58 smaller objects in the last year), Lowell Observatory’s LONEOS project (10 and 44), and the University of Arizona’s Spacewatch project (2 and 54). The Lunar and Planetary Laboratory Catalina Sky Survey has gotten back on line in the last few months of the year after an imager upgrade, obtaining 8 discoveries, 2 of them larger than 1 km. The chart below summarizes the progress to date on finding the NEAs greater than 1 kilometer in size. A noticeable increase in the discovery rate occurs after the NEO Observation Program started in 1998. Budget. The FY 2004 budget for this program is $4,062K, a 2.8% increase to the previous year. CURRENT SURVEY OPERATIONS Detection. The NEO Observation Program wholly funds the operations of four search projects and partially funds another. Routine operation of these assets is highly automated, in order to maximize the sky coverage obtained each month. Ground-based telescopes can only effectively operate at night during the two to three weeks of the month opposite the full moon, due to the sky brightness it causes, and when weather (cloud cover) permits accessible clear sky. Telescope movement, pointing, and imaging operations are all computer controlled via pre-scripted software routines to optimize sky coverage and therefore maximize object detections. The images taken each night are then post-processed to detect moving objects relative to the star background and obtain accurate measurements, called “observations”, of any detected object’s motion relative to the star background (a process called “astrometrics”). A group of these observations, usually a set taken from three to five images of the same patch of sky at slightly different times each night, is called a “track”. These show the relative motion of an object, which can then be analyzed with other observations of the same object to determine its orbit. These observation tracks are then formatted for bulk telecommunications to the Minor Planet Center. On a productive night, a search project may extract hundreds of observations on moving objects from its imaging data, most of which will be on Main Belt Asteroids and only a small fraction, perhaps one or two if lucky, will be determined to be NEOs. The search teams also routinely find comets in their collected images. The Minor Planet Center. All observations thought to be natural small bodies (asteroids, comets and now Kuiper Belt Objects in the outer Solar System) are sent to the Minor Planet Center (MPC), operated by the Smithsonian Astrophysical Observatory at Cambridge, Massachusetts, under the direction of Dr Brian Marsden. The MPC is internationally recognized and officially chartered by the International Astronomical Union to confirm the discovery of new objects in the Solar System and confer their official designations. A modest amount of NASA funding is sent to the MPC to support their work in confirming NEO detections. The MPC receives observations from around the world, with a significant percentage coming from an informal international network of amateur asteroid hunters. The orbital analyst at MPC attempts to correlate them with the positions of tens of thousands of already known objects. Failing that, the MPC will provisionally designate the observations as a possible new object, determine an “initial” orbit for it, and place it on a list for objects awaiting “confirmation”. This list of provisional objects, along with their predicted current positions, is available via the MPC web site for the community of observers to use in attempts to obtain additional “follow-up” observations to confirm the existence and orbit parameters of a new object. The observation processing at the MPC is highly automated, as it must be with a staff of only three to four analysts operating with a very limited budget. However, initial orbit determination often requires some analyst’s massaging of the orbit fit to obtain the lowest residuals across what may be observations with some inherent errors. Because individual search sites can only do the roughest of orbit calculations based on their own limited data, the MPC is, in most cases, the first place where it will be known if a newly found object poses an impact hazard to the Earth. Often a family of possible orbits is initially obtained which must be narrowed with additional observations. For newly found NEOs, the MPC solicits additional observations from the community via a web-based “NEO Confirmation Page”, and in the most critical cases, via phone calls to known observers in whatever part of the world is most likely to have the earliest accessibility to viewing the object. Follow-up Observations. Additional observations, either obtained by another observer later the same night or on a subsequent night, even by the same facility that first discovers an object, are essential to confirming the objects existence and developing a more accurate orbit for the object. For the most accurate orbit, it is best for the observations to be obtained several days to a week or more after the initial set in order to obtain a longer observed “arc” of the orbit and, therefore, a broader fit of observation data. However, for NEOs, the time allowed to elapse must be traded off between obtaining a broader arc and getting an orbit established before the object is lost, either because the initial orbit was too far in error, or, more likely, the object is so small that it simply cannot be seen after only a few days of its closest approach to Earth. The informal network of amateur astronomers does much of the follow-up observation work today. However, the search for NEOs is beginning to enter an era when the objects being detected are simply too faint to be seen by the equipment affordable to most amateurs. Therefore, in the future, search systems must ensure they have enough survey capacity available to do their own follow-up on new objects in a timely manner. High-accuracy Orbit Determination. The best orbit determination requires enough observations spread over a sufficient arc of the orbit to provide the best resolution of motion for the object and reduce the influence of subsets of data with may have some components of error. Again, getting the best results can be somewhat of an art form, but the best orbital modeling for this reside with the NEO Program Office established by NASA at the Jet Propulsion Laboratory in Pasadena, California, and managed by Dr. Donald Yeomans. This office also supports the orbit determination and navigation for NASA’s interplanetary missions to asteroids, comets, and moons of other planets. Its NEO work is fully funded by NASA, and the high-accuracy orbit determination capability is nicely complementary to the MPC’s observation processing and initial orbit determination abilities. The NEO Program Office is able to use its orbital modeling capability to predict the position of any known NEO up to 200 years into the future, taking into account all the known gravitational influences and orbital perturbations of the Sun, planets, and moons in the Solar System. This can be done with a very high degree of precision for asteroids that have been tracked for extended periods, particularly multiple orbits, or for which high-precision observations have been taken by planetary radar. High-precision radar observations can greatly reduce the position and motion errors for the subset of objects that come close enough to the Earth to allow its use. High-precision prediction of newly discovered NEO orbits allows them to be separated into those whose orbits will not be a collision hazard to Earth for the foreseeable future and those which are in orbits that pass close enough to Earth’s that they may someday pose a hazard. These “Potentially Hazardous Asteroids (PHAs)” are about a 20% subset of all NEOs found. Of course, known and unknown errors in the NEO’s orbital parameters can propagate out to significant uncertainty in the position when predictions are done decades into the future. Therefore, periodic observation of known objects, especially those known to be in potentially hazardous orbits, must be done to update the last known position and reduce the orbit errors. Low Probability, High Consequence Events on Short Timelines A central premise of the current survey effort is that in the relatively short 10-year period, the search teams would be able to find almost all asteroids of greater than 1 kilometer dimension that might pose a threat of impact – many years to multiple decades before any such event. It could perhaps even provide many centuries advanced notice, since this level of event is thought to happen only once or twice in a million years. Hypothetically, this would allow ample time to develop the techniques and technologies that may be required to deflect or mitigate a predicted disaster. But until the total population of these objects is known, there is always a chance that an object bound for a nearer term impact may be discovered, similar to the real-life scenario which unfolded when Comet Shoemaker-Levy 9 was discovered in March 1993 inbound for a July 1994 impact on Jupiter. The results of a recent study by a Science Definition Team commissioned by NASA’s Solar System Exploration Division show that it is entirely appropriate that we search for the larger NEOs first because, all factors considered, that is where the greatest risk for an undetected asteroid on an impact trajectory lies, principally due to the widespread devastation it would cause. It is orders of magnitude above what smaller, sub-kilometer sized impactors would produce. Completion of the current effort to find these large objects will do much to reduce the uncertain risk of which we have now become aware. But more frequent would be the discovery of a relatively small asteroid on a potential impact trajectory with Earth, as this occurs more often. Since the optical sensors used in the survey detect the brightness of the object against the sky background, which can only be approximately related to an asteroid’s size based on assumed reflectivity of light, the search systems are as capable of finding smaller asteroids at closer range as larger objects much farther away. They are designed to detect 1 kilometer sized asteroids at least 50 million kilometers distant but can also detect an asteroid a dozen meters in size within the Moon’s distance from Earth. Operational experience with the current systems shows that for every 1-kilometer or greater sized asteroid found, there are three to four smaller sized asteroids also discovered. But the true ratio of smaller asteroids, say 100-meter or larger objects to 1-kilometer or larger objects, is thought to be closer to 100 to 1. Because of the limitations of the search systems, the discovery of smaller asteroids is in a significantly smaller volume about the Earth -- an object one tenth the size of another must be about hundred times closer to be seen by the sensor, assuming equal reflectivity of their surfaces. If the sensor can detect a 1 kilometer sized asteroid at 50 million kilometers, it should theoretically also see a 100-meter asteroid at 500,000 kilometers. However, at planetary relative orbital velocities, if the object is on collision course with the Earth, it may cover even this distance in less than one day. Thus the detection of a relatively small asteroid on a collision trajectory with Earth could also come with a relatively short reaction time. A 100 meter asteroid on direct collision with Earth could do significant damage at the surface as this is estimated to result in an approximately 50 megaton energy release at or perhaps slightly above the surface. This would result in much loss of life if the impact were in a populated area. It is therefore prudent that we begin to put in place some contingency plans, such as an internal NASA notification plan we are drafting, to deal with such a relatively unlikely but extremely high-consequence event. Again I thank you for the opportunity to appear and would be happy to respond to any questions.
Witness Panel 2
Dr. Michael D. GriffinAdministratorNational Aeronautics and Space Administration (NASA)
Testimony of Michael D. Griffin to United States Senate Committee on Commerce, Science, and Transportation Subcommittee on Science, Technology, and Space Hearing on Near Earth Objects SR-253 7 April 2004 Mister Chairman and members of the subcommittee, thank you for giving me this opportunity to comment on the greatest natural threat to the long-term survivability of mankind, an asteroid impact with the Earth. Throughout its history, the Earth has continuously been bombarded by objects ranging in size from dust particles to comets or asteroids greater than 10 km in diameter. Although the probability of the Earth being hit by a large object in this century is low, the effects of an impact are so catastrophic that it is essential to prepare a defense against such an occurrence. The first step in that defense is a system to identify and catalog all potential impactors above the threshold of significant damage, approximately 100 meters in diameter. Later, the remainder of a comprehensive Earth-protection system could be assembled so that it would be ready to deflect a potential impactor shortly after it is identified. In 1998, NASA embraced the goal of finding and cataloging, within 10 years, 90% of all near-Earth objects (NEOs) with diameters greater than 1 km. Impacts by objects of this size and larger could result in worldwide damage, and the possible elimination of the human race. The current system is not sufficient to catalog the population of smaller NEOs. While there are thought to be nearly a thousand objects with diameters greater than 1 km, there are a great many smaller NEOs that could devastate a region or local area. The exact NEO size distribution is not known; however a good current estimate is that there are more than 5 times as many objects with diameters greater than 1/2 km than there are with diameters greater than 1 km. This multiplication of numbers for smaller diameters continues for all sizes at least down to those just large enough to make it through the atmosphere. Thus, if there are about 700 NEOs of 1 km or greater, there are more than 150,000 NEOs with diameters greater than 100 m. The Tunguska event in Siberia in 1908 destroyed an area 50 km in diameter and is believed to have been caused by an impactor less than 50 m in diameter. The average speed of objects colliding with Earth is about 20 km/s (about 45,000 miles per hour). At these speeds the energy of impact is 44 times the explosive power of the same mass of TNT. Thus, the energy released by the impact of a 100 m object is about equivalent to a 50 megaton bomb. The impacts at Tunguska in 1908, Sikhote-Alin (about 270 miles northeast of Vladivostok) in February 1947, and the recently identified objects that have had near misses with Earth, all show us that impacts with the ability to wipe a large metropolitan area can be expected during the next 100 years. A great deal has been learned about the nature of the threat in the last decade. It is vital to understand the characteristics of NEOs to know how to defend against a potential impactor. An improved theoretical understanding of the population of NEOs has clarified their evolution through interactions with the planets of our solar system. It has helped us understand their numbers and their distribution in the different classes of orbits. On the practical side, the progress of several space missions has greatly improved our understanding of the physical and chemical characteristics of these objects. A great deal still needs to be done since only a handful of these objects have been observed from sufficiently close distances to see their surface structure, and only one asteroid has been orbited. The Near Earth Asteroid Rendezvous (NEAR) mission orbited and landed on 433-Eros and was able to get the first estimates of the internal structure and composition of a NEO. However, there is still a great deal more that will have to be known about an object if it becomes necessary to deflect it from a collision course with Earth. Opportunities In addition to the threat that NEOs represent, they are also potential suppliers of resources for future manned space exploration. In order to use these resources, a much more detailed knowledge of their composition and physical characteristics will be required before the technologies to produce fuels or construction materials from NEOs can be developed. Current and Future Technologies for Earth Protection It is estimated that a 30-year advance warning would be required to have a reasonable assurance of deflecting a NEO from a collision with Earth. Thus, if a future impactor were identified today, the time to explore the characteristics of the NEO, develop a deflection system, deliver it to the NEO, and apply the deflection early enough to prevent an impact, requires about a 3-decade lead time. The deflection technologies available today, which are chemical rockets and nuclear weapons, both have limited abilities to slow down or speed up an asteroid. A 100 m object has a mass of the order of 1 million tons, and a 1 km object has a mass of the order of 1 billion tons. To prevent an object from colliding with Earth, it must be sped up or slowed down by about 7 cm/s (about 1/6 of an mile per hour) divided by the number of years in advance that the change is applied. The fuel that can be contained in a medium-sized scientific spacecraft could successfully deflect a 100 m body if it were pushed about 15 years in advance. The Space Shuttle’s main engines and the fuel contained in the large external tank could successfully deflect a 1 km diameter object if it were applied about 20 years in advance. Nuclear weapons carry much greater impulse for their mass. However, they deliver that impulse so quickly that they are more likely to break up the body than to deflect it. Because NEOs are in their own orbits around the Sun, the pieces of a disrupted object will tend to come together one half of an orbital period later. Therefore, the successful use of nuclear weapons for deflection will require the development of techniques for slowing the delivery of the impulse to the NEO and will probably also require many small weapons to be used to deflect a single NEO. The orbital mechanics required to approach a potential impactor also require it to be identified early. It may take 5 years or more for any deflector mission to rendezvous with a NEO in an arbitrary Earth-crossing orbit. What Remains to be Done An overall Earth protection system must have three components. First, a search system is needed to identify any potential NEO impactors. Second, a series of detailed investigation missions are needed to understand the structure, composition, rotational state, and other physical properties of potential impactors. And finally, deflection technologies are needed to change the speed of a NEO to ensure that it will not impact Earth. Search systems The United States and other countries around the world have concentrated on the first part of the Earth-protection system. At the current rate of discovery, the group of observatories that are finding and cataloging NEOs will come close to achieving their goal of identifying 90% of the greater than 1-km diameter NEO population by 2008. More than 50% of the expected population has already been discovered and discoveries continue to be made each month. While this effort will retire most of the risk of a global catastrophe, the size distribution of NEOs shows us that there are a great many more small objects than larger ones. Their numbers increase by a factor of about 220 for a diameter that is reduced by a factor of 10. This very large number of small-to-modest sized objects represents the greatest remaining threat to regional safety that is not being addressed. The equipment used by current NEO surveys is sized to find the largest objects. Some sub-kilometer objects are found serendipitously; however, these telescope systems are not optimized to find the smaller objects. A NASA NEO Science Definition Team recently examined the requirements for extending the NEO search to smaller diameters and showed that a system to accomplish the discovery and cataloging of 90% of all NEO greater than 100 m diameter within 10 years could be accomplished with a single Discovery-class spacecraft in a heliocentric orbit at about 0.7 AU. This modestly priced system (the Discovery class is about $300 million full mission cost) could be constructed and put on-station in four to five years. Detailed Examination of NEOs Several space missions that are contributing to the detailed investigations of NEOs and comets have been launched and others are currently in development. As stated above, the NEAR mission provided the first detailed information on the mass, shape, structure, and composition of an asteroid. However, we know from ground-based spectroscopic data that there is a great deal of variability among these objects. The Giotto and Deep Space 1 missions took close images of comets Halley and Borelli. The Stardust mission will be returning with dust particles from comet Wild 2 in January of 2006. The Deep Impact mission will create a crater in comet Tempel 1 to learn about the internal composition of comets. And the DAWN mission will examine the composition of asteroids 1 Ceres and 4 Vesta, two of the largest planetoids in the solar system. These missions are making steady progress in our understanding of the formation of the solar system and the characteristics of the small bodies within it. Continuation of this series of investigations is vital to our future ability to deal with the threat and opportunities of NEOs. Deflection Technologies While there has been a great deal of theoretical examination of deflection techniques, no practical systems exist at this time. As the search systems and detailed examination missions progress, it is important to continue the development of deflection system technologies so that a full Earth-protection system could be deployed rapidly if a future impactor is discovered by the search systems. Summary The threat to life on Earth from NEOs is real even though the likelihood of a severe impact during the next few years is low. The most important thing that is needed in order to deal with this risk is an improved search system. Recent studies have shown that a search spacecraft that can catalog 90% of the remaining NEOs larger than 100 m in diameter over 10 years of operation can be launched within 4 or 5 years at the cost of a NASA Discovery-class mission. In addition, the pace of mission developments for detailed examination of small solar system bodies should continue undiminished. This is clearly summarized by the cartoon below, originally published in New Yorker magazine in 1998.
Dr. Grant Stokes
Thank you, Mr. Chairman, for the opportunity to present to the subcommittee information on the subject of Near Earth Objects. In recent years, there has been an increasing appreciation for the hazards posed by near-Earth objects (NEOs), those asteroids and periodic comets (both active and inactive) whose motions can bring them into the Earth’s neighborhood. In August of 2002, NASA chartered a Science Definition Team to study the feasibility of extending the search for near-Earth objects to smaller limiting diameters. The formation of the team was motivated by the good progress being made toward achieving the so-called Spaceguard goal of discovering 90% of all near-Earth objects (NEOs) with diameters greater than 1 km by the end of 2008. This raised the question of what, if anything should be done with respect to the much more numerous smaller, but still potentially dangerous, objects. The team was tasked with providing recommendations to NASA as well as the answers to the following 7 specific questions: 1. What are the smallest objects for which the search should be optimized? 2. Should comets be included in any way in the survey? 3. What is technically possible? 4. How would the expanded search be done? 5. What would it cost? 6. How long would the search take? 7. Is there a transition size above which one catalogs all the objects, and below which the design is simply to provide warning? Team Membership The Science Definition Team, which I lead, was composed of experts in the fields of asteroid and comet search, including the Principal Investigators of two major asteroid search efforts, experts in orbital dynamics, NEO population estimation, ground-based and space-based astronomical optical systems and the manager of the NASA NEO Program Office. In addition, the Department of Defense (DoD) community provided members to explore potential synergy with military technology or applications. The Team members are listed in the following table along with their institutions. Dr. Grant H. Stokes (Chair) MIT Lincoln Laboratory Dr. Donald K. Yeomans (Vice-Chair) Jet Propulsion Laboratory/Caltech Dr. William F. Bottke, Jr. Southwest Research Institute Dr. Steven R. Chesley Jet Propulsion Laboratory/Caltech Jenifer B. Evans MIT Lincoln Laboratory Dr. Robert E. Gold Johns Hopkins University, Applied Physics Laboratory Dr. Alan W. Harris Space Science Institute Dr. David Jewitt University of Hawaii Col. T.S. Kelso USAF/AFSPC Dr. Robert S. McMillan Spacewatch, University of Arizona Dr. Timothy B. Spahr Smithsonian Astrophysical Observatory Dr./Brig. Gen. S. Peter Worden USAF/SMC Ex Officio Members Dr. Thomas H. Morgan NASA Headquarters Lt. Col. Lindley N. Johnson(USAF, ret.) NASA Headquarters Team Support Don E. Avery NASA Langley Research Center Sherry L. Pervan SAIC Michael S. Copeland SAIC Dr. Monica M. Doyle SAIC Analysis Process The Team approached the task using a cost/benefit methodology whereby the following analysis processes were completed: Population estimation – An estimate of the population of near-Earth objects (NEOs), including their sizes, albedos and orbit distributions, was generated using the best methods in the current literature. We estimate a population of about 1100 near-Earth objects larger than 1 km, leading to an impact frequency of about one in half a million years. To the lower limit of an object’s atmospheric penetration (between 50 and 100 m diameter), we estimate about half a million NEOs, with an impact frequency of about one in a thousand years. Collision hazard – The damage and casualties resulting from a collision with members of the hazardous population were estimated, including direct damage from land impact, as well as the amplification of damage caused by tsunami and global effects. The capture cross-section of the Earth was then used to estimate a collision rate and thus a yearly average hazard from NEO collisions as a function of their diameter. We find that damage from smaller land impacts below the threshold for global climatic effects is peaked at sizes on the scale of the Tunguska air blast event of 1908 (50-100 m diameter). For the local damage due to ocean impacts (and the associated tsunami), the damage reaches a maximum for impacts from objects at about 200 m in diameter; smaller ones do not reach the surface at cosmic speed and energy. Search technology – Broad ranges of technology and search systems were evaluated to determine their effectiveness when used to search large areas of the sky for hazardous objects. These systems include ground-based and space-based optical and infrared systems across the currently credible range of optics and detector sizes. Telescope apertures of 1, 2, 4, and 8 meters were considered for ground-based search systems along with space-based telescopes of 0.5, 1, and 2 meter apertures. Various geographic placements of ground-based systems were studied, as were space-based telescopes in low-Earth orbit (LEO) and in solar obits at the Lagrange point beyond Earth and at a point that trailed the planet Venus. Search simulation – A detailed simulation was conducted for each candidate search system, and for combinations of search systems working together, to determine the effectiveness of the various approaches in cataloging members of the hazardous object population. The simulations were accomplished by using a NEO survey simulator derived from a heritage within the DoD, which takes into account a broad range of “real-world” effects that affect the productivity of search systems, such as weather, sky brightness, zodiacal background, etc. Search system cost - The cost of building and operating the search systems described herein was estimated by a cost team from SAIC. The cost team employed existing and accepted NASA models to develop the costs for space-based systems. They developed the ground-based system cost estimates by analogy with existing systems. Cost/benefit analysis – The cost of constructing and operating potential survey systems was compared with the benefit of reducing the risk of an unanticipated object collision by generating a catalog of potentially hazardous objects (PHOs). PHOs, a subset of the near-Earth objects, closely approach Earth’s orbit to within 0.05 AU (7.5 million kilometers). PHO collisions capable of causing damage occur infrequently, but the threat is large enough that, when averaged over time, the anticipated yearly average of impact-produced damage is significant. Thus, while developing a catalog of all the potentially hazardous objects does not actually eliminate the hazard of impact, it does provide a clear risk reduction benefit by providing awareness of potential short- and long-term threats. The nominal yearly average remaining, or residual, risk in 2008 associated with PHO impact is estimated by the Team to be approximately 300 casualties worldwide, plus the attendant property damage and destruction. About 17% of the risk is attributed to regional damage from smaller land impacts, 53% to water impacts and the ensuing tsunamis, and 30% to the risk of global climatic disruption caused by large impacts, i.e. the risk that is expected to remain after the completion of the current Spaceguard effort in 2008. For land impacts and all impacts causing global effects, the consequences are in terms of casualties, whereas for sub-kilometer PHOs causing tsunamis, the “casualties” are a proxy for property damage. According to the cost/benefit assessment done for this report, the benefits associated with eliminating these risks justify substantial investment in PHO search systems. PHO Search Goals and Feasibility The Team evaluated the capability and performance of a large number of ground-based and space-based sensor systems in the context of the cost/benefit analysis. Based on this analysis, the Team recommends that the next generation search system be constructed to eliminate 90% of the risk posed by collisions with sub-kilometer diameter PHOs. Such a system would also eliminate essentially all of the global risk remaining after the Spaceguard efforts are complete in 2008. The implementation of this recommendation will result in a substantial reduction in risk to a total of less than 30 casualties per year plus attendant property damage and destruction. A number of search system approaches identified by the Team could be employed to reach this recommended goal, all of which have highly favorable cost/benefit characteristics. The final choice of sensors will depend on factors such as the time allotted to accomplish the search and the available investment. Answers to Questions Stated in Team Charter What are the smallest objects for which the search should be optimized? The Team recommends that the search system be constructed to produce a catalog that is 90% complete for potentially hazardous objects (PHOs) larger than 140 meters. Should comets be included in any way in the survey? The Team’s analysis indicates that the frequency with which long-period comets (of any size) closely approach the Earth is roughly one-hundredth the frequency with which asteroids closely approach the Earth and that the fraction of the total risk represented by comets is approximately 1%. The relatively small risk fraction, combined with the difficulty of generating a catalog of comets, leads the Team to the conclusion that, at least for the next generation of NEO surveys, the limited resources available for near-Earth object searches would be better spent on finding and cataloging Earth-threatening near-Earth asteroids and short-period comets. A NEO search system would naturally provide an advance warning of at least months for most threatening long-period comets. What is technically possible? Current technology offers asteroid detection and cataloging capabilities several orders of magnitude better than the presently operating systems. NEO search performance is generally not driven by technology, but rather resources. This report outlines a variety of search system examples, spanning a factor of about 100 in search discovery rate, all of which are possible using current technology. Some of these systems, when operated over a period of 7-20 years, would generate a catalog that is 90% complete for NEOs larger than 140 meters. How would the expanded search be done? From a cost/benefit point-of-view, there are a number of attractive options for executing an expanded search that would vastly reduce the risk posed by potentially hazardous object impacts. The Team identified a series of specific ground-based, space-based and mixed ground- and space-based systems that could accomplish the next generation search. The choice of specific systems will depend on the time allowed for the search and the resources available. What would it cost? For a search period no longer than 20 years, the Team identified several systems that would eliminate, at varying rates, 90% of the risk for sub-kilometer NEOs, with costs ranging between $236 million and $397 million. All of these systems have risk reduction benefits which greatly exceed the costs of system acquisition and operation. How long would the search take? A period of 7-20 years is sufficient to generate a catalog 90% complete to 140-meter diameter, which will eliminate 90% of the risk for sub-kilometer NEOs. The specific interval depends on the choice of search technology and the investment allocated, as shown in the figure below. The cost of various space-based and ground-based search systems are plotted against the number of search years required to reduce by 90% the sub-global risk from impacts by sub-kilometer sized objects. Is there a transition size above which one catalogs all the objects, and below which the design is simply to provide warning? The Team concluded that, given sufficient time and resources, a search system could be constructed to completely catalog hazardous objects with sizes down to the limit where air blasts would be expected (about 50 meters in diameter). Below this limit, there is relatively little direct damage caused by the object. Over the 7-20 year interval (starting in 2008) during which the next generation search would be undertaken, the Team suggests that cataloging is the preferred approach down to approximately the 140-meter diameter level and that the search systems would naturally provide an impact warning of 60-90% for objects as small as those capable of producing significant air blasts. Science Definition Team Recommendations The Team makes three specific recommendations to NASA as a result of the analysis effort: Recommendation 1 – Future goals related to searching for potential Earth-impacting objects should be stated explicitly in terms of the statistical risk eliminated (or characterized) and should be firmly based on cost/benefit analyses. This recommendation recognizes that searching for potential Earth impacting objects is of interest primarily to eliminate the statistical risk associated with the hazard of impacts. The “average” rate of destruction due to impacts is large enough to be of great concern; however, the event rate is low. Thus, a search to determine if there are potentially hazardous objects (PHOs) likely to impact the Earth within the next few hundred years is prudent. Such a search should be executed in a way that eliminates the maximum amount of statistical risk per dollar of investment. Recommendation 2 – Develop and operate a NEO search program with the goal of discovering and cataloging the potentially hazardous population sufficiently well to eliminate 90% of the risk due to sub-kilometer objects. The above goal is sufficient to reduce the average casualty rate from about 300 per year to less than 30 per year. Any such search would find essentially all of the larger objects remaining undiscovered after 2008, thus eliminating the global risk from these larger objects. Over a period of 7-20 years, there are a number of system approaches that are capable of meeting this search metric with quite good cost/benefit ratios. Recommendation 3 – Release a NASA Announcement of Opportunity (AO) to allow system implementers to recommend a specific approach to satisfy the goal stated in Recommendation 2. Based upon our analysis, the Team is convinced that there are a number of credible, current technology/system approaches that can satisfy the goal stated in Recommendation 2. The various approaches will have different characteristics with respect to the expense and time required to meet the goal. The Team relied on engineering judgment and system simulations to assess the expected capabilities of the various systems and approaches considered. While the Team considers the analysis results to be well grounded by current operational experience, and thus, a reasonable estimate of expected performance, the Team did not conduct analysis at the detailed system design level for any of the systems considered. The next natural step in the process of considering a follow-on to the current Spaceguard program would be to issue a NASA Announcement of Opportunity (AO) as a vehicle for collecting search system estimates of cost, schedule and the most effective approaches for satisfying the recommended goal. The AO should be specific with respect to NASA’s position on the trade between cost and time to completion of the goal. The complete Science Definition Team Report may be accessed online at: http://neo.jpl.nasa.gov/neo/neoreport030825.pdf I thank you for the opportunity to appear and would be happy to respond to any questions. Dr. Grant Stokes MIT Lincoln Laboratory
Dr. Ed Lu
Thank you for the opportunity today to discuss a bold new proposal to demonstrate altering the orbit of an asteroid. I represent the B612 foundation, a group of astronomers, engineers, and astronauts, concerned about the issue of asteroid impacts. Recent developments have now given us the potential to defend the Earth against these natural disasters. To develop this capability we have proposed a spacecraft mission to significantly alter the orbit of an asteroid in a controlled manner by 2015. Why move an asteroid? There is a 10 percent chance that during our lifetimes there will be a 60 meter asteroid that impacts Earth with energy 10 megatons (roughly equivalent to 700 simultaneous Hiroshima sized bombs). There is even a very remote one in 50,000 chance that you and I and everyone we know, along with most of humanity and human civilization, will perish together with the impact of a much larger kilometer or more sized asteroid. We now have the potential to change these odds. There are many unknowns surrounding how to go about deflecting an asteroid, but the surest way to learn about both asteroids themselves as well as the mechanics of moving them is to actually try a demonstration mission. The first attempt to deflect an asteroid should not be when it counts for real, because there are no doubt many surprises in store as we learn how to manipulate asteroids. Why by 2015? The time to test, learn, and experiment is now. A number of recent developments in space nuclear power and high efficiency propulsion have made this goal feasible. The goal of 2015 is challenging, but doable, and will serve to focus the development efforts. How big of an asteroid are we proposing to move? The demonstration asteroid should be large enough to represent a real risk, and the technology used should be scaleable in the future to larger asteroids. We are suggesting picking an asteroid of about 200 meters. A 200 meter asteroid is capable of penetrating the atmosphere and striking the ground with an energy of 600 megatons. Should it land in the ocean (as is likely), it will create an enormous tsunami that could destroy coastal cities. Asteroids of about 150 meters and larger are thought to be comprised of loose conglomerations of pieces, or rubble piles, while smaller asteroids are often single large rocks. The techniques we test on a 200 meter asteroid should therefore also be applicable to larger asteroids. What does “significantly alter the orbit” mean? If proposed asteroid searches are enacted, we expect to have decades or more of warning before an impact. Given this amount of warning, to prevent an impact only requires that the orbital velocity of an asteroid be altered by a small amount, less than of order 1 cm/sec, or about .02 MPH. This is a tiny velocity increment, considering that the orbital speeds of asteroids are of order 70,000 MPH. However, this is still a very difficult task since the mass of a 200 meter asteroid is of order 10 million tons. Why does the asteroid need to be moved in a “controlled manner”? If the asteroid is not deflected in a controlled manner, we risk simply making the problem worse. Nuclear explosives for example risk breaking up the asteroid into pieces, thus turning a speeding bullet into a shotgun blast of smaller but still possibly deadly fragments. Explosions also have the drawback that we cannot accurately predict the resultant velocity of the asteroid – not a good situation when trying to avert a catastrophe. Conversely, moving an asteroid in a controlled fashion also opens up the possibility of using the same technology to manipulate other asteroids for the purposes of resource utilization. How can this be accomplished? This mission is well beyond the capability of conventional chemically powered spacecraft. We are proposing a nuclear powered spacecraft using high efficiency propulsion (ion or plasma engines). Such propulsion packages are currently already under development at NASA as part of the Prometheus Project. In fact, the power and thrust requirements are very similar to the Jupiter Icy Moons Orbiter spacecraft, currently planned for launch around 2012. The B612 spacecraft would fly to, rendezvous with, and attach to a suitably chosen target asteroid (there are many candidate asteroids which are known to be nowhere near a collision course with Earth). By continuously thrusting, the spacecraft would slowly alter the velocity of the asteroid by a fraction of a cm/sec – enough to be clearly measurable from Earth. What will we learn from this? It is important to remember that this mission is merely a first attempt to learn more about the mechanics of asteroid deflection. There are a number of technical complications, as well as many unknowns about the structure and composition of asteroids. However, the way to make progress is to build, fly, and test. Much of what we will learn is generic to many proposed asteroid deflection schemes, with the added benefit of being able to answer important scientific questions about asteroids themselves. The best way to learn about asteroids is to go there. How does this fit into the new Exploration Initiative at NASA? In the near term, this mission would be an ideal way to flight test the nuclear propulsion systems under development as part of the Prometheus Project. It could also serve as a precursor to a crewed mission to visit an asteroid. Such missions have been proposed as intermediate steps to test spacecraft systems for eventual longer term crewed missions to Mars. In the longer term, the ability to land on and manipulate asteroids is an enabling technology for extending human and robotic presence throughout the solar system. If we are to truly open up the solar system, this mission is a good way to start. It is likely that someday we will utilize asteroids for fuel, building materials, or simply as space habitats. The B612 mission would mark a fundamental change in spacecraft in that it would actually alter in a measurable way an astronomical object, rather than simply observing it. Human beings must eventually take charge of their own destiny in this manner, or we will someday go the way of the dinosaurs when the next great asteroid impact occurs.
Mr. Rusty Schweickart
Testimony of Russell L. Schweickart, Chairman, B612 Foundation, before the Subcommittee on Science, Technology and Space of the Senate Commerce Committee 7 April 2004 Chairman Brownback, Senator Breaux, members of the Committee: Introduction First I’d like to thank you for the invitation to speak with you today about this emerging public policy issue of near Earth objects (NEOs) threatening life on Earth. One might have thought, just a few years ago, that the subject of asteroids was one for space wonks and wanna-be astronauts and astronomers. But today the realization is rapidly dawning on the media and the general public that asteroids are a subject of more than passing interest! More and more people are coming to know that some few of these asteroids do not silently pass the Earth, but indeed crash in, largely unannounced. On the rare occasions when this happens they can wreak havoc of a magnitude unprecedented in human history. At the upper limit impacts by large asteroids have caused global destruction leading to the virtually instantaneous extinction of life for most of the species living at the time. The dinosaurs were momentary witnesses to a billion megaton event of this kind 65 million years ago. At the lower limit of concern, but occurring much more frequently, we are dealing with events with an explosive force of 10-15 megatons. It is worth pointing out, however, that these small, most frequent events are more powerful than the blast from the most powerful nuclear weapon in the current U.S. nuclear arsenal. Given the extremely low frequency of these natural events in combination with the extremely grave consequences when they occur, we find ourselves challenged to properly place this subject in our normal list of priorities. Inattention to infrequent events, regardless of their impact, is the “default” solution of choice given the crowd of issues continually burning around our feet. Therefore the Committee is to be congratulated for its foresight and exemplary public service in realizing the importance of dealing with this issue now. History Perhaps the best logic path to bring the Committee to appreciate our recommendations for action is to briefly outline the key realities the founders of the B612 Foundation faced when we first came together back in October 2001. We are primarily a group of technical experts familiar with or working within the fields of space exploration and planetary science. We are astronauts, astronomers, engineers and a few others who are knowledgeable about the subject of comets and asteroids and their history of impacts with the Earth and other solar system bodies. We came together out of a deep concern that the threat to life implied in our knowledge of near Earth asteroids (NEAs) was not resulting in any organized effort to take action to protect the public from this hazard. We came together to explore whether or not something could be done, and if so, whether we could trigger a program to protect the public. In summary, we faced the following facts: 1) Asteroid impacts with Earth have, do, and will continue to occur with devastating consequences to life. 2) Our detection program (the Spaceguard Survey) has produced a good statistical characterization of the overall threat and actual knowledge that at least 60% of the asteroids larger than 1 kilometer in diameter will not strike the Earth in the next 100 years. 3) Many impacts by asteroids less than 1 km in diameter, however, which occur hundreds of times more frequently than those over 1 kilometer, will cause unacceptable devastation at both local and regional levels. 4) The increasing capability of our detection programs in the next several years will result in a dramatic increase in the discovery rate of these smaller but very dangerous asteroids. 5) The media and the general public will become ever more aware of this threat and concerned that something should be done about it. 6) A known threat that can potentially destroy millions of lives AND can be predicted to occur ahead of time, AND prevented, cannot responsibly go unaddressed. This inexorable logic led us to decide to take action and examine whether preventive measures could be taken to mitigate this threat, and if so, what specific course of action we would recommend. The Challenge It became immediately clear to us that the combination of advanced propulsion technologies and small space qualified nuclear reactors, both operating in prototype form already, would be powerful enough, with reasonable future development, to deflect most threatening asteroids away from a collision with the Earth, given a decade or more of advance warning. Nevertheless we saw two immediate problems. First we lack the specific knowledge of the characteristics of NEAs necessary to design anything approaching a reliable operational system. We could readily show that the technology would exist within a few years to get to and land on an asteroid. We also determined that after arriving at the asteroid we would have enough propulsive energy available to successfully deflect the asteroid from an Earth impact a decade or so later. What was missing however was knowledge about the structure and characteristics of asteroids detailed enough to enable successful and secure attachment to it. Second we recognized that before we would be able to gather such detailed information about NEAs there would likely be many public announcements about near misses and possible future impacts with asteroids which would alarm the general public and generate a growing demand for action. We felt strongly that there needed to be some legitimate answer to the inevitable question which will be put to public officials and decision makers, “and what are you doing about this?” These two considerations led us to the conclusion that the most responsible course of action would be to mount a demonstration mission to a NEA (one of our choosing) which would accomplish two essential tasks; 1) gather critical information on the nature of asteroid structure and surface characteristics, and 2) while there, push on the asteroid enough to slightly change its orbit thereby clearly demonstrating to the public that humanity now has the technology to protect the Earth from this hazard in the future. We furthermore determined that this demonstration mission could be done with currently emerging capabilities within 10-12 years. We therefore adopted the goal of “altering the orbit of an asteroid, in a controlled manner, by 2015”. Reflecting the work that we have done to bring this goal to realization, a number of us wrote a descriptive article for Scientific American magazine entitled, The Asteroid Tugboat. Scientific American published it in the November 2003 issue of the magazine. I have provided reprints of this article to the Committee and I would like to submit a copy with this testimony and ask that it be incorporated in the record. Implementation A key to implementing this mission is NASA’s Prometheus Program. Shortly after B612 Foundation began work on outlining a mission to explore and deflect an asteroid NASA announced the formation of its Prometheus Program to develop and demonstrate technologies to permit routine human and robotic activity in space “beyond low Earth orbit”. The key technologies which NASA recognized would enable this capability are identical with what we had determined were necessary to demonstrate the capability to land on and deflect a near Earth asteroid, i.e., high performance electric propulsion systems and the space nuclear electric power systems to power them. Shortly after announcing the Prometheus Program NASA announced the Jupiter Icy Moons Orbiter (JIMO) mission complete with schematic representations of the spacecraft. Integral to the design of this mission were the very high performance engines and space nuclear power system which would be necessary to enable our B612 mission. We therefore adopted, as an explicit element of our design, the JIMO/Prometheus capabilities, recognizing that this was the most likely path to meeting the demonstration goal that we had set. Mounting a mission to assure the public that when we discover an asteroid “with our name on it” we can deflect it from a life threatening impact on Earth does not require the development of additional new technologies. The key capabilities required are already “in the pipeline” of the existing Prometheus Program. No new NASA money is required, nor is a change in NASA’s mission called for. What is required is that the B612 mission be incorporated within the Prometheus Program… a matter of policy. Indeed, if one examines the technical requirements associated with the B612 mission, one sees not only a mission ideally suited to demonstrating the Prometheus technology, but a mission notably less demanding than the currently planned JIMO mission. One could then quite easily consider the B612 mission as either a follow-on or a precursor to the JIMO mission, depending on NASA’s technical judgment as to where it fits most logically in their mission model. The B612 mission also fits well into the President’s Space Exploration Initiative. This mission both utilizes and graphically demonstrates the key enabling technologies for routine future operations “beyond low Earth orbit”. It is an ideal way to demonstrate the technology and the greatly enhanced propulsive capability implicit in the Prometheus exploration program. In executing such a mission humankind will, for the first time in its history, have altered the trajectory of a cosmic body, a demonstration of evolving capability in space technology and exploration if there ever was one! Additional Perspective A few final comments are perhaps appropriate. Near Earth asteroids are a reality which is here to stay. In fact they will become far more prominent in the public mind as time goes on and our detection of them continues to improve. It is therefore appropriate that we take a more circumspect look at these sometimes unruly, but ever-present, neighbors. Near Earth asteroids are, in fact, both a threat and an opportunity. Certainly we need to learn more about our capability to protect life here on Earth, and the sooner the better. Visiting asteroids can also teach us a great deal about the origins of the solar system, and perhaps even the origins of life. Unlike the material of the Earth, which has been melted and processed through extensive geologic activity, the materials of small asteroids have not been so extensively reprocessed. They are fossil building blocks left over from the formation of the planets and as such can teach us a great deal about the original material from which the planets formed. Perhaps even more important, asteroids, and especially the near Earth asteroids, are also the most readily accessible and rich reservoir of non-terrestrial resources available to us. The new space initiative has emphasized our determination to return to the Moon and then extend our capability outward to Mars and beyond. One of the purposes advocated for returning to the Moon is to explore and potentially develop the capability to utilize the resources there for human benefit. The possibility of extracting oxygen, water and perhaps other materials from lunar soils has long been advocated as a potential capability for reducing the cost of future space operations. Yet these same resources, and others in rich abundance, characterize the makeup of asteroids. Unlike lunar materials, which are largely depleted of heavy minerals, the asteroids are quite rich in metallic elements, as well as those minerals which may provide water and oxygen. Furthermore it is significantly less expensive to fly to and from selected near Earth asteroids than to and from the Moon due to the virtual absence of gravitational forces associated with these bodies. When commercial, entrepreneurial activity emerges into deep space it will undoubtedly include the development and exploitation of in-situ resources and services. Given the critical importance of benefit/cost analysis in any commercial venture it would be surprising if utilization of asteroidal resources, especially water, is not one of the first deep space initiatives attracting private capital. Given then the infrequency of actually having to deflect an asteroid in order to avoid an Earth impact it is unlikely that humanity will ever need to develop a stand-alone planetary defense system. However, given the commercial, as well as the scientific value implicit in near Earth asteroids it is highly likely that operations to and from the asteroids will become a routine part of human space operations. One can readily imagine a time when visiting, using and even moving near Earth asteroids becomes a routine human capability. Simply calling on the “Ace Asteroid Mining and Moving Company” to nudge asteroid 2018 FA322 gently out of the way may then be all that is required to prevent an otherwise devastating event. While the above scenario is somewhat fanciful, it is, given time, only slightly so. In the meanwhile, in the immediate future, we will be discovering an increasing number of potentially life threatening NEAs and the public will become justifiably concerned. Without a legitimate answer to this concern for their safety this concern could morph into alarm. While many lives are lost every year in natural disasters of one kind or another, there are few natural disasters that can reliably be predicted, much less prevented. Throughout human experience we have been faced with comforting and compensating the devastated after the disaster is over. With near Earth asteroid impacts, however, we are confronted with a massive natural disaster that can be both predicted AND prevented, and the public will come to understand that this is the case. Given the justifiable public expectation of being protected from both natural and manmade disasters it is incumbent on us to address this known threat responsibly. We therefore make the following specific recommendations: 1) We call on the Congress to task NASA with increasing the capability of the current Spaceguard Survey consistent with the recommendations of the recent NASA Near-Earth Object Science Definition Team report . 2) We call on Congress to direct NASA to incorporate the B612 mission goal of demonstrating the capability of landing on, exploring, and deflecting an asteroid as part of its Prometheus Program. 3) We call on Congress to request that OSTP initiate a high level study to develop a US Government policy for both national and international response to the deflection of near Earth asteroids.