US space policy and planetary defense

2243aby James C. Howe
The meteor over Chelyabinsk, Russia, in February 2013 brought new awareness of the threats posed by near Earth objects and new questions about what the US and other governments should do about them. (credit: Wikimedia Commons)Our solar system is populated by a wealth of other orbiting bodies, including hundreds of thousands of asteroids and comets that have already been discovered, with some scientists estimating a total asteroid population of over a billion. While most asteroid orbits are concentrated in a belt between Mars and Jupiter, some are on elliptical trajectories that cross the orbital plane of Earth. Comets, which cross Earth’s path much less frequently, have a wide range of orbital periods, from several years to several millennia.1
Numerous asteroid collisions with Earth and its atmosphere have been documented over the life of the planet: scientists believe the impact of a 10-kilometer-wide asteroid millions of years ago killed all species of dinosaurs and extinguished most life on Earth.2 In February 2013, in an event captured on hundreds of videos, an asteroid approximately 15–20 meters in diameter exploded 30 miles above Chelyabinsk, Russia, damaging buildings and injuring more than 1,000 people. While telescopic surveys have identified the vast majority of the largest asteroids that pass near Earth, only about one percent of smaller, yet nonetheless dangerous asteroids, have been cataloged.3
“Planetary defense” is the term associated with locating asteroids and comets that have the potential for impacting Earth and employing technical means for diverting them from a collision course (because of the rarity of comets, asteroids are the prime focus of planetary defense policies.) The general idea is that if a threatening asteroid can be identified years or decades ahead of impact, current space technologies and hardware can be used to nudge the asteroid off its current orbit to avoid striking Earth: even a change in velocity of a centimeter per second may be enough to prevent a collision. For large asteroids or those located only a few years before projected impact, the use of nuclear weapons to deflect or fragment the asteroid may be the only option.
The concept of defending against an asteroid strike began to generate significant policy interest after astronomers witnessed fragments of Comet Shoemaker-Levy 9 striking the planet Jupiter in July 1994. American and international efforts in the wake of this event led to the identification of most of the larger asteroids that cross Earth’s orbit, but hundreds of thousands of smaller asteroids undiscovered. The Chelyabinsk event has helped catalyze more intense international activity to address this threat, with the United Nation’s Space Mission Planning and Advisory Group currently tasked with determining actions that could be taken in response to discovery of a threatening asteroid.4
The following review will examine what the current US space policy regarding planetary defense, and whether policy refinements should be made, The analysis will show that American policymaking efforts in the realm of planetary defense should be bolstered to improve the nation’s ability to respond to a real-world event, as well as to provide stronger leadership for the world community.
International law and planetary defense
There is no language in any standing international space treaty that deals with the issue of detection and mitigation of potentially hazardous asteroids or comets. Four major space treaties have been ratified by the United States and the other major spacefaring nations, and there is no direct mention in them of the threat from collision with naturally occurring space objects. Nonetheless, there are a host of provisions in international space law that are supportive of the general concept of planetary defense, even if the topic is not overtly discussed.
The Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, Including the Moon and Other Celestial Bodies (better known as the Outer Space Treaty), is the fundamental source of international space law. Written at the height of the Cold War, when the world’s two space powers were locked in a race to establish supremacy in space, the Outer Space Treaty focused on allowing freedom of access to space and preserving the cosmos for peaceful use for the benefit of all humanity. The core elements of the treaty provide a strong conceptual foundation for an international effort to locate, track, and mitigate potentially threatening asteroids. In the treaty’s preamble, for example, great emphasis is put on preserving outer space for the betterment of all nations, a sentiment repeated many times in the document. Article III mandates that space activities be carried out in accordance with existing international law in order to help preserve peace and security, while Article IX stresses the principles of international cooperation and mutual assistance.5
A second treaty that provides foundational support for notional planetary defense cooperation is the 1979 Agreement Governing the Activities of States on the Moon and Other Celestial Bodies (aka the Moon Agreement). Although never ratified by the US or most other space powers, the Moon Agreement reflects the position of many non-spacefaring nations in regard to the utilization of natural resource found in space. This treaty reemphasizes the Outer Space Treaty’s focus on the peaceful use of space, and specifically addresses the need for strong international cooperation in space activities, stating that “International co-operation in pursuance of this Agreement should be as wide as possible and may take place on a multilateral basis, on a bilateral basis, or through international intergovernmental organizations.”6 Such a construct would be essential in mobilizing international actions to mitigate the projected collision of a threatening asteroid with Earth.
US national space policy
As a signatory to the Outer Space Treaty, US space policy has been written to conform with the general provisions of accepted international space law. Similar to these treaties, there has not been, until very recently, any direct mention in US top-level policy of the hazards posed by asteroid collisions with Earth. The most recent strategic space policy document, the National Space Policy of the United States of America, issued in 2010, is the first to address the topic: it directs NASA to pursue technology “to detect, track, catalog, and characterize near-Earth objects (NEOs) to reduce the risk of harm to humans from an unexpected impact on our planet.”7
The 2010 space policy stresses international cooperation and identifies several specific areas for possible expanded collaboration, including environmental monitoring, communications, search and rescue, science, and exploration, but makes no mention in this section of locating and deflecting potentially hazardous space objects. Throughout the document, however, are sprinkled several broader policy goals that generically would support international efforts to counter an asteroid threat: a pledge for reinvigorated US leadership to expand space operations for the betterment of all nations, reinforcement of the right to use space to benefit all mankind, assurance that the US may use space for collective self-defense, and a dedication to enhanced responsible behavior and security in space.8 The potential for US leadership in an asteroid deflection mission also is supported by a second policy document, the National Space Transportation Policy, which directs the development of heavy lift space systems capable of escaping low Eerth orbit for exploration of other celestial bodies, “including an asteroid and Mars.”9
The George W. Bush administration’s space policy, while not directly mentioning planetary defense, makes three key supportive assertions. First, the policy stresses the need to encourage enhanced cooperation with other nations for peaceful purposes and to bolster national and homeland security. Second, the document places emphasis on using space-based resources to improve disaster warning systems (while intended to increase readiness for hurricanes and other terrestrial disasters, the concept applies to the detection of threatening asteroids). Third, the policy mentions the need to improve international cooperative efforts to enhance national security interests, including planetary observation systems.10
Interestingly, the Clinton Administration’s top-level space policy, issued during a period of significantly heightened awareness and concern over NEOs, makes no mention of the asteroid threat phenomenon. The policy lists five major goals, the first two of which can be construed as obliquely applying to planetary defense: enhancing scientific knowledge of the solar system and universe, and improving the national security of the US. Aside from these generalities, the policy also provides several specific directives, including, for example, for NASA to establish a robotic presence on Mars by 2000 and to develop a new program to ascertain characteristics of planets orbiting other stars. Yet despite the policy specificity established for similar niche missions, there is no stated policy for detecting and countering threatening asteroids and comets.11
The space policies of the George H.W. Bush, Reagan, and Carter Administrations placed emphasis on general goals supporting the use of space for the betterment of all nations, but also had no mention of NEOs. National Space Policy Directive 1, issued in 1989, mentions twice in its opening paragraphs the need to cooperate with other spacefaring nations for peaceful purposes and to “enhance the security and welfare of mankind”12 —policy goals that would be supportive of an international planetary defense mission. The 1982 and 1988 space policies issued by President Reagan included even more general assertions of the need for international cooperative efforts, and specifically mentioned enhancing the nation’s civil space program to expand understanding of the solar system and its component bodies.13 President Carter’s space policy made more generalized statements on the goal of increasing knowledge of the universe and enhancing international cooperation.14
Earlier policy, back to the start of the Space Age, was no different in respect to its lack of mention of planetary defense. For example, with the Apollo program at its height, President Nixon sought recommendations on future direction for the nation’s space program, and directed Vice President Agnew to conduct a thorough analysis. The report of the Space Task Group in 1969 offered three visions for the nation’s future space policies, including manned missions to Mars.15 Throughout the Space Task Group’s report were numerous detailed recommendations concerning the direction of scientific effort, technological development, and manned space missions, along with a strong emphasis that the US “promote a sense of world community through a [space] program which provides opportunity for broad international participation and cooperation.”16 There was, however no mention of asteroids or the NEO threat.
While national space policy only recently came to address the NEO issue, the fundamental precepts of previous policies has been indirectly supportive of efforts that would be needed to detect and mitigate a threatening asteroid. But because planetary defense never was seen as a priority for America’s space efforts, it did not garner until very recently any specific mention or direction in these strategic-level policies.
Congressional, agency, and nongovernmental policy actions
While not receiving primary policy attention, solid work in the arena of planetary defense was being carried out for decades in the research community, the executive branch, and through the direction of Congress. Much of this activity was catalyzed by the seminal Shoemaker-Levy comet strike in 1994.
During the first three decades of the space age, as American policy focused on manned space flight and a host of other national priorities, the scientific community took rudimentary steps to detect and track threatening asteroids. By the late 1980s a number of planetary defense workshops had been held that built consensus around establishing a coordinated international effort to address the threat of potentially hazardous objects (PHOs).17 In 1990, the American Institute of Aeronautics and Astronautics (AIAA) released a position paper that highlighted the threat from NEOs; this paper gained wide attention and prompted Congress to direct NASA to more thoroughly analyze the issue.18 In 1992, NASA presented to Congress a report titled The Spaceguard Survey, which outlined the threat posed by PHOs and advocated for an enhanced and coordinated international effort, led by the United States, to detect threatening asteroids and comets.19 In response, the House Committee on Science, Space, and Technology held a public hearing on March 24, 1993, the first ever to address the issue of Earth-threatening asteroids.20
The timing of this Congressional attention was fortuitous, for only a year later millions of people around the world watched telescopic images that showed Comet Shoemaker-Levy 9 colliding with Jupiter, the first direct observation in human history of a collision between celestial bodies. Torn by Jupiter’s gravitational pull into 21 separate pieces, each up to two kilometers in diameter, the impacts from the comet created massive clouds of debris, thousands of miles in diameter: the combined force of the impacts released far more energy than was contained in all nuclear weapons on Earth.21 The implication was strikingly clear: the solar system was a dangerous place and a similar impact on Earth would have catastrophic consequences for humanity.
The Shoemaker-Levy event prompted intense congressional interest in the NEO issue. Late in 1994, the House of Representatives passed the Aeronautics and Space Policy Act of 1994, which in Section 129 included prescriptive action for NASA:
(a) REQUIREMENT- To the extent practicable, the National Aeronautics and Space Administration, in coordination with the Department of Defense and the space agencies of other countries, shall identify and catalogue within 10 years the orbital characteristics of all comets and asteroids that are greater than 1 kilometer in diameter and are in an orbit around the sun that crosses the orbit of the Earth.
(b) PROGRAM PLAN- By February 1, 1995, the Administrator shall submit to the Congress a program plan, including estimated budgetary requirements for fiscal years 1996 through 2000, to implement subsection (a). 22
Unfortunately, the Bill did not make its way to the President for signature and the legislation remained in limbo. Nonetheless, NASA convened a second working group—this one headed by Dr. Gene Shoemaker, co-discoverer of the Shoemaker-Levy comet—to refine the 1992 Spaceguard Survey.23 The results of these findings were presented to Congress in 1995 and the effort formally named the Near Earth Object Survey. In early 1997, Dr. Shoemaker testified about the need for added funding to accelerate the NEO detection program: the House of Representatives concurred and in the Civilian Space Authorization Act, Fiscal Years 1998 and 1999, indicated the House’s support for an accelerated detection regime by NASA, requiring the agency to develop a cost-estimate and plan for detecting all NEOs within 10 years. The House had made clear their legislative intent: in 1998 NASA announced new and improved goals that centered on locating 90 percent of NEOs larger than one kilometer in diameter within a decade.24
The congressional and NASA activities were mirrored by progress made overseas. Following an organizing meeting in Vulcano, Italy, in 1995, NEO detection programs were implemented in a number of countries, coordinated under the auspices of the International Astronomical Union (IAU).25 The United States, Japan, and the European Space Agency played key leadership roles in these efforts. A non-profit organization called the Spaceguard Foundation was established with headquarters in Italy; the Minor Planet Center of the Harvard-Smithsonian Center for Astrophysics was designated the clearinghouse for all NEO-related observations and data; and dozens of observatories around the world were enlisted in the NEO detection effort. Through this international coordination a vast library of information about NEOs and PHOs was and continues to be cataloged, with all observations made available to the public.26
A firm congressional mandate to further improve NEO detection policies was set in 2005 with the passage of the George E. Brown, Jr. Near-Earth Object Survey Act, which was enacted as part of the National Aeronautics and Space Administration Authorization Act of 2005. This legislation markedly improved the US goals for detection of NEOs, mandating that NASA oversee a program to detect, catalog, and track 90 percent of all NEOs greater than140 meters in diameter within 15 years.27 The new policy requirement vastly expanded the population of asteroids and comets that NASA would be responsible for locating. However, as with past policies, there was no mention of activities related to mitigation should a threatening asteroid be detected.
Congressional direction to the executive branch continued in an effort to further refine the NEO detection effort. In the Consolidated Appropriations Act of 2008, the National Research Council was chartered to study both the detection of near earth objects as well as potential mitigation strategies. This study, published in 2010, found that NASA funding was grossly insufficient for meeting the policy goals set in 2005.28 Following that study, funding for NEO detection programs increased to more than $20 million per year, and the 2011 NASA Strategic Plan included a specific policy goal of identifying and characterizing small asteroids with the potential for threatening life on Earth.29 This strategic focus was built off legislation in 2010 that codified NASA’s role in planetary defense:
Congress declares that the general welfare and security of the United States require that the unique competence of the Administration be directed to detecting, tracking, cataloguing, and characterizing near-Earth asteroids and comets in order to provide warning and mitigate the potential hazard of such near-Earth objects to the Earth.30
Policy and funding are closely inter-related, and the NASA budget request for NEO detection activities in fiscal years 2012 and 2013 was set at $20.4 million. However, the Administration’s funding request for fiscal year 2014, issued in the wake of the Chelyabinsk event, showed growing awareness of the need to further enhance NEO detection efforts, nearly doubling federal spending on NEO observations to $40.5 million. From 2015 and forward, however, spending was projected to return to the lower level of $20.5 million per year.31 The omnibus appropriations legislation signed into law in January 2014 supported this one-year boost in funding.32
Additionally, in June 2013, NASA issued a “Grand Challenge” to the public at large to obtain ideas and recommendations related to finding and mitigating threatening asteroids. This initiative is designed to unearth innovative and cost-effective means for detecting all potentially threatening PHOs and protecting Earth from them, and is designed for NASA to engage “other government agencies, international partners, industry, academia, and citizen scientists.”33
Policy initiatives were not limited to Congress and NASA, however. One highly innovative nonprofit institution set out to make a major contribution to the NEO detection effort. Retired astronauts Rusty Schweikart and Ed Lu establishsed the B612 Foundation in 2002, initially to determine means for mitigating a known asteroid threat. After several years of research, they came to the conclusion that asteroid deflection was possible using existing technologies, but that much work was needed in identifying the thousands of mid-sized asteroids that remained undetected by terrestrial telescopes.34
In 2012, the B612 Foundation announced a program to finance and build the Sentinel space telescope, which would be placed in an orbit around the sun similar to the orbit of the planet Venus. Facing away from the Sun at all times, Sentinel’s infrared
telescope is designed to have an unobstructed view of the cosmos and will be able to detect a vast number of city-killer and nation-killer NEOs in its expected six-and-a-half years of operation. Sentinel will be manufactured by Ball Aerospace, the company responsible for developing the Kepler and Spitzer space telescopes, and is slated to be launched as soon as June 2018. The B612 Foundation expects to identify hundreds of thousands of previously unknown mid-sized NEOs during the lifespan of the Sentinel mission, and will share this data worldwide. Funding for the Sentinel program is through charitable contributions, with no federal expenditures currently expected.35
Finally, the Chelyabinsk event spurred greater international action on the NEO issue, particularly with the United Nations’ Committee on the Peaceful Uses of Outer Space. In October 2013 the UN General Assembly authorized the creation of an International Asteroid Warning Network, tasked with sharing information about threatening asteroids, to build on the existing capabilities of the Spaceguard Foundation and the Minor Planet Center, and to accelerate detection efforts for mid-sized asteroids. Further, a Space Mission Planning and Advisory Group (SMPAG) was established to serve as an international forum for developing profiles for asteroid deflection missions. The SMPAG’s first round of policy discussions were held in early February 2014 and the group is expected to develop its first set of recommendations by 2016.36
Analysis of US policy
Overall, US policy dedicated to the issue of planetary defense has gone through a complete cycle of the national policymaking process: the issue was placed on the policy agenda, policy was formulated, the executive branch implemented the policy and observed the outcome, and changes were made to improve the policy framework.37
For the first 35 years of the American space program, planetary defense was, at best, an ancillary policy issue for NASA and a succession of presidential administrations. It was not until the world witnessed the enormous destructive power of Comet Shoemaker-Levy 9 that serious policy consideration was given to the issue, at all levels of government. The escalating series of policy decisions enacted by Congress and executed by NASA during the late 1990s and into the new century cumulatively improved the nation’s policy stance with respect to developing a suitable capability to detect and provide early warning for a large asteroid on a collision course with Earth.
For decades, putting planetary defense on the policy agenda was stymied by the lack of a strong advocacy coalition backing the creation of NEO detection programs. Until the early 1990s, only the science community and a small cadre of NASA experts, members of Congress, and their staffs, paid close attention to the issue, with national security, human spaceflight, and commercial interests paying it little heed. Without the focusing event of Shoemaker-Levy 9, it is likely that NEO detection policy would have advanced far more slowly, if at all. Fortunately, in the wake of that comet’s impact with Jupiter 20 years ago, congressional and executive branch leaders recognized the seriousness of the asteroid threat and implemented the policy actions that have helped establish a moderately effective, yet incomplete, NEO detection and mitigation posture.
Policy formulation has been enshrined in legislation and implemented through actions of the executive branch, as NASA established and refined the Near Earth Object Survey. However, it soon became clear that the mandate of the original policies—to detect and track the majority of NEOs greater than one kilometer is size—was insufficient, and policy changes were enacted to broaden the population of asteroids to be detected, to include all NEOs greater than 140 meters in diameter.
A second focusing event, the well-documented explosion of the Chelyabinsk bolide, further catalyzed governmental action, leading to a temporary increase in NASA funding and a set of new initiatives such as the 2013 Grand Challenge. Coupled with inclusion of NEO detection in the administration’s 2010 top-level space policy document and in the 2011 NASA Strategic Plan, planetary defense has, for the first time in the nation’s history, become a top-tier policy issue, no longer the province of a small interest group.
Nonetheless, current US space policy remains inadequate in three major areas and it is unclear how this refreshed attention to the planetary defense issue will translate into additional policy refinements.
The first area of weakness in national space policy regards identification of the mid-sized city-killer and nation-killer asteroids, of which, cumulatively, nearly 99 percent remain undetected. Focusing only on asteroids of greater than 140 meters in diameter neglects the enormous population of smaller but nonetheless dangerous NEOs. It would be prudent to expand current policy to include detection of all asteroids that can pose a significant hazard to mankind, e.g., the city-killer and larger space objects.
Virtually all of NASA’s space surveys have been from terrestrial observatories, which face significant limitations created by having to peer through miles of atmosphere along with the inability to detect objects approaching from the direction of the sun. NASA has conducted detection surveys using orbiting space telescopes, but these efforts also come with limitations. Most prominently, the Wide-field Infrared Survey Explorer (WISE) spacecraft, which was launched in 2009 for deep space infrared imaging and deactivated two years later due to technical issues, was reactivated specifically for the NEO detection mission in 2013. The WISE space telescope since has discovered hundreds of previously unknown asteroids, including dozens of NEOs. Unfortunately, the low Earth orbit of the telescope is not ideal for asteroid detection, the telescope’s optics cannot detect most mid-sized and small NEOs, and the current mission extension is expected to last only three years.38
Much needed is an asteroid detection platform specifically designed to find and track the thousands of unlocated city-killer and nation-killer asteroids. The B612 Foundation’s Sentinel spacecraft is ideal for this mission and, once launched, this telescope is expected to provide the most comprehensive mapping of objects in the inner solar system ever conducted. That such a powerful and important detection tool is being designed, funded, manufactured, and operated through private funding, and not dollars appropriated by the federal government, is testimony to a significant weakness in US national space policy.
A second policy deficiency is the lack of government initiative in developing a set of mitigation strategies to respond to a threatening asteroid once it is discovered. The increased policy interest in NEOs since Shoemaker-Levy has focused almost exclusively on detection: relatively little progress has been made in developing a national or international framework for diversion of an asteroid found to be on a collision course with Earth. Since the Chelyabinsk incident, the administration has begun to marshal resources and intellectual capital for developing long-range mitigation plans, but at the current pace it will be several years, if not decades, before demonstrable progress has been made.
Associated with asteroid diversion strategies are a number of policy and legal issues that will need to be addressed by the US and the international community. Prime among them is the subject of liability. For example, should an asteroid diversion mission go awry and the asteroid is instead deflected to a different impact location on Earth, it is unclear what parties, if any, will be liable for damages. Clearly the nations undertaking an asteroid diversion operation will seek liability protections, but current international law, as embodied in the Outer Space Treaty and the 1972 Convention on International Liability for Damage Caused by Space Objects, is silent on the issue of planetary defense.39 International consensus and revisions to these treaties, or a new international agreement, will be needed to address such a nuanced issue.
Similarly, there are significant policy and legal difficulties tied to the use of nuclear weapons in space to change the velocity of an approaching asteroid. One of the principles embodied in Article IV of the Outer Space Treaty is an outright ban on placing nuclear weapons or other weapons of mass destruction in orbit around the planet, or stationing nuclear weapons anywhere else in space.40 International agreement will be necessary to allow a nuclear-based asteroid diversion effort; alternatively, in a situation where consensus is impossible to achieve, the US could withdraw from the treaty in order to act unilaterally—a decision that would be highly controversial on the international stage. Also, it could be argued that a nuclear device employed to protect the planet from an asteroid strike is not a weapon as defined under international law, considering that it is not designed to attack another nation and that its “sole purpose is to… defend against threatening natural objects from space.”41 Whether or not such a legal argument would stand up to scrutiny remains to be seen.
The final area of weakness in US space policy vis-à-vis NEO detection and mitigation is in the assignment of responsibilities among the various agencies within the federal government. The current national space policy directs NASA to detect and track NEOs “in cooperation with other departments, agencies, and commercial partners” and makes no mention of specific responsibilities for developing asteroid deflection strategies, technology, and missions.42 The ambiguity in this directive requires clarification in order to establish concrete roles and responsibilities for the various federal agencies that will be needed to play a role in a NEO diversion effort. In the scenario where nuclear weapons would be employed to divert an asteroid, for example, it would be essential for the Department of Defense (DOD), which maintains the US nuclear arsenal, to be intimately involved in any such effort, yet there is no mention of a DOD role in planetary defense in any existing US space policy.
Providing a more comprehensive and detailed assignment of responsibility among agencies is essential for assuring smooth interagency coordination should a NEO crisis arise. Along these lines, an essential first step is for the next iteration of US space policy to designate a lead federal agency to coordinate the government’s response to an approaching asteroid; NASA or the Air Force Space Command should be considered for this role. Through a clear assignment of responsibilities made well in advance of a real-world asteroid event, the interagency community can plan, train, and ready itself should a diversion mission be needed to spare Earth from an asteroid impact.
Unlike other calamitous natural disasters—earthquakes, hurricanes, tsunamis, and severe drought—most asteroid strikes are preventable: they are the only significant natural hazard that can be avoided using existing technology. As a major asteroid impact on Earth could kill millions of people or potentially even endanger human civilization, it is essential that the threat be taken seriously by policymakers of all nations, particularly those with the resources and technological acumen to detect and mitigate a potential collision.
In recent decades, and particularly due to the focusing events of the Shoemaker-Levy impact and the Chelyabinsk bolide, planetary defense has moved from the realm of science fiction into mainstream science fact. It is no longer a question of if an asteroid will strike Earth and cause serious damage; it is only a question of when. The next major asteroid strike could be next week, in fifty years, or in five thousand: currently there is no way to tell. With the proper application of resources and through a relatively modest effort, however, the vast majority of potentially hazardous asteroids in the solar system can be detected and tracked, likely within the next two decades. With such detection technology readily available, the nation would be derelict in not pursuing a vigorous program now to safeguard the planet from an unanticipated asteroid impact.
Sixty-five million years ago, when an asteroid ten kilometers across hurtled into the Yucatan Peninsula, it triggered a chain of environmental changes that led the dinosaurs to extinction and cleared a path for the ascendancy of mammals on the planet—including the human race. In this sense, the road to primacy of the human species was paved by a catastrophic asteroid collision with Earth. Today, with the modern technology of the space age at its disposal, humanity has, for the first time, the opportunity to assure that its long-term survival is not endangered by a similarly random celestial event.

Автор: Teymur Kasamanli Рубрика: SPACE NEWS