The Space Reviewin association with SpaceNews

meteor trail
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)

US space policy and planetary defense

<< page 1: congressional, agency, and nongovernmental policy actions

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 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.

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.

Focusing only on asteroids of greater than 140 meters in diameter neglects the enormous population of smaller but nonetheless dangerous NEOs.

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.

oday, 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.

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.


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  35. Ed Lu, Testimony to the U.S. House of Representatives Committee on Science, Space, and Technology, April 10, 2013.
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