Over the past quarter century, concern about impacts by comets and asteroids has gone from a joke (the "giggle factor") to a serious issue for science and public policy. The current interest in cosmic impacts dates from the discovery in 1980 that an impact caused the end-Cretaceous mass extinction that ended the age of the dinosaurs. This example demonstrated that our planet was vulnerable to global environmental damage even from relatively small impacts. Also during the 1980s, telescopic discoveries of near-Earth asteroids (NEAs) began to penetrate public consciousness.

In the early 1990s, the U.S. Congress requested that NASA study the impact hazard, ways to increase the discovery rate of NEAs, and possible defense or mitigation technologies. These studies stimulated the first quantitative estimates of the impact hazard by Clark Chapman and David Morrison, and a plan for a survey suggested by Gene Shoemaker based on automated CCD technology as demonstrated by Tom Gehrels. On the defense side, the U.S. national energy labs (Los Alamos and Livermore) and their Russian counterparts suggested nuclear explosives to deflect or disrupt incoming NEAs, with Edward Teller as their most visible advocate. These nuclear defense studies focused on short warning times using an extension of missile defense technology, while the astronomers and NASA proposed telescopic surveys to provide years or decades of advanced warning. Advocates of both approaches, as well as experts on the orbits and physical properties of asteroids and comets, contributed to the definitive volume on the impact hazard published by University of Arizona Press in 1994. In 1998 NASA formally began the Spaceguard Survey, with the goal of discovering and tracking 90% of the NEAs larger than 1 km (the ones that could risk a global disaster if they hit). The Spaceguard data also enabled improved study of the population of NEAs and quantitative estimates of the hazard as a function of impactor size; as summarized in the NASA Science Definition Team report of 2003. Since then, there has been no major change in our understanding of the statistical hazard. The primary goal of Spaceguard and other proposed surveys is not to improve our statistics, but to search out individual hazardous objects, in response to the desire of decision makers and the public for warning of the next damaging impact.

This historical overview continues with a brief look at progress over the past decade, including studies of NEA orbits (and keyholes), better understanding of the effects of small (Tunguska-class) impacts, debates about the role of impact tsunamis, radar studies that demonstrate the prevalence of binary NEAs, the Japanese Hayabusa mission to study Itokawa and return samples to Earth, 2008TC3 as the first NEA discovered in space before its impact, developing international agreements on impact hazard collaboration, proposals for the next generation deep surveys, and the recent decision in the U.S. to fly human missions to NEAs as stepping stones to Mars.

The US NEO Program continues to make significant progress to find the population of large and hazardous NEOs. Two noteworthy events have occurred for the program since the last PDC in 2009, 1) the US Administration’s announcement that NEOs would be a target for human spaceflight endeavors in the mid-2020s, accompanied by a sizable increase to the NASA NEO Program budget request, and 2) a year of operations of the Widefield Infrared Survey Explorer (WISE) spacecraft for which data processing was enhanced to detect solar system objects, and especially NEOs. NASA’s NEO program plans will continue to ensure the hazardous asteroid threat will receive high-level attention and make improvements in capability for the next decade.

In November 2008 member states of the European Space Agency approved the first phase of a new programme on Space Situational Awareness (SSA). The SSA programme initially consists of 3 segments: Space Surveillance and Tracking, Space Weather and Near-Earth Objects (NEO). As of January 2011, 13 ESA members have subscribed to the SSA programme. The approved Preparatory Programme Phase of the SSA covers the period 2009-2012. This should be followed by the SSA Operational Programme Phase for which a proposal will be prepared in 2012.

The following items are seen as main services and tasks to be provided by the SSA-NEO system:

This talk will present a history of the consideration of the topic of NEOs at the United Nations ranging from UNISPACE in 1999 through to current discussions within Action Team 14 and the Working Group on NEOs. It will outline the strategy and approach for dealing with NEOs within the UN framework and consider allied work within the OECD and other bodies which have led to the current position. In particular the talk will present lessons learnt to date in developing an appropriate policy framework and engaging the key stakeholders.