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We investigate the feasibility of using a medium-powered (5kW) ground-based laser combined with a ground-based telescope to prevent collisions between debris objects in low-Earth orbit (LEO), for which there is no current, effective mitigation strategy. The scheme utilizes photon pressure alone as a means to perturb the orbit of a debris object. Applied over multiple engagements, this alters the debris orbit sufficiently to reduce the risk of an upcoming conjunction. We employ standard assumptions for atmospheric conditions and the resulting beam propagation. Using case studies designed to represent the properties (e.g. area and mass) of the current debris population, we show that one could significantly reduce the risk of more than half of all debris-debris collisions using only one such laser/telescope facility. We speculate on whether this could mitigate the debris fragmentation rate such that it falls below the natural debris re-entry rate due to atmospheric drag, and thus whether continuous long-term operation could entirely mitigate the Kessler syndrome in LEO, without need for relatively expensive active debris removal.

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Journal Articles
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Cornell University Library
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Jan M. Stupl
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Abstract:

This critical review of the new political science literature on the causes of nuclear weapons proliferation consists of four parts. The first section briefly presents what we know about which states developed nuclear weapons and which states started but abandoned weapons development programs. I highlight the problems that result from uncertainty about the accuracy and completeness of the data. The second and third sections review the literature on the spread of the technical capability to develop nuclear weapons. We still lack robust knowledge about the relationship between the development of civilian nuclear power programs and nuclear weapons acquisition. The next two sections review the literature on the demand for nuclear weapons. Comparative case studies and statistical studies have improved our understanding of the diversity of motives for weapons development and restraints, but serious gaps in our knowledge remain. The sixth section outlines alternative theories about the potential impact of the nuclear Non-Proliferation Treaty (NPT) on nuclear weapons programs decisions. Finally, I lay out a future research agenda to address the weaknesses in our current understanding of the causes of nuclear proliferation

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Annual Review of Political Science
Authors
Scott D. Sagan
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"Alexander Betts is one of a handful of scholars who have mastered the complex field of Global Migration Governance. This large and impressive volume covers the topic from every conceivable angle, and it gets the difficult mix of empirical analysis and policy recommendation right. As the global conversation about migration governance continues over the coming years, this work will remain the standard reference."--Randall Hansen, Research Chair in Political Science, University of Toronto 

"An invaluable contribution to migration research and studies of global governance more broadly. Drawing on useful concepts derived from International Relations, the excellent contributions draw a picture of a multilayered, fragmented and yet quite encompassing set of formal and informal governance arrangements that mirror the diversity of challenges associated with global population flows."--Sandra Lavenex, Professor of International Politics, University of Lucerne 

Unlike many other trans-boundary policy areas, international migration lacks coherent global governance. There is no United Nations migration organization and states have signed relatively few multilateral treaties on migration. Instead sovereign states generally decide their own immigration policies. However, given the growing politicization of migration and the recognition that states cannot always address migration in isolation from one another, a debate has emerged about what type of international institutions and cooperation are required to meet the challenges of international migration. Until now, though, that emerging debate on global migration governance has lacked a clear analytical understanding of what global migration governance actually is, the politics underlying it, and the basis on which we can make claims about what 'better' migration governance might look like.

In order to address this gap, Global Migration Governance brings together a group of the world's leading experts to consider the global governance of different aspects of migration. The chapters offer an accessible introduction to the global governance of low-skilled labor migration, high-skilled labor migration, irregular migration, lifestyle migration, international travel, refugees, internally displaced persons, human trafficking and smuggling, diaspora, remittances, and root causes. Each of the chapters explores the three same broad questions: What, institutionally, is the global governance of migration in that area? Why, politically, does that type of governance exist? How, normatively , can we ground claims about the type of global governance that should exist in that area? Collectively, the chapters enhance our understanding of the international politics of migration and set out a vision for international cooperation on migration. 

Contents: 

  1. "Introduction: Global Migration Governance", Alexander Betts 
  2. "Low-Skilled Labour Migration", Christiane Kuptsch and Philip Martin 
  3. "High-Skilled Labour Migration", Alexander Betts and Lucie Cerna 
  4. "Irregular Migration", Franck Duvell 
  5. "International Travel", Rey Koslowski 
  6. "Lifestyle Migration", Caroline Oliver 
  7. "Environmental Migration", Jane McAdam 
  8. "UNHCR and the Global Governance of Refugees", Gil Loescher and James Milner 
  9. "Internally Displaced Persons", Khalid Koser 
  10. "Human Trafficking and Smuggling", Susan Martin and Amber Callaway 
  11. "Remittances", Anna Lindley 
  12. "Diasporas", Alan Gamlen 
  13. "Root Causes", Stephen Castles and Nicholas Van Hear 
  14. "Conclusion", Alexander Betts
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Books
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Oxford University Press
Authors
Alexander Betts
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0199600457
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Reuben W. Hills Conference Room

Benjamin Valentino Associate Professor of Government Speaker Dartmouth College

CISAC
Stanford University
Encina Hall, E202
Stanford, CA 94305-6165

(650) 725-2715 (650) 723-0089
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The Caroline S.G. Munro Professor of Political Science
The Bass University Fellow in Undergraduate Education  
Senior Fellow, Freeman Spogli Institute for International Studies
rsd25_073_1160a_1.jpg PhD

Scott D. Sagan is the Caroline S.G. Munro Professor of Political Science, the Bass University Fellow in Undergraduate Education, and a Senior Fellow at the Center for International Security and Cooperation, where he previously served as the social science co-director. He is the Inaugural Harry Frank Guggenheim Fellow for Nuclear Ethics and Security at the Carnegie Council for Ethics in International Affairs (2026-2027). Sagan also serves as co-chair of the American Academy of Arts and Sciences’ Committee on International Security Studies. Before joining the Stanford faculty, he was a lecturer in the Department of Government at Harvard University and served as special assistant to the director of the Organization of the Joint Chiefs of Staff in the Pentagon.

Sagan is the author of Moving Targets: Nuclear Strategy and National Security (Princeton University Press, 1989); The Limits of Safety: Organizations, Accidents, and Nuclear Weapons (Princeton University Press, 1993); and, with co-author Kenneth N. Waltz, The Spread of Nuclear Weapons: An Enduring Debate (W.W. Norton, 2012). He is the co-editor of Insider Threats (Cornell University Press, 2017) with Matthew Bunn; and co-editor of The Fragile Balance of Terror (Cornell University Press, 2022) with Vipin Narang. Sagan was also the guest editor of a two-volume special issue of Daedalus: Ethics, Technology, and War (Fall 2016) and The Changing Rules of War (Winter 2017).

Recent publications include “Creeds and Contestation: How US Nuclear and Legal Doctrine Influence Each Other,” with Janina Dill, in a special issue of Security Studies (December 2025); “Kettles of Hawks: Public Opinion on the Nuclear Taboo and Noncombatant Immunity in the United States, United Kingdom, France, and Israel”, with Janina Dill and Benjamin A. Valentino in Security Studies (February 2022); “The Rule of Law and the Role of Strategy in U.S. Nuclear Doctrine” with Allen S. Weiner in International Security (Spring 2021); “Does the Noncombatant Immunity Norm Have Stopping Power?” with Benjamin A. Valentino in International Security (Fall 2020); and “Just War and Unjust Soldiers: American Public Opinion on the Moral Equality of Combatants” and “On Reciprocity, Revenge, and Replication: A Rejoinder to Walzer, McMahan, and Keohane” with Benjamin A. Valentino in Ethics & International Affairs (Winter 2019).

In 2022, Sagan was awarded Thérèse Delpech Memorial Award from the Carnegie Endowment for International Peace at their International Nuclear Policy Conference. In 2017, he received the International Studies Association’s Susan Strange Award which recognizes the scholar whose “singular intellect, assertiveness, and insight most challenge conventional wisdom and intellectual and organizational complacency" in the international studies community. Sagan was also the recipient of the National Academy of Sciences William and Katherine Estes Award in 2015, for his work addressing the risks of nuclear weapons and the causes of nuclear proliferation. The award, which is granted triennially, recognizes “research in any field of cognitive or behavioral science that advances understanding of issues relating to the risk of nuclear war.” In 2013, Sagan received the International Studies Association's International Security Studies Section Distinguished Scholar Award. He has also won four teaching awards: Stanford’s 1998-99 Dean’s Award for Distinguished Teaching; Stanford's 1996 Hoagland Prize for Undergraduate Teaching; the International Studies Association’s 2008 Innovative Teaching Award; and the Monterey Institute for International Studies’ Nonproliferation Education Award in 2009.     

Former co-director, Center for International Security and Cooperation
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Date Label
Scott D. Sagan Co-Director, CISAC; Professor of Political Science, Stanford University Speaker
Anne Harrington de Santana Postdoctoral Fellow, CISAC Commentator
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Reuben W. Hills Conference Room

Rod Ewing Visiting Professor at CISAC; Edward H. Kraus Distinguished University Professor in the Department of Geological Sciences at the University of Michigan Speaker
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Reuben W. Hills Conference Room

Riqiang Wu Nuclear Security Fellow at CISAC and PhD Student at Tsinghua University, China Speaker
Seminars
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Abstract
I will begin this talk with a short discussion of the function of warning in the US national security community, and the analytic methodology used by US intelligence agencies (in 1941 and since) to address the problem of warning. I will then present a formal model for crisis warning consisting of a Partially Observable Markov Decision Process (POMDP) intended to assist an intelligence analyst in deciding when to issue an alert to a foreign policy principal decision maker such as the President. The lead time demanded by the principal is a key element in the model. I will spend the remainder of the talk illustrating this warning model in the context of the brewing crisis in the Pacific from July to December 1941, and present results from test runs of the model using historical raw intelligence data from that period. While a probabilistic approach to warning is not a new idea, this research addresses three outstanding issues left unresolved from past efforts to develop such an approach:

  1. The need to process multiple dependent signals in a manner that is combinatorially feasible;
  2. Incorporation of the time dimension in which intelligence data is received into the inference, and the effect of dynamics on a warning decision where a finite horizon is imposed;
  3. Consideration of the fact that the analyst serves as an advisor to the principal decision maker but is not completely aware of the principal’s preference set.

Together with my thesis advisor, Prof Elisabeth Pate-Cornell, I am currently writing a paper that covers the presented material, and I hope to incorporate feedback from this presentation into the paper. Because the paper is currently a work in progress, I am not distributing it at this time.


David Blum attends Stanford University, where he is a 3rd year Ph.D. student in the Department of Management Science & Engineering as well as a U.S. Department of Defense SMART Scholar. He is currently developing a probabilistic model of national security crises, with the goal of improving crisis early warning. His interests also include targeting in counter-terrorism, signatures of WMD proliferation, and models of decisions made by adversarial actors as games with incomplete information. He is a graduate intern in the Counter-Proliferation Operations-Intelligence Support program at Lawrence Livermore National Laboratory.

Between 2004 and 2008 David worked at the U.S. Department of Defense as an operations research analyst. He deployed twice to Iraq, in 2007 and 2008, where,  as member of Multi-National Corps Iraq, he provided direct analytic support to conventional and special operations units. He received his Master's degree from MIT in political science, concentrating in security studies, and his Bachelor's degree from Columbia University in history and physics.

Reuben W. Hills Conference Room

David Blum Predoctoral Fellow, CISAC Speaker
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Reuben W. Hills Conference Room

Francis Gavin Director, Robert S. Strauss Center for International Security & Law Speaker University of Texas at Austin
Mira Rapp-Hooper PhD Student Speaker Columbia University
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