Interplanetary Trajectory Design for the Asteroid Robotic Redirect Mission Alternate Approach Trade Study

This paper presents mission performance analysis methods and results for the Asteroid Robotic Redirect Mission (ARRM) option to capture a free standing boulder on the surface of a 100 m or larger NEA. It details the optimization and design of heliocentric low-thrust trajectories to asteroid targets for the ARRM solar electric propulsion spacecraft. Extensive searches were conducted to determine asteroid targets with large pick-up mass potential and potential observation opportunities. Interplanetary trajectory approximations were developed in method based tools for Itokawa, Bennu, 1999 JU3, and 2008 EV5 and were validated by end-to-end integrated trajectories

Salerno's model of DNA reanalysed: could solitons have biological significance?

We investigate the sequence-dependent behaviour of localised excitations in a toy, nonlinear model of DNA base-pair opening originally proposed by Salerno. Specifically we ask whether ``breather'' solitons could play a role in the facilitated location of promoters by RNA polymerase. In an effective potential formalism, we find excellent correlation between potential minima and {\em Escherichia coli} promoter recognition sites in the T7 bacteriophage genome. Evidence for a similar relationship between phage promoters and downstream coding regions is found and alternative reasons for links between AT richness and transcriptionally-significant sites are discussed. Consideration of the soliton energy of translocation provides a novel dynamical picture of sliding: steep potential gradients correspond to deterministic motion, while ``flat'' regions, corresponding to homogeneous AT or GC content, are governed by random, thermal motion. Finally we demonstrate an interesting equivalence between planar, breather solitons and the helical motion of a sliding protein ``particle'' about a bent DNA axis.Comment: Latex file 20 pages, 5 figures. Manuscript of paper to appear in J. Biol. Phys., accepted 02/09/0

Empirical Essays on Natural Resource Exploitation

Failures to conserve wildlife do not typically arise from an absence of conservation policies; they occur when existing policies are ineffective. From national laws prohibiting the killing of African elephants to international agreements governing the exploitation of marine animals, behavioral responses and enforcement capacity shape the extent to which conservation policies improve or worsen conservation outcomes. Causal estimates of the effects of conservation policies and their underlying mechanisms are largely unavailable, limiting the extent to which declines in wildlife abundance and biodiversity can be reduced and reversed. In this dissertation, I use causal inference econometrics, high-resolution data, and economic theory to begin to fill this knowledge gap. In its three chapters, I uncover how a conservation policy backfires when it implicitly communicates valuable information to firms, how deterrence is possible even when enforcement is difficult, and how exogenous shocks can increase illegal behavior. First, I establish that regulations aimed at mitigating common-pool extraction externalities in the world’s largest fishery backfire substantially and exacerbate inefficiencies. The most important biological externality in Peru’s anchoveta fishery is the harvesting of juvenile anchoveta. To reduce juvenile catch, the regulator temporarily closes areas where the share of juvenile catch is high. By combining administrative microdata with biologically richer data from fishing firms, I isolate variation in closures that is due to the regulator's lower resolution data. I estimate substantial temporal and spatial spillovers from closures. Closures increase total juvenile catch by 50% because closure announcements implicitly signal that fishing before, just outside, and after closures is high productivity. Second, managing global marine resources by assigning property rights could align economic and conservation incentives, but only if unauthorized resource use is deterred. Exclusive Economic Zones (EEZs) are country-level property rights to marine resources, covering approximately 39% of the ocean’s surface and accounting for more than 95% of global marine fish catch. However, EEZs might not be respected by unauthorized resource users because the cost of monitoring and enforcing such large areas may be prohibitive. Here I provide the first evidence that EEZs are in fact respected by unauthorized resource users. Using global, high-resolution fishing effort datasets and the ecologically arbitrary boundaries between EEZs and the high seas, I find that unauthorized foreign fishing is 81% lower just inside EEZs compared to just outside. Consistent with the high cost of enforcing EEZ boundaries, this deterrence effect is concentrated in EEZs that are most valuable near their boundaries. These results suggest that property rights institutions can enable effective governance of global marine resource use. Finally, poaching is the greatest threat to the survival of elephants and other commercially valuable species. There are many hypothesized drivers of wildlife poaching, but few empirical estimates of their causal effects on poaching levels. In this paper, I provide the first causal estimates of a spatially-varying driver of wildlife poaching. Using elephant poaching and armed conflict data spanning 13 years and 77 sites in 39 countries across Africa and Asia, I find that the onset of a new conflict near elephant populations significantly increases contemporaneous elephant poaching levels by 12-22%. I leverage a variety of econometric methods to show that these estimates are plausibly causal and robust to alternative specifications and different measures of conflict and poaching. I estimate that conflict accounts for the illegal killing of 80,000 elephants between 2002 and 2014. To protect elephants, governments and NGOs should increase support to affected areas when conflicts begin

Empirical Essays on Natural Resource Exploitation

Failures to conserve wildlife do not typically arise from an absence of conservation policies; they occur when existing policies are ineffective. From national laws prohibiting the killing of African elephants to international agreements governing the exploitation of marine animals, behavioral responses and enforcement capacity shape the extent to which conservation policies improve or worsen conservation outcomes. Causal estimates of the effects of conservation policies and their underlying mechanisms are largely unavailable, limiting the extent to which declines in wildlife abundance and biodiversity can be reduced and reversed. In this dissertation, I use causal inference econometrics, high-resolution data, and economic theory to begin to fill this knowledge gap. In its three chapters, I uncover how a conservation policy backfires when it implicitly communicates valuable information to firms, how deterrence is possible even when enforcement is difficult, and how exogenous shocks can increase illegal behavior. First, I establish that regulations aimed at mitigating common-pool extraction externalities in the world’s largest fishery backfire substantially and exacerbate inefficiencies. The most important biological externality in Peru’s anchoveta fishery is the harvesting of juvenile anchoveta. To reduce juvenile catch, the regulator temporarily closes areas where the share of juvenile catch is high. By combining administrative microdata with biologically richer data from fishing firms, I isolate variation in closures that is due to the regulator's lower resolution data. I estimate substantial temporal and spatial spillovers from closures. Closures increase total juvenile catch by 50% because closure announcements implicitly signal that fishing before, just outside, and after closures is high productivity. Second, managing global marine resources by assigning property rights could align economic and conservation incentives, but only if unauthorized resource use is deterred. Exclusive Economic Zones (EEZs) are country-level property rights to marine resources, covering approximately 39% of the ocean’s surface and accounting for more than 95% of global marine fish catch. However, EEZs might not be respected by unauthorized resource users because the cost of monitoring and enforcing such large areas may be prohibitive. Here I provide the first evidence that EEZs are in fact respected by unauthorized resource users. Using global, high-resolution fishing effort datasets and the ecologically arbitrary boundaries between EEZs and the high seas, I find that unauthorized foreign fishing is 81% lower just inside EEZs compared to just outside. Consistent with the high cost of enforcing EEZ boundaries, this deterrence effect is concentrated in EEZs that are most valuable near their boundaries. These results suggest that property rights institutions can enable effective governance of global marine resource use. Finally, poaching is the greatest threat to the survival of elephants and other commercially valuable species. There are many hypothesized drivers of wildlife poaching, but few empirical estimates of their causal effects on poaching levels. In this paper, I provide the first causal estimates of a spatially-varying driver of wildlife poaching. Using elephant poaching and armed conflict data spanning 13 years and 77 sites in 39 countries across Africa and Asia, I find that the onset of a new conflict near elephant populations significantly increases contemporaneous elephant poaching levels by 12-22%. I leverage a variety of econometric methods to show that these estimates are plausibly causal and robust to alternative specifications and different measures of conflict and poaching. I estimate that conflict accounts for the illegal killing of 80,000 elephants between 2002 and 2014. To protect elephants, governments and NGOs should increase support to affected areas when conflicts begin