Buoyant Venus station mission feasibility study for 1972 and 1973 launch opportunities. Volume 2 - Trajectory analysis for 1972 and 1973 missions Final report

Trajectory analysis for 1972 and 1973 buoyant Venus station missio

Deorbit Maneuver and Targeting Strategy for Unmanned Mars Landers

Several deorbit maneuver strategies for unmanned Mars soft landers are evaluated in terms of propulsive efficiency, targeting capability, communication link geometry, and sensitivity to system uncertainties. These strategies include (1) minimum deorbit impulse, (2) minimum entry condition uncertainties, (3) minimum variation in the lander antenna aspect angle during entry, (4) minimum communication range from the lander to the orbiting spacecraft during entry. The selected maneuver strategy is a combination of the above which restricts orbiter lead angles to the range between 0 deg and -10 deg. The analysis covers a range of elliptical orbits with periapsis altitudes of 500 to 2500 KM and apoapsis altitudes of 10,000 to 20,000 KM. The nominal orbit which is selected in order to best satisfy all mission considerations is 1300 KM by 12,500 KM (hp x hA) . Mission considerations include orbit orientation of the orbiting spacecraft for planet surface mapping, landing site location between 15 to 30 degrees from the terminator for entry TV imaging, and orbit characteristics which insure a 50-year orbit lifetime and non-occultation of either the Sun or Star Canopus for 30 days after encounter. These constraints, coupled with the uncertainties introduced by trans-Mars navigation uncertainty and orbit insertion maneuver uncertainties, are used in the definition of minimum targeting flexibility required to land at a preselected location (latitude and longitude) and the regions of Mars which can be selected for landing. The selection of a landing site after surveillance from orbit where as much targeting flexibility as possible is desired is also considered. Two aspects of the error analysis are considered. The first deals with the range of orbits relative to a preselected nominal which might be experienced. The sources leading to this range uncertainty include cruise navigation, orbit insertion maneuver, and orbit trim maneuver. The deorbit maneuver strategy must be capable of compensating for these orbit uncertainties if a preselected landing site is to be acquired

Study of direct versus orbital entry for Mars missions. Volume 3 - Appendix A - Launch vehicle performance and flight mechanics

Titan 3 launch vehicle performance and flight mechanics analyses - direct versus orbital entry for Mars mission

A jump-growth model for predator-prey dynamics: derivation and application to marine ecosystems

This paper investigates the dynamics of biomass in a marine ecosystem. A stochastic process is defined in which organisms undergo jumps in body size as they catch and eat smaller organisms. Using a systematic expansion of the master equation, we derive a deterministic equation for the macroscopic dynamics, which we call the deterministic jump-growth equation, and a linear Fokker-Planck equation for the stochastic fluctuations. The McKendrick--von Foerster equation, used in previous studies, is shown to be a first-order approximation, appropriate in equilibrium systems where predators are much larger than their prey. The model has a power-law steady state consistent with the approximate constancy of mass density in logarithmic intervals of body mass often observed in marine ecosystems. The behaviours of the stochastic process, the deterministic jump-growth equation and the McKendrick--von Foerster equation are compared using numerical methods. The numerical analysis shows two classes of attractors: steady states and travelling waves.Comment: 27 pages, 4 figures. Final version as published. Only minor change

Transverse Momentum Dependent Parton Distribution/Fragmentation Functions at an Electron-Ion Collider

We present a summary of a recent workshop held at Duke University on Partonic Transverse Momentum in Hadrons: Quark Spin-Orbit Correlations and Quark-Gluon Interactions. The transverse momentum dependent parton distribution functions (TMDs), parton-to-hadron fragmentation functions, and multi-parton correlation functions, were discussed extensively at the Duke workshop. In this paper, we summarize first the theoretical issues concerning the study of partonic structure of hadrons at a future electron-ion collider (EIC) with emphasis on the TMDs. We then present simulation results on experimental studies of TMDs through measurements of single spin asymmetries (SSA) from semi-inclusive deep-inelastic scattering (SIDIS) processes with an EIC, and discuss the requirement of the detector for SIDIS measurements. The dynamics of parton correlations in the nucleon is further explored via a study of SSA in D (`D) production at large transverse momenta with the aim of accessing the unexplored tri-gluon correlation functions. The workshop participants identified the SSA measurements in SIDIS as a golden program to study TMDs in both the sea and valence quark regions and to study the role of gluons, with the Sivers asymmetry measurements as examples. Such measurements will lead to major advancement in our understanding of TMDs in the valence quark region, and more importantly also allow for the investigation of TMDs in the sea quark region along with a study of their evolution.Comment: 44 pages 23 figures, summary of Duke EIC workshop on TMDs accepted by EPJ

Quasi-stationary regime of a branching random walk in presence of an absorbing wall

A branching random walk in presence of an absorbing wall moving at a constant velocity $v$ undergoes a phase transition as the velocity $v$ of the wall varies. Below the critical velocity $v_c$, the population has a non-zero survival probability and when the population survives its size grows exponentially. We investigate the histories of the population conditioned on having a single survivor at some final time $T$. We study the quasi-stationary regime for $v<v_c$ when $T$ is large. To do so, one can construct a modified stochastic process which is equivalent to the original process conditioned on having a single survivor at final time $T$. We then use this construction to show that the properties of the quasi-stationary regime are universal when $v\to v_c$. We also solve exactly a simple version of the problem, the exponential model, for which the study of the quasi-stationary regime can be reduced to the analysis of a single one-dimensional map.Comment: 2 figures, minor corrections, one reference adde

30% land conservation and climate action reduces tropical extinction risk by more than 50%

Limiting climate change to less than 2°C is the focus of international policy under the climate convention (UNFCCC), and is essential to preventing extinctions, a focus of the Convention on Biological Diversity (CBD). The post‐2020 biodiversity framework drafted by the CBD proposes conserving 30% of both land and oceans by 2030. However, the combined impact on extinction risk of species from limiting climate change and increasing the extent of protected and conserved areas has not been assessed. Here we create conservation spatial plans to minimize extinction risk in the tropics using data on 289 219 species and modeling two future greenhouse gas concentration pathways (RCP2.6 and 8.5) while varying the extent of terrestrial protected land and conserved areas from <17% to 50%. We find that limiting climate change to 2°C and conserving 30% of terrestrial area could more than halve aggregate extinction risk compared with uncontrolled climate change and no increase in conserved area