A procedure for calculating the damping in multi-element space structures

A procedure is outlined for estimating the damping in a multi-element space structure by incorporating distributed material damping and discrete nonlinear joint properties into a linear analysis. Tests have been conducted in which the transient response of a truss member is measured in free fall in a vacuum in order to obtain precise material damping characteristics. The force-state mapping technique is then used to identify the localized nonlinearities in joints by mapping the force transmitted through the joint as a function of the full mechanical state of the joint. The identified nonlinear joint parameters are then linearized using an equivalent energy approach which finds the equivalent linear stiffness and linear viscous damping by equating the integrated work done and energy dissipated by the nonlinearity to those of a spring and damper undergoing sinusoidal motion. The distributed material damping and localized nonlinear effects are then incorporated to form a linearized damped finite element model. Finally, an eigenvalue perturbation analysis is developed to explore the effect of introducing damping at the joints on the overall dynamics of the truss, and to obtain design guidance on where supplemental joint damping might optimally be added.     

On the analysis of electric arc process stability in plasma systems of ignition with allowance for GTE combustion chamber parameters

An approach to the analysis of electric arc process stability in plasma systems of ignition is considered depending on the ignition system power circuit parameters, speed of plasma-generating air, and combustion chamber inlet pressure. Also solved is the problem on determination of the calculated value of the maximum admissible speed of plasma-generating air that corresponds to the critical regime of stable arcing in plasma spark plug at the GTE start.     

Generalization of experimental data on two-phase critical efflux through axisymmetric channels

The results of studying the characteristics of a two-phase flow being formed during adiabatic water efflux through axisymmetric cylindrical and Laval nozzle channels are presented. Experiments were carried out with saturated water in the range of initial pressures 0.6–4.0 MPa. The fluid efflux was performed into the air with atmospheric pressure. The generalizing relations for calculating thrust pulse and critical flowrate were obtained.     

Interstellar Mapping and Acceleration Probe (IMAP): A New NASA Mission

The Interstellar Mapping and Acceleration Probe (IMAP) is a revolutionary mission that simultaneously investigates two of the most important overarching issues in Heliophysics today: the acceleration of energetic particles and interaction of the solar wind with the local interstellar medium. While seemingly disparate, these are intimately coupled because particles accelerated in the inner heliosphere play critical roles in the outer heliospheric interaction. Selected by NASA in 2018, IMAP is planned to launch in 2024. The IMAP spacecraft is a simple sun-pointed spinner in orbit about the Sun-Earth L1 point. IMAP’s ten instruments provide a complete and synergistic set of observations to simultaneously dissect the particle injection and acceleration processes at 1 AU while remotely probing the global heliospheric interaction and its response to particle populations generated by these processes. In situ at 1 AU, IMAP provides detailed observations of solar wind electrons and ions; suprathermal, pickup, and energetic ions; and the interplanetary magnetic field. For the outer heliosphere interaction, IMAP provides advanced global observations of the remote plasma and energetic ions over a broad energy range via energetic neutral atom imaging, and precise observations of interstellar neutral atoms penetrating the heliosphere. Complementary observations of interstellar dust and the ultraviolet glow of interstellar neutrals further deepen the physical understanding from IMAP. IMAP also continuously broadcasts vital real-time space weather observations. Finally, IMAP engages the broader Heliophysics community through a variety of innovative opportunities. This paper summarizes the IMAP mission at the start of Phase A development.     

To Calculation of Regenerative Cooling of a Liquid Fuel Rocket Engine Chamber

This paper demonstrates that in transition from the one-dimensional longitudinal-channel motion of the coolant in the regenerative cooling system of the liquid propellant engine to the twodimensional (interchannel) channel motion (transpiration) through a porous mesh material (PMM), the hydraulic losses decrease. Experimental data on PMM hydraulic resistance coefficients and heat transfer in porous paths with the interchannel coolant transpiration (ICCT) is presented.     

Magnetic Field Amplification in Galaxy Clusters and Its Simulation

We review the present theoretical and numerical understanding of magnetic field amplification in cosmic large-scale structure, on length scales of galaxy clusters and beyond. Structure formation drives compression and turbulence, which amplify tiny magnetic seed fields to the microGauss values that are observed in the intracluster medium. This process is intimately connected to the properties of turbulence and the microphysics of the intra-cluster medium. Additional roles are played by merger induced shocks that sweep through the intra-cluster medium and motions induced by sloshing cool cores. The accurate simulation of magnetic field amplification in clusters still poses a serious challenge for simulations of cosmological structure formation. We review the current literature on cosmological simulations that include magnetic fields and outline theoretical as well as numerical challenges.