The use of the tethered satellite system to perform low density aerothermodynamics studies

The Tethered Satellite System (TSS) is a cooperative space system development activity of the U.S.A. and Italy. It is comprised of the Tether Satellite (TS) and the deployer. Within TSS, the Shuttle Tethered Aerothermodynamic Research Facility (STARFAC) concept has the potential to provide access to vast portions of the upper atmosphere for atmospheric and aerothermodynamic research. The feasibility and capability of the TSS to operate as a continuous open wind tunnel and to perform low density aerothermodynamic studies are investigated. This is accomplished through a modified version of the TS simulation program (SKYHOOK). The results indicate that STARFAC concept is both feasible and practical. The TS can go below 100 km but, if thrust is used, large velocity variation (delta V) maneuvers and an attitude control are required; if a satellite lift is considered, large tether tension is produced and an attitude control is required

Surface Pyrolysis of High Energy Materials

The Arrhenius zero-order phenomenological pyrolysis law, commonly used in conjunction with the Vieille ballistic law to study pressure-driven burning of energetic materials, is revisited. Motivated by experimental and theoretical work performed in 1984 in this Laboratory , a relationship among several interplaying parameters is found under steady-state conditions. This relationship corresponds to the Jacobian of the pyrolysis sensitivity parameters used in the Zeldovich-Novozhilov approach. The Arrhenius pyrolysis is still expressed in terms of a global surface activation energy, but consistency with the experimental ballistic law may require an explicit pressure dependence as well. This conclusion is supported by a variety of arguments drawn from different areas. The linear dependence of the pre-exponential factor on surface activation energy (known as kinetic compensation) is proved and extended to the pressure exponent, for any given experimental data set under steady burning. Experimental results are reported for about a dozen solid propellants of different nature. The effects of surface pyrolysis explicit pressure dependence, although modest on steady-state burning, are potentially far-reaching for unsteady regime and/or unstable burning. The paper is mainly focussed on pressure-driven burning and Arrhenius pyrolysis, but the implemented method is believed to apply in general. Thus, enforcing KTSS zero-order phenomenological pyrolysis with the Vieille ballistic law yields similar results and requires an explicit pressure dependence. In case, the Zeldovich ballistic law is enforced instead of the classical Vieille law, no explicit pressure dependence is required. The unifying concept for these different trends is the pyrolysis Jacobian as a consistency requirement between the implemented steady pyrolysis and ballistic laws.

Hot Plasma Detected in Active Regions by HINODE/XRT and SDO/AIA

Multiple ratios of Hinode/XRT filters showed evidence of a minor very hot emission measure component in active regions. Recently also SDO/AIA detected hot plasma in the core of an active region. Here we provide estimates showing that the amount of emission measure of the hot component detected with SDO is consistent with that detected with Hinode/XRT

Effect of amide-based compounds on the combustion characteristics of composite solid rocket propellants

Oxamide (OXA) and azodicarbonamide (ADA) are among the known burning rate suppressants used in composite solid rocket propellants. Much research has been carried out to understand mechanism of suppression but literature about the action of OXA and ADA on the combustion characteristics of propellant is still scarce. Here, a systematic study on coolant-based propellants has been undertaken spanning from thermal analyses of ingredients to a variety of burning processes of the corresponding propellants. Thermal gravimetric analysis and differential thermal analysis on individual coolants are carried out to study their behaviour with temperature. It was noticed that the thermal decomposition of OXA exhibits only endothermic effects, whereas that of ADA presents both endothermic and exothermic effects. Successive experiments on solid propellant looking at burning rate characterization, condensed combustion product collection and visualization, pressure deflagration limit and thermochemical analysis gave a greater insight and enabled better understanding of the action of coolants during combustion. It is proposed that OXA and ADA are acting on both the condensed and gas phases. Also, the nature of coolant is a key parameter, which affects the burning rate pressure index. Increase of agglomerate size and of pressure deflagration limit was obtained in the coolant-based propellants, confirming the trend given in the literature. Keywords: Composite propellant, Ammonium perchlorate, Burning rate suppressant, Combustion characteristic

Stratospheric Ozone Response in Experiments G3 and G4 of the Geoengineering Model Intercomparison Project (GeoMIP)

Geoengineering with stratospheric sulfate aerosols has been proposed as a means of temporarily cooling the planet, alleviating some of the side effects of anthropogenic CO2 emissions. However, one of the known side effects of stratospheric injections of sulfate aerosols is a decrease in stratospheric ozone. Here we show results from two general circulation models and two coupled chemistry climate models that have simulated stratospheric sulfate aerosol geoengineering as part of the Geoengineering Model Intercomparison Project (GeoMIP). Changes in photolysis rates and upwelling of ozone-poor air in the tropics reduce stratospheric ozone, suppression of the NOx cycle increases stratospheric ozone, and an increase in available surfaces for heterogeneous chemistry modulates reductions in ozone. On average, the models show a factor 20-40 increase of the sulfate aerosol surface area density (SAD) at 50 hPa in the tropics with respect to unperturbed background conditions and a factor 3-10 increase at mid-high latitudes. The net effect for a tropical injection rate of 5 Tg SO2 per year is a decrease in globally averaged ozone by 1.1-2.1 DU in the years 2040-2050 for three models which include heterogeneous chemistry on the sulfate aerosol surfaces. GISS-E2-R, a fully coupled general circulation model, performed simulations with no heterogeneous chemistry and a smaller aerosol size; it showed a decrease in ozone by 9.7 DU. After the year 2050, suppression of the NOx cycle becomes more important than destruction of ozone by ClOx, causing an increase in total stratospheric ozone. Contribution of ozone changes in this experiment to radiative forcing is 0.23 W m-2 in GISS-E2-R and less than 0.1 W m-2 in the other three models. Polar ozone depletion, due to enhanced formation of both sulfate aerosol SAD and polar stratospheric clouds, results in an average 5 percent increase in calculated surface UV-B

A wide field X-ray telescope for astronomical survey purposes: from theory to practice

X-ray mirrors are usually built in the Wolter I (paraboloid-hyperboloid) configuration. This design exhibits no spherical aberration on-axis but suffers from field curvature, coma and astigmatism, therefore the angular resolution degrades rapidly with increasing off-axis angles. Different mirror designs exist in which the primary and secondary mirror profiles are expanded as a power series in order to increase the angular resolution at large off-axis positions, at the expanses of the on-axis performances. Here we present the design and global trade off study of an X-ray mirror systems based on polynomial optics in view of the Wide Field X-ray Telescope (WFXT) mission. WFXT aims at performing an extended cosmological survey in the soft X-ray band with unprecedented flux sensitivity. To achieve these goals the angular resolution required for the mission is very demanding ~5 arcsec mean resolution across a 1-deg field of view. In addition an effective area of 5-9000 cm^2 at 1 keV is needed.Comment: Accepted for publication in the MNRAS (11pages, 3 table, 13 figures

Detection of X-ray Resonance Scattering in Active Stellar Coronae

An analysis of Lyman series lines arising from hydrogen-like oxygen and neon ions in the coronae of the active RS CVn-type binaries II Peg and IM Peg, observed using the {\it Chandra} High Resolution Transmission Grating Spectrograph, shows significant decrements in the Ly$\alpha$/Ly$\beta$ ratios as compared with theoretical predictions and with the same ratios observed in similar active binaries. We interpret these decrements in terms of resonance scattering of line photons out of the line-of-sight; these observations present the first strong evidence for this effect in active stellar coronae. The net line photon loss implies a non-uniform and asymmetric surface distribution of emitting structures on these stars. Escape probability arguments, together with the observed line ratios and estimates of the emitting plasma density, imply typical line-of-sight sizes of the coronal structures that dominate the X-ray emission of $10^{10}$ cm at temperatures of $3\times 10^6$ K and of $10^8$ cm at $10^7$ K. These sizes are an order of magnitude larger than predicted by simple quasi-static coronal loops models, but are still very small compared to the several $10^{11}$ cm radii of the underlying stars.Comment: Accepted for publication on ApJ Letters. 14 pages, 2 figure

Studying the Underlying Event in Drell-Yan and High Transverse Momentum Jet Production at the Tevatron

We study the underlying event in proton-antiproton collisions by examining the behavior of charged particles (transverse momentum pT > 0.5 GeV/c, pseudorapidity |\eta| < 1) produced in association with large transverse momentum jets (~2.2 fb-1) or with Drell-Yan lepton-pairs (~2.7 fb-1) in the Z-boson mass region (70 < M(pair) < 110 GeV/c2) as measured by CDF at 1.96 TeV center-of-mass energy. We use the direction of the lepton-pair (in Drell-Yan production) or the leading jet (in high-pT jet production) in each event to define three regions of \eta-\phi space; toward, away, and transverse, where \phi is the azimuthal scattering angle. For Drell-Yan production (excluding the leptons) both the toward and transverse regions are very sensitive to the underlying event. In high-pT jet production the transverse region is very sensitive to the underlying event and is separated into a MAX and MIN transverse region, which helps separate the hard component (initial and final-state radiation) from the beam-beam remnant and multiple parton interaction components of the scattering. The data are corrected to the particle level to remove detector effects and are then compared with several QCD Monte-Carlo models. The goal of this analysis is to provide data that can be used to test and improve the QCD Monte-Carlo models of the underlying event that are used to simulate hadron-hadron collisions.Comment: Submitted to Phys.Rev.