Effects of modifications to the space shuttle entry guidance and control systems

A nonlinear six degree of freedom entry simulation study was conducted to identify space shuttle guidance and control system software modifications which reduce the control system sensitivity to the guidance system sampling frequency. Several modifications which eliminated the control system sensitivity and associated control limit cycling were examined. The result of the modifications was a reduction in required reaction control system fuel

Development of the reentry flight dynamics simulator for evaluation of space shuttle orbiter entry systems

A nonlinear, six degree of freedom, digital computer simulation of a vehicle which has constant mass properties and whose attitudes are controlled by both aerodynamic surfaces and reaction control system thrusters was developed. A rotating, oblate Earth model was used to describe the gravitational forces which affect long duration Earth entry trajectories. The program is executed in a nonreal time mode or connected to a simulation cockpit to conduct piloted and autopilot studies. The program guidance and control software used by the space shuttle orbiter for its descent from approximately 121.9 km to touchdown on the runway

Ab initio investigation of intermolecular interactions in solid benzene

A computational strategy for the evaluation of the crystal lattice constants and cohesive energy of the weakly bound molecular solids is proposed. The strategy is based on the high level ab initio coupled-cluster determination of the pairwise additive contribution to the interaction energy. The zero-point-energy correction and non-additive contributions to the interaction energy are treated using density functional methods. The experimental crystal lattice constants of the solid benzene are reproduced, and the value of 480 meV/molecule is calculated for its cohesive energy

Transient intensity changes of cosmic rays beyond the heliospheric termination shock as observed at Voyager 1

This paper continues our studies of temporal variations of cosmic rays beyond the heliospheric termination shock (HTS) using Voyager 1 (V1) data when V1 was beyond 94 AU. This new study utilizes cosmic ray protons and electrons of several energies. Notable transient decreases of 5–50% are observed in galactic cosmic ray nuclei and electrons at V1 shortly after similar decreases are observed at Voyager 2 (V2) still inside the HTS. These decreases at V1 appear to be related to the large solar events in September 2005 and December 2006 and the resulting outward moving interplanetary shock. These two large interplanetary shocks were the largest observed at V2 after V1 crossed the HTS at the end of 2004. They were observed at V2 just inside the HTS at 2006.16 and 2007.43 providing timing markers for V1. From the timing of the intensity decreases observed at V1 as the shocks first reach the HTS and then later reach V1 itself, we can estimate the shock speed beyond the HTS to be between 240 and 300 km s^(−1) in both cases. From the timing of the decreases observed when the shock first reaches the HTS and then several months later encounters the heliopause, we can estimate the heliosheath thickness to be 31 ± 4 and 37 ± 6 AU, respectively, for the two sequences of three decreases seen at V1. These values, along with the distances to the HTS that are determined, give distances from the Sun to the heliopause of 121 ± 4 and 124 ± 6 AU, respectively

At Voyager 1 Starting on about August 25, 2012 at a Distance of 121.7 AU From the Sun, a Sudden Disappearance of Anomalous Cosmic Rays and an Unusually Large Sudden Increase of Galactic Cosmic Ray H and He Nuclei and Electron Occurred

At the Voyager 1 spacecraft in the outer heliosphere, after a series of complex intensity changes starting at about May 8th, the intensities of both anomalous cosmic rays (ACR) and galactic cosmic rays (GCR) changed suddenly and decisively on August 25th (121.7 AU from the Sun). The ACR started the intensity decrease with an initial e-folding rate of intensity decrease of ~1 day. Within a matter of a few days, the intensity of 1.9-2.7 MeV protons and helium nuclei had decreased to less than 0.1 of their previous value and after a few weeks, corresponding to the outward movement of V1 by ~0.1 AU, these intensities had decreased by factors of at least 300-500 and are now lower than most estimates of the GCR spectrum for these lower energies and also at higher energies. The decrease was accompanied by large rigidity dependent anisotropies in addition to the extraordinary rapidity of the intensity changes. Also on August 25th the GCR protons, helium and heavier nuclei as well as electrons increased suddenly with the intensities of electrons reaching levels ~30-50% higher than observed just one day earlier. This increase for GCR occurred over ~1 day for the lowest rigidity electrons, and several days for the higher rigidity nuclei of rigidity ~0.5-1.0 GV. After reaching these higher levels the intensities of the GCR of all energies from 2 to 400 MeV have remained essentially constant with intensity levels and spectra that may represent the local GCR. These intensity changes will be presented in more detail in this, and future articles, as this story unfolds.Comment: 13 Pages, 5 Figure

Termination shock particle spectral features

Spectral features of energetic H ions accelerated at the termination shock may be evidence of two components. At low energies the energy spectrum is ~E^(–1.55), with break at ~0.4 MeV to E^(–2.2). A second component appears above ~1 MeV with a spectrum of E^(–1.27) with a break at ~3.2 MeV. Even though the intensities upstream are highly variable, the same spectral break energies are observed, suggesting that these are durable features of the source spectrum. The acceleration processes for the two components may differ, with the lower energy component serving as the injection source for diffusive shock acceleration of the higher energy component. Alternatively, the spectral features may result from the energy dependence of the diffusion tensor that affects the threshold for diffusive shock acceleration

Voyager observations of galactic and anomalous cosmic rays in the helioshealth

Anomalous cosmic rays display large temporal variations at the time and location where Voyager 1 (V1) crossed the heliospheric termination shock (2004.86) (94AU, 34°N). On a short time scale (3 months) there was a large decrease produced by a series of merged interaction regions (MIR), the first of which was associated with the intense Oct./Nov. 2003 solar events. On a longer time scale there is a remarkable correlation between changes in the galactic cosmic ray (GCR) intensity and those of 10–56 MeV/n ACR He and 30–56 MeV H extending over a 4.3 year period with the GCRs exhibiting their expected behavior over this part of the 11 and 22 year solar activity and heliomagnetic cycle. The relative changes in the ACR and GCR are the same for both the short term and long term variations. The comparative V1/V2 ACR and GCR spectra in the foreshock and heliosheath indicate that at this time most of the higher energy ACRs are not being accelerated near V1 but must have their source region elsewhere — possibly near the equatorial region of the TS as was suggested in our first paper on the TS crossing (1)

Analysis of a rotating advanced-technology space station for the year 2025

An analysis is made of several aspects of an advanced-technology rotating space station configuration generated under a previous study. The analysis includes examination of several modifications of the configuration, interface with proposed launch systems, effects of low-gravity environment on human subjects, and the space station assembly sequence. Consideration was given also to some aspects of space station rotational dynamics, surface charging, and the possible application of tethers

Shearing Box Simulations of the MRI in a Collisionless Plasma

We describe local shearing box simulations of turbulence driven by the magnetorotational instability (MRI) in a collisionless plasma. Collisionless effects may be important in radiatively inefficient accretion flows, such as near the black hole in the Galactic Center. The MHD version of ZEUS is modified to evolve an anisotropic pressure tensor. A fluid closure approximation is used to calculate heat conduction along magnetic field lines. The anisotropic pressure tensor provides a qualitatively new mechanism for transporting angular momentum in accretion flows (in addition to the Maxwell and Reynolds stresses). We estimate limits on the pressure anisotropy due to pitch angle scattering by kinetic instabilities. Such instabilities provide an effective ``collision'' rate in a collisionless plasma and lead to more MHD-like dynamics. We find that the MRI leads to efficient growth of the magnetic field in a collisionless plasma, with saturation amplitudes comparable to those in MHD. In the saturated state, the anisotropic stress is comparable to the Maxwell stress, implying that the rate of angular momentum transport may be moderately enhanced in a collisionless plasma.Comment: 20 pages, 9 figures, submitted to Ap

Josephson Currents in Quantum Hall Devices

We consider a simple model for an SNS Josephson junction in which the "normal metal" is a section of a filling-factor $\nu=2$ integer quantum-Hall edge. We provide analytic expressions for the current/phase relations to all orders in the coupling between the superconductor and the quantum Hall edge modes, and for all temperatures. Our conclusions are consistent with the earlier perturbative study by Ma and Zyuzin [Europhysics Letters {\bf 21} 941-945 (1993)]: The Josephson current is independent of the distance between the superconducting leads, and the upper bound on the maximum Josephson current is inversely proportional to the perimeter of the Hall device.Comment: Revtex4. 22 pages 9 figures. Replaced version has minor typos fixed and one added referenc