A PC-based magnetometer-only attitude and rate determination system for gyroless spacecraft

This paper describes a prototype PC-based system that uses measurements from a three-axis magnetometer (TAM) to estimate the state (three-axis attitude and rates) of a spacecraft given no a priori information other than the mass properties. The system uses two algorithms that estimate the spacecraft's state - a deterministic magnetic-field only algorithm and a Kalman filter for gyroless spacecraft. The algorithms are combined by invoking the deterministic algorithm to generate the spacecraft state at epoch using a small batch of data and then using this deterministic epoch solution as the initial condition for the Kalman filter during the production run. System input comprises processed data that includes TAM and reference magnetic field data. Additional information, such as control system data and measurements from line-of-sight sensors, can be input to the system if available. Test results are presented using in-flight data from two three-axis stabilized spacecraft: Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) (gyroless, Sun-pointing) and Earth Radiation Budget Satellite (ERBS) (gyro-based, Earth-pointing). The results show that, using as little as 700 s of data, the system is capable of accuracies of 1.5 deg in attitude and 0.01 deg/s in rates; i.e., within SAMPEX mission requirements

Advantages of estimating rate corrections during dynamic propagation of spacecraft rates: Applications to real-time attitude determination of SAMPEX

This paper describes real-time attitude determination results for the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX), a gyroless spacecraft, using a Kalman filter/Euler equation approach denoted the real-time sequential filter (RTSF). The RTSF is an extended Kalman filter whose state vector includes the attitude quaternion and corrections to the rates, which are modeled as Markov processes with small time constants. The rate corrections impart a significant robustness to the RTSF against errors in modeling the environmental and control torques, as well as errors in the initial attitude and rates, while maintaining a small state vector. SAMPLEX flight data from various mission phases are used to demonstrate the robustness of the RTSF against a priori attitude and rate errors of up to 90 deg and 0.5 deg/sec, respectively, as well as a sensitivity of 0.0003 deg/sec in estimating rate corrections in torque computations. In contrast, it is shown that the RTSF attitude estimates without the rate corrections can degrade rapidly. RTSF advantages over single-frame attitude determination algorithms are also demonstrated through (1) substantial improvements in attitude solutions during sun-magnetic field coalignment and (2) magnetic-field-only attitude and rate estimation during the spacecraft's sun-acquisition mode. A robust magnetometer-only attitude-and-rate determination method is also developed to provide for the contingency when both sun data as well as a priori knowledge of the spacecraft state are unavailable. This method includes a deterministic algorithm used to initialize the RTSF with coarse estimates of the spacecraft attitude and rates. The combined algorithm has been found effective, yielding accuracies of 1.5 deg in attitude and 0.01 deg/sec in the rates and convergence times as little as 400 sec

Proton acceleration by irradiation of isolated spheres with an intense laser pulse

We report on experiments irradiating isolated plastic spheres with a peak laser intensity of 2-3 x 10(20) W cm(-2). With a laser focal spot size of 10 mu m full width half maximum (FWHM) the sphere diameter was varied between 520 nm and 19.3 mu m. Maximum proton energies of similar to 25 MeV are achieved for targets matching the focal spot size of 10 mu m in diameter or being slightly smaller. For smaller spheres the kinetic energy distributions of protons become nonmonotonic, indicating a change in the accelerating mechanism from ambipolar expansion towards a regime dominated by effects caused by Coulomb repulsion of ions. The energy conversion efficiency from laser energy to proton kinetic energy is optimized when the target diameter matches the laser focal spot size with efficiencies reaching the percent level. The change of proton acceleration efficiency with target size can be attributed to the reduced cross-sectional overlap of subfocus targets with the laser. Reported experimental observations are in line with 3D3V particle in cell simulations. They make use of well-defined targets and point out pathways for future applications and experiments.DFG via the Cluster of Excellence Munich-Centre for Advanced Photonics (MAP) Transregio SFB TR18NNSA DE-NA0002008Super-MUC pr48meIvo CermakCGC Instruments in design and realization of the Paul trap systemIMPRS-APSLMUexcellent Junior Research FundDAAD|ToIFEEuropean Union's Horizon research and innovation programme 633053Physic

Neutrino induced transitions between the ground states of the A=12 triad

Neutrino induced reactions on $^{12}$C, an ingredient of liquid scintillators, have been studied in several experiments. We show that for currently available neutrino energies, $E_{\nu} \le$ 300 MeV, calculated exclusive cross sections $^{12}$C$_{gs}(\nu,l)$$^{12}$N$_{gs}$ for both muon and electron neutrinos are essentially model independent, provided the calculations simultaneously describe the rates of several other reactions involving the same states or their isobar analogs. The calculations agree well with the measured cross sections, which can be therefore used to check the normalization of the incident neutrino spectrum and the efficiency of the detector.Comment: 9 pages REVTEX, 2 postscript figures, text and figures available at http://www.krl.caltech.edu/preprints/MAP.htm

Observation of Parity Violation in the Omega-minus -> Lambda + K-minus Decay

The alpha decay parameter in the process Omega-minus -> Lambda + K-minus has been measured from a sample of 4.50 million unpolarized Omega-minus decays recorded by the HyperCP (E871) experiment at Fermilab and found to be [1.78 +/- 0.19(stat) +/- 0.16(syst)]{\times}10^{-2}. This is the first unambiguous evidence for a nonzero alpha decay parameter, and hence parity violation, in the Omega-minus -> Lambda + K-minus decay.Comment: 10 pages, 7 figure

de Haas-van Alphen Effect in the Two-Dimensional and the Quasi-Two-Dimensional Systems

We study the de Haas-van Alphen (dHvA) oscillation in two-dimensional and quasi-two-dimensional systems. We give a general formula of the dHvA oscillation in two-dimensional multi-band systems. By using this formula, the dHvA oscillation and its temperature-dependence for the two-band system are shown. By introducing the interlayer hopping $t_z$, we examine the crossover from the two-dimension, where the oscillation of the chemical potential plays an important role in the magnetization oscillation, to the three-dimension, where the oscillation of the chemical potential can be neglected as is well know as the Lifshitz and Kosevich formula. The crossover is seen at $4 t_z \sim 8 ta b H /\phi_0$, where a and b are lattice constants, $\phi_0$ is the flux quantum and 8t is the width of the total energy band. We also study the dHvA oscillation in quasi-two-dimensional magnetic breakdown systems. The quantum interference oscillations such as $\beta-\alpha$ oscillation as well as the fundamental oscillations are suppressed by the interlayer hopping $t_z$, while the $\beta+\alpha$ oscillation gradually increases as $t_z$ increases and it has a maximum at $t_z/t\approx 0.025$. This interesting dependence on the dimensionality can be observed in the quasi-two-dimensional organic conductors with uniaxial pressure.Comment: 11 pages, 14 figure

Global Monitoring of Atmospheric Trace Gases, Clouds and Aerosols from UV/vis/NIR Satellite Instruments: Currents Status and Near Future Perspectives

A new generation of UV/vis/near‐IR satellite instruments like GOME (since 1995), SCIAMACHY (since 2002), OMI (since 2004), and GOME‐2 (since 2006) allows to measure several important stratospheric and tropospheric trace gases like O_3, NO_2, OClO, HCHO, SO_2, BrO, and H_2O as well as clouds and aerosols from space. Because of its extended spectral range, the SCIAMACHY instrument also allows the retrieval of Greenhouse gases (CO_2, CH_4) and CO in the near IR. Almost all of the tropospheric trace gases are observed by these instruments for the first time. From satellite data it is possible to investigate the temporal and spatial variation. Also different sources can be characterised and quantified. The derived global distributions can serve as input and for the validation of atmospheric models. Here we give an overview on the current status of these new instruments and data products and their recent applications to various atmospheric and oceanic phenomena

Flexible energy conversion and storage via high-temperature gas-phase reactions: The piston engine as a polygeneration reactor

Piston engines are typically considered devices converting chemical energy into mechanical power via internal combustion. But more generally, their ability to provide high-pressure and high-temperature conditions for a limited time means they can be used as chemical reactors where reactions are initiated by compression heating and subsequently quenched by gas expansion. Thus, piston engines could be “polygeneration” reactors that can flexibly change from power generation to chemical synthesis, and even to chemical-energy storage. This may help mitigating one of the main challenges of future energy systems – accommodating fluctuations in electricity supply and demand. Investments in devices for grid stabilization could be more economical if they have a second use. This paper presents a systematic approach to polygeneration in piston engines, combining thermodynamics, kinetics, numerical optimization, engineering, and thermo-economics. A focus is on the fuel-rich conversion of methane as a fuel that is considered important for the foreseeable future. Starting from thermodynamic theory and kinetic modeling, promising systems are selected. Mathematical optimization and an array of experimental kinetic investigations are used for model improvement and development. To evaluate technical feasibility, experiments are then performed in both a single-stroke rapid compression machine and a reciprocating engine. In both cases, chemical conversion is initiated by homogeneous-charge compression-ignition. A thermodynamic and thermo-economic assessment of the results is positive. Examples that illustrate how the piston engine can be used in polygeneration processes to convert methane to higher-value chemicals or to take up carbon dioxide are presented. Open issues for future research are addressed

Tricritical behavior of the frustrated XY antiferromagnet

Extensive histogram Monte-Carlo simulations of the XY antiferromagnet on a stacked triangular lattice reveal exponent estimates which strongly favor a scenario of mean-field tricritical behavior for the spin-order transition. The corresponding chiral-order transition occurs at the same temperature but appears to be decoupled from the spin-order. These results are relevant to a wide class of frustrated systems with planar-type order and serve to resolve a long-standing controversy regarding their criticality.Comment: J1K 2R1 4 pages (RevTex 3.0), 4 figures available upon request, Report# CRPS-94-0