Image compression systems on board satellites

On-board image compression systems aim to increase the amount of data stored in the on-board mass memory and transmitted to the ground station. This paper presents an overview and analysis of the state-of-the-art in on-board image compression systems. Compression methods and systems implementations are reviewed. Statistical analysis and developing trends are given. A new architecture of an on-board image compression system for future disaster monitoring multi-satellite missions in LEO is described.     

Contribution of secondaries to the radiation environment on space missions.

Calculations to predict the radiation environment for spacecraft in low earth orbit sometimes ignore the contribution from secondary radiation products. However, the contribution of secondaries, particularly neutrons, on heavy spacecraft or in planetary bodies can be of concern for biological systems. The Shuttle Activation Monitor (SAM) and Cosmic Radiation Effects and Activation Monitor (CREAM) experiments provide valuable data on secondary (as well as primary) radiation effects. Comparisons have been made between induced activity from flight-exposed samples, induced activity in a ground-irradiated sample, and Monte Carlo-derived predictions with and without secondaries. These comparisons show that for a flight-exposed sample, predictions which omit the secondary contribution result in a spectrum that is too low by a factor of 2. The addition of the secondaries results in a predicted spectrum that closely matches the measured data.     

The accuracy of ionogram-derived N(h) profiles

At the Millstone Hill station the Incoherent Scatter Radar (ISR) and a Digisonde 256 are simultaneously operating. Some characteristic true heights determined by both instruments are compared with each other, possible reasons for observed difference are indicated.     

Observations of compact X-ray binaries with the Chandra X-ray Observatory

The Chandra X-ray Observatory was launched on July 23, 1999. The first X-ray photons were detected on August 12 of that same year. Subsequently observations with the Observatory, which features sub-arcsecond angular resolution, have revolutionized our understanding of the X-ray emitting sky providing hosts of spectacular energy-resolved images and high-resolution spectra. Here we present a brief overview of Chandra X-ray Observatory observations of compact X-ray binaries.     

Robust Preprocessing for Kalman Filtering of Glint Noise

The non-Gaussian character of glint noise is demonstrated by exploratory data analysis. This non-Gaussian behavior is characterized by outliers in the form of glint spikes. Since glint noise is processed by an angle-tracking Kalman filter, and since the latter is quite nonrobust, strategies are proposed to minimize the effect of these glint spikes. One of the strategies, which involves robust preprocessing of the data, is pursued in detail. Finally, some results of a planar missile simulation are presented that clearly demonstrate the merits of the robust preprocessing strategy.     

The radial diffusion of trapped particles induced by fluctuating magnetospheric fields

Small fluctuations in magnetospheric electric and magnetic fields lead to random changes in the radial positions of trapped particles. The characteristics of this radial diffusion are described theoretically in terms of the statistical properties of the field fluctuations, in particular the power spectra of the various spatial components. A large body of trapped particle data demonstrates that diffusion with the predicted properties actually takes place. These data include the average radial and energy distributions and the time variations in particle fluxes. This radial diffusion has a major influence on the structure of the radiation belts; and since the net flow of particles is inward at most positions of the magnetosphere, the process acts as a strong source of trapped particles. Further experiments are needed to establish the importance of this mechanism relative to magnetic storm effects and to collective instabilities.     

嫦娥四号能量中性原子观测揭示太阳风与月面相互作用新特征

与地球不同,月球暴露在太阳风中.太阳风注入到月面,与月壤相互作用,部分太阳风质子以能量中性原子(Energetic Neutral Atom,ENA)的形式被月表散射.另外,月球局部地区的磁异常能阻挡太阳风到达月面,并形成微磁层,成为月面天然的保护屏障.然而以往相关的观测数据都来自轨道器,月面的真实情况无从知晓.嫦娥四...     

Atom-Based Test of the Equivalence Principle

We describe a test of the equivalence principle with quantum probe particles based on atom interferometry. For the measurement, a light pulse atom interferometer based on the diffraction of atoms from effective absorption gratings of light has been developed. A differential measurement of the Earth’s gravitational acceleration g for the two rubidium isotopes ⁸⁵Rb and ⁸⁷Rb has been performed, yielding a difference Δg/g=(1.2±1.7)×10^?7. In addition, the dependence of the free fall on the relative orientation of the electron to the nuclear spin was studied by using atoms in two different hyperfine states. The determined difference in the gravitational acceleration is Δg/g=(0.4±1.2)×10^?7. Within their experimental accuracy, both measurements are consistent with a free atomic fall that is independent from internal composition and spin orientation.