Time distribution of the precipitable water vapor in central Saudi Arabia and its relationship to solar activity

Water vapor is the most important greenhouse gas. It plays a major role in the dynamics of atmospheric circulation, radiation exchange within the atmosphere, and climate variability. Knowledge of the distribution of water vapor is important for understanding climate change and global warming.     

F2 layer characteristics and electrojet strength over an equatorial station

The data presented in this work describes the diurnal and seasonal variation in hmF2, NmF2, and the electrojet current strength over an African equatorial station during a period of low solar activity. The F2 region horizontal magnetic element H revealed that the Solar quiet Sq(H) daily variation rises from early morning period to maximum around local noon and falls to lower values towards evening. The F2 ionospheric current responsible for the magnetic field variations is inferred to build up at the early morning hours, attaining maximum strength around 1200 LT. The Sq variation across the entire months was higher during the daytime than nighttime. This is ascribed to the variability of the ionospheric parameters like conductivity and winds structure in this region. Seasonal daytime electrojet (EEJ) current strength for June solstice, March and September equinoxes, respectively had peak values ranging within 27–35 nT (at 1400 LT) , 30–40 nT (at 1200 LT) and 35–45 nT (at 1500 LT). The different peak periods of the EEJ strength were attributed to the combined effects of the peak electron density and electric field. Lastly, the EEJ strength was observed to be higher during the equinoxes than the solstice period.     

1989年3月太阳活动引起的电离层骚扰

本文利用我国,苏联,日本和澳大利亚等国16个电离层观测站的资料,分析了1989年3月太阳耀斑引起的大电离层骚扰特征。     

Plasma flow variations and energetic protons upstream of the earth’s bow shock: A statistical study

Foreshock is a special region located upstream of the Earth’s bow shock characterized by the presence of various plasma waves and fluctuations caused by the interaction of the solar wind plasma with particles reflected from the bow shock or escaping from the magnetosphere. On the other hand, foreshock fluctuations may modify the bow shock structure and, being carried through the magnetosheath, influence the magnetopause. During the years 1995–2000, the INTERBALL-1 satellite made over 10,000 hours of plasma and energetic particles measurements in the solar wind upstream of the Earth’s bow shock. We have sorted intervals according to the level of solar wind ion flux fluctuations and/or according to the flux of back-streaming energetic protons. An analysis of connection between a level of ion flux fluctuations and fluxes of high-energy protons and their relation to the IMF orientation is presented.     

Numerical techniques for generating and refining solar sail trajectories

Like all applications in trajectory design, the design of solar sail trajectories requires a transition from analytical models to numerically generated realizations of an orbit. In astrodynamics, three numerical strategies are often employed. Differential correctors (also known as shooting methods) are perhaps the most common techniques. Finite-difference methods and collocation schemes are also employed and are successful in generating trajectories with pseudo-continuous control histories. These three numerical techniques are employed here to generate periodic trajectories displaced below the Moon in a circular restricted three-body system. All these approaches reveal trajectory options within the design space for solar sail applications.     

Test alert service against very large SEP Events

The Aragats Solar Environment Center provides real time monitoring of different components of secondary cosmic ray fluxes. We plan to use this information to establish an early warning alert system against extreme, very large solar particle events with hard spectra, dangerous for satellite electronics and for the crew of the Space Station. Neutron monitors operating at altitude 2000 and 3200 m are continuously gathering data to detect possible abrupt variations of the particle count rates. Additional high precision detectors measuring muon and electron fluxes, along with directional information are under construction on Mt. Aragats. Registered ground level enhancements, in neutron and muon fluxes along with correlations between different species of secondary cosmic rays are analyzed to reveal possible correlations with expected times of arrival of dangerous solar energetic particles.     

Reconciling space object observed and solar pressure albedo-areas via astrometric and photometric data fusion

There are many Resident Space Objects (RSOs) in the Geostationary Earth Orbit (GEO) regime, both operational and debris. The primary non-gravitational force acting on these RSOs is Solar Radiation Pressure (SRP), which is sensitive to the RSO’s area-to-mass ratio. Sparse observation data and mismodeling of non-gravitational forces has constrained the state of practice in tracking and characterizing RSOs. Accurate identification, characterization, tracking, and motion prediction of RSOs is a high priority research issue as it shall aid in assessing collision probabilities in the GEO regime, and orbital safety writ large. Previous work in characterizing RSOs has taken a preliminary step in exploiting fused astrometric and photometric data to estimate the RSO mass, shape, attitude, and size. This works, in theory, since angles data are sensitive to SRP albedo-area-to-mass ratio, and photometric data are sensitive to shape, attitude, and observed albedo-area. By fusing these two data types, mass and albedo-area both become observable parameters and can be estimated as independent quantities. However, previous work in mass and albedo-area estimation has not quantified and assessed the fundamental physical link between SRP albedo-area and observed albedo-area. The observed albedo-area is always a function of the SRP albedo-area along the line of sight of the observer. This is the physical relationship that this current research exploits. It is shown through simulation that due to this physical link, and through the fusion of astrometric and photometric data, it is possible to observe the mass of a space object when the area is not known. Results for data from 100 trajectories generated from randomly sampled initial conditions are shown. It is seen that even when the area of the object is not known, the uncertainty in mass can be lowered from an initial value of 800?kg to the range 500–700?kg for 72% of the samples, 200–500?kg for 13% of the samples, and 0–200?kg for 15% of the samples. It is further shown that although the uncertainties are large, the actual errors in mass are much lower, with the error RMS being less than 100?kg for 30% of the samples, between 100 and 200?kg for another 30%, and between 200 and 300?kg for 24% of the samples.     

PROBA-3 mission and the Shadow Position Sensors: Metrology measurement concept and budget

PROBA-3 is a space mission of the European Space Agency that will test, and validate metrology and control systems for autonomous formation flying of two independent satellites. PROBA-3 will operate in a High Elliptic Orbit and when approaching the apogee at 6·10⁴ Km, the two spacecraft will align to realize a giant externally occulted coronagraph named ASPIICS, with the telescope on one satellite and the external occulter on the other one, at inter-satellite distance of 144.3 m. The formation will be maintained over 6 hrs across the apogee transit and during this time different validation operations will be performed to confirm the effectiveness of the formation flying metrology concept, the metrology control systems and algorithms, and the spacecraft manoeuvring. The observation of the Sun’s Corona in the field of view [1.08;3.0]R_Sun will represent the scientific tool to confirm the formation flying alignment. In this paper, we review the mission concept and we describe the Shadow Position Sensors (SPS), one of the metrological systems designed to provide high accuracy (sub-millimetre level) absolute and relative alignment measurement of the formation flying. The metrology algorithm developed to convert the SPS measurements in lateral and longitudinal movement estimation is also described and the measurement budget summarized.     

Variation of ionospheric electron and ion temperatures during periods of minimum to maximum solar activity by the SROSS-C2 satellite over Indian low and equatorial latitudes

To study the variation of ionospheric electron and ion temperatures with solar activity the data of electron and ion temperatures were recorded with the help of Retarding Potential Analyzer payload aboard Indian SROSS-C2 satellite at an average altitude of ∼500 km. The main focuses of the paper is to see the diurnal, seasonal and latitudinal variations of electron and ion temperatures during periods of minimum to maximum solar activity. The ionospheric temperatures in the topside show strong variations with altitude, latitude, season and solar activity. In present study, the temperature variations with latitude, season and solar activity have been studied at an average altitude ∼500 km. The peak at sunrise has been observed during all seasons, in both electron and ion temperatures. Further, the ionospheric temperatures vary with latitude in day time. The latitudinal variation is more pronounced for low solar activity than for high solar activity.     

太阳帆板驱动机构的表面充放电效应研究

空间等离子体环境效应导致的卫星表面充放电是造成卫星在轨工作异常及故障的重要原因之一. 太阳帆板驱动机构（Solar Array Drive Assembly,SADA）是长寿命、大功率卫星电传输环节的关键部件,易成为充放电效应的对象,可使卫星丧失能源,导致整星失效. 为验证空间等离子体环境导致的表面充放电对SADA特别是其功率传输可靠性和安全性的影响,利用等离子体环境模拟试验装置,模拟地球同步轨道（Geostationary Orbit,GEO）等离子体环境,针对SADA进行试验研究. 结果表明,使用两种不同绝缘材料的SADA在空间等离子体模拟环境下表现没有明显区别,表面充放电未对设计合理的SADA正常工作造成明显影响. 研究结果对未来GEO轨道SADA等空间机构的可靠性和安全性设计具有一定指导意义.