Operations of a spaceflight experiment to investigate plant tropisms

Plants will be an important component in bioregenerative systems for long-term missions to the Moon and Mars. Since gravity is reduced both on the Moon and Mars, studies that identify the basic mechanisms of plant growth and development in altered gravity are required to ensure successful plant production on these space colonization missions. To address these issues, we have developed a project on the International Space Station (ISS) to study the interaction between gravitropism and phototropism in Arabidopsis thaliana. These experiments were termed TROPI (for tropisms) and were performed on the European Modular Cultivation System (EMCS) in 2006. In this paper, we provide an operational summary of TROPI and preliminary results on studies of tropistic curvature of seedlings grown in space. Seed germination in TROPI was lower compared to previous space experiments, and this was likely due to extended storage in hardware for up to 8 months. Video downlinks provided an important quality check on the automated experimental time line that also was monitored with telemetry. Good quality images of seedlings were obtained, but the use of analog video tapes resulted in delays in image processing and analysis procedures. Seedlings that germinated exhibited robust phototropic curvature. Frozen plant samples were returned on three space shuttle missions, and improvements in cold stowage and handing procedures in the second and third missions resulted in quality RNA extracted from the seedlings that was used in subsequent microarray analyses. While the TROPI experiment had technical and logistical difficulties, most of the procedures worked well due to refinement during the project.     

A multiobjective optimization approach to determine the parameters of stepped frequency pulse train

Frequency stepping techniques are commonly used in modern radar system to get high range resolution with the disadvantage that its autocorrelation function (ACF) yield undesirable “grating lobes”. Wider mainlobe deteriorates the range resolution capability of the waveform and higher peak sidelobe either hides the small targets or causes the false target detection. Several techniques have been used to choose the parameters of linear frequency modulated (LFM) pulse train to suppress the grating lobes without paying much attention to the mainlobe width and peak sidelobe level. In this paper a multiobjective optimization (Nondominated Sorting Genetic Algorithm-II (NSGA-II)) approach is proposed to optimize the parameters of the LFM pulse train to achieve reduced grating lobes, low peak sidelobe level and narrow mainlobe width. The optimization problem has been studied in two different ways: first one is associated with the reduction of grating lobes and the minimization of peak sidelobe level of the ACF with constraints and second one is related to the minimization of the peak sidelobe level and mainlobe width of the ACF with constraints. Simulation studies have been carried out to justify the potentiality of the proposed approach.     

Atmospheric dynamics on Venus and Mars

New results from Pioneer Orbiter observations indicate a continued vortex organization of the cloud level atmosphere in either hemisphere, centered over respective poles. Significant changes in the magnitude of the cloud level zonal circulation over a period of several years have been detected. A strong signature of the solar tidal circulation has been detected in the atmospheric circulation with the lowest speeds occurring in equatorial latitudes about 20° upstream of the sub-solar point. Finally, a solar-locked persistent spatial structure has been discovered in the variance of the ultraviolet brightness measured from brightness normalized images of Venus. Vega balloons (drifting at about 53 km altitude near 7°N and 7°S latitudes) have also provided some unique observations of atmospheric circulation, significant among them being the strong vertical motions, the zonality of their drift speeds as well as a significant temperature difference between the two balloons. The temperature difference which amounts to 6.5°K on average is currently being interpreted as a temperature variation with longitude or time.

Diagnostic modelling efforts towards simulating the atmospheric circulation on Venus are continuing and have provided some clues about the processes that maintain them but have not yet been successful in explaining the superrotation of the atmosphere.

Knowledge of the Martian atmospheric dynamics on the other hand is still limited by lack of adequate observations. Numerical modelling of the Martian atmosphere continues to provide most of the information about the atmospheric circulation. The situation regarding the paucity of observations should improve with the completion of the proposed Mars Observer mission. The low circular polar orbit planned provides an excellent opportunity to study the Martian atmosphere.     

A PC based test system for an on-board computer

This paper presents a robust method of testing a processor based on-board computer used in the Indian remote sensing satellite (IRS-1C). The novelty of this scheme lies in a judicious mix of software and hardware approaches adopted to realise this PC-based system. All the electrical interfaces (like telemetry, Telecommand, timer and star sensor) are simulated. They are fabricated as add-on cards to PC-AT (ISAbus). The on-board computer controls two star sensors apart from handling three telemetry streams and accepting more than one hundred Telecommands     

Orbital and Attitude Prediction Accuracy Requirements for Satellites Engaged in Remote Sensing and Scientific Missions

The criteria for selecting the orbital and attitude prediction accuracy requirements for communications satellites have been investigated in a previous paper by the author. The present paper extends the analysis to the satellites engaged in remote sensing and scientific missions. A unified approach has been developed to examine the problem of the prediction accuracy requirements for the two missions.     

Correlation of Binarized Images

Correlator technique has been used in pattern recognition applications. We introduce a correlation performance measure, peak to background ratio (PBR), defined as the ratio of the peak intensity to the average background variation in a single correlation output. Using this performance measure, we analyze the binary correlator and show that the binarization of the images can result in better performance. We consider a real-time implementation of the binary correlator, using VLSI technology. The analytical results are supported by computer simulations.     

An attitude control approach for compensation of satellite drift in elliptic synchronous orbits

This paper explores the possibility of developing a new attitude control method for satellites in elliptic, 24-hour orbits, in order to compensate for the effect of longitudinal periodic drift relative to the ground station. A simple solar attitude control technique has been proposed for achieving the fixed apparent satellite orientation with respect to the ground segment of the space mission. The proposed control approach appears to be quite attractive for various satellite applications as it can substantially overcome the problems created by the continual periodic angular drift as well as undesirable pitching excitation in the elliptic orbits. Generalizing the analytically developed open-loop control policy results in a significant improvement of the controller performance.     

Evaluation and utilization of CloudSat and CALIPSO data to analyze the impact of dust aerosol on the microphysical properties of cirrus over the Tibetan Plateau

The present study elucidates on the evaluation of two versions (V3 and V4.10) of vertical feature mask (VFM) and aerosol sub-types data derived from the Cloud-Aerosol LiDAR and Infrared Pathfinder Satellite Observations (CALIPSO), and its utilization to analyze the impact of dust aerosol on the microphysical properties of cirrus over the Tibetan Plateau (TP). In conjunction to the CALIPSO, we have also used the CloudSat data to study the same during the summer season for the years 2007–2010 over the study area 25–40°N and 75–100°E. Compared to V3 of CALIPSO, V4.10 was found to have undergone substantial changes in the code, algorithm, and data products. Intercomparison of both versions of data products in the selected grid between 30–31°N and 83–84°E within the study area during 2007–2017 revealed that the VFM and aerosol sub-types are in good agreement of ～95.27% and ～82.80%, respectively. Dusty cirrus is defined as the clouds mixed with dust aerosols or existing in dust aerosol conditions, while the pure cirrus is that in a dust-free environment. The obtained results illustrated that the various microphysical properties of cirrus, namely ice water content (IWC), ice water path (IWP), ice distribution width (IDW), ice effective radius (IER), and ice number concentration (INC) noticed a decrease of 17%, 18%, 4%, 19%, and 10%, respectively due to the existence of dust aerosol, consistent with the classical “Twomey effect” for liquid clouds. Moreover, the aerosol optical depth (AOD) showed moderate negative correlations between ?0.4 and ?0.6 with the microphysical characteristics of cirrus. As our future studies, in addition to the present work undertaken, we planned to gain knowledge and interested to explore the impact of a variety of aerosols apart from the dust aerosol on the microphysical properties of cirrus in different regions of China.     

Variation of ionospheric total electron content in Indian low latitude region of the equatorial anomaly during May 2007–April 2008

The ionospheric total electron content (TEC), derived by analyzing dual frequency signals from the Global Positioning System (GPS) recorded near the Indian equatorial anomaly region, Varanasi (geomagnetic latitude 14°, 55′N, geomagnetic longitude 154°E) is studied. Specifically, we studied monthly, seasonal and annual variations as well as solar and geomagnetic effects on the equatorial ionospheric anomaly (EIA) during the solar minimum period from May 2007 to April 2008. It is found that the daily maximum TEC near equatorial anomaly crest yield their maximum values during the equinox months and their minimum values during the summer. Using monthly averaged peak magnitude of TEC, a clear semiannual variation is seen with two maxima occurring in both spring and autumn. Statistical studies indicate that the variation of EIA crest in TEC is poorly correlated with Dst-index (r = −0.03) but correlated well with Kp-index (r = 0.82). The EIA crest in TEC is found to be more developed around 12:30 LT.