Solar wind-Venus interaction affecting ionospheric electron density profile

The equilibrium electron density profile has been computed and compared with measured profiles by Venera 9 and Mariner 5 and 10. The computed electron density profile is seen to show discrepancies with measured data. The contribution of solar wind interaction induced convection to equilibrium electron density profile has been estimated. It is found that the convective processes are less important at lower altitudes, whereas at higher altitudes its contribution becomes dominant. The night side Venus ionosphere is formed due to the transport of O⁺ and impact ionization of neutral gases by suprathermal electrons. The discrepancies in theoretical and measured electron density profiles provide clear indication of additional energy source of solar wind origin.     

Impact of four dimensional assimilation of satellite data on long-range simulations over the Indian region during monsoon 2006

A number of experiments were conducted to study the impact of updating model basic fields by satellite data (Quick Scatterometer (QSCAT) surface winds and Atmospheric Infrared Sounder (AIRS) temperature and humidity profiles) on long-range simulation during the Indian summer monsoon 2006. The Pennsylvania State University/National Center for Atmospheric Research (PSU/NCAR) mesoscale model version5 (MM5) and its four dimensional data assimilation (FDDA) technique was used for the numerical simulations. The spatial distribution and temporal variation in model simulated basic meteorological parameters and rainfall were verified against the observed fields from National Center for Environmental Prediction (NCEP) analysis and Tropical Rainfall Measuring Mission (TRMM), respectively. The overall analysis of the results from QSCAT surface wind assimilation as compared to control simulation (CNT; without the satellite data assimilation) suggest that a better representation of a single level wind field during model integration fail to make significant improvement in the model simulation both in the basic meteorological parameters and rainfall. The assimilation of temperature and humidity profiles from the AIRS during model integration significantly improved the rainfall prediction during monsoon period. It is found that the improvement in rainfall prediction is attributed to improved thermodynamics structure due to AIRS profile assimilation and the degree of improvement is more in temperature prediction as compared to humidity prediction. It is also found that the prediction over the regions, such as south west part of India and foothills of Himalaya, where a complex orography exists, is not significantly benefited from satellite data assimilation which highlights the need of improvement in the model in addition to a better representation of atmospheric state.     

VTOL Aircraft Control Output Tracking Sensitivity Design

A method is presented for reducing trajectory sensitivity and achieving robust asymptotic tracking for linear feedback systems when there are parameter perturbations and disturbance inputs. The controller consists of a servocompensator containing the modes of the reference signals and disturbance inputs, a stabilizing feedback loop, and a feedforward compensator. Application of the method to the design of a vertical takeoff and landing (VTOL) aircraft flight control system is discussed. The use of a precompensator allows performance maneuvers such that the aircraft tracks desired trajectories and the feedforward and feedback signals aid in reducing the trajectory sensitivity to variations of parameters due to change in airspeed and to wind gust. Simulation results are presented to show the robust tracking, disturbance rejection, and sensitivity reduction capabilities of the flight control system.     

Nonlinear Adaptive Attitude Control of Spacecraft

A model reference adaptive control law is presented for largeangle rotational maneuvers of spacecraft using reaction jets. It isassumed that the various parameters of the spacecraft arecompletely unknown, and unknown but bounded disturbancetorques are acting on the spacecraft. The controller includes adynamic system in the feedback path. Simulation results arepresented to show that fast, large angle rotational maneuvers can beperformed using the adaptive controller in spite of uncertainty inthe system.     

Future of Venus Research and Exploration

Despite the tremendous progress that has been made since the publication of the Venus II book in 1997, many fundamental questions remain concerning Venus’ history, evolution and current geologic and atmospheric processes. The international science community has taken several approaches to prioritizing these questions, either through formal processes like the Planetary Decadal Survey in the United States and the Cosmic Vision in Europe, or informally through science definition teams utilized by Japan, Russia, and India. These questions are left to future investigators to address through a broad range of research approaches that include Earth-based observations, laboratory and modeling studies that are based on existing data, and new space flight missions. Many of the highest priority questions for Venus can be answered with new measurements acquired by orbiting or in situ missions that use current technologies, and several plausible implementation concepts have been studied and proposed for flight. However, observations needed to address some science questions pose substantial technological challenges, for example, long term survival on the surface of Venus and missions that require surface or controlled aerial mobility. Missions enabled by investments in these technologies will open the door to completely new ways of exploring Venus to provide unique insights into Venus’s past and the processes at work today.