This article discusses the dynamic state analysis of underwater towed-cable when tow-ship changes its speed in a direction making parabolic profile path. A three-dimensional model of underwater towed system is studied...This article discusses the dynamic state analysis of underwater towed-cable when tow-ship changes its speed in a direction making parabolic profile path. A three-dimensional model of underwater towed system is studied. The established governing equations for the system have been solved using the central implicit finite-difference method. The obtained difference non-linear coupled equations are solved by Newton＇s method and satisfactory results were achieved. The solution of this problem has practical importance in the estimation of dynamic loading and motion, and hence it is directly applicable to the enhancement of safety and the effectiveness of the offshore activities.展开更多
Once after the satellite launch,one of the main works for any satellite mission is to calibrate the onboard sensors.Especially the sensor development and testing environment are different than working space environmen...Once after the satellite launch,one of the main works for any satellite mission is to calibrate the onboard sensors.Especially the sensor development and testing environment are different than working space environments.Apart from that,during spacecraft launch,sensors experience high physical disturbances which can change the sensor parameters.But in actual operation time,the measurement by the sensors should be very accurate;otherwise,there will be a chance that the payload will be off-targeted.So,before starting regular payload operations,the onboard sensor calibration is extremely important.Satellites may have absolute sensors like star sensors and relative sensors like gyroscopes.Almost all the satellites of the Indian Space Research Organization(ISRO),are having gyro sensors that provide accurate body rate information.These gyro sensors are electromechanical devices.It has inherent drifts,especially with various operating temperature environments.These gyro sensors are calibrated using absolute sensors like star sensors.The details gyro calibration process with star sensor have been mentioned in this paper.With proper theoretical understanding,this paper describes how the onboard gyro measurements and onboard star sensors measurements are taken and how using Matlab and System Tool Kit(STK)software the gyro parameters are derived.Finally,the derived values were uplinked to the spacecraft and from onboard performance certified that the derived values are correct.The same process can be applied to any other satellite to calibrate gyro sensors.展开更多
The spacecraft Sun outage is a phenomenon whereby radio signals from a spacecraft are obscured by the solar radiation.These interferences occur,because the ground station antenna does not distinguish between the Sun’...The spacecraft Sun outage is a phenomenon whereby radio signals from a spacecraft are obscured by the solar radiation.These interferences occur,because the ground station antenna does not distinguish between the Sun’s energy and its intended communication signal with the spacecraft.In this paper,a geometrical Sun outage prediction model is developed and a comparative study is performed with the model given by Ma et al.(Earth Sci Res 7(1):106–109,2018).The solar outage prediction model is incorporated in the Satellite Precise Orbit Propagator which is a high-fidelity numerical orbit propagator,and the NORAD compatible two-line element(TLE)analytical propagator for the Earth orbiting spacecraft.Using the propagator,the spacecraft solar outage over a ground station antenna can be easily predicted either knowing its state vector or TLE.展开更多
In this paper,a high-fidelity satellite orbit propagator,namely the Satellite Precise Orbit Propagator(SPOP),is developed for the Earth orbiting satellites.The SPOP numerically integrates the perturbed two-body differ...In this paper,a high-fidelity satellite orbit propagator,namely the Satellite Precise Orbit Propagator(SPOP),is developed for the Earth orbiting satellites.The SPOP numerically integrates the perturbed two-body differential equations of motion in the Earth Mean Equator and Equinox of 2000(EME2000/J2000)reference frame using Cowell’s formulation and explicit Runge–Kutta class of integrator with the fixed time step size.Various perturbing forces are included in the numerical propagator such as a simple two-body problem up to J_(6)terms for the academic purpose,full force gravitational field model using the spherical harmonics for the high precision orbit propagation in view of the commercial use,atmospheric drag,third-body gravity,solar radiation pressure,Earth radiation pressure due to albedo,and relativistic effect correction.In addition,SPOP also has the feature to predict the satellite ephemeris and orbit products using the NORAD compatible two-line element(TLE)through SGP4/SDP4 analytical propagator.展开更多
文摘This article discusses the dynamic state analysis of underwater towed-cable when tow-ship changes its speed in a direction making parabolic profile path. A three-dimensional model of underwater towed system is studied. The established governing equations for the system have been solved using the central implicit finite-difference method. The obtained difference non-linear coupled equations are solved by Newton＇s method and satisfactory results were achieved. The solution of this problem has practical importance in the estimation of dynamic loading and motion, and hence it is directly applicable to the enhancement of safety and the effectiveness of the offshore activities.
文摘Once after the satellite launch,one of the main works for any satellite mission is to calibrate the onboard sensors.Especially the sensor development and testing environment are different than working space environments.Apart from that,during spacecraft launch,sensors experience high physical disturbances which can change the sensor parameters.But in actual operation time,the measurement by the sensors should be very accurate;otherwise,there will be a chance that the payload will be off-targeted.So,before starting regular payload operations,the onboard sensor calibration is extremely important.Satellites may have absolute sensors like star sensors and relative sensors like gyroscopes.Almost all the satellites of the Indian Space Research Organization(ISRO),are having gyro sensors that provide accurate body rate information.These gyro sensors are electromechanical devices.It has inherent drifts,especially with various operating temperature environments.These gyro sensors are calibrated using absolute sensors like star sensors.The details gyro calibration process with star sensor have been mentioned in this paper.With proper theoretical understanding,this paper describes how the onboard gyro measurements and onboard star sensors measurements are taken and how using Matlab and System Tool Kit(STK)software the gyro parameters are derived.Finally,the derived values were uplinked to the spacecraft and from onboard performance certified that the derived values are correct.The same process can be applied to any other satellite to calibrate gyro sensors.
文摘The spacecraft Sun outage is a phenomenon whereby radio signals from a spacecraft are obscured by the solar radiation.These interferences occur,because the ground station antenna does not distinguish between the Sun’s energy and its intended communication signal with the spacecraft.In this paper,a geometrical Sun outage prediction model is developed and a comparative study is performed with the model given by Ma et al.(Earth Sci Res 7(1):106–109,2018).The solar outage prediction model is incorporated in the Satellite Precise Orbit Propagator which is a high-fidelity numerical orbit propagator,and the NORAD compatible two-line element(TLE)analytical propagator for the Earth orbiting spacecraft.Using the propagator,the spacecraft solar outage over a ground station antenna can be easily predicted either knowing its state vector or TLE.
文摘In this paper,a high-fidelity satellite orbit propagator,namely the Satellite Precise Orbit Propagator(SPOP),is developed for the Earth orbiting satellites.The SPOP numerically integrates the perturbed two-body differential equations of motion in the Earth Mean Equator and Equinox of 2000(EME2000/J2000)reference frame using Cowell’s formulation and explicit Runge–Kutta class of integrator with the fixed time step size.Various perturbing forces are included in the numerical propagator such as a simple two-body problem up to J_(6)terms for the academic purpose,full force gravitational field model using the spherical harmonics for the high precision orbit propagation in view of the commercial use,atmospheric drag,third-body gravity,solar radiation pressure,Earth radiation pressure due to albedo,and relativistic effect correction.In addition,SPOP also has the feature to predict the satellite ephemeris and orbit products using the NORAD compatible two-line element(TLE)through SGP4/SDP4 analytical propagator.
