Vikram Sarabhai Space Centre

About: Vikram Sarabhai Space Centre is a facility organization based out in Thiruvananthapuram, India. It is known for research contribution in the topics: Aerosol & Ultimate tensile strength. The organization has 2092 authors who have published 3058 publications receiving 47975 citations. The organization is also known as: VSSC.

A Third-Order Theory for the Effect of Drag on Earth Satellite Orbits

Abstract: Analytical theory for the motion of near-Earth satellite orbits with the air drag effect is developed in terms of the KS elements, utilizing an analytical oblate exponential atmospheric model. The series expansions include up to cubic terms in e (eccentricity) and c (a small parameter dependent on the flattening of the atmosphere). Due to the symmetry of the KS element equations, only one of the eight equations is integrated analytically to obtain the state vector at the end of each revolution. Numerical comparisons are made with nine test cases, selected to cover a wide range of eccentricity with perigee heights near to 300 km at three different inclinations. A comparison of three orbital parameters: semi-major axis, eccentricity and argument of perigee, perturbed by air drag with oblate atmosphere is made with the previously developed second-order theory. It is found that with the present theory with increase in eccentricity there is improvement in semi-major axis and eccentricity computations over the second-order theory.

Conducting Fabrics as a Shield Against Electromagnetic Interference (EMI)

Abstract: The paper reports a method to design and develop a highly flexible EMI shielding material based on newly emerging technology of in situ grafting of conducting polymers onto insulating surfaces such as fabrics.

Wind Speed dependence of Air-Sea Exchange parameters over the Indian Ocean during INDOEX, IFP-99

Abstract: . Air-Sea exchange of momentum, heat and moisture over the oceanic surface plays an important role in understanding several processes spanning various scales of atmospheric and oceanic motions. The present study provides estimates of air-sea exchange parameters along the cruise track of the Intensive Field Phase of Indian Ocean Experiment (INDOEX, IFP-99) conducted on board Oceanic Research Vessel (ORV) Sagar Kanya during 20 January–12 March 1999 for a large region of the Indian Ocean. The study is aimed at acquiring a better understanding of the wind speed dependence of air-sea interaction parameters, such as roughness lengths for wind (z0), temperature (z0t) and hu-midity (z0q), which play a key role in the determination of the air-sea exchange coefficients and interface fluxes across the tropical oceans. The variation of drag coefficient (CD), sensible heat and water vapor exchange coefficients (CH and CE), are also discussed in relation to the wind speed. An empirical relation is derived between the estimated values of drag coefficients and the observed values of wind speeds for the hitherto data-sparse regions over the tropical Indian Ocean. Key words. Oceanography: physical (air-sea interaction) Meteorology and atmospheric dynamics (ocean-atmosphere interaction) – Oceanography: physical (marine meteorology)

Study on Variants of Solution Treatment and Aging Cycle of Titanium Alloy Ti6Al4V

Abstract: Ti6Al4V with two different chemical compositions, one rich and the other lean in α-stabilizer oxygen were selected to study the effect of quench severity during solution treatment and their aging response. These two coupons were taken from two differently processed wrought products viz. rolled ring and closed die forging. The coupons were then subjected to solution treatment followed by employing different cooling rates to vary the quench severity and different aging treatments by changing the aging temperature and time. The microstructure and mechanical properties thus obtained are correlated with respect to the heat treatment conditions. It is noted that there is a significant increase in strength of the alloy retaining the ductility when it is aged in the aging temperature regime of 550-650 °C and time of 8 h. Role of higher oxygen content is noted, which is more pronounced with higher severity of quench (by water quenching). Specimens representative of different heat treatment conditions were characterized using optical microscope, electron back-scattered diffraction, and electron microscope. The presence of martensitic (α′) structure along with uniform distribution of fine primary α, secondary α precipitates and refined β-grains, twins in the microstructure helps in improving the strength of the material. Also, during high temperature aging of 700 °C, which incidentally falls in the range of annealing temperature of the alloy, overaging occurs which is similar to effect of annealing and hence retains the ductility as well.