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.

Analysis of optimal strategies for soft landing on the Moon from lunar parking orbits

Abstract: Optimal trajectory design of a probe for soft landing on the Moon from a lunar parking orbit by minimizing the fuel required is obtained. The problem is formulated as an optimal control problem with the thrust direction being the control variable. Using the maximum principle of Pontryagin, the control variable is expressed as a function of co-state variables and the problem is converted into a two-point boundary value problem. The two-point boundary value problem is solved using an optimization technique, i.e., controlled random search. The strategies such as • direct landing from a lunar parking orbit using powered braking • direct landing from an intermediate orbit using powered braking • by executing powered braking in two phases: through horizontal braking and vertical landing are analyzed and an optimal strategy that achieves the goals is suggested. Also, appropriate design parameters are selected using this analysis.

Graphite oxide–iron oxide nanocomposites as a new class of catalyst for the thermal decomposition of ammonium perchlorate

Abstract: Graphite oxide (GO) is receiving increased attention due to its special surface properties and layered structure for the synthesis of GO containing nanocomposites. It is possible that integration of GO sheets and iron oxide nanoparticles may result in enhanced properties and enlarge the application range. Herein, we report the effect of Fe2O3–GO nanocomposite as a new class of catalyst for the decomposition of ammonium perchlorate (AP), a rocket propellant oxidizer, and study the effect of Fe2O3 : GO ratio on the catalytic activity. The material was characterized by X-ray diffraction and Raman spectroscopy and the formation of Fe2O3 and GO were confirmed. FESEM analysis showed that the Fe2O3 nanoparticles are highly dispersed between and on the graphene layers. With the addition of 3% of the composite with 1 : 1 Fe2O3–GO ratio, the decomposition temperature of AP was reduced by 45 °C, showing a high catalytic activity for the new composite. The high catalytic activity of the in situ synthesized Fe2O3–GO composite may be attributed to the uniform distribution of iron oxide nanoparticles which in turn provide a number of active sites on the surface due to the presence of GO.

Diurnal variability of the atmospheric boundary layer height over a tropical station in the Indian monsoon region

Abstract: . The diurnal variation of atmospheric boundary layer (ABL) height is studied using high-resolution radiosonde observations available at 3 h intervals for 3 days continuously from 34 intensive campaigns conducted during the period December 2010–March 2014 over a tropical station Gadanki (13.5° N, 79.2° E; 375 m), in the Indian monsoon region. The heights of the ABL during the different stages of its diurnal evolution, namely, the convective boundary layer (CBL), the stable boundary layer (SBL), and the residual layer (RL) are obtained to study the diurnal variabilities. A clear diurnal variation is observed in 9 campaigns out of the 34 campaigns. In 7 campaigns the SBL did not form in the entire day and in the remaining 18 campaigns the SBL formed intermittently. The SBL forms for 33–55 % of the time during nighttime and 9 and 25 % during the evening and morning hours, respectively. The mean SBL height is within 0.3 km above the surface which increases slightly just after midnight (02:00 IST) and remains almost constant until the morning. The mean CBL height is within 3.0 km above the surface, which generally increases from morning to evening. The mean RL height is within 2 km above the surface which generally decreases slowly as the night progresses. The diurnal variation of the ABL height over the Indian region is stronger during the pre-monsoon and weaker during winter season. The CBL is higher during the summer monsoon and lower during the winter season while the RL is higher during the winter season and lower during the summer season. During all the seasons, the ABL height peaks during the afternoon (∼ 14:00 IST) and remains elevated until evening (∼ 17:00 IST). The ABL suddenly collapses at 20:00 IST and increases slightly in the night. Interestingly, it is found that the low level clouds have an effect on the ABL height variability, but the deep convective clouds do not. The lifting condensation level (LCL) is generally found to occur below the ABL for the majority of the database and they are randomly related.

Evaluation by various experimental approaches of the crosslink density of urethane networks based on hydroxyl-terminated polybutadiene

Abstract: Crosslink density (CLD) is an important characteristic for elastomeric polymer networks. The mechanical and viscoelastic properties of the elastomers are critically dependant on the CLD. Several methods have been adopted for its determination, but swelling and stress–strain methods continue to be more popular because of the convenience associated with these techniques. In this article, the determination of CLD of allophanate–urethane networks based on hydroxyl-terminated polybutadiene and toluene diisocyanate with swelling and stress–strain methods is reported. The Flory–Rhener relationship was applied to calculate CLD from the swelling data. CLDs were also calculated from the initial slope of the stress–strain curve (Young's modulus), Mooney–Rivlin plots, equilibrium relaxation moduli, and dynamic mechanical properties. A comparison was drawn among the values obtained with the various methods. Although the CLD values obtained from Mooney–Rivlin plots were slightly lower than those obtained from swelling data, the values obtained with Young's modulus and storage modulus were considerably higher. The values obtained with swelling and equilibrium relaxation moduli data were very close to each other. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3129–3133, 2007