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Karthikeyan B.,Systems Integration Group | Karthikeyan B.,Indian Institute of Technology Kharagpur | Hariharan V.K.,Systems Integration Group | Sanyal S.,Indian Institute of Technology Kharagpur
IEEE Transactions on Plasma Science | Year: 2013

This paper presents a computation of the absolute free space capacitance and electrostatic body potential of a spacecraft using moment method with triangular patch modeling. Expressions are derived numerically and the moment integral is evaluated. The capacitance of a square plate is computed to validate the approach. Finally, the free space capacitance of a typical spacecraft is computed for various configurations and body potential is evaluated. The derived expressions are simple and suitable for developing the charging analysis tool. As this approach is more general, it can be easily applied to any practical spacecraft configuration. © 2013 IEEE.


Rao C.K.,Systems Integration Group | Mathur P.,Systems Integration Group | Pathak S.,Systems Integration Group | Sundaram S.,Systems Integration Group | And 2 more authors.
Journal of Optics (India) | Year: 2013

Compact Antenna Test Facility (CATF) is configured to carry out antenna characterization and also for checkout of the fully integrated spacecraft with antenna and other subsystems. The CATF is used for the measurement of radiation pattern, gain, return loss, cross polar isolation, precise identification of the bore-sight axis, EIRP and gain/temperature (G/T ratio) of the antenna system under the simulated zero-gravity environment. During the test, the spacecraft is positioned on the Device Under Test (DUT) Positioner, which is about 5 m above ground and the geometric axis of the spacecraft is represented by an optical mirror cube which is correlated with RF (Radio Frequency) axis of the facility in order to match the nominal reflector bore-sight with the Nominal Plane Wave axis (NPA) of the Facility. Special fixtures are used to simulate the zero-gravity environment. Novelty of this paper lies in the development of technique which synergies the optical alignment systems and Close Range Photogrammetry (CRP) for correlating the optical axis of the spacecraft with the RF axis of test facility. This paper describes the details of the new technique, general description of the facility and the various alignment measurement systems used for alignment of spacecraft and its subsystems. The paper further claims advantages of CRP over other methods of measurement in terms of time & effort saving, real time measurement capability, measurement of critical geometries in inaccessible orientations & development of methodology to derive RF & optical axis without the use of physical features as references on the spacecraft body. © 2012 Optical Society of India.


Rao C.K.,Systems Integration Group | Ramjee S.,Systems Integration Group | Mathur P.,Systems Integration Group | Jain R.,Systems Integration Group | And 3 more authors.
Journal of Spacecraft Technology | Year: 2011

Ocean Color monitor is flown to orbit with Oceansat-2 spacecraft. During in-orbit operations provision is made to tilt the Electro-optics about the Pitch axis by ± 20° with reference to nadir to avoid the sun glint from sea surface. An on-board angular resolver is used to read the angular rotation of Ocean Color Monitor (OCM) for the given pulses through telemetry command. This study is carried out to calibrate the resolver during ground level measurements, which involves real time measurement of the system to derive 3D rotations and translations of the system in response to pulse through telemetry command. Close Range Photogrammetry (CRP) is used to measure the rotation of OCM in response to a given telemetry pulse.the integrated level there is no physical feature accessible to define either OCM or spacecraft axis. CRP is used to measure the 3D-coordinates of retro reflective targets fixed on OCM and Spacecraft. A total of 14 sets of independent measurements were carried out using CRP. Mathematical transformation and best-fit analysis is carried out on 3D measured data to derive the axis of rotation for OCM. Further computation is made to find the stability of OCM about Roll and Yaw axis during the rotation. Auto-collimation measurement data is used as reference to compare the accuracy of CRP and resolver. Comparison between Auto-collimation and CRP shows accuracy lie within 0.002° and the difference between CRP and resolver angle (commanded angle through telemetry) lie within 0.01°. This paper describes the measurements and mathematical computation carried out using CRP, resolver and auto-collimation. The paper further claims advantages of CRP over other methods of measurement like time and effort saving, real time measurement capability, measurement of critical geometries in inaccessible orientations and development of methodology to derive axis of a rotating members without the use of physical features as references.


Yadav R.K.,Systems Integration Group | Manoj B.S.,Indian Institute of Space Science and Technology
2013 Annual IEEE India Conference, INDICON 2013 | Year: 2013

Despite remarkable advancements in the area of computer networks in recent past, the behavior of the network protocol stack is not completely understood. Our knowledge of interaction of a given protocol in one layer of the stack with protocols in other layers is limited. There is no well known model of the protocol stack that can reveal the protocol parameter interrelationships. We propose a framework built on ideas from the fields of advanced machine learning and computer vision to tackle this problem. Our framework makes use of undirected Probabilistic Graphical Models to determine relationships among protocol parameters of different layers. We sample protocol parameters under predefined network scenarios and perform structure learning of their dependency relationships. Subsequently, we obtain graphical model of the protocol stack which is the most important contribution of this paper. We then estimate the node and edge potentials of the graphical model in the parameter estimation step based on collected data and learnt the structure of the protocol stack. We believe that many of the challenges posed by today's cognitive networks can be properly addressed by making useful inferences from our modeling. As an example, we show that it is possible to predict network latency in terms of Round Trip Time (RTT) fairly accurately given knowledge of only its neighbor protocol parameters in the graphical model. © 2013 IEEE.


Arun K.S.,Systems Integration Group | Sekar A.,Systems Integration Group | Govinda K.V.,Satellite Center
Applied Mechanics and Materials | Year: 2014

In general, aerostatic bearings are flat bearings and the stringent manufacturing tolerances in geometric dimensions and profile will make the bearing ideal for obtaining high stiffness during measurement. Aerostatic Spherical Bearing (ASB) on the contrary is a special bearing which provides a frictionless pivot and allows three degrees of rotational freedom. Methods involved in manufacturing and realizing a highly stiff ASB is discussed in this paper. ASB components viz. Stator and Rotor of hemi-spherical in geometry are the critical components to be machined, which are used in Mass properties and Dynamic Balancing Measurement machine (MaPDBM). MaPDBM is used to measure mass, center of gravity, moments of inertia and static & dynamic unbalance of spacecraft. An air film of 25-50 μm thickness separates the stator and rotor during measurement, thus forming an aerostatic bearing. Precise Machining, Thermal treatments to ensure crash-proof design, Special processes like lapping for profile correction, Geometrical and profile measurements during different stages in the sequence for controlling the bearing parameters using Coordinate Measurement Machine (CMM) are the challenges involved in the machining and realization of the ASB components and the same is discussed in this paper. © (2014) Trans Tech Publications, Switzerland.

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