V. K. Hariharan

Lumped Element Model for Spacecraft Surface Charging Studies

The external surfaces of a spacecraft exposed to Earths magnetospheric plasma can build up differential voltages which can result in an electrostatic discharge (ESD). This discharge may induce transient electromagnetic interference (EMI) in the electronics circuitry and may give rise to switching anomalies or system failure under certain environmental conditions. This paper outlines the development of Lumped Element Model (LEM) of a spacecraft for surface charging studies. A numerical solution procedure using method of moments and triangular patch modelling to determine the capacitance of conducting objects in free space has been developed. Differential equations of spacecraft charging have been derived and the surface charging of INSAT-2E spacecraft has been simulated. The results obtained for INSAT-2E using LEM concept are compared with those obtained using the NASA Charging Analysis Program (NASCAP) for a similar satellite. Using LEM of a conducting plate located in free space, and with the help of circuit simulation software, the transient structural current due to a blow-off discharge is predicted. Power supply lines, command and control lines, lines connected to antenna probes, switches and thence to microwave devices can pick up ESD transients. Hence ESD immunity should be built into microwave subsystem as well. Techniques of hardening microwave subsystem against on-board ESD have also been outlined.

Development of circuit model for spacecraft charging studies

The external surfaces of a spacecraft exposed to Earths magnetospheric plasma can build up differential voltages which can result in an electrostatic discharge (ESD). This discharge may induce transient electromagnetic interference (EMI) in the electronics circuitry and may give rise to switching anomalies or system failure under certain environmental conditions. This paper outlines the development of circuit model of a spacecraft for surface charging studies by assuming Maxwellian distribution function to represent the plasma particles in space. Analytical expressions for charging and discharging current sources of the geosynchronous Earth orbit (GEO) plasma have been obtained. A numerical solution procedure using method of moments and triangular patch modelling to determine the capacitance of conducting objects in free space has been developed. Differential equations of spacecraft charging have been derived and the surface charging of INSAT-2E spacecraft has been simulated.

High Power Combline Filter for Deep Space Applications

An S-band, compact, high power filter, for use in the Mars Orbiter Mission (MOM) of Indian Space Research Organization (ISRO), has been designed and tested for multipaction. The telemetry, tracking, and commanding (TT&C) transponder of MOM is required to handle continuous RF power of 200 W in the telemetry path besides simultaneously maintaining an isolation of greater than 145 dBc to its sensitive telecommand path. This is accomplished with the help of a complex diplexer, requiring high power, high rejection transmit path filter, and a low power receive path filter. To reduce the complexity in the multipaction-free design and testing, the transmit path filter of the diplexer is split into a low rejection filter integral to the diplexer and an external high rejection filter. This paper highlights the design and space qualification phases of this high rejection filter. Multipaction test results with 6 dB margin are also presented. Major concerns of this filter design are isolation, insertion loss, and multipaction. Mission performance of the on-board filter is normal.

Electromagnetic field to unshielded wire coupling model

The problem of determining the currents induced in termination networks at the ends of a transmission line by an incident electromagnetic field is quite important in determining the electromagnetic compatibility of electronic systems. The coupling of EM field to unshielded wire over a ground plane has been analysed for vertically and horizontally polarised incident E fields. Experimental results are given for the vertically polarised case. It has been shown that the coupled voltage can be reduced either by reducing the height of the wire over the ground plane or by using a terminating capacitance.

Simulation of the response of external ESD protection circuits for CMOS ICs

CMOS ICs are highly susceptible to electrostatic discharge (ESD) induced voltage/current stresses. The IC manufacturer provides an on-chip protection circuit for improving the ESD susceptibility threshold of CMOS devices. However, device failures continue to occur due to electrical overstress (EOS) or due to ESD. For example, the CD4050B device has a built in immunity level of 2 kV for the human body model (HBM) ESD waveform. Hence the EOS/ESD failures noticed in these devices may be either due to a HBM-ESD stress level which is higher than 2 kV or due to other types of work practice/area related ESD stress waveform. Thus, there appears to be a need for providing external ESD protection circuits such that the device performance is not affected adversely. This paper gives an account of studies made using SPICE and MC4 circuit simulation software, to determine the effectiveness of some of the HBM-ESD external protection circuits.

Effectiveness of various shield termination methods of cables

This paper presents the investigation on the effectiveness of the various shield termination methods to be adopted in spacecrafts. The emission characteristics of various shield termination methods such as such as pigtail, halo technique, EMI back shell, and overall shielding was studied. Experiment was performed in the anechoic chamber to analyze the radiated emissions in the frequency range of 20 kHz to 50 MHz. It was demonstrated that, the shielding effectiveness of the halo technique is 10 dB better than the pigtail method. The EMI back shell and overall shielding based termination methods provides the effectiveness 35 dB better than the pigtail method.

EMI modelling and analysis of power switching circuit

This paper deals with the modeling and estimation of differential mode conducted emissions from a DC/DC Converter (buck converter) which operates at 295 kHz. Typical Buck converter is modeled as ac equivalent circuit and simulations are carried out. Fixed resistive load impedance is considered for the simulation and conducted emissions are simulated in frequency range of 10 kHz to 1MHz. Practical Conducted emissions tests are carried out and these results are compared with simulation results.

Mitigation of spurious noise signals in telemetry parameters in resourcesat-2A spacecraft

This paper brings out the technique employed to mitigate the spurious noise seen riding on the telemetry parameter signals from subsystems, in particular Wheel Drive Electronics (WDE). WDEs are used for speed control of Reaction Wheels (RW). Four numbers of Reaction Wheels are mounted in tetrahedral configuration in the spacecraft. The combined vector of all the wheels obtained by varying wheel speeds is used to orient the spacecraft in orbit. The wheel speed and motor current parameters of these actuators are very critical signals as these are used to determine health of the Reaction Wheels thereby determining the pointing accuracy of the spacecraft platform. On these signals, spurious noise was observed to be riding during wheel operations. These noise signals were spike-like and minimum amplitude of 0.5 V. The process to locate the source of these noise signals and their mitigation is presented in this paper.

NASA ISRO Synthetic Aperture RADAR (NISAR) spacecraft magnetic field studies

The objective of this study is to optimize the location of the magnetometer in the presence of the magnetic torquers on the NASA ISRO Synthetic Aperture RADAR (NISAR) Spacecraft which involves identifying the locations of minimum magnetic field areas due to magnetic torquers. The modelling and simulation are carried out with the help of Computer Simulation Technology (CST) software. Magneto static solver is used to find out the Magnetic field at various places inside/outside of spacecraft.

Noise coupled to unshielded wire due to computed transient electromagnetic fields generated by ESD events in spacecraft

Spacecraft when placed in plasma, spacecraft charging occurs which results in ESD discharge. This paper focuses on ESD fields radiated in spacecraft level and the noise coupled to a nearby wire when it is exposed to these radiated fields. A dipole model is considered to predict the transient radiated fields. The ESD current data is experimentally obtained in order to obtain the noise coupled to nearby wire. Furthermore, telegraphers equations have been employed to compute the induced current and voltage. Additionally, the fields radiated and noise coupled to the wire under various conditions are computed and plotted.