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Plasma Technology for Space Missions

Updated: Feb 9, 2023

I took part in a meeting to celebrate the 25th anniversary of a centre I had set up in the Institute for Plasma Research to develop and transfer plasma-mediated technologies to industries. I recall the exact moment when the idea of what would later become the Facilitation Centre for Industrial Plasma Technologies (FCIPT) came to me. In early 1990, I was escorting Prof Ramaseshan, former Director of the Indian Institute of Science, around the ADITYA tokamak, which we had commissioned at the Institute for Plasma Research (IPR) in late 1989. It is a complex device with magnetic field coils, vacuum vessels, turbo-molecular pumps and diagnostics. After appreciating everything about the device and what we had done, he asked me how many people would be affected by what we did with ADITYA.

I had never asked this question myself. So I enlarged the ambit of the question and asked how many people would be affected by what we had done over the years at PRL and IPR, developing the rich experimental knowledge base created over two decades of producing and manipulating plasmas to support fundamental research.

Mulling over this, I had an epiphany and the idea of finding short-term commercial applications of the plasma physics knowledge we had acquired over many years crystallised. Plasma properties like the response to external electromagnetic energy fields, collective phenomena like waves and oscillations, energy transport through instabilities, high chemical reactivity, microscopic electric fields, sheaths, radiation and particle flux mediate plasma processing.

The Plasma Processing activities took on a qualitatively different form when we set up FCIPT in a rented building in the industrial area of Gandhinagar in 1997 to act as a bridge with industry. We consolidated all technology development, demonstration, incubation, and commercialization activities here. FCIPT had a multi-disciplinary group of physicists, material scientists, chemists and engineers and infrastructure for process and instrumentation development for plasma technologies. The manufacture and supply of complete reactors to industries and research institutions is an integral part of the technology transfer process. Financial self sufficiency was a target from the beginning.

FCIPT is a path breaker in India in converting physics-based research into commercially and societally valuable devices and processes in basic research organizations. Over the years, we have learned how to use the plasma environment to do various useful things.

Extending our plasma physics knowledge to the space programme started with the indigenisation of the nitriding of solar panel drive gear of ISRO satellites, which was previously being done by a British company. We also supplied a space-quality plasma nitriding system to ISRO for in-house use.

In 2004 a conversation with some ISRO scientists made us aware of the problem of the failure of the solar panels on their satellites due to arcing. Satellites in orbit are embedded in a plasma environment and the charging due to energetic electrons raise their potential over the plasma potential. The glow to arc transition is time dependent and the prolonged high potential state leads to arcing and subsequent damage of the panels.

We proposed to ISRO to set up a Satellite-Plasma Interaction Experiment (SPIX) where the solar cell assembly would be exposed to a plasma similar to the Low Earth Orbit (LEO) environment. The assembly would be charged by an electron beam to large potentials. Arc initiation and development would be measured with Langmuir probes and CCD camera and current transformer. The data received will be analysed and used in the modelling. The experimental data and insight on the physical phenomena generated from modelling would be used to conceptualise remedial measures. Recommendations would be made on improved materials, surface modification of materials used to make them arc resistant, configurational and layout changes etc. The system was upgraded to SPIX II facility in 2008 to simulate the Geosynchronous Earth Orbit (GEO) environment meeting International standards by improving data acquisition methods, arc location identification, prevention of unwanted surges from the electronics, correlation of visual and electrical signals to confirm the nature of the arc and to be able to classify the arcs. Both SPIX I and II have generated data of substantial value to ISRO.

Another interaction with ISRO was in the area of Hall thrusters. Such thrusters are deployed in satellites to facilitate orbital insertion, correct their orbital positions and stationkeeping.

Conventional electrostatic ion accelerators use a grid to separate the space charge used to accelerate the ions. In Hall thrusters, this is replaced by a strong radial magnetic field perpendicular to the flow. This magnetic field localises electrons creating a virtual cathode which pulls the ions out, and impede the counterflow of electrons in the accelerating field. The space-charge limitation which limits the beam current and hence the thrust of ion engines is absent. After using Russia-made Hall thrusters for many missions, ISRO developed their own Hall thrusters and the BN/SiO2 anode liner material. Our contribution was in the extensive diagnostics done in the ISAC facilities in Bangalore to characterise the plasma plume emanating from the Hall thruster developed by them and measure their thrust in Newtons. VSSC wanted us to qualify the liner material through erosion studies. For this purpose, IPR developed a low energy ion beam facility equipped with in-situ erosion measurement to test the material developed by VSSC under thruster operating conditions. Based on a large number of erosion experiments performed by the IPR, feedback was given to VSSC to improve the material properties. The study showed 20% less erosion compared with the imported anode liner material, while maintaining all other required properties. The indigenously developed anode liner material for a 300 mN Stationary Plasma Thruster (SPT) has cleared all quality tests and is approved for use in the TDS-O1 mission in PSLV C54 [1].

Higher power plasma thrusters are critical for interplanetary missions. Chemical thrusters produce a speed of the order of 4,440 m/s, limited by the molecular mass of the product(s), the amount of energy available from the chemical reaction that produces them and how much of that energy comes out as thermal energy of the products and to a smaller extent, the efficiency of the engine design, specifically the combustion chamber and nozzle. The higher the combustion energy per molecule, the faster you can expel that molecule out of the nozzle.

A thruster which has recently come in news is the Variable Specific Impulse Magneto-plasma Rocket (VASIMR) engine being developed for the NASA Mars mission. With the hot plasma particles achieving speeds of the order of 10 km/sec, these thrusters can, on long time scales make the spacecraft achieve such speeds.

The gas is ionized by the Helicon mode RF discharge. The second RF antenna, called the Ion Cyclotron Heating (ICH) section, heats the plasma to extreme temperatures (on the order of one million degrees Kelvin) [2] and is ejected from the nozzle to produce thrust. However, the ions are orbiting perpendicular to the rockets motion. In the VASIMR’s magnetic nozzle, as the magnetic field lines expand, the spiral paths of the ions elongate which produces very high exhaust velocities in the range of 50 km/s.

Another critical area for interplanetary missions is the space craft hygiene. The Committee of Space Research has strict protocols to protect the space environment from “harmful contamination” which would endanger the integrity of the scientific exploration of outer space including the search for life [3]. Plasma sterilization is a process not only compatible with modern spacecraft, but it also enables successful removal and inactivation of most resistant microbial species isolated in spacecraft assembly facilities. FCIPT started work in this field with a contract from Johnson & Johnson to characterise their vacuum sterilisers. With the development of cold plasma sources, sterilisation can now be done on soft and hard materials without enclosing them in vacuum.

With the space sector reforms of 2020, a number of private companies and start-ups have begun to participate in the space programmes in India. The meeting at FCIPT had a liberal representation from these companies. It will be interesting to see how in future we would be able to develop collaborative project with them.

[1] [2] [3] Thomas Cheney, Christopher Newman, Karen Olsson-Francis, Scott Steele, Victoria Pearson, Simon Lee,Planetary Protection in the New Space Era: Science and Governance, Front. Astron. Space Sci., 13 November 2020

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