What is Electric Propulsion?
Think of traditional rocket engines as powerful sprinters, using chemical combustion to create a massive, short-lived burst of energy to escape Earth's gravity. Electric propulsion, on the other hand, is like a marathon runner. It uses electrical power,
typically from a satellite's solar panels, to generate a gentle but continuous thrust. Instead of burning vast amounts of chemical fuel, these systems use small quantities of inert gases like xenon. An electric field ionises (positively charges) the gas particles and accelerates them out of a thruster at very high speeds, pushing the spacecraft forward. The thrust is very low—sometimes compared to the force of a single sheet of paper resting on your hand—but over weeks and months in the vacuum of space, it can produce significant changes in velocity with incredible fuel efficiency.
The Mass-Saving Advantage
The single biggest advantage of electric propulsion is the dramatic reduction in propellant mass. For a conventional communication satellite weighing around four tonnes, nearly half its launch weight can be chemical fuel needed for orbit raising and station-keeping manoeuvres throughout its life. With an electric propulsion system, the required propellant mass can shrink by as much as 90%, from two tonnes down to just 200 kilograms. This weight saving is a game-changer. It means the 'freed-up' mass can be dedicated to more valuable hardware, such as extra transponders on a communication satellite, which translates directly into more revenue-generating capacity. Alternatively, it allows ISRO to launch equally capable satellites on smaller, less expensive rockets, reducing launch costs and increasing scheduling flexibility.
More Kilometres to the Litre
This incredible fuel efficiency directly translates into a longer mission life for satellites. Since satellites can stay operational for as long as they have fuel to maintain their correct orbital position and orientation, a more efficient engine means more years of service. A typical communication satellite has an operational life of about 15 years, limited by its onboard chemical propellant. By using electric propulsion, which is five to six times more efficient, ISRO can significantly extend this lifespan. This not only provides better value for money on each mission but also ensures the continuity of critical services like broadcasting, weather monitoring, and navigation without the need for frequent and costly replacements.
ISRO’s Electric Journey
ISRO's exploration of electric propulsion isn't new, but its commitment to indigenous development is a major leap forward. In 2017, the GSAT-9 satellite used an electric propulsion system for station-keeping, but the core thruster technology was imported. The organisation has since been focused on creating its own fully homegrown systems. A key milestone has been the development and successful long-duration testing of a 300mN Stationary Plasma Thruster. These indigenous thrusters are slated to be validated on an upcoming Technology Demonstration Satellite (TDS-01) before being integrated into future communication satellites like the GSAT-20, which is planned to be India's first satellite to use electric propulsion for both raising its orbit and maintaining it.
A Strategic Leap for India's Space Ambitions
Adopting electric propulsion is more than just an engineering upgrade; it is a strategic move that enhances ISRO's competitive edge. Lighter satellites open the door to launching more missions on its own reliable launchers like the PSLV and LVM3, reducing dependence on foreign launch providers. While the low thrust means it takes longer for satellites to reach their final orbit—months instead of weeks—the long-term benefits are immense. This technology is a crucial enabler for more ambitious deep-space missions, such as those to Mars or Venus, where high efficiency over long travel times is essential. By mastering this technology, ISRO is positioning India as a more versatile and cost-effective player in the global space market, ready for the next era of space exploration and commerce.
