Chemical vs. Electric: A Tale of Two Thrusts
Traditionally, satellites have relied on chemical propulsion. Think of it like a series of powerful, short bursts of a car's engine to get up to speed and change lanes. This method uses chemical propellants that burn to create a strong, immediate push.
It’s effective but has a major drawback: the fuel is heavy. For a typical large communications satellite, the propellant can account for more than half of its total weight at launch. Electric propulsion, on the other hand, is more like a gentle, continuous push that builds up over a long time. Instead of burning chemicals, it uses electrical power, often from solar panels, to accelerate and expel tiny charged particles (ions) of a gas like xenon to create thrust. While the thrust is much weaker at any given moment, its incredible efficiency means a little bit of propellant goes a very long way.
The Mass Reduction Advantage
The single biggest benefit of electric propulsion is the dramatic weight savings. Because electric systems are five to six times more efficient than chemical ones, a satellite needs far less propellant. For example, a 4,000 kg communication satellite that would normally need about 2,000 kg of chemical fuel can achieve the same mission with just a few hundred kilograms of xenon gas. This massive reduction in weight has a cascading effect on mission cost and capability. Launching mass into space is incredibly expensive, so a lighter satellite means a cheaper launch. Alternatively, the weight saved on fuel can be reallocated to the satellite's primary purpose—its payload. This means ISRO can pack more transponders, sensors, or scientific instruments onto a single satellite, increasing its functionality and the value derived from a single launch.
Extending Life and Enhancing Maneuverability
A satellite's operational life is often limited by how much fuel it has for "station-keeping"—the small adjustments needed to maintain its correct orbit. With the high fuel efficiency of electric propulsion, these manoeuvres consume a tiny fraction of the propellant compared to chemical thrusters. This allows satellites to stay in their designated orbital slots and remain functional for much longer. A standard 15-year lifespan for a geostationary satellite could be significantly extended, offering a better return on investment. This superior efficiency also grants satellites greater maneuverability for complex orbital changes or collision avoidance, which is increasingly important in crowded orbits.
ISRO’s Electric Ambitions
ISRO has been strategically developing this capability. The journey began with satellites like GSAT-9 in 2017, which used an imported electric thruster for some functions. Building on this, the space agency has focused on creating its own fully indigenous systems. A major milestone is the development of a 300 millinewton (mN) stationary plasma thruster, which has undergone extensive testing. This home-grown technology is slated to be validated on an upcoming Technology Demonstration Satellite (TDS-01). The recently launched GSAT-20 (also called GSAT-N2), a powerful communication satellite, is a prime example of this strategy, using electric propulsion for orbit raising, a first for an ISRO satellite of its kind. This move signals a clear shift away from reliance on chemical propellants for key satellite operations.
