By:
Dhruvika Srivastava
Every satellite, rocket, and astronaut is basically falling forever. And that’s what we call an orbit. Orbits and propulsion are practically inseparable; one decides where you go, the other decides how you get there.
In astronomy, an orbit is the repeating curved path that one object in space follows around another under the influence of gravity, the mutual attraction between objects with mass. The greater an object’s mass, the stronger its gravitational pull. At the same time, an orbiting body carries momentum, the tendency to continue moving in a straight line. The delicate balance between gravity pulling inward and momentum pushing outward creates the graceful curved trajectory we call an orbit. This path can be nearly circular or elliptical (oval-shaped), depending on the object’s speed and distance. Objects in orbit are known as satellites—these can be natural, like moons, or artificial, like the International Space Station.
Different types of orbits serve different purposes. Low Earth Orbit (LEO), just a few hundred kilometres above us, is like the front row at a concert—close to the action. Including the International Space Station and thousands of satellites, which bring internet to remote corners of the world. Higher up, Geostationary Orbit (GEO) is like the VIP lounge. Satellites stay fixed over one spot and are used for weather monitoring, TV broadcasting, and keeping your Netflix connection smooth. Then there are polar orbits, which act like photographers, passing over the poles and scanning every inch of Earth, used for mapping, climate monitoring, and even a little spying. And finally, elliptical orbits are the most dramatic ones, stretching into oval paths that allow satellites to linger longer over certain regions, like Russia’s Molniya satellites used for high-latitude communications.
Of course, none of this would be possible without propulsion, the big push that gets satellites into orbit in the first place. Propulsion is the process of generating force to move an object forward. It involves a power source and a system that converts that power into a propulsive force. Rocket propulsion is the process of generating thrust to move a rocket. It works by expelling mass (propellant) at high speed in the opposite direction of desired motion, causing the rocket to move forward due to Newton's third law of motion. The "action" of ejecting gas creates an "equal and opposite reaction" that propels the rocket.
Rocket propulsion systems can be categorised into different types, including chemical rockets (liquid and solid), ion rockets, and cold gas propulsion, each with its characteristics and applications. Think of chemical rockets as energy drinks: they provide a massive, explosive boost but burn out quickly. Ion thrusters, on the other hand, are like green tea: gentle, slow, but incredibly efficient, perfect for long journeys through deep space. While cold gas propulsion is like letting go of a balloon, the escaping gas pushes it in the opposite direction. Simple, gentle, and perfect for small course corrections in space.
But now, recent innovations in orbits and propulsion are transforming how we reach and operate in space. Reusable rockets, like SpaceX’s Falcon 9 and Europe’s upcoming Maia launcher, are cutting costs by acting more like high-tech race cars than single-use fireworks. Meanwhile, electric and green thrusters are emerging as efficient alternatives to chemical rockets, offering longer lifespans and cleaner operations. India’s Bellatrix Aerospace is even developing “air-breathing” thrusters that sip particles from Earth’s upper atmosphere to stay in orbit. Looking further ahead, solar sails are proving that spacecraft can ride on sunlight, as NASA’s 2024 ACS3 mission showed with an 80 m² sail.
In the end, orbits and propulsion are more than just equations and engines—they are the very tools that let humanity step off its home planet and explore the universe. From the delicate balance of gravity and momentum that keeps satellites circling Earth to the powerful bursts and futuristic sails that carry us outward, this dance of physics drives every leap we make into space. And with innovations making spaceflight smarter, greener, and more reusable, the story of orbits and propulsion is the story of our future among the stars.
