Do Artificial Satellites Use Fuel to Orbit the Earth? Understanding Their Energy Sources

Artificial satellites are the backbone of modern communication, weather monitoring, navigation, and scientific discovery, orbiting Earth at varying altitudes to serve a multitude of purposes. A frequently asked question is whether these satellites require fuel to maintain their orbital paths and what energy sources power their operations. This article delves deeper into the mechanics of satellite orbits, their energy requirements, and emerging technologies that are shaping the future of satellite operations, while also addressing how these insights can be applied in educational and practical contexts.

The Physics of Orbital Motion: No Fuel Needed for Orbiting

Artificial satellites do not use fuel to sustain their orbital motion around the Earth. This phenomenon is governed by fundamental physics, specifically Newton’s first law of motion (an object in motion stays in motion unless acted upon by an external force) and the law of universal gravitation. When a satellite is launched, it is propelled into space by a rocket that imparts a specific velocity—called the orbital velocity—required to keep it in a stable orbit.

For instance, a satellite in Low Earth Orbit (LEO) at 400 kilometers altitude, such as the Indian Space Research Organisation’s (ISRO) RISAT-2BR1, travels at approximately 7.8 kilometers per second (28,000 km/h). This speed balances the gravitational pull of the Earth, creating a continuous free-fall state where the satellite falls toward Earth but moves forward fast enough to “miss” it, resulting in a circular or elliptical orbit. In the vacuum of space, where there’s no air resistance, this motion persists without the need for fuel to keep the satellite moving.

However, satellites do require fuel for specific operational adjustments:

Orbit Correction: In LEO, faint atmospheric drag can slow a satellite, causing its orbit to decay. Small thrusters using propellants like hydrazine or ion propulsion systems (e.g., xenon gas) are used to perform periodic boosts. The International Space Station (ISS), for example, uses about 7,000 kilograms of fuel annually to maintain its orbit at 400 kilometers.
Attitude Control: Satellites must maintain proper orientation to point solar panels at the Sun or instruments at Earth. This is achieved using reaction control thrusters or momentum wheels, which may require minimal fuel.
Deorbiting or Graveyard Orbits: At the end of their lifespan, LEO satellites use fuel to deorbit and burn up in the atmosphere, while geostationary satellites (at 35,786 kilometers) move to a higher “graveyard orbit” to avoid cluttering operational space.

Energy Sources for Satellite Operations

While orbiting requires no fuel, satellites need energy to power onboard systems like transponders, cameras, and sensors. The primary energy sources include:

Solar Power: Most satellites rely on solar panels equipped with photovoltaic cells to convert sunlight into electricity. This electricity is stored in lithium-ion batteries for use during eclipses. ISRO’s GSAT-30, a communication satellite launched in 2020, generates 6,000 watts using solar panels to support its transponders, enabling broadcasting and telecommunication across India.
Nuclear Power: For missions where sunlight is limited, such as deep space probes, Radioisotope Thermoelectric Generators (RTGs) are used. RTGs generate electricity from the heat produced by the radioactive decay of plutonium-238. NASA’s Voyager 2, operational since 1977 and now over 24 billion kilometers from Earth as of 2025, uses RTGs to power its instruments in the dim reaches of interstellar space.
Chemical Batteries: Some short-duration missions use chemical batteries, but these are typically non-rechargeable and used alongside solar panels.

Future Innovations in Satellite Propulsion and Energy

The space industry is undergoing a transformation with technologies aimed at reducing fuel dependency and enhancing sustainability:

Electric Propulsion: Ion thrusters, which use electricity (often from solar panels) to ionize a propellant like xenon and expel it at high speeds, are far more efficient than chemical thrusters. SpaceX’s Starlink satellites, numbering over 6,000 as of 2025, use krypton-based ion thrusters for orbit adjustments, significantly extending their operational life with minimal fuel.
Solar Sails: These lightweight structures use the pressure of sunlight to propel satellites, eliminating the need for fuel. NASA’s Solar Cruiser, launched in early 2025, is testing this technology, aiming to pave the way for fuel-free propulsion in future missions.
On-Orbit Refueling: Companies like Orbit Fab are developing “gas stations in space,” allowing satellites to be refueled in orbit. In 2024, Orbit Fab successfully demonstrated this technology with a small satellite, potentially revolutionizing how satellites are maintained.

Practical Applications and Educational Outreach

Understanding satellite mechanics and energy sources has practical applications:

Space Debris Management: By using fuel-efficient propulsion systems, satellites can better manage their end-of-life deorbiting, reducing space debris—a growing concern with over 36,500 objects larger than 10 cm tracked in orbit as of 2025.
Educational Initiatives: Schools and universities can use this knowledge to develop STEM programs. For example, students can build model satellites with solar panels to learn about energy conversion, or simulate orbital mechanics using software like NASA’s GMAT (General Mission Analysis Tool).