A space station is a large artificial structure placed in orbit and designed to support people, scientific experiments, technology demonstrations, observation, or other activities over an extended period. Unlike a conventional spacecraft designed mainly to travel from one location to another, a space station functions primarily as an orbital laboratory, habitation facility, staging platform or operational base.
It normally contains pressurised living or working areas, environmental-control systems, electrical power generation and storage, communications equipment, computers, navigation systems and mechanisms for docking visiting spacecraft. Because humans may remain aboard for weeks or months, crewed stations require systems that provide breathable air, temperature regulation, water management, waste handling, fire detection and other life-support functions. A station therefore represents a much more complex environment than an ordinary satellite.
The orbital environment creates distinctive engineering requirements. A space station in low Earth orbit travels at several kilometres per second, continuously falling around Earth while its orbital velocity causes its path to curve rather than intersect the planet. Astronauts aboard experience apparent weightlessness because the station and everything inside it are undergoing orbital free fall together. The station nevertheless remains subject to gravity, atmospheric drag at very high altitudes, radiation, micrometeoroids and orbital debris.
Drag gradually reduces orbital energy, so many low-Earth-orbit stations require periodic reboost manoeuvres to maintain their orbit. Visiting spacecraft can also provide propulsion support, supplies and crew transportation. Station operators therefore combine onboard systems with external launch vehicles, cargo spacecraft and crewed spacecraft to maintain long-duration operations.
A space station is usually divided into modules or functional sections. Laboratory modules provide controlled environments for scientific experiments, while habitation areas contain crew quarters and facilities for eating, hygiene and daily living. Other sections can contain exercise equipment, airlocks, storage, robotic systems, control facilities, docking ports or external experiment platforms. Large solar arrays convert sunlight into electricity, while batteries or other energy-storage systems supply power during periods when the station passes through Earth's shadow. Thermal-control systems remove excess heat generated by electronics, life support and human activity. Radiators reject this heat into space. The integration of these systems allows the station to operate continuously even though its environment differs radically from conditions on Earth's surface.
Scientific research is a major reason for operating space stations. Microgravity changes fluid behaviour, combustion, crystal growth, biological processes and other physical phenomena, allowing researchers to study processes that cannot easily be reproduced on Earth. Experiments may investigate human physiology during prolonged spaceflight, plant growth, materials science, fundamental physics, medicine or manufacturing techniques. Stations can also serve as testbeds for equipment intended for future missions, including life-support technologies, robotics and systems for spacecraft maintenance. Earth observation and educational activities can form additional functions. The scientific value comes partly from the ability to conduct repeated experiments over extended periods and modify procedures as crews learn from earlier results.
Human habitation makes maintenance fundamentally different from the operation of an ordinary uncrewed satellite. Astronauts can inspect equipment, replace components, conduct repairs and install new experiments. Extravehicular activity, commonly called a spacewalk, allows crew members to work outside the pressurised structure using specialised spacesuits and tools. Robotic arms can manipulate equipment and assist with visiting spacecraft, reducing the need for some external human operations. Resupply missions deliver food, water, gases, spare parts, experimental materials and other consumables. Crew rotations allow stations to remain operational beyond the endurance of a single expedition. This combination of human intervention, robotics and resupply gives a space station capabilities that cannot easily be achieved by an autonomous satellite.
The concept developed from earlier orbital spacecraft and crewed programmes in which engineers explored how humans could live and work in space for increasing periods. Early stations demonstrated technologies for orbital habitation, docking, resupply, scientific work and long-duration human spaceflight. Later programmes developed larger modular stations assembled from multiple launches, with international cooperation becoming an important characteristic of some major projects.
A station can therefore be understood as both an engineering system and an operational programme requiring launch infrastructure, mission control, crew training, scientific planning and international or organisational coordination. Its construction may take years, and the completed orbital facility can remain active for a much longer period than any individual launch vehicle.
Space stations have important limitations. Launching large structures into orbit is expensive and technically difficult, and station components must survive launch loads before being assembled or deployed in space. Long-duration exposure to radiation and microgravity creates hazards for human health, while orbital debris can threaten pressurised modules and external equipment. Life-support systems must operate reliably because evacuation to Earth is not immediate.
The station's orbit also determines what regions of Earth or space it can observe and what spacecraft can conveniently visit it. Despite these limitations, a station provides a unique combination of persistent human presence, controlled experimental environments and access to the space environment, making it an important platform for research and for developing technologies associated with sustained human activity beyond Earth.
The term “space station” is distinct from “spacecraft”, although a station is itself a type of spacecraft. A spacecraft generally refers to a vehicle designed for operation in space, whereas a station is specifically configured for prolonged occupation or sustained orbital activity. A satellite can be uncrewed and perform a particular service or observation function, while a space station is usually much more complex and may accommodate people.
Space stations can also be distinguished from space habitats proposed for locations such as the Moon or Mars because a station traditionally refers to an orbital facility, although future terminology may vary. Their defining concept is persistent infrastructure in space rather than a short-duration journey, and their continued usefulness depends on reliable life support, power, communications, orbital maintenance, resupply and human or robotic operations.
