Orbital spaceflight

Space travel that places a spacecraft into orbit around Earth or another celestial body. It differs from suborbital flight because the spacecraft reaches sufficient sideways velocity to keep falling around the body rather than returning directly to its surface.

Orbital mechanics: The study of the motion of spacecraft and other objects under gravity. It describes the trajectories and velocity changes that make orbital flight possible.
Suborbital spaceflight: Spaceflight that reaches space but lacks the speed to complete an orbit around a celestial body. It reaches space without achieving the sustained sideways motion that defines orbital flight.
Sputnik 1: The first artificial Earth satellite, launched by the Soviet Union on October 4, 1957. Its successful orbit began the era of artificial satellites and the space race.
Communications satellite: An artificial satellite that relays radio-frequency signals between distant locations on Earth or in space. Orbital placement enables broad coverage for television, telephone, and data links.
Space Race: The Cold War competition between the United States and Soviet Union to achieve milestones in space exploration. Early orbital achievements became highly visible measures of national power and technical capacity.
Orbital velocity: The speed an object needs to remain in a particular orbit around a celestial body. A spacecraft must reach sufficient sideways speed to avoid falling back to the surface.
Escape velocity: The minimum speed needed for an object to escape a celestial body’s gravitational influence without further propulsion. Reaching orbit requires less speed than escaping Earth, though both depend on gravity and motion.
Vostok 1: The 1961 Soviet mission that carried Yuri Gagarin on the first human spaceflight. It demonstrated that a person could survive a complete orbit around Earth.
Earth observation satellite: An artificial satellite that collects information about Earth’s surface, atmosphere, or oceans. Repeated orbital passes provide large-scale environmental and geographic measurements.
Satellite navigation: Positioning and timing determined from signals transmitted by satellites in orbit. Orbital constellations have made precise navigation available for civilian and military use.

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