Orbital spaceflight

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An orbital spaceflight (or orbital flight) is a spaceflight in which a spacecraft is placed on a trajectory where it could remain in space for at least one orbit. To do this around the Earth, it must be on a free trajectory which has an altitude at perigee (altitude at closest approach) around 80 kilometers (50 mi); this is the boundary of space as defined by NASA, the US Air Force and the FAA. To remain in orbit at this altitude requires an orbital speed of ~7.8 km/s. Orbital speed is slower for higher orbits, but attaining them requires greater delta-v. The Fédération Aéronautique Internationale has established the Kármán line at an altitude of 100 km (62 mi) as a working definition for the boundary between aeronautics and astronautics. This is used because at an altitude of about 100 km (62 mi), as Theodore von Kármán calculated, a vehicle would have to travel faster than orbital velocity to derive sufficient aerodynamic lift from the atmosphere to support itself.^{[1]: 84 [2]}

Due to atmospheric drag, the lowest altitude at which an object in a circular orbit can complete at least one full revolution without propulsion is approximately 150 kilometres (93 mi).

The expression "orbital spaceflight" is mostly used to distinguish from sub-orbital spaceflights, which are flights where the apogee of a spacecraft reaches space, but the perigee is too low.^[3]