Orbital spaceflight

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An orbital spaceflight (or orbital flight) is a spaceflight where the spacecraft is placed on a trajectory that does not intersect with a planetary surface for at least one orbit.

To do this around the Earth, it must have an altitude at perigee higher than 100 km (which is the conventional boundary of space), and have a horizontal speed higher than orbital speed, which is usually about 7-8 km/s depending on the altitude. Another way of saying this, is the outward centrifugal force on the spacecraft due to its angular velocity is greater than or equal to the inward force due to gravity. Note that with this definition, an orbital spaceflight need not complete a full orbit.

The expression "orbital spaceflight" is mostly used to distinguish from sub-orbital spaceflights, which are flights where the spacecraft reaches space but does not have a high enough angular velocity to enter into orbit. The required speed to achieve orbit with known methods is about 9.3 km/s (18,000 mph), while some sub-orbital spacecraft can reach space without travelling faster than 1.1 km/s to 1.3 km/s (2,500 mph to 3,000 mph).