1 Answers
A sub-orbital spaceflight is a spaceflight in which the spacecraft reaches outer space, but its trajectory intersects the atmosphere or surface of the gravitating body from which it was launched, so that it will not complete one orbital revolution or reach escape velocity.
For example, the path of an object launched from Earth that reaches the Kármán line above sea level], and then falls back to Earth, is considered a sub-orbital spaceflight. Some sub-orbital flights have been undertaken to test spacecraft and launch vehicles later intended for orbital spaceflight. Other vehicles are specifically designed only for sub-orbital flight; examples include crewed vehicles, such as the X-15 and SpaceShipOne, and uncrewed ones, such as ICBMs and sounding rockets.
Flights which attain sufficient velocity to go into low Earth orbit, and then de-orbit before completing their first full orbit, are not considered sub-orbital. Examples of this include Yuri Gagarin's Vostok 1, and flights of the Fractional Orbital Bombardment System.
A flight that does not reach space is still sometimes called suborbital, but is not a 'suborbital spaceflight'. Usually a rocket is used, but experimental sub-orbital spaceflight has also been achieved with a space gun.