Sub-orbital spaceflight

A sub-orbital spaceflight (or sub-orbital flight) is a spaceflight that does not involve putting a vehicle into orbit. Manned and unmanned sub-orbital flights have been undertaken to test spacecraft and launch vehicles intended for later orbital flight, but some vehicles have been designed exclusively to reach space sub-orbitally: manned vehicles such as the X-15 and SpaceShipOne, and unmanned ones such as ICBMs and sounding rockets.

Overview

During freefall the trajectory is part of an elliptic orbit as given by the orbital equation. The perigee distance is less than the radius of the Earth, hence the ellipse intersects the Earth. The major axis is vertical, the semi-major axis is more than one half of the radius of the Earth, and almost always less than the radius.

Related Topics:
Freefall - Trajectory - Elliptic orbit - Orbital equation - Perigee - Ellipse - Semi-major axis

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If the objective is just to reach space, sub-orbital flights are appealing because this is very much easier (it simply means going higher than the edge of space) than to achieve orbit (which requires a velocity of about 8 km/s (18,000 mph)). A dedicated sub-orbital spacecraft can therefore be built and operated much more cheaply than an orbital spacecraft. Less powerful sub-orbital craft may not reach speeds much higher than around 1.1 km/s to 1.3 km/s (2,500-3,000 mph).

Related Topics:
Edge of space - Velocity - Km/s - Mph

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However, for intercontinental ballistic space flights, like that of an ICBM, or a possible future commercial spacecraft, a typical speed is / might be 7 km/s.

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For more information on the difference between sub-orbital and orbital spaceflights, refer to the article Difference between sub-orbital and orbital spaceflights.

Related Topics:
Orbital spaceflight - Difference between sub-orbital and orbital spaceflights

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