Outer space

Outer space (also called just space) as a name for a region, refers to the relatively empty parts of the Universe, outside the atmospheres of celestial bodies. The term outer space is used to distinguish it from airspace and terrestrial locations. Although outer space is certainly spacious, it is now known to be far from empty, and filled with a tenuous plasma.

Space does not equal orbit

A common misunderstanding about the boundary to space is that orbit occurs by reaching this altitude. There is a major difference between sub-orbital and orbital spaceflights, however. Achieving orbit requires orbital speed, and this can theoretically occur at any altitude. Atmospheric drag precludes an orbit that is too low.

Related Topics:
Orbit - Difference between sub-orbital and orbital spaceflights - Orbital speed

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Minimal altitudes for a stable orbit around the Earth begin at around 350 km (220 miles) above mean sea level, so to actually perform an orbital spaceflight, a spacecraft would need to go higher and (more importantly) faster than what would be required for a sub-orbital spaceflight.

Related Topics:
Orbital spaceflight - Sub-orbital spaceflight

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Reaching orbit requires tremendous speed. A craft has not reached orbit until it is circling Earth so quickly that the upward centrifugal "force" cancels the downward gravitational force on the craft. Having climbed up out of the atmosphere, a craft entering orbit must then turn sideways and continue firing its rockets to reach the necessary speed; for low Earth orbit, the speed is about 7.9 km/s (18,000 mph). Thus, achieving the necessary altitude is only the first step in reaching orbit.

Related Topics:
Centrifugal "force" - Gravitational force - Low Earth orbit

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The energy required to reach velocity for low earth orbit (32 MJ/kg) is about twenty times the energy to reach the corresponding altitude (10 kJ/km/kg).

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