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. The deepest visible-light image of the cosmos. ... Atmosphere is the general name for a layer of gases that may surround a material body of sufficient mass. ... Airspace means the portion of the atmosphere controlled by a particular country or, more generally, any specific portion of the atmosphere. ...

As Earth's atmosphere has no abrupt cut-off, but rather thins gradually with increasing altitude, there is no definite boundary between the atmosphere and space. The altitude of 100 kilometers or 62 miles established by the Federation Aeronautique Internationale is the most widely used definition as the boundary between atmosphere and space. In the United States, persons who travel above an altitude of 50 miles (80 kilometers) are designated as astronauts. 400,000 feet (75 miles or 120 kilometers) marks the boundary where atmospheric effects become noticeable during re-entry. (See also Karman line.) Earths atmosphere is the layer of gases surrounding the planet Earth and retained by the Earths gravity. ... The Fédération Aéronautique Internationale (FAI) is a standard setting and record-keeping body for aeronautics and astronautics. ... U.S. Space Shuttle astronaut Bruce McCandless II using a manned maneuvering unit. ... Atmospheric entry is the transition from the vacuum of space to the atmosphere of any planet or other celestial body. ... Layers of Atmosphere (NOAA) The Karman Line is an internationally designated altitude commonly used to define outer space. ...

Milestones on the way to space

• 4.6 km (15,000ft) - FAA requires supplemental oxygen for aircraft pilots and passengers
• 5.3 km (17,400ft) - Half of the earth's atmosphere is below this altitude
• 16 km (52,500ft) - Pressurized cabin or pressure suit required
• 18 km (59,000ft) - Upper limit of the Troposphere
• 20 km (65,600ft) - Water at room temperature boils without a pressurized container (the popular notion that bodily fluids would start to boil at this point is false because the confines of the body generate enough pressure to prevent actual boiling)
• 24 km (78,700ft) - Regular aircraft pressurization systems no longer function
• 32 km (105,000ft) - Turbojets no longer function
• 45 km (148,000ft) - Ramjets no longer function
• 50 km (164,000ft) - Stratosphere ends
• 80 km (262,000ft) - Mesosphere ends
• 100 km (328,000ft)- Aerodynamic surfaces no longer function

Reentry from orbit begins at 122 km (400,000ft). FAA may refer to: Federal Aviation Administration in the United States Fleet Air Arm in the UK Royal Navy Fuerza Aérea Argentina in Argentina This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... The troposphere is the lowermost portion of Earths atmosphere and the one in which most weather phenomena occur. ... A Pratt and Whitney turbofan engine for the F-15 Eagle is tested at Robins Air Force Base, Georgia, USA. The tunnel behind the engine muffles noise and allows exhaust to escape. ... For the fictional method of interstellar travel, see Bussard ramjet. ... The Stratosphere is also a major hotel and casino resort in Las Vegas. ... The mesosphere (from the Greek words mesos = middle and sfaira = ball) is the layer of the Earths atmosphere that is directly above the stratosphere and directly below the thermosphere. ... An airfoil (in American English, or aerofoil in British English) is a specially shaped cross-section of a wing or blade, used to provide lift or downforce, depending on its application. ...

Space does not equal orbit

A common misunderstanding about the boundary to space is that orbit occurs by reaching this altitude. Orbit, however, requires orbital speed and can theoretically occur at any altitude. Atmospheric drag precludes an orbit that is too low. For other meanings of the term orbit, see orbit (disambiguation) In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity. ... The orbital speed of a body, generally a planet, a natural satellite, an artificial satellite, or a multiple star, is the speed at which it orbits around the barycenter of a system, usually around a more massive body. ...

Minimal altitudes for a stable orbit 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. An orbital spaceflight (or orbital flight) in the general sense is a spaceflight where the spacecraft reaches the height of, and through having an appropriate velocity enters into, orbit around an astronomical body. ... A sub-orbital spaceflight (or sub-orbital flight) is a spaceflight that does not involve putting a vehicle into orbit. ...

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 7.9km per second (18,000 mph). Thus, achieving the necessary altitude is only the first step in reaching orbit. The expression centrifugal force is used to express that if an object is being swung around on a string the object seems to be pulling on the string. ... This article covers the physics of gravitation. ... A low Earth orbit (LEO) is an orbit in which objects such as satellites are below intermediate circular orbit (ICO) and far below geostationary orbit, but typically around 350 - 1400 km above the Earths surface. ...

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).

See also

• Karman line
• Astronaut wings
• Difference between sub-orbital and orbital spaceflights
• space and survival
• space colonization
• space exploration
• space science
• space technology
• astronomy