A low Earth orbit (LEO) is an orbit around Earth with an altitude between 160 kilometers (99 mi) (orbital period of about 88 minutes), and 2,000 kilometers (1,200 mi) (about 127 minutes). Objects below approximately 160 kilometers (99 mi) will experience very rapid orbital decay and altitude loss. The orbital velocity needed to maintain a stable low Earth orbit is about 7.8 km/s, but reduces with increased orbital altitude.

With the exception of the manned lunar flights of the Apollo program, all human spaceflights have taken place in LEO (or were suborbital). The altitude record for a human spaceflight in LEO was Gemini 11 with an apogee of 1,374.1 kilometers (853.8 mi). All manned space stations to date, as well as the majority of satellites, have been in LEO.

Orbital characteristics

Objects in LEO encounter atmospheric drag in the form of gases in the thermosphere (approximately 80–500 km up) or exosphere (approximately 500 km and up), depending on orbit height. Objects in LEO orbit Earth between the atmosphere and below the inner Van Allen radiation belt. The altitude is usually not less than 300 km for satellites, as that would be impractical due to atmospheric drag.

A geocentric orbit involves any object orbiting the Earth, such as the Moon or artificial satellites. In 1997 NASA estimated there were approximately 2,465 artificial satellite payloads orbiting the Earth and 6,216 pieces of space debris as tracked by the Goddard Space Flight Center. Over 16,291 previously launched objects have decayed into the Earth's atmosphere.

List of terms and concepts

Geocentric orbit types

The following is a list of different geocentric orbit classifications.

Altitude classifications

Inclination classifications

Eccentricity classifications

Directional classifications

Geosynchronous classifications

Special classifications

Non-geocentric classifications

Tangential velocities at altitude

See also

References

External links

NewSpace—formerly alt.space; also "new space", and entrepreneurial space—are umbrella terms for a movement and philosophy often affiliated with, but not synonymous with, an emergent private spaceflight industry. Specifically, the terms are used to refer to a community of relatively new aerospace companies working to develop low-cost access to space or spaceflight technologies and advocates of low-cost spaceflight technology and policy.

Origin

The term alt.space was first used in the early 1980s to describe companies that were making serious efforts to reach outer space without cooperation with NASA, other governmental agencies, or their contractors. Near the end of the 1990s, a dramatic increase in companies engaging in this process led to the common usage of the phrase "new space companies"; "NewSpace" and "entrepreneurial space" are now the most commonly used terms, though "alt.space" is still occasionally found.

Definition

NewSpace is a term that has had some variation in meaning since "supplanting the geekier 'alt.space' moniker" after about 2006.