GCAT: General Catalog of Artificial Space Objects

Jonathan C. McDowell

Definitions

Orbital Categories

The following table gives the abbreviations I use to summarize different orbital categories (notably, in the OpOrbit field of the object catalogs.) LEO is (the upper part of) Low Earth Orbit; LLEO is Lower LEO, below 600 km. GEO is Geosynchronous Earth Orbit.


`Height' h is defined as geocentric semi-major axis minus Earth equatorial radius: (a-6378.0 km); i.e. average of conventional perigee (hp) and apogee (ha) heights. Heights are in km, inclination in degrees.


One common conventional upper boundary of LEO is a 2 hour period (and it's enshrined in code as part of the SGP4 model.) Orbital period makes the most sense for defining boundaries between there and GEO, while height makes the most sense for the lower boundaries. This makes the definition scheme a bit patchwork - sorry.


Some people use a height of 2000 km as the upper boundary of LEO instead of 2 hours (1681 km). I like that better and In retrospect I wish I'd gone with it, but it's too late to change now. (At least for this release.)


CodeNamePeriod (hr:min)Height (km)Inclination (deg)Eccentricity
ATM Atmosphericha below 80
SO Suborbital hp below 0, ha above 80
TA Trans-Atm. hp from 0 to 80, ha above 80
LLEO/E Lower LEO/Equatorialh 80 to 6000 to 25
LLEO/I Lower LEO/Intermediateh 80 to 60025 to 85
LLEO/P Lower LEO/Polarh 80 to 60085 to 95
LLEO/S Lower LEO/Sun-Sync h 80 to 60095 to 104
LLEO/R Lower LEO/Retrogradeh 80 to 600104 to 180
LEO/E Upper LEO/EquatorialUp to 2:00h 600 to 16810 to 25
LEO/I Upper LEO/IntermediateUp to 2:00h 600 to 168125 to 85
LEO/P Upper LEO/PolarUp to 2:00h 600 to 168185 to 95
LEO/S Upper LEO/Sun-Sync Up to 2:00h 600 to 168195 to 104
LEO/R Upper LEO/RetrogradeUp to 2:00h 600 to 1681104 to 180
MEO Medium Earth Orbit 2:00 - 23:00 0.00-0.50
HEO Highly Elliptical orbit4:03 - 23:00 0.50-0.92
HEO/M Molniya 11:30 - 12:30 62.0 - 64.0 0.50 - 0.77
GTO Geotransfer10:00 - 12:30 0.0 - 85.0 0.50 - 0.77
GEO/S Stationary 23:55.5-23:56.50.0 - 3.0 0.00 - 0.01
GEO/I Inclined GEO23:55.5-23:56.53.0 - 25.0 0.00 - 0.05
GEO/T Synchronous 23:55.5-23:56.50.0 - 180.0 0.00 - 0.85
GEO/D Drift GEO 23:00 - 25:00 0.0 - 3.0 0.00 - 0.05
GEO/SIInclined GEO23:55.5-23:56.53.0 - 25.0 0.00 - 0.05
GEO/IDInclined Drift23:41 - 24:11 3.0 - 25.0 0.00 - 0.05
GEO/NSNear-sync 23:00 - 25:00 0.0 - 180.0 0.0 - 0.85
VHEO Very High Earth OrbitAbove 25:00 0.0 - 180.00.0 - 1.00
DSO Deep Space Orbit h above 145688 to 318200 0.0 to 1.0
CLO Cislunar/Translunar h from 318200 to 1.5 million 0.0 to 1.0
EEO Earth Escape h less than 1.5 million Above 1.0
HCO Heliocentric h more than 1.5 millionHeliocentric e 0.0 to 1.0
PCO Planetocentric Central body not Earth or Sun
SSE Solar System Escape Heliocentric e above 1.0