# Graveyard orbit

(Redirected from Disposal orbit)

A graveyard orbit, also called a junk orbit or disposal orbit, is an orbit that lies away from common operational orbits, typically a supersynchronous orbit well above synchronous orbit. Satellites are moved into such orbits at the end of their operational life to reduce the probability of colliding with operational spacecraft or generating space debris.

A graveyard orbit is used when the change in velocity required to perform a de-orbit maneuver is too large. De-orbiting a geostationary satellite requires a delta-v of about 1,500 metres per second (4,900 ft/s), whereas re-orbiting it to a graveyard orbit only requires about 11 metres per second (36 ft/s).[1]

For satellites in geostationary orbit and geosynchronous orbits, the graveyard orbit is a few hundred kilometers above the operational orbit. The transfer to a graveyard orbit above geostationary orbit requires the same amount of fuel as a satellite needs for about three months of stationkeeping. It also requires a reliable attitude control during the transfer maneuver. While most satellite operators try to perform such a maneuver at the end of their satellites' operational lives, through 2005 only about one-third succeeded.[2] However, as of 2011, most recently decommissioned geosynchronous spacecraft were said to have been moved to a graveyard orbit.[3]

According to the Inter-Agency Space Debris Coordination Committee (IADC)[4] the minimum perigee altitude ${\displaystyle \Delta {H}\,}$ above the geostationary orbit is:

${\displaystyle \Delta {H}=235{\mbox{ km}}+\left(1000C_{R}{\frac {A}{m}}\right){\mbox{ km}}}$

where ${\displaystyle C_{R}\,}$ is the solar radiation pressure coefficient (typically between 1.2 and 1.5 N/m² or Pa) and ${\displaystyle {\frac {A}{m}}\,}$ is the aspect area [m²] to mass [kg] ratio of the satellite. This formula includes about 200 km for the GEO-protected zone to also permit orbit maneuvers in GEO without interference with the graveyard orbit. Another 35 kilometres (22 mi) of tolerance must be allowed for the effects of gravitational perturbations (primarily solar and lunar). The remaining part of the equation considers the effects of the solar radiation pressure, which depends on the physical parameters of the satellite.

In order to obtain a license to provide telecommunications services in the United States, the Federal Communications Commission (FCC) requires all geostationary satellites launched after March 18, 2002, to commit to moving to a graveyard orbit at the end of their operational life.[5] U.S. government regulations require a boost, ${\displaystyle \Delta {H}}$, of about 300 km.[6]

A spacecraft moved to a graveyard orbit will typically be passivated.

Uncontrolled objects in a near geostationary [earth] orbit (GEO) exhibit a 53-year cycle of orbital inclination[7] due to the interaction of the earths tilt with the lunar orbit. The orbital inclination varies ± 7.4°, at up to 0.8°pa.[7]:3