thumb|An example of a graveyard orbit – [[ECEF|Earth fixed frame<br>]]
A graveyard orbit, also called a junk orbit or disposal orbit, is an orbit that lies away from common operational orbits. One significant graveyard orbit is a supersynchronous orbit well beyond geosynchronous orbit.<!-- as of 2017, there are no common supersynchronous graveyard orbits in common use around non-terran celestial bodies --> Some satellites are moved into such orbits at the end of their operational life to reduce the probability of colliding with operational spacecraft and generating space debris.
Overview
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 , whereas re-orbiting it to a graveyard orbit requires only about .
For satellites in geostationary orbit and geosynchronous orbits, the graveyard orbit is a few hundred kilometers beyond the operational orbit. The transfer to a graveyard orbit beyond 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 plan to perform such a maneuver at the end of their satellites' operational lives, through 2005 only about one-third succeeded. Given the economic value of the positions at geosynchronous altitude, unless premature spacecraft failure precludes it, satellites are moved to a graveyard orbit prior to decommissioning.
According to the Inter-Agency Space Debris Coordination Committee (IADC) the minimum recommended perigee altitude <math>\Delta{H}</math> beyond the geostationary orbit is
:<math>\Delta{H} = 235\mbox{ km} + C_\mathrm{R} \frac{A \left[ \mathrm{m}^2 \right]}{m \left[ \mathrm{kg} \right]} \cdot 1000\mbox{ km}</math>
where
:<math>C_\mathrm{R}</math> is the satellite's solar radiation pressure coefficient, whose value is between 1 (for absorption) and 2 (for specular reflection),
:<math>A</math> is its aspect area,
:<math>m</math> is its mass.
This formula includes for the GEO-protected zone to also permit orbit maneuvers in GEO without interference with the graveyard orbit. Another 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 lives. U.S. government regulations require a boost, <math>\Delta{H}</math>, of about . In 2023 DISH received the first-ever fine by the FCC for failing to de-orbit its EchoStar VII satellite according to the terms of its license.
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 due to the interaction of the Earth's tilt with the lunar orbit. The orbital inclination varies ± 7.4°, at up to 0.8°pa.
See also
- List of orbits
- SNAP-10A – nuclear reactor satellite, remaining in a sub-synchronous Earth orbit for an expected 4,000 years
- Spacecraft cemetery, in the Pacific Ocean