|
A graveyard orbit is an orbit where spacecraft are intentionally placed at the end of their operational life. It is a measure performed in order to lower the probability of collisions with operational spacecraft and of the generation of additional space debris. It is used when the delta-v required to perform a de-orbit maneuver would be too high. De-orbiting a geostationary satellite would require a delta-v of about 1,500 m/s while re-orbiting it to a graveyard orbit would require about 11 m/s.
For satellites in a geostationary orbit the graveyard orbit would be few hundred kilometers above the operational orbit. The transfer to graveyard orbit above geostationary orbit however requires the same amount of fuel that a satellite needs for approximately 3 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 the operational life only one third succeed in doing so.
According to the Inter-Agency Space Debris Coordination Committee (IADC) [1] (http://www.iadc-online.org/docs_pub/IADC-UNCOPUOS-final.pdf) the minimum perigee altitude <math>\Delta{H} \,<math> above the geostationary orbit should be:
- <math>\Delta{H} = 235 km + \left ( C_R \frac{A}{m} \right )<math>
where <math>C_R \,<math> is the solar radiation pressure coefficient and <math>\frac{A}{m}<math> is the aspect area to mass 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. 35 km have to be foreseen to consider the effects of gravitational perturbations. The remaining part of the equation consideres the effects of the solar radiation pressure which depend on the physical parameters of the satellite.
|
