Purpose
Geostationary orbit (GEO) at 35,786 km is a finite resource — only one ring of slots exists above the equator. When a GEO satellite reaches end of life, deorbiting it would require an impractical amount of fuel (the atmosphere is far below). Instead, operators use their remaining fuel to boost the satellite approximately 300 km above GEO into a "graveyard" or "supersynchronous" orbit, clearing the valuable slot for a replacement.
How It Works
The Inter-Agency Space Debris Coordination Committee (IADC) recommends a minimum raise of 235 km plus an allowance for solar radiation pressure effects. This places retired satellites in a stable orbit where they will not drift back into the operational GEO belt. The manoeuvre is called a "passivation and disposal" sequence — the satellite also vents remaining propellant and discharges batteries to reduce explosion risk.
How Many Objects Are There?
Hundreds of defunct satellites occupy graveyard orbits. They will remain there essentially forever — there is no atmospheric drag at GEO altitude. This is an accepted trade-off: the graveyard region is vast and sparsely populated, making collision risk negligible compared to the value of keeping GEO clear.