A graveyard orbit is a parking zone a few hundred kilometres above geostationary height, where old GEO satellites are moved at the end of their lives.
Satellites in low orbit eventually fall back and burn up. Geostationary satellites are far too high for that. Left alone, a dead satellite would stay in the geostationary belt and drift through other satellites' slots.
So at the end of its life, an operator uses the satellite's last fuel to push it higher, out of the belt. The disposal zone above GEO is often called the graveyard orbit.
International space-debris guidelines (from the Inter-Agency Space Debris Coordination Committee, IADC) say the low point of the disposal orbit should be at least 235 km plus an extra margin above geostationary height. The margin depends on how strongly sunlight pushes on that satellite. The aim is that it will not return to the protected zone within 100 years.
The disposal orbit should also be nearly circular, with an eccentricity of 0.003 or less.
The fuel bill is small. Lifting a satellite 400 km above GEO takes a speed change of roughly 15 m/s, compared with about 1.5 km/s that a satellite needs to round out a typical transfer orbit at the start of its life.
ISRO retired INSAT-4B in January 2022. Its final orbit was about 340 km above geostationary height, and it was the 21st Indian geostationary satellite to go through such disposal. The fuel for the move had been set aside in its fuel budget from the start.
GSAT-12, launched on 15 July 2011, was retired the same way on 23 March 2023. GSAT-12 had carried 12 extended C-band transponders. ISRO estimated it needed to rise at least 261 km. Seven burns lifted it to a nearly circular orbit about 400 km above GEO. Four more burns changed its inclination. Then ISRO made it safe — 'passivated' it — by using up leftover fuel, discharging batteries and switching off transmitters and moving parts.
INSAT-3DS holds a slot in the geostationary belt that graveyard orbits are meant to keep clear; its estimated position stays fixed over the equator. See a working GEO satellite
The IADC guideline gives the minimum rise of the disposal perigee above GEO as
ΔH = 235 km + 1,000 × C_R × A/m
where C_R is the solar-radiation-pressure coefficient, A is the satellite's area facing the Sun in m², and m is its mass in kg.
The 235 km is a fixed margin above the geostationary belt. The second term grows for satellites that are light for their size, because sunlight pushes them around more.
Worked numbers. ISRO's estimate for GSAT-12 was 261 km, so 1,000 × C_R × A/m = 26, meaning C_R × A/m = 0.026 m²/kg. ISRO actually raised it to about 400 km, leaving extra margin.
How much fuel does that take? For a small change in a circular orbit, Δv ≈ v × Δa / (2a). At GEO, v = 3.07 km/s and a = 42,164 km, so lifting by 400 km costs about 3.07 × 400 / 84,328 = 0.0146 km/s — roughly 15 m/s. That is small next to a GTO-to-GEO burn of about 1.5 km/s, but it must be reserved from the start of the mission.
Once there, the satellite is no longer synchronous. Its period is about 20 minutes longer than a sidereal day, so it drifts westward around the belt by about 5° a day — circling above the working satellites rather than through them.
Bringing a satellite down from 35,786 km to re-enter would need far more fuel. A small boost of a few hundred kilometres clears the busy geostationary belt for much less.
Removing stored energy that could make it break up: venting leftover fuel, discharging batteries, and switching off transmitters and moving parts.
GSAT-12, raised to about 400 km above GEO in March 2023 (or INSAT-4B, about 340 km above GEO in January 2022).