Understanding Orbital Slot
How a slot is assigned
Slots are not sold over a counter — they are coordinated through the ITU by national governments, a process separate from listing the spacecraft itself under the UN Registration Convention. An operator's administration submits a filing that is published internationally, then negotiates ('coordinates') with everyone whose existing networks its satellite might interfere with. Once conflicts are resolved, the assignment is recorded in the Master International Frequency Register (MIFR) and gains international protection. To curb countries hoarding positions they never use — so-called 'paper satellites' — a filing must be brought into use within seven years: a working satellite has to be parked at the slot and held there for a continuous 90-day period. Two broad regimes govern who gets access:
| Regime | How it works | Example bands |
|---|---|---|
| Planned bands | Each country is guaranteed a slot and frequencies reserved in advance, protecting future access | BSS Appendix 30/30A; FSS Appendix 30B |
| Coordination bands | First-come, first-served; new entrants must coordinate with existing users to avoid interference | Most C-, Ku- and Ka-band FSS |
Why the arc is finite — and slots so valuable
The geostationary orbit is a single circle about 265,000 km in circumference, and every satellite in it shares that one line. As a rule of thumb, spacecraft using the same frequencies are spaced roughly 2° of longitude apart — around 1,500 km along the ring — which implies on the order of 180 positions around the full circle. Operators wring far more capacity from the arc by re-using frequencies across different bands, polarisations and narrow spot beams, and by colocation: flying several satellites together as a cluster inside one slot. Even so, the best positions are scarce, because a slot's worth depends on the ground beneath it. A satellite over the mid-Atlantic sees both the Americas and western Europe at a usable elevation angle, while one above an empty stretch of ocean reaches almost no one — which is why longitudes serving North America, Europe and East Asia are the most fiercely contested.
Holding a slot: station-keeping and end of life
A geostationary satellite will not naturally stay put. The gravity of the Sun and Moon tilts its orbit into an increasingly inclined path (a north–south drift), while the slight lumpiness of Earth's gravity nudges it east or west along the arc. To stay inside its ±0.1° box the satellite fires thrusters every few weeks — a steady propellant cost that ultimately sets the mission's lifetime. When fuel runs low the operator raises the satellite a few hundred kilometres above the arc into a graveyard orbit, clearing the slot, and normally launches a replacement first so the valuable position is never left empty. Allow a slot to sit vacant and the ITU filing that protects it can lapse — handing the opening to a rival.