Graveyard orbit

A graveyard orbit is a special path in space used to store old spacecraft. These orbits are also called junk orbits or disposal orbits. They sit far away from the paths used by active, working satellites. The main goal is to keep working spacecraft safe from collisions. When satellites crash, they create space debris, which is dangerous junk. Moving old satellites to these orbits reduces the chance of such accidents.

Moving a satellite can be a difficult process. Engineers must calculate the change in velocity needed for the move. This change in velocity is known as delta-v. For a satellite in geostationary orbit, falling down to Earth is very hard. It requires a delta-v of about 1,500 m/s to de-orbit. However, moving up to a graveyard orbit is much easier. This transfer only requires a delta-v of about 11 m/s. This move uses the same fuel as three months of stationkeeping.

There are different ways to handle satellites depending on their altitude. For satellites in geostationary or geosynchronous orbits, the graveyard orbit is just a few hundred kilometers higher. These satellites are often moved before they stop working entirely. This is because the positions at geosynchronous altitude have high economic value. However, the transfer requires reliable attitude control during the maneuver. Attitude control is how a spacecraft manages its orientation in space. Through 2005, only about one-third of satellite operators successfully completed these maneuvers.

Scientists use complex math to determine the safest height for these orbits. The Inter-Agency Space Debris Coordination Committee, or IADC, provides a specific formula. This formula calculates the minimum recommended perigee altitude. Perigee is the point in an orbit closest to Earth. The formula considers the mass of the satellite and its aspect area. It also includes the solar radiation pressure coefficient. This coefficient is a value between 1 for absorption and 2 for specular reflection. These factors help ensure the protected zone remains clear for active maneuvers.

Rules and regulations help manage these orbits to prevent chaos. In the United States, the Federal Communications Commission, or FCC, sets strict requirements. Any geostationary satellite launched after March 18, 2002, must commit to moving to a graveyard orbit. U.S. government regulations even require a specific boost of about 274 m/s. These rules ensure companies take responsibility for their equipment. In 2023, DISH became the first company to receive an FCC fine. This was because they failed to de-orbit their EchoStar VII satellite properly.

Satellites in near-geostationary orbits face unique environmental challenges. Uncontrolled objects in these areas show a 53-year cycle of orbital inclination. Inclination is the angle of the orbit relative to the Earth's equator. This cycle happens because of the interaction between Earth's tilt and the lunar orbit. The inclination varies by plus or minus 7.4 degrees. This change happens at a rate of up to 0.8 degrees per year. Once in a graveyard orbit, a spacecraft will typically be passivated. Passivation means removing energy sources to prevent accidental explosions.

New approaches are needed as space becomes more crowded. Large satellite networks in Low Earth Orbit, or LEO, use different methods. Unlike high graveyard orbits, these satellites use disposal orbits that decay naturally. Atmospheric drag, which is the friction from thin air, pulls these satellites down. This causes them to reenter the atmosphere and burn up within one year. Companies like SpaceX and OneWeb have committed to this method. This ensures that thousands of new satellites do not create long-term junk.