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Graveyard Orbits and the Satellite Afterlife

 

 

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Monday, October 31, 2016

As Halloween approaches, the ghouls, ghosts and zombies are preparing to rise from their graves and once again roam the planet. But, perhaps, this year, our earthly graveyards are not the only ones to keep an eye on...

Graveyard Orbits and the Satellite Afterlife

In the vast darkness of deep space, far beyond the reaches of normal orbits, there is another graveyard¬; one filled the “bodies” of dead satellites—the Graveyard Orbit.

Although we may not have to fear the rise of zombie satellites, this Halloween we are taking a closer look at the satellite afterlife.

Like everything else, satellites don’t last forever. They have a limited fuel capacity and surviving the harsh conditions of launch, orbiting Earth at thousands of miles an hour and the extremes of outer space can put a lot of wear and tear on them.  

So where do satellites go when they die?

For satellites orbiting closer to Earth, operators lower the orbit of a decommissioned satellite so that it will naturally re-enter the atmosphere within 25 years (known as the “25-year Rule”). As the satellite begins to fall back toward Earth, the heat from air friction will burn up the satellite, causing it to disintegrate before it ever reaches the surface. 

However, use of the 25-year rule is permitted only if an operator can show by analysis that the probability of injury or property damage is less than 1 in 10,000.  

If the operator determines that this is greater than 1 in 10,000, a “controlled deorbit” is required.  During a controlled deorbit, engineers use the satellite’s remaining fuel to slow it down until it falls out of orbit into a pre-determined broad ocean area dubbed the “Spacecraft Cemetery.”  

Many satellites, like NOAA’s POES and DMSP satellites, were designed before the 25-year rule was implemented. At the time, if the probability of damage or injury was less than 1 in 10,000, operators simply shut off the spacecraft and left it in orbit, meaning every POES and DMSP satellite NOAA has ever operated is still in orbit and will be for at least 500 years!

Spacecraft designed after these practices were adopted, such as the Suomi NPP and JPSS satellites, will be required to perform a controlled deorbit in the future.

Not all satellites can simply burn up in the atmosphere, though.

Satellites in higher orbits, such as NOAA’s Geostationary Operational Environmental Satellites (GOES) orbiting 22,300 miles above the Earth, would require too much fuel to slow down, significantly cutting into their operational life-spans  (not to mention the distance they would have to fall!).

Instead, these satellites perform one final fuel burn, sending them into graveyard orbits. Current U.S. guidelines require a spacecraft to be raised to an orbit at least 300 km higher, well out of the way of the busier operational orbits below.   

The most recent NOAA satellite put to rest in a graveyard orbit was GOES-12. The final maneuver occurred in August 2013, after 3,788 days in service.

Once satellites reach this final orbit their instruments and subsystems are shut down, the remaining fuel is depleted and they are left to orbit in peace.