Overview: Here you'll learn all about how spacecraft are decommissioned and destroyed. You'll learn all about where the satellites go, how they are positioned in their final orbits, how they are destroyed in the Earth's atmosphere and much more.
So far we have discussed the first five phases of space operations, from launch all the way through mission completion. What happens after a successful mission and where does the spacecraft go?
Spacecraft Disposal may be the last part of a satellite’s life in space, but it’s important that disposal of old satellites is discussed and accounted for in the mission planning phase. A certain amount of fuel or propellant must be pre-allocated to push the finished satellite into a higher or lower orbit. Final orbit planning, instrument deactivation, and satellite disposal must be fully planned even before the satellite is launched!
When a satellite has completed its mission and there is no more use for it, the mission control center sends a series of commands to shut down the instruments onboard and decommission the satellite.
Once that series of commands is sent, the satellite receives the uplink, executes those commands to deactivate its instruments, and moves into its final orbit for disposal.
There are hundreds of satellites in orbit around the Earth right now. When the satellite has completed its mission, it is a good idea to move it away from other satellites to avoid crashes. If one satellite crashes into another, it could create an explosion of “space junk” that could damage or even destroy other satellites!
Gravity plays a big part in mission operations and spacecraft disposal. Gravity is strong around the Earth, and satellites are placed at a specific distance away to fulfill their respective missions; not too far, not too close.
Remember that the gravity of the Earth will constantly be pulling down everything in orbit slowly over time.
When it’s time to dispose of a satellite, it needs to either be pushed further away into space, or it needs to be brought down into the Earth’s atmosphere so it can burn up. Let’s discuss both methods…
For disposal, a satellite can be pushed up with propellant into something called a “supersynchronous” or “graveyard” orbit.
Raising the orbit of a decommissioned satellite to this very high altitude means it will be far away from any other on-going missions and won’t be a danger. The Earth’s gravity will still be pulling on it, but the orbit decay time is hundreds or thousands of years.
Another disposal method is lowering the satellite orbit into the Earth’s atmosphere. Objects entering the Earth’s atmosphere are usually burned up in the incredible heat.
But just in case a satellite won’t be totally burned up, the mission operators often target the final dumping site of the surviving debris in the South Pacific Ocean, far away from populated areas.
Some satellites, like NASA’s Tracking and Data Relay Satellite, are in much higher orbits than other low Earth orbiting satellites.
These orbits are called “geostationary” orbits and are good for communications and data relay functions.
It makes much more sense to place these satellites into a supersynchronous orbit for their disposal, because they are not as strongly affected by the Earth’s gravity as those in lower Earth orbit due to their greater distance from the Earth.
Skylab was NASA’s first space station in orbit around the Earth and operated during the 1970’s. NASA anticipated that some pieces of Skylab would survive the re-entry due to its size. And in 1979, Skylab broke up during re-entry with many pieces hitting parts of eastern and southern Australia.
If a significant portion of a satellite is expected to land on the Earth somewhere, the mission planners ensure that debris will impact the ocean or the surface in sparsely populated regions.
In 2011, UARS, the Upper Atmosphere Research Satellite re-entered Earth’s atmosphere after failing to burn up properly.
This satellite was approximately the size of a school bus and broke up into multiple pieces after re-entry.
Fortunately, the odds of space debris ever hitting a human being are incredibly small. But this is another example of why properly planned mission disposal is essential.
Spacecraft Disposal is a brief but critical part of a successful mission for NASA. This training module concludes the story of Space Operations.