The Sky is Falling and That’s Okay
Austin Morris, Director of Engineering
3 minute read
There has been a lot of attention recently on objects in space returning to the Earth, especially with several noteworthy reentries in the last few months. In late March 2021, a SpaceX Falcon9 second stage lit up the sky above the Pacific Northwest as it burned up on its descent. A few weeks later, there was the Chinese Long March 5B rocket body that reentered in early May, which came down in the Indian Ocean off the coast of the Maldives.
Yet what hasn’t been discussed much recently is the fact that orbital reentries are much more common than you probably think. Though it may sound like cause for fright, there is an average of one tracked orbital object that reenters the Earth’s atmosphere every single day. The reality is that, more often than not, an object reentering the atmosphere is a good thing because it is one fewer object in space. As we have detailed in columns previously, collision risk of objects in orbit increases dramatically with the amount of objects in orbit. In other words, the more stuff there is in space, the more likely that things start to collide, creating serious problems for those of us who enjoy having access to GPS, weather prediction, internet, telecommunications, and so on.
This is where the importance of controlled reentries comes in. When satellites are built and launched, they typically have a predetermined life expectancy, whether that is a number of months or as long as a decade or two. Once that satellite has completed its mission or reached the end of its life, it should be removed from orbit by reducing its altitude and bringing it back into the atmosphere. In doing this, a satellite operator provides a controlled reentry for that object, wherein it has a known and predictable trajectory, and enters at a rate and direction that assures that the object will burn away entirely on reentry. This ensures that nothing either on the planet or above it is damaged by the object.
Where this process starts to get sensationalized news articles like those of late is when objects are reentering uncontrolled. This is a different situation as there is no way to be sure whether the object will burn up entirely or if pieces of it may reach the ground or oceans because the object is on an unknown and unpredictable trajectory. This trajectory is considered unpredictable because, as mentioned in Adam’s previous Column “Speed is King”, the incredible speeds at which orbital objects are traveling makes conventional physics go slightly out the window. A brick is arguably not a very aerodynamic shape, but when moving fast enough, it can still generate lift. Any object traveling at orbital speeds and entering the atmosphere can have a variety of different effects. It could generate enough lift to skip off the atmosphere like a stone on a pond, or it could descend through the atmosphere so quickly and force oxygen molecules into each other so rapidly that it resembles nuclear fusion on the surface of the craft, or it could have any number of changes in its flight path throughout. This is why I refer to uncontrolled reentries as unpredictable, and why these reentries are typically featured in news articles.
On occasion, the story does not end with a fireball in the atmosphere and instead some amount of debris makes it to the surface. While this has a very low likelihood of happening, it has happened before and will happen again (stay tuned for a future column where I will dive into some further explanation and examples). For now, suffice it to say that uncontrolled reentries like those seen recently are examples of what we should be working to avoid. We can do this by continuing the work that is already done to minimize the likelihood and severity of mistakes made by human error and by putting new policy in place to ensure that those who are intentionally ignorant of good practice are not permitted to launch objects like these into orbit without sufficient plans to remove them in a controlled matter and reduce risk. Pushing to enact these kinds of policy, as well as providing additional means for controlled removal of uncontrolled objects, are just a few examples of the work necessary in the pursuit of #KeepingSpaceClearForAll.
Recommended column to read next: Why We Can’t “Just Blow It Up”