To LEO and Back Again
Austin Morris, Director of Engineering
4 minute read
In my previous column, The Sky is Falling and That’s Okay, I discussed the fact that there is an average of one orbital object that reenters Earth’s atmosphere every day. I also described why it is typically better for these objects to reenter than to stay in orbit, to ensure that they burn away into nothingness and cause no risk of damage to other objects. This is because the enormous amount of air friction that is encountered when entering the atmosphere at orbital speeds creates such an unbearable amount of heat that very few objects can survive it long enough to slow down and descend to the surface.
As one might imagine, in crewed spaceflight it is important to have a method by which you can safely return your crew to the ground. Early pioneers spent a great deal of time and effort devising return trajectories which minimized the heating effects of reentry, along with selecting shapes and materials that would be best able to help the capsule survive. One concept to help survive reentry is called ablation, where pieces of your heat shield break off and take heat with them, helping the main body of your craft keep its cool. Ablative heat shields were first described as early as 1920 by Robert Goddard (for whom NASA’s Goddard Space Flight Center is named), who likened the concept to the same method by which meteors can enter the atmosphere and make it to the ground with a relatively low temperature in their core. Cork is a great example of a material used for this. There are indeed methods other than ablation. In the case of tungsten, which is a dense metal with the highest melting point of all discovered elements, it simply doesn’t care about the heat and continues on through the atmosphere unchanged but a little toasty.
All these points of successful entry, descent, and landing are hugely important developments in ensuring safe crewed spaceflights. However, it does open up another question: What happens when objects make it back to the surface by accident? As mentioned previously, it is exceptionally difficult to create objects that can survive reentry unharmed. However, with an object large enough and containing enough mass, it is certainly possible to have fragments of that object survive reentry and impact the surface of the Earth. For example, in January 1978, the nuclear-powered Soviet satellite Kosmos 954 reentered and crashed down in the Northwest Territories of Canada. In July 1979, the U.S. space station Skylab came down and scattered debris across Australia. These are harrowing events that shed light on the fact that we as a species need to do better in maintaining control and security of our objects in orbit.
When incidents like these occur, there is often no clear way to predict where exactly the object will land. Typically the greatest cause for concern comes when there is risk of the objects coming down on land, as it poses risk to not only human infrastructure but to human life. Fortunately for that concern, roughly 70% of the Earth’s surface area is covered by water, meaning the likelihood of objects coming down on land is much lower than that of it coming down in a body of water. As for the remaining 30%, most of it consists of deserts, the arctic, and empty parking lots, making injury from falling debris exceptionally rare. If the preferred disposal method is indeed to splash down in a body of water, the next thing to consider is what risk is posed to the environment from an ecological perspective when objects in orbit come crashing down into the oceans.
Most objects in orbit are made up of a combination of metals and composites in their main structures, solar panels, computer hardware, and so on. Depending on the type of object, it may also carry propulsion, which can carry residual amounts of fuels or propellants with a variety of different materials ranging from kerosene or liquid hydrogen to liquid oxygen, or even the non-reactive inert gases Argon, Krypton, and Xenon. Even though objects from orbit represent an extremely insignificant amount of material pollution in the Earth’s waters, manufactured components generally do not belong in the ocean. There are a few options to prevent these objects from landing where they do not belong. As previously mentioned, these objects can be responsibly deorbited in a manner that allows for them to burn up entirely. Alternatively, these objects can remain in orbit and be reclaimed and repurposed to be made into something new. I believe this is the real future of space and space debris, which is why KMI is working with others in the industry to come together on a solution that allows material already in orbit to stay in orbit and have a future life after being recycled.
Space provides unlimited opportunities for better protecting the environment on Earth, from NOAA weather satellites to wildfire tracking satellites recently in development. It is the responsibility of aerospace companies in this rapidly growing industry to develop processes for protecting our environment, both on Earth and in space, by managing the reentry of objects responsibly, or better yet by allowing old and expired objects to be repurposed or recycled in orbit. KMI is working to develop the capabilities to enable this sustainable space ecosystem on our mission of #KeepingSpaceClearForAll.
Recommended column to read next: Solar Panels and Nuclear Spacecraft