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What goes up must come down, right? But what if that “what” is a satellite, and what if it could land in your own backyard?

When a satellite in Low Earth Orbit reaches the end of its operational life, it doesn’t just float in space forever. Eventually, it begins a process known as re-entry, where it falls back toward Earth, often at high speed and under extreme heat. Sometimes this return is controlled, carefully guided to break up over the ocean, but more often, satellites or fragments of space debris re-enter uncontrolled, with little certainty about where they’ll land.

Such uncertainty drives Lily Flannery’s research. A PhD student at �ʹڲ�Ʊ Canberra, Lily is working to improve the way we predict where these objects might fall and reduce the risks to people, property, and the environment.

“I couldn’t believe how poor these predictions are. I figured that someone had worked out the maths and physics behind this long ago, but the more I looked into it, I realised just how much guesswork and simplification went into predicting uncontrolled satellite re-entries,” Lily says.  

Her work investigates why the leading software tools used in the industry often give very different answers when trying to predict the same event, and how those predictions can be made more reliable.

“As we see more and more objects launched with advanced materials and longer lifespans, we can’t just assume they’ll burn up on the way down or safely land in the ocean. That assumption is outdated,” Lily says. 

Lily’s research contributes to the growing global conversation about space sustainability, a movement that aims to ensure space remains usable, safe, and secure for future generations.

“To allow us to continue using re-entry as a safe and sustainable disposal strategy, we need legislators to think seriously about what happens when something goes wrong. Right now, the existing guidelines are rarely enforced and weren’t designed for the scale of what we’re dealing with today,” Lily says.  

It’s a delicate balance for re-entry researchers; having to model with enough detail to be useful, but not so much that the simulation becomes unmanageable or inaccurate due to unknowns.  

“In reality, we never know everything we need to make a perfect prediction, things like the satellite’s exact design, the way it might tumble, the condition of the atmosphere it’s falling through, or even what the solar weather is doing that day,” Lily says.

So, could a satellite really crash in your backyard?

“The reality is, we can’t currently predict re-entries accurately enough to rule it out. Right now, even saying which continent an uncontrolled satellite will land on can be a stretch.”

That doesn’t mean panic, but it does mean action and collaboration. 

“I’d love to see a global, collaborative effort to improve re-entry prediction tools. Better predictions mean safer skies and safer Earth” Lily says.