In the past week alone, we’ve seen two separate incidents of space debris blasting back to Earth in unexpected places.
On Saturday, there was the uncontrolled return of a Chinese Long March 5B missile over Malaysia. Yesterday, outlets reported on some spacecraft parts that have surfaced in regional New South Wales – now confirmed to be from a SpaceX Crew-1 mission.
As the space industry grows, it’s safe to say that such incidents will only become more frequent — and they could pose a risk.
But how much risk exactly?
Pieces of metal are racing towards us
Space debris refers to the leftover components of a space system that are no longer needed.
It could be a satellite that has reached the end of its life (such as the International Space Station), or parts of a rocket system that have reached their target and are discarded.
To date, China has launched three Long March 5B missiles, each of which has been deliberately left in uncontrolled orbit. This means there was no way of knowing where they would land.
As for the SpaceX debris found in the Snowy Mountains, SpaceX is controlling its rocket parts out of orbit and designing other components to burn upon re-entry into Earth’s atmosphere.
But as you can see from the latest news, things don’t always go according to plan.
So how dangerous is space debris really?
Well, as far as we know, only one person has ever been hit by it. Lottie Williams, a resident of Tulsa, Oklahoma, was struck by a stretch in 1997. It was about the size of her hand and was said to have come from a Delta II missile. She picked it up, took it home and reported it to authorities the next day.
However, with more and more objects going into space and coming back down, the chances of someone or something getting hit increase. This is especially true for large, uncontrolled objects like the Long March 5B.
Of the three launches of this rocket model:
Should I be concerned then?
There are many different estimates of the probability of space debris hitting someone, but most are in the range of one in 10,000.
This is the chance each person who is affected, anywhere in the world. However, the chance of a special person being hit (like you or me) is on the order of one in a trillion.
There are several factors behind these estimates, but let’s focus on one important one for now.
The image below shows the orbital path the recent Long March 5B-Y3 rocket has followed during its last 24 hours (different objects take different orbital paths), as well as the reentry location highlighted in red.
As you can see, the rocket orbits over the land for a considerable time.
In these orbits in particular, the vehicle spends about 20 percent of its time overland. A broad estimate tells us that 20 percent of the land is inhabited, meaning there is a 4 percent chance that the Long March 5B will return over an inhabited area.
This may seem quite high. But when you consider how much “inhabited land” is actually covered by people, the chances of injury or death are significantly reduced.
The risk of material damage, on the other hand, is greater. It can be as high as 1 percent for a given return of the Long March 5B.
Also, the overall risk of space debris will increase as the number of objects launched and re-entering the atmosphere increases. The current plans of companies and space organizations around the world include many, many more launches.
The Chinese space station Tiangong should be ready by the end of this year. And South Korea recently became the seventh country to launch a satellite payload heavier than a ton — with plans to expand its space sector (along with Japan, Russia, India and the United Arab Emirates).
It is very likely that the chance of being hit will only increase (but will hopefully remain very small).
How can we be prepared?
Two questions come to my mind:
- Can we predict the return of debris?
- What can we do to reduce the risk?
Let’s start with predictions.
Predicting where an object in uncontrolled orbit will enter Earth’s atmosphere can be a daunting challenge. The general rule of thumb says that the uncertainty of the estimated return time will be between 10 percent and 20 percent of the remaining orbital time.
This means that an object with a predicted return time of 10 hours has an uncertainty margin of about an hour. So if an object orbits the Earth every 60 to 90 minutes, it can enter just about anywhere.
Improving this uncertainty margin is a major challenge and requires a lot of research.
Even then, we’re unlikely to be able to predict an object’s reentry location more accurately than within a range of 1000 kilometers.
Ways to Reduce Risk
Reducing risk is a challenge, but there are a number of options.
First, all objects launched into orbit must have a plan to safely move to an uninhabited area. This is usually the SPOUA (South Pacific Ocean Uninhabited Area) – also known as the “spacecraft cemetery”.
There is also the option of carefully designing components so that they disintegrate completely upon return. If everything burns when it hits the upper atmosphere, there is no significant risk anymore.
There are already some guidelines that minimize the risk of space debris, such as the United Nations guidelines for the long-term sustainability of space activities, but the mechanisms for this have not been specified.
In addition, how do these guidelines apply internationally and who can enforce them? Such questions remain unanswered.
In short, should you worry about getting hit by space debris? For now, no. Is further space debris research important for the future? Absolute.
Fabian Zander, senior research fellow aerospace engineering, University of South Queensland
This article is republished from The Conversation under a Creative Commons license. Read the original article.