麻豆传媒

ON 11 July 1979, shards of a space station , the first US outpost in space, was supposed to plunge into the ocean 1300 kilometres off South Africa, but it took longer to disintegrate than predicted.

The above the Indian Ocean, sending debris into the water and across a . Thankfully, nobody was injured. But the incident served as a stark reminder that what we launch into space doesn鈥檛 simply disappear.

Today, there are thousands of satellites in orbit, and the number is growing fast. The concern isn鈥檛 only that one of these will land on someone鈥檚 head. Certainly, our rush to fill space above Earth has significantly upped the odds of cataclysmic collisions in orbit that might rain stuff down on us. But space debris 鈥� defunct satellites, bits of rockets and fragments scattered by crashes 鈥� is only half of the problem. Satellites are unintentional mirrors, reflecting sunlight and obscuring our view of the stars. They are even making it harder to see threats coming our planet鈥檚 way from outer space.

Many insist that when it comes to such problems, we are approaching a tipping point. 鈥淚f something doesn鈥檛 happen, we stand to lose the skies in three years,鈥� says , a cosmologist at the University of San Francisco, California. 鈥淭he skies will change forever.鈥�

The pressure is on for something to change. There is no shortage of people seeking answers, but the big question is: can they be found and applied before it is too late?

We have been littering space for decades. In 1979, when Skylab plunged to Earth, it was one of just over . In mid 2019, there were . Today, there are .

The US government larger than 10 centimetres in diameter in Earth鈥檚 orbit, and more than half a million pieces smaller than that. Although you might think of it floating around gently, space debris is often moving at speeds in excess of 28,000 kilometres per hour. Moreover, it is hard to track. Whereas active satellites reveal their positions via on-board GPS, dead ones and all other debris can only be tracked by ground-based radar. The smaller stuff is sometimes invisible to such systems.

All of which means there will inevitably be collisions, which can be dangerous for active satellites and increase the chances of bits of debris falling to Earth and causing damage. In 2009, a derelict Russian military satellite slammed into an active one operated by Iridium Satellite LLC, a private US company. Both satellites were destroyed, causing some issues with Iridium鈥檚 communications service and creating .

Collisions could be avoided. The Space Surveillance Network, part of a branch of the US military called the Space Force, uses a global array of telescopes and radar systems to track objects and assess the likelihood of two crashing. If one or both are active satellites, another part of the Space Force lets the operators know so that action can be taken, usually by commanding the craft to fire thrusters.

But as low Earth orbit 鈥� , this gets trickier. A major collision, perhaps one that will take out some vital satellite infrastructure, is already inevitable. But it could be much worse than that. If you have ever watched the 2013 film Gravity, then you have seen . This occurs when, beyond a critical threshold of objects in orbit, one collision鈥檚 spray of debris causes many more collisions, creating an unstoppable cascade.

The problem is that these cascades unfold very slowly and it could be centuries before major collisions are happening constantly, says , a space debris expert at the University of Southampton, UK. 鈥淲e鈥檙e looking out for some sign that this collision cascade has started,鈥� he says. 鈥淚 think that all the evidence points to the fact that it already has. And it probably started decades ago.鈥�

If low Earth orbit gets crammed with satellites, and collisions turn that orbital highway into a shooting gallery, 鈥渢hen we鈥檝e got the issue of trying to get through all this stuff to go to the moon鈥�, says , a space debris expert at the University of Buffalo. 鈥淥ur astronauts are going to be in danger of being hit by this stuff.鈥�

One saving grace so far has been that space junk often gets dragged into the lower atmosphere and burns up. Unfortunately, as we have recently discovered, climate change means the rate at which this happens may decline, making orbital overcrowding worse.

In the upper atmosphere, the sun鈥檚 extreme ultraviolet radiation splits molecular oxygen into two oxygen atoms that collide with carbon dioxide molecules, releasing infrared energy. Adding more carbon dioxide to the upper atmosphere increases this effect. As more infrared energy is released, it escapes into space and so the upper atmosphere cools. In this more frigid environment, the particles lose energy and the upper atmosphere contracts.

This phenomenon was , and has been . But Lewis and his colleagues recently realised it is influencing the lifetime of space junk. When falling orbital debris meets atmospheric particles, the object experiences drag. This causes the size of its orbit to shrink, bringing it closer to the denser, lower atmosphere in which it will eventually be incinerated. The climate change-induced contraction of the upper atmosphere will reduce the drag that debris experiences as it spirals toward us. This means it will stay in orbit for longer.

A recent , co-authored by Lewis, found that objects in low Earth orbit will stay up there for 30 per cent longer even if we restrict carbon dioxide emissions to successfully keep the global average temperature rise to 1.5掳C this century. On current mitigation pledges, way more CO₂ is heading skyward and we are on track for 2.7掳C of warming. This means the time junk stays up there will probably be even longer.

Out of space

As if all that doesn鈥檛 sound bad enough, we have also found a different way to clutter space 鈥� one that has arguably more profound consequences for people back on Earth.

named Starlink, owned and operated by SpaceX. Having multiple small satellites acting together or sharing orbital planes, known as constellations, isn鈥檛 a new concept. But the sheer number of Starlink satellites led to a new word, .

The rationale for constellations that can cover a large proportion of Earth鈥檚 surface might seem laudable. The European Union鈥檚 , for example, provides free information on marine pollution, deforestation, the movements of refugees, air quality and ice cap melting. California-based company . Both aid an array of experts, from academics to emergency managers.

Starlink satellites are one way to get internet access to many remote communities that don鈥檛 have it. 鈥淭here鈥檚 a lot of people in Northern Canada, particularly First Nations, who don鈥檛 have good internet,鈥� says , an astronomer at the University of Regina in Canada. 鈥淪tarlink is going to be a huge, huge advantage for them.鈥�

The problem is megaconstellation satellites are so bright and so numerous that they threaten to diminish our view of the night sky. 鈥淭hese satellites, on average, are about a billion times brighter than the faintest things astronomers can see,鈥� says , an umbrella organisation for several US-funded observatories.

鈥淥ur astronauts are going to be in danger of being hit by this stuff鈥�

Simulations show that with 65,000 satellites in the sky 鈥� a possible near-future scenario 鈥� this kind of light pollution would affect the entire planet. 鈥淭he stars will still be there, but you鈥檒l be looking at them through a grid of moving satellites,鈥� says Lawler. Even in once-shadowed parts of the world, the Milky Way and meteor showers could eventually be washed out. Satellites could even obscure our efforts to watch out for incoming asteroids that could kill all life on the planet (see 鈥�Asteroid watch鈥�).

The rush to space also has uncomfortable parallels with centuries of colonisation, where those with the least power suffered the most. Many Indigenous communities , such as for telling the time, for precipitating sociocultural or religious events and for wayfinding at sea. Even the potential benefits won鈥檛 reach everyone, as costs are too high for many internet-starved nations. 鈥淲e shouldn鈥檛 have to choose between having astronomy and having the internet,鈥� says Lawler. Starlink didn鈥檛 respond to a request for comment.

So how did we end up here, and what can we do about the growing downsides? The UN鈥檚 , humanity鈥檚 first attempt at legislating for activity in orbit and beyond, says space is an open realm that anyone can use. But the treaty, which took force in 1967, didn鈥檛 foresee the rise of private space companies or their constellations. Neither did individual nations. There are no internationally binding laws that apply to the operation of constellations. As long as satellites are doing what they are supposed to, governments can鈥檛 interfere.

People are taking matters into their own hands. Various groups are experimenting with contraptions that remove debris from orbit. , a project led by researchers at the University of Surrey, UK, has successfully trialled the capture of debris using spacecraft armed with and . In August 2021, Japanese firm Astroscale managed to recapture a small satellite it launched into space using another .

鈥淧eople are trying to survive, and so the skies aren鈥檛 on their mind鈥�

None of these prototypes are trying to capture real debris yet. If they did, they might be pulled along by the momentum of such objects and become another sizable piece of space junk, says Crassidis. Moving between orbital altitudes to capture lots of debris would also require more fuel than these missions are currently capable of carrying.

Most experts agree that space junk must be regulated on an international level. One option is for different altitude ranges to belong exclusively to different nations and private companies, which would cut down on collisions in the first place. But, politically, an international body that deals with this is difficult to envisage at present.

The future impact of megaconstellations appears just as disheartening. Scientists have held , with no agreement on what is best to do. One thing is certain: megaconstellations are here to stay. 鈥淲e have to accept that the landscape is changing,鈥� says , director of Lowell Observatory in Flagstaff, Arizona.

Software may eventually be capable of partially filtering out bright Starlink trails from telescope views, but this won鈥檛 be a panacea. Eventually, some astronomy done on Earth will , out of the way. But doing that for all observations would be prohibitively expensive. It would also be bad for science 鈥渂ecause for the same amount of money, we won鈥檛 be able to afford nearly as many telescopes鈥�, says , an astronomer at the Center for Astrophysics in Cambridge, Massachusetts.

Slow it down

Starlink has worked on dimming its constellation by painting the craft black and, during later launches, by adding asun-blocking visor. But 鈥渢here鈥檚 no way the companies can make the satellites faint enough to be invisible to research telescopes鈥�, says Hall. And even if dimming efforts continue to bear fruit, the staggering number of satellites will always present a problem.

Some think confrontation may be a better option. 鈥淲e鈥檙e not going to stop them, but we need to slow them down until we regroup grassroots community advocacy, in my opinion, that can partner with professional societies,鈥� says Venkatesan. 鈥淎nd we slow them down through lawsuits.鈥�

One legal challenge already in the works 鈥� based on an argument put forward by attorney Ramon Ryan 鈥� involves a law that requires agencies to assess if their future actions are going to cause environmental harm. Minor actions are exempt from this law. The Federal Communications Commission (FCC) 鈥� which satellites 鈥� has applied this exception to almost everything it does. This means Starlink launches are exempt, while satellites launched by NASA 鈥� another federal agency 鈥� do require an environmental review.

Viasat, a Starlink competitor based in California, has launched a court action to try to halt the approval of 3000 Starlink satellites until after an environmental review is conducted. The case is currently working its way through the US Court of Appeals.

Optimistically, the US may one day adopt strict legal mandates on megaconstellations and space junk. But who is to say that China 鈥� gearing up for its own And for the countries that do choose to legislate such actions in space, will the voices of their Indigenous peoples be heeded? History suggests not, but New Zealand provides a hopeful note in this regard. Every branch of the New Zealand government 鈥� including the Indigenous M膩ori communities before doing anything.

The sky can be saved, but the solutions aren鈥檛 simple. They involve everyone, from all walks of life, and the hourglass is nearly empty. As the covid-19 pandemic has shown us, when a global crisis emerges, 鈥渋t鈥檚 much harder to take action later鈥攁nd much more expensive鈥�, says Lewis. 鈥淵ou have to act when it looks like everything is fine.鈥�

Venkatesan worries that a confluence of multiple crises 鈥� the pandemic, climate change, racial inequality, gender disparities, erosion of democracy 鈥� may hobble efforts to salvage the starry night. 鈥淧eople are trying to survive, and so the skies are not on their mind,鈥� she says. 鈥淲ho wants to read about another crisis?鈥�

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