Bullets in orbit: can we fix the danger of space junk?

Back in the 1960s a young NASA aerospace engineer called Donald Kessler had a worrying idea. 

Kessler was studying asteroids. He noticed that when these giant space rocks crashed into each other they created a whole heap of smaller rocks, which in turn crashed into each other and created more rocks – a kind of self-perpetuating domino effect.

He realised it was just a matter of time before the same thing happened with satellites. Only, those collisions could be more disastrous.

While the asteroids were crashing around between Mars and Jupiter, the satellites were in what’s called ‘low Earth orbit’, starting just 200km from our planet’s surface.

At the time, the world's space programme was in its infancy. But Don Kessler and a colleague predicted the first collision to damage a satellite would happen sometime between 1989 and 1997.

Their estimate was pretty much spot on – a French spy craft was hit by a piece of an Ariane rocket in 1996. Then in 2009 there was a far bigger crash between a Russian Kosmos satellite and an American Iridium.

Both were destroyed, and more than 2300 trackable fragments were generated.

The domino effect had started.  

Wandering bullets

Dr Laura Pirovano is an ‘orbital dynamics specialist’; until last year she was a postdoctoral researcher at Te Pūnaha Ātea - Auckland Space Institute and her job involved finding and tracking space debris. 

It’s a crazy-difficult task, as she explained to Nikki Mandow for the fourth episode of Ingenious, the University of Auckland’s new research podcast.

“There are roughly 5000 active satellites in space, and there are more than 30,000 large bits of debris that we know of – pieces of satellites damaged as the result of a collision or an explosion,” Pirovano says. 

“But if you go smaller, if you go below one-centimeter size, there are estimated to be more than 130 million pieces.” 

A one-centimeter diameter piece of debris – something the size of a large blueberry – doesn’t sound like it's too dangerous. But travelling at between seven and eight kilometres a second (that’s 25 times the speed of sound), this little hunk of metal could completely destroy a satellite, Pirovano says. 

NASA has had to replace windows on space shuttles because they’ve been broken by flecks of paint travelling at enormous speeds.

“These tiny, tiny objects are basically just wandering bullets.”

Don Kessler argued that once started, the snowballing impact of satellite collisions causing debris and then more collisions and more debris, would be hard to stop. The process became known as the Kessler Syndrome; taken to its extremes, space junk whizzing out-of-control around lower Earth orbit could ultimately make sending satellites into space too risky.

Some scientists believe we are already in that era of the Kessler Syndrome; some say that we are approaching fast.

And that could be catastrophic, says Dr Priyanka Dhopade, a specialist in space sustainability at the University of Auckland’s Faculty of Engineering and Design. Because these days, the data we get from satellites is used for everything from internet services to weather forecasting, from environmental monitoring to gathering information on global ship movements for economic decision-making.

And uses for space will only increase, she says.

“Space junk is a pressing issue. If we are going to build space stations or labs in orbit, we need to be able to dodge this sort of debris.

“The worst case scenario is Earth’s orbit being completely crowded and polluted with debris, because that risks everyone's access to space.”

Globally, scientists are adopting a three-pronged approach to avoid space catastrophe.

Monitoring, like that carried out by Dr Laura Pirovano and her team, aims to find and track as many bits of space junk as possible. If it looks like one of the tracked pieces is heading for an active satellite, a quick alert makes sure the satellite’s owner can move it out of harm's way.

The second prong involves technology that can locate and capture derelict satellites – either pushing them into a lower orbit (where they re-enter the earth’s orbit and burn up), or moving them into  “graveyard orbits” where there isn’t much other traffic.

Several global companies are working on that problem, but it’s slow-going.

Bolt-on deorbiting tech

The third prong in managing space junk is making sure new satellites are designed so they move out of crowded orbits at the end of their mission. And that’s another area where the University of Auckland is making waves – or rather sails.

Dr Ben Taylor is a senior research fellow at the Space Institute, and co-founder of Frond Space Systems.

The spin-out company has designed a drag sail – something like a large kite – which can fold up into a small box and is attached to a satellite before launch.

Then at the end of the satellite’s life, the box opens, the sail unfolds, and its surface area creates a drag on the spacecraft, enough to pull it into the earth’s atmosphere, where it will burn up.

“The idea behind this system is you accelerate a satellite’s deorbiting lifetime, so we're not adding to the amount of debris that's up there. This is designed to bring stuff down within five years, but ideally, within a year or so.”

Frond recently made its first commercial sale – a drag sail system for Gilmore Space, the Queensland company aiming to launch Australia’s first commercial rocket into space. 

Taylor and his team are also in final testing to put a drag sail onto the Space Institute’s own CubeSat satellites, the first of which is due for launch in the middle of the year.

“We're demonstrating it on our first CubeSat here. But actually the technology can be applied to any spacecraft within a certain range of altitude and mass.” 

There’s also the potential in the future for the drag sail to be retrofitted onto a spacecraft, Taylor says.

“In our initial phase, we're looking to make sure it's attached prior to launch – you can bolt it on quite late in the day. But we are also looking at ways we can attach these things to debris objects already in space.”