Low-Earth orbit is a rubbish dump.
In 1983, a speck of paint moving at 6km/sec smashed a window aboard the Space Shuttle Challenger. In 2009, Kosmos 2251 ploughed into Iridium 33 at a combined speed of 42,120km/h. In 2021, International Space Station astronauts piled into their lifeboat as a debris cloud from a deliberately destroyed satellite passed around them.
The 2022 International Space University Adelaide Conference on Space Junk defined the exponential growth in orbital debris as one of the greatest challenges of the century. The cultural, legal, political and economic implications are enormous.
There are 30,000 objects being tracked in low-Earth orbit. Tens of thousands more are too small to be seen. And the junk just keeps piling up.
Rockets are launching at an increasing rate, carrying hundreds of new satellites into orbit every month.
Within a few short years, most of these will be dead. But they’ll still be taking up valuable space in the narrow orbital lanes above our heads as collision risks.
That’s bad for business. And bad for everybody.
Which is why the ISU Space Junk conference addressed what’s being done about it.
Satellite funeral plans
Until now, it’s mostly been a matter of fire-and-forget for space entrepreneurs.
Why bother putting an engine on your satellite to de-orbit it once it dies? That only takes up weight and space. And costs money. That’s a triple blow to the balance sheet.
But what goes up and doesn’t come down will hang around, and become a problem.
That means not having an engine has itself become a risk: Can your satellite dodge all that junk? Will it be destroyed before turning a profit?
Astroscale chief engineer Gene Fujii told the conference that regulation and economics would have to play a part in solving the space junk problem.
“We’re having discussions with commercial operators to get a business model together that’s both sustainable and affordable for them,” he said.
One such idea is what Astroscale calls an “end of life” service.
It seems simple enough. It involves producing small docking plates that can be attached to satellites. These make it possible for an orbital garbage truck to grapple them.
Then there’s the prospect of providing a kind of roadside assistance in orbit.
“What if you don’t need to launch another satellite to replace an old one? Finding a way to use what’s already there helps with sustainability,” he said.
This will involve subscribing to a service and fitting future satellites with suitable access components. But existing debris, such as rocket bodies and old satellites, don’t come with docking facilities.
The alternative? Magnets. Harpoons. Nets. Towlines. The pros and cons of numerous options are being explored and tested.
In January this year, China’s SJ-21 satellite was observed pulling the disabled Compass G2 (Beidou) navigation satellite out of a heavily trafficked piece of geosynchronous orbit.
Cleaning up our act
Chief scientist of Adelaide-based Neumann Space Paddy Neumann told the ISU conference that orbital objects retain value – even if inert.
“When it comes to everything in space, someone has spent thousands of dollars per kilogram sending it up there,” he said. “It has value just for that. If you can reuse it, that means that’s mass you don’t have to bring up again from Earth.”
That’s good business. Not to mention mitigation of the associated mess of cultural and legal issues.
“You can use that mass for more communications and transponders for your comms mission, a larger lens for your Earth observation mission, more life support for your people – all these important things.”
At the core of his proposal is recycling space junk as fuel. His team is developing a pulsed cathodic arc propulsion system. Put simply, it uses physics similar to an arc welder – with the plasma it produces directed as thrust.
A demonstrator is due to go into space later this year.
“Where this all comes together is the fact that we can use anything solid and conductive as a propellant,” he said. “This includes materials such as aluminium, titanium, magnesium, steel – all the various materials used to build spacecraft. Since they’re already up there, we can use recycled and repurposed junk as a fuel and thus help to propel junk-hunting spacecraft to the next job site.”
Neumann Space is working with NASA and CisLunar to prove that this recovery, refining and refuelling process is viable. In this case, the experiment will focus on 6061 aluminium – the most common material in spacecraft construction.
And the waste?
“The metal gets burnt down into basically a gas, and it becomes very, very tenuous very quickly,” he said. “So you no longer have a problem.”
This really is rocket science
Whether you are talking grappling hooks, nets or satellite tow trucks, one challenge is common to every space junk clean-up idea: rendezvous and proximity operations (RPO). That’s the ability of a recovery satellite to match orbit with a target and then compensate for any erratic tumble.
The first hurdle is figuring out what challenges any recovery attempt will face.
Sydney-based HEO Robotics co-founder Will Crowe told the conference that every object would need careful inspection. That’s a lot of work.
And that’s why HEO Robotics is putting small cameras on satellites that wouldn’t usually have them. It’s also commandeering satellite cameras when they’re otherwise not in use while passing over oceans. These then take high-definition snapshots of passing objects – be they live spacecraft or debris.
“We’re using 25 already. So we’re able to tell things about those objects,” Crowe said. “What is its size? What is it made of?”
Even this basic information is often unknown. Earth-based records are often misrepresented, he said. This is because of efforts to protect national and commercial secrets.
“We’ve got one example of a rocket body that was launched by … we won’t name any names, as sometimes it’s a bit of a sticky issue as to who’s doing what in space. But this rocket body is actually twice as long as it was reported upon launch.”
Other issues are less sinister. What’s its altitude? What is its spin rate? Is it damaged? How fast is its orbit deteriorating?
“So it’s essential to do these assessments before you go in with a really expensive, active debris removal spacecraft,” he told the conference. “It’s not just about removing debris after a satellite becomes debris, but also to help customers understand what’s happening to their satellite so it doesn’t become debris in the first place.”