Ask ARSE makes its triumphant return with a question about space debris...
And where it's headed.
"Hey guys Marc here. I was watching a Starlink launch on Facey and realised I dunno what happens to all the space junk when we're done with it? Cheers guys keep up the good work."
Thanks for the question, Matt.
And a very good one at that.
First off, what is space debris?
Debris is usually one or more of the following:
- Derelict spacecraft and upper stages of launch vehicles
- Carriers of multiple payloads
- Debris released during spacecraft separation from the launch vehicle
- Spacecraft or upper stage explosions or collisions
- Solid rocket motor effluents
- Tiny paint flecks released by thermal stress or small particle impacts
There are more than 22,000 objects larger than 10cm currently being tracked by the U.S. Space Surveillance Network. While 1,000 of these are operational spacecraft, that means 21,000 pieces of debris are zooming around Earth at 29000 km/h that can cause catastrophic damage to spacecraft.
The height of space debris in our orbit is the biggest factor for space debris. Take the ISS for example. Anything that comes from the ISS - old equipment, supply tanks, tools, chips of paint/insulation - will hastily reenter the atmosphere like a post-beer curry. Anything under 600km will normally fall back to Earth within a few years.
The stuff in higher orbits is a different story. Higher orbits are above 1,000km and are expected to orbit for about 100 years or more. Debris here is exposed to less drag from our atmosphere because the higher they are the less air.
When satellites in geosynchronous orbit retire, they're pushed into a zone called a "graveyard orbit" which is exactly what it sounds like. Graveyard orbits are used when the change in velocity required to perform a de-orbit manoeuvre is too large.
It's just easier.
Debris in a graveyard orbit is expected to stay out of the way for about 4,000 years. A bit optimistic as orbits can be altered by outside forces that can lead to collisions and new paths for the debris.
The big question everyone wants to know is, "Does it ever disintegrate?"
Well, yes. Everything disintegrates eventually due to drag. Objects disintegrate in orbit from collisions as mentioned, micrometeoroid impacts, thermal expansion and contraction, over-pressurisation, malfunctions to name a few. All of these play some role in the wear and tear of artificial debris.
Heck, even a Chinese space-based weapon might do it for you.
Question numero dos that often follows is, "Is space debris a problem?"
In short, yes.
Below is the amount of debris that is being tracked by the ESA, although not to scale.
It's important to remember images like this are NOT representative of size. Some of these chunks look like the size of Hawaii. This is an overstatement and doesn't add to the real credibility of the debris issue. Debris is often time spreads hundreds - if not thousands - of kilometres apart.
For every debris collision, there's a shotgun blast of shrapnel with smaller objects taking their place. Plus they're on a new unpredictable course and potentially headed for spacecrafts/stations.
This creates a give-and-take. Yes, the likelihood of said debris colliding with another object is higher. However, it lowers the amount of potential damage as the debris is now smaller.
The below image is a 7mm-diameter circular chip in an ISS quadruple glazed fused-silica and borosilicate-glass window.
The culprit was allegedly a paint fleck, no more than a few thousandths of a millimetre across travelling at 34,500 km/h.
We mentioned earlier how 10cm diameter debris can be catastrophic to spacecraft. Now you see why.
Thankfully the ISS is can be (and routinely is) moved out of the way of any incoming debris sharing its orbit.
The third most pressing question about debris is, "Will it ever get cleaned up?"
At least, not for the foreseeable future which seems to be focussed on creating more debris.
The only way debris is getting cleaned up at this stage is by reentry and burning up in our atmosphere. But the chances of graveyard orbit debris doing that is low. Because it was too much effort to drop it back into our orbit in the first place.
Still, others have tried and failed (to get funding) at resolving to get a plausible means of debris extraction. As we mentioned earlier, debris is spread out over a vast amount of space dozens of times larger than Earth.
We don't have a colossal street sweeper, a magnificent magnet, or a super vacuum to clean up adjacent space. Mostly because if anything touches the debris and gives it velocity (without matching its orbit and speed) will cause another impact and send the object hurtling away.
Instead, space agencies like NASA and the ESA work with common agreements that reduce the amount of debris permission, After all, you don't have to clean the mess you don't make, right?
An example is making sure fuel tanks are run dry or vented so they don't burst from sunlight rapidly expanding them.
But the inevitable truth is it is a major issue. Some are not adhering to the agreements and, sadly, it will get worse before it gets better.