Of the many daily deadly threats to life, one you are least likely to think of is space debris. But be warned: some of it crashes through Earth's atmosphere, while other bits pose a risk to your future life in space.
A graveyard orbit sounds so peaceful, doesn't it? Just imagine: you, as a decommissioned satellite, up there in a geosynchronous or geostationary orbit, not so much pushing up the daisies as just floating about.
You would be about 35,000 kilometers (22,000 miles) above Earth. Out of sight and out of mind. Or so you would think.
Increasingly, though, dead satellites are very much on the minds of scientists. And some of those scientists have the higher orbits in their sights, because just as with people, when we die, satellites have a tendency to decompose. When satellites decompose, tiny bits of paint or other components can drift back down to the more congested lower orbits and potentially cause all manner of problems.
It's not just the dead ones either. In June, a geostationary communications satellite, called AMC-9 lost, lost contact with its operator, SES, and then apparently started to fragment. It may have been hit by space debris, but SES has yet to confirm.
One launched every minute
We still don't really know how to capture and dispose of all the exiting junk. But we keep sending new satellites into space, one-by-one, two-by-two, and soon for massive constellations.
There are about 750,000 objects larger than 1 centimeter orbiting Earth - big enough to have the impact of a hand grenade
To add to that, there's a debate whether it's better to keep sending junk farther out into space, into those graveyard orbits, or whether it's better to let it all burn up in the Earth's atmosphere, so it's gone for good.
"If everybody puts their debris in a graveyard orbit, eventually the graveyard orbit will fill up," says Louis Wei-yu Feng of the University of Cape Town. "That debris is not going away, it's still there, it's just not in an operational zone. So personally I think it's better to get rid of it, rather than put it away and worry about it later."
Wei-yu Feng is working on a device called Medusa, which uses a shape memory alloy to capture objects of about 10-20 centimeters in diameter. Space debris that small can do a lot of damage in space – even tiny fragments can rip holes like grenades into spacecraft.
"What's important about space debris is that our lives are very connected to space technology," says Wei-yu Feng.
Think GPS and other global positioning systems, like Galileo or GLONASS, your favorite TV channels or constant communication, Earth observation and weather forecasts. All these things are connected to satellite technology.
"Space debris is a threat to those space assets," says Wei-yu Feng. "And when debris hits an operational satellite it's almost certain the thing will break into pieces."
The death star awaits
Modern satellite technology has inbuilt mechanisms for deorbiting after the end of its operational life. There are other devices, like nets, harpoons and tethers that are being developed to drag derelict satellites out of any given danger zone – they would be made to decelerate and burn up in the Earth's atmosphere.
But there have been no successful tests in space, so these are all just ideas.
On the flipside, there's another idea to yank dead satellites farther out to a final resting (or rusting) place at a "Terminus," like the final stop.
The concept is called Necropolis. It would involve a "Hunter" spacecraft rounding up derelict satellites that pose a threat in the geosynchronous environment before transferring them to the Terminus, which would be higher than a graveyard orbit.
There, they could be stored under control for something approaching eternity. Satellites could even make their own way to the Terminus when their operations end.
And once a Terminus is fully stacked, you could conceivably attach more to it. And in the end you might form a massive "death star."
"If you put all of the dead satellites in one location then they can't collide with each other or anything else, they would be in a permanently known location, where they can't be a hazard for future space missions," says Roger Longstaff, a consultant with Guest Associates (Europe). Longstaff has been working with Mark Hempsell of Hempsell Astronautics on the Necropolis idea.
Longstaff says geostationary orbits tend to be "ignored because the perceived risk is much lower," and then he goes on to say he thinks the risk may higher in GEO, and the graveyard orbit there is itself becoming a risk.
"It is the most valuable orbit, there is a trillion dollars worth of satellites up there and if we make a mistake and there is a cascade [of space debris collisions] in geostationary orbit, it is there forever," says Longstaff. "There is no air drag to bring anything down."
Put it on the back burner?
Yes, the satellites in GEO are expensive, but then when has anything in space been cheap?
But perhaps there's more focus on low-Earth orbit (at an altitude of about 160 to 2,500 kilometers) because far more satellites orbit there, and that at much higher velocities – a difference of 500-800 meters per second in GEO as opposed to 10 kilometers per second in LEO.
"When you have objects hitting at 10 kilometers per second, your spacecraft begins to act like fluids," says Dr. Darren McKnight of Integrity Applications Incorporated. "When they act like fluids they break up into smaller pieces. There's a hypervelocity in the material and the objects will go through each other and produce two clouds. Both act like fluids as they break up, and you get a lot more debris."
Meanwhile, in geosynchronous orbit, McKnight says "luckily everybody is on the merry-go-round" – a well-known figure of eight. Some of the objects have velocity, but it's like a conga-line.
"All the dead stuff on the figure of eight sinks up. It all goes up together and all goes down together. They don't pose a risk to each other, they only pose a risk to the operational spacecraft on the merry-go-round," says McKnight.
Which is still a risk. Wouldn't it be better just to deal with it? Do what we do with junk on Earth: bin it.
"Well it goes both ways, it depends on where your chaser spacecraft goes" says Wei-yu Feng. "But personally I think going to a lower altitude and letting it burn up is better than taking it somewhere else and letting it pile up."