We often think of environmental problems as something that only effects the natural world and things back on earth, but there’s a growing environmental problem in space, which could have very serious consequences if it isn’t contained. The issue of orbital debris from expired satellites and spent rocket stages, which is gradually building up in space, making operations in space increasingly difficult and dangerous.
A couple of weeks ago India was criticised for destroying one of its own satellites. This test produced a large cloud of debris (some 400 pieces) flying around the earth at twenty times the speed of sound (to put that in prospective that means a small 1g speck of debris has the same destructive energy as a 20mm cannon round!). This brought to the fore the topic of Kessler syndrome, whereby as the density of objects in orbit increases, then eventually the probability of collisions raises to the point where it becomes a near certainty. Which means one collision leads to another, which leads to more and so on, until eventually the earth is surrounded by a layer of lethal debris.
There’s currently 600,000 pieces of space junk up there already. And collisions between space junk and satellites does indeed occur (although its usually disused satellites in uncontrolled orbits). Every few months the space station has to change its course to avoid a dangerous piece of debris and it has been hit before (though fortunately not sufficient to cause a breach). The danger is that eventually this debris problem will build to a point where space operations become impossible.
One particularly worrying item of debris is the European Space Agency’s ENVISAT. This unexpectedly stopped working in 2012 (possibly an internal failure, as it was past its design life, but it could have been hit by debris). Now the trouble is that while most of the satellites were talking about are only about the size of a washing machine, or maybe a small car, ENVISAT is closer to the size of a school bus. Given the fact its in a relatively high and inclined orbit (meaning its going to take a long time to decay and fall back to earth, plus it crosses the path of many other objects on the way down) the odds of it being involved in a collision are rather high, as are the odds that this debris will go on to produce more collisions. In fact, the Europeans are so concerned about it they are already working on a mission to intentionally de-orbit ENVISAT.
This is really the worst case scenario. One large collision produces a large shower of debris, which unleashes a chain reaction of further collisions, creating a cascade. Hence the concerns over ENVISAT or the recent Indian missile test. The end result would be something similar to what’s portrayed in the movie “gravity”. The only real difference is timing. While in the movie such a cascade takes minutes, in truth it would take days, or more likely weeks, months or even years. But even so, the problem is that once the debris density reaches a critical threshold, there’s not a lot we can do about it. Like so many environmental problems, it reaches a tipping point and from that point onwards, the process becomes unstoppable. Hence a wait and see policy isn’t a good idea.
So, what would the consequences of this be? Well the satellites at most intimidate risk would be those in low earth orbit. This includes earth observation and remote sensing, weather satellites, spy sats, cell phones, various science experiments, most notably the Hubble space telescope. All of these services could quickly go down.
For astronauts in orbit how big a risk they are at depends on where the cascade starts. If it starts above them (e.g. ENVISAT), its going to take sometime for the debris to make it down to their altitude (its at about 800 km’s up, while the ISS is at about 400 km’s). Sufficiently long that they could potentially stay in orbit and missions to the ISS could continue for period. But if the debris cascade starts below them its more of a problem (hence the anger at the Indians), as they have to travel back down through the debris to safety. That said, debris at a lower altitude does decay and reenter the atmosphere much more quickly (so possibly they could try to ride it out).
Either way, beyond a certain point, it will be too risky to remain, meaning they’ll probably be eventually given orders to abandon the ISS. In theory, the station can be remotely operated from the ground, but not indefinitely. And the worse case scenario is that the ISS gets hit. Even if there’s nobody on board, the amount of debris that would generate would be enormous, its the size of a football field! And worse, while some of that debris would eventually burn up upon re-entry, not all of it would come down straight away, plus the danger is that any large part of it that do falls out of orbit in an uncontrolled manner won’t be guaranteed to burn up completely. When you consider that its orbit takes it over heavily populated areas such as the eastern US seaboard, central Europe, the middle east, Eastern India and SE Australia, you can see the problem. The decision might have to be taken to deliberately try and deorbit the station (effectively scuttling it) while it was over the Pacific.
So the immediate consequences would be, we lose certain vital satellite services and an end to human space flight for some extended period of time. Other satellites in higher geostationary, quasi-synchronous orbits or higher still, would not be immediately effected. This includes most long range communication satellites, TV signals and the GPS network. However, we’d only be able to communicate with them when they are directly overhead. Not a problem if you are the US and you’ve got lots of massive dishes all over the world, but a bit issue if you are China, Russia (or ironically India), as it means you can only talk to some of your sat’s at certain times of the day. You would be blind to what’s going on the other side of the world.
Furthermore, those satellites in high orbits won’t last forever. The typical life span of a satellite is about 5-10 years. So once enough of those satellites go down, we risk losing those services as well, unless replacements can be launched.
So while we won’t wake up one day to find that GPS systems don’t work (that said, some older GPS system DID stop working recently due to a roll over of GPS system dates), the long term implications are still pretty severe. We’d lose weather forecast data pretty much immediately, which is vital to the safety of aircraft, ships at sea, predicting renewable energy production and advising farmers on when to harvest/sow crops. Lost of satellite communications would cut off many isolated communities, notably in the far north. They’d literally go from one day being able to tweet instantly, to the most up to date information coming in on via sled dogs (limited to how fast the dogs can move).
And while GPS services would take sometime to fail, given the vital function they perform, the consequences of losing it would be fairly dire. And I’m not talking about motorists being unable to navigate to Starbucks for a caramel latte. I’m talking about ships and aircraft getting lost. Many of the alternatives, such as the Loran system of radio beacons, have fallen into disuse. Certainly all pilots and ship captains have been taught how to navigate by compass, map and Sextant. But we’re talking about having pilots and mariners digging up their college notes and relearn something they’ve not had to practice for years. And inevitably they’ll get it wrong.
Which means planes flying into mountains and ships ending up on the rocks. It means crops rotting in the fields due to unexpectedly poor weather, it means medical emergencies which go unanswered. Because in the era before we had satellites, this sort of stuff happened all of the time. So we’d be talking a minimum of several thousand extra deaths per year if we lose access to satellites. So this is kind of a big deal. Even if you think space travel is a waste of money, you might feel a bit different if all of these services were lost.
There are solutions to this problem. It is possible for example to armour a spacecraft to be resistant to debris. Such technology has been tested out in space, but only on smaller capsules (typically those on the way to the ISS or the ISS itself). Building entire upper rocket stages and satellites with such armour would make them heavier, delivering a smaller payload, which would make them more expensive to launch, which would probably limit the number of launches. So while I’d argue certain vital space services would be maintained, whatever the cost (for the reasons outlined above, we just can’t afford to lose them!), that’s pretty much going to swallow up the whole space budget and leave little money for anything else (such as crewed missions, or space science).
As for clearing the debris, some will fall back to earth by itself eventually. There are proposed missions to deorbit key satellites that pose a danger. And the introduction of several low cost launch vehicles (ESA’s Vega or Spacex Falcon rocket family) makes such missions a lot more viable. That said, such mission risk generating more debris (as they involve a further space launch) and if they were to fail, you’d risk making the worst of an already bad situation.The idea of reusable space launch vehicles and even refurbish-able satellites (using a reusable launch vehicle to retrieve them from orbit) is another option. Alternatively we just fit them with a “kill vehicle” that either deorbits them or pushes them into a graveyard orbit. However the problem with all of these options is that it requires some sort of recognised “authority” to enforce such rules. And space is kind of a commons, one that risks becoming another proof of the tragedy of the commons.
But the concern is that this all might turn out to be too little too late. Like I said, the problem with Kessler syndrome is that a wait and see policy will likely mean waiting until we are passed the point of no return. Only by taking action now can these problems be tackled.