Oct 20 2008
Silent but deadly
I didn’t mean to leave my political post at the top for so long. Sorry, folks.
I was getting ready to go to Rome to present a paper and I hate to travel, so I was stressing some. As excuses go, it sucks, but there you have it.
Today, I want to talk about pollution. Before you roll your eyes (I know, too late), let me add that the focus will be on space pollution. Why?
That’s a very good question.
Space, even before we set forth in it, wasn’t exactly empty. Although it’s large so, the earth and the space of this solar system are constantly bombarded with a multitude of small impactors going very very fast. Most is ice and dust from comets and most are very very small but, since they impact at 20 km/s (or faster) they get a lot of bang in a tiny package. See kinetic energy is a product of mass and the square of the velocity. When two objects hit at a high relative velocity, that energy can either bounce off (changing the trajectory of both, though how much depends on relative mass) or it causes damage with the kinetic comparable to the kinetic energy lost, generally to both the impactor and the impacted item. How much depends on the materials and angles and a lot of other factors, but speed is really one of those factors.
To get a feel for the speed we’re talking about with micrometeoroids, a high speed sniper bullet can go on the order of 900 m/s. At 20 km/s, a meteoroid is going 22X faster, that’s 484X more energy for the same massed particle. Fortunately, most micrometeoroids are much smaller and less dense than a rifle bullet, but it means that tiny bits of dust can do considerable damage. (And, for some meteor showers/storms, like Leonids, velocity may be in the 70 km/s range.)
None of that, however, is manmade. Orbital debris, sometimes called space debris, is our little contribution to the problem. Orbital debris is bits of flotsam jettisoned or released from orbiting spacecraft, derelict satellites, leftover stages from rockets and fragmentation debris from many sources, including spacecraft that exploded, collided or destroyed. The good news is that the maximum possible velocities are less than meteoroid velocity (most low earth orbit impacts at 7-10 km/s), but that’s still 10X faster than bullets. It’s also the extent of the good news.
OK, there’s a little more. There are facilities worldwide that track larger debris. They’re always fighting for funding, though, and they are also limited to large debris, like those larger than 10 cm long (about 4 inches), which means we can generally track a dead satellite or rocket stage and usually track a discarded wrench, but not a nut or bolt we lost. We have other facilities that can “count” smaller particles down to a few mm in length. Note the difference though between counting and tracking. With tracking we know where a piece of debris generally is and can move out of the way (generally) if we need to. With counting, we have a snapshot of how much debris went over a counting radar at a given time and a given altitude. We might know some directional info and other data bits but we can’t say where that bit of debris we counted is three days later. We can’t get out of the way and we won’t see it coming.
And there’s a lot more debris up there than there used to be. Part of that is high launch rates and irresponsible practices, many of which are now curbed thanks to international efforts, like venting propellant tanks so they don’t explode and providing for deorbiting or moving defunct satellites to safe orbits so they don’t contribute to the problem. But those steps only help mitigate for satellites we send up from now on. They can’t undo the environment that’s already up there. Irresponsible catastrophes like the Chinese satellite destruction, with its rain of debris at high orbit, certainly don’t help.
In fact, there is a theoretical point where, even if we don’t send anything else up, the environment will get worse on it’s own. Once there’s sufficient debris up there that collisions cause debris to be created faster than it can decay away, it’s out of our hands. And several experts think we’re already there for some orbits.
There’s a lesson there for people who don’t think we really make a difference in our environment. Clearly, we can. It also means that, when we pollute our environment, we rarely think about the real consequences and, more frighteningly, may not be aware of the real impacts down the road for our carelessness. Global warming is an excellent example.
Of course, I’ve barely scratched the surface of useful tidbits on this topic (it’s fascinating). Here are some links of great places for more reading.
Don Kessler’s publications
NASA’s Orbital Debris office
Orbital Debris Quarterly
ESA’s ESOC
The orbital debris images from NASA really hit home the point.
What’s your opinion on basting the debris into the sun as some have suggested?
The problem with the debris is twofold.
One, it’s prohibitively expensive to go find each and every piece of debris and deorbit it (sending into the sun would take, literally, tons more energy and is only useful in cartoons with Superman). You have to have a probe that can find an item, rendezvous, install a propulsion unit to deorbit it and break away. Ideally, this debris cleaner would remove multiple items before deorbiting itself. But it’s a very sophisticated set of requirements and bringing up that many propulsive units - well, I don’t see it being practical except, perhaps for the very largest debris, if that.
The other problem is that small and very small debris can do serious damage and there’s no handy way to eradicate it. You can’t track it so there’s not searching it down. It’s estimated that, for a high velocity on-orbit collision, an item 1/1250th the size of the other can cause “total break up”. That means something only a kg in size can take out something the size of a car. But, debris much smaller can still do serious harm, like punching holes in manned modules or fluid thermal controls system, compromising thermal shields and taking out antennas or electronic boxes. The more collisions we have, the more smaller and harder to address objects there are out there.
I didn’t know this when I wrote this, but the International Association for the Advancement of Space Safety is honoring Donald Kessler (linked above) with an award for the efforts he’s made for space safety. One of the publications listed, I think, is a description of him fighting for taking the meteoroid risk seriously early in the space program.
There was a time when this got little notice, but it’s now a driving risk, for Station, for Shuttle and for Exploration. But I don’t know if it’s too late to solve the problem.
That can happen. I hope it isn’t and we have time to learn, to change our ways, but reality will be what is whatever we want it to be.
I don’t know for sure what reality is. I DO know it’s a real risk and we’ll be paying to protect our orbiting craft for some time because of it.
In theory, one could do that IF it were trackable and IF it were in the exact same orbit. In fact, the Shuttle has picked up a few defunct satellites or items that needed to be retrieved like the Long Duration Exposure Facility, which is, oddly, where we got a lot of data.
Unfortunately, most of the damaging debris we’ll never see until it hits. It’s too small to track. And what we can track is often at a different orbit or inclination. If the orbits don’t match, it can be coming by at km/hour. You don’t try to catch that. What the Shuttle and/or Station try to do is dodge it.
It’s the unmanned stuff that’s hard to move and prevent collisions. Unfortunately, when they hit, they rain down smaller debris that put even the manned spacecraft at risk. There is good news that the ISS was designed with debris in mind and can take a much bigger hit than the Shuttle. It needs to since it’s up there 24/7.
Fascinating stuff. Dangerous, too. Have you left for Rome yet? I hope you have a great time there! I’d love to see Rome–though I know the travel there is a pain.
Let me know when you get back!
Actually, I’m in Rome now, about to go to the conference’s gala dinner. One more day of conference, and I come back on Friday.
Why apologize? Rocket scientists have sense of humor too.
I had no idea there was such a thing as manmade space pollution. My conclusion is, inevitably, that if we can possibly screw something up, we will. *sigh*
Baron, I don’t object to people making mistakes. What bothers me is making the same damn mistakes over and over. I think we’re learning on this topic, though it would have been nice to clue in earlier. But, on other topics, like global warming, there’s a lesson and steps we could take today aren’t being taken. I don’t want us to end up having painted ourselves into another ugly corner.
Random, true, but we can be good, too. Admittedly, being good gets less press.