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Spec Tech: Space Debris

July 8, 2010

Every once in a while there a news station hears about some satellite collision or some rocket upper stage failure and, briefly, we are reminded about the problem of space junk. Over the last 53 years of humans launching objects into space we have gotten into the habit of leaving some extra pieces floating around. NORAD tracks tens of thousands individual bits of space debris through various optical and radio tracking techniques. There is estimated to be as many as 600,000 pieces larger than a centimeter.

Space Junk

Just what is all the junk? Wrappers from all that astronaut ice cream? Most is actually pretty benign: flecks of paint, or ablative material from rocket engines. There is some larger stuff in there too: loose bolts, empty fuel tanks, dead satellites, and even a bag of tools.

There are a couple of interesting implications for all this material floating around. Not too long ago I was talking to a friend of mine, Liz Argall, about a large alien ship approaching Earth. We were wondering how much it would interfere with our local ecosystem of communication and science satellites. And what about space debris? Luckily space is huge. Despite there being so much junk, there is also a huge volume that it occupies. And so the chances that a ship near Earth would get hit by anything is pretty low. Also assuming you have a ship large and complex enough to survive interstellar travel a few loose screws wont hurt it.

In fact it’s unlikely that anyone here would notice these collisions. There are reports of people seeing flashes on the Moon caused by meteorites slamming into its rocky surface. For a while no one believed the observations until someone finally caught an event on camera. Now we actually look for them. But these flashes are associated with heavy, solid objects hitting the Moon. A solid meteorite about a few inches wide can hit the moon with one Gigajoule of energy, the equivalent of about a quarter ton of TNT. But even then it’s pretty hard to see unless you are looking for it. Most space debris collisions are going to be nearly undetectable from the ground.

Dangerous future

So if alien space ships won’t cause to much commotion, what will? There is a theory call the Kessler Syndrome. Proposed by a NASA scientist in the 70’s it proposes that there is a critical density of junk and satellites at which point random collisions create more debris, which collides with more objects, causing yet more junk until all of low Earth orbit is unusable and all our communication satellites get destroyed. There is, of course, some debate about how likely of a scenario this is. But it is possible. As it stands the International Space Station has be moved a couple of times a year in order to avoid a “close call”. Being cautious is good. Still, actual collisions with any working satellite are rare.

Hopefully we’ll get to cleaning up some of the junk somehow. Proposed methods include a laser broom (heating one side of an object with a laser beam so that the hot side throws off material and slows down until if falls back to earth) or sweeper satellites built to collect the larger pieces and plunge them back to Earth (and safely burn up on re-entry). Luckily there is a natural cleaning mechanism—the Earths atmosphere. Below about 300km there is enough drag from occasional air molecules that light objects fall out of orbit in a few years.

4 Comments leave one →
  1. July 8, 2010 1:00 pm

    That’s for debris which is moving at orbital speeds. If you are really going to write SF about relativistic starships fighting, you are going to have to deal with the problem of relativistic debris from those battles. Imagine a chunk of material with a mass of even just one kilogram colliding with anything at 0.97c — 97% the speed of light. The kinetic energy of such an object is staggering.

    Orbital speed, 1kg object:
    ½mv² = ½(1.00kg)(8000 m/s)² = 32,000,000 J of kinetic energy
    (Of course, for an orbital impact, you have to consider the relative velocity between the two objects. Running into an object going in the same direction at 50 m/s is not the same as colliding with it in opposite directions at 16,000 m/s.)

    Relativistic speed, 0.97c, 1 kg object:
    (gamma)mc²=(4.113)(1.00kg)(299,800,000 m/s)²=369,700,000,000,000,000 J of kinetic energy
    This is some 11.6 billion times as much. If you have relativistic space debris running into you or your planet, it’s going to hurt. (grin)

    Dr. Phil

  2. Nathan Bergey permalink
    July 8, 2010 5:16 pm

    An excellent point! I was really just thinking about what humans have put into orbit around Earth, and that any kind of object near Earth is going to be at orbital speeds (unless they just want to “buzz the tower”).

    But relativistic travel is a whole other problem! Presumably a little piece of anything could do a lot of damage if it hit you going 0.97c. Do you have any suggestions as to how SF ships might avoid, deflect or absorb impacts of such magnitude?

    • July 8, 2010 7:52 pm

      My very first published story, The Gravediggers: “The dirty little secret of interstellar war: someone has to clean up the mess from a relativistic wreck. Radar Specialist Ken Walaciowski, newly assigned to the USFS Marabou, has no idea what’s in store for him or why his new radar can simultaneously track sixty-four billion objects.”

      It’s a thorny problem, but in terms of relative velocities, the pieces aren’t moving all that fast from the center of mass. So if you can catch the pieces early enough… You can vaporize the smallest pieces with lasers. If you access to a “graser” — a graviton laser-type device — you can attract and collect them with gravity. Or just send a bunch of automated space robots to go collect the bigger pieces.

      Gotta love that pseudo-Physics 29th century technology. (grin)

      Dr. Phil

  3. July 8, 2010 9:36 pm

    One word: Planetes.

    Of course, it’s unlikely we’d ever try to solve the problem by physically picking up the garbage, but the show was still pretty fun and it stuck extremely close to current science.

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