Steering Clear: The Science of Space Junk
Thursday, January 12th, 2012
By Theras Wood
The term “Space Junk” can conjure images of torn plastic bags and broken toasters floating about in the ether, but artificial orbital debris (a technical name for manmade space junk) is actually composed of anything from paint flakes to dead batteries. On second thought, space junk sounds like pretty innocuous stuff, even if over 6,000 tons of it orbits the Earth.
Late January 11, 2012, the International Space Station team was informed that a piece of Iridium satellite debris was being closely tracked near the ISS orbit. According to NASA, the size of the fragment is approximately 10 cm in diameter; a rather large object in the world of space debris. A day later, the ISS team was told to schedule a debris avoidance maneuver for Friday January 13, coincidently the same day the IMAX documentary ‘Space Junk 3D’ hits theatres. With the ultimate goal of bringing space junk out of the realm of science fiction, the makers of ‘Space Junk 3D’ want to put you up close and personal with the ring of the debris ― natural and manmade ― that encircles the perimeter of the Earth’s atmosphere.
Junk of a Certain Age
For over fifty years, space debris has been accumulating up to 22,000 miles above Earth. ‘Space Junk 3D’ hopes to educate the public on potential hazards and solutions to what it suggests is an increasingly volatile area. The film will include in-your-face accounts of space collisions and the colossal Meteor Crater in Arizona, USA (‘the best preserved crater on Earth’).
The Father of Space Junk
Donald J. Kessler, former senior scientist at NASA, and “Father of Space Junk,” lends his hand to the project by emphasizing the importance of protecting the Earth’s orbit and shining new light on this little-publicized realm of science. Kessler was the first to predict that the debris orbiting the Earth could lead to random collisions, creating increasingly smaller pieces of debris that could would into contact with operational spacecraft ― a process titled “The Kessler Syndrome”. The theory predicts that as the debris fragments repeatedly collide, they become increasingly smaller, culminating in rings of space dust around the Earth ― much like the rings of Saturn.
Look Up, Way Up
Space debris is studied using Space Situational Awareness, whereby scientists study what is in space, where it is in space, and where it is going. Analysts use the studies to predict collisions and issue warnings when two objects appear to be on the same path. The studies are called conjunction assessments. Associations like the Space Data Association (SDA) offer satellite controllers “automated warning alerts” based on these assessments, at which point satellite operators can move their spacecraft onto a safer course.
The Space Surveillance Network (SSN) is one such command centre that studies these phenomena, and one that ‘Space Junk 3D’ features. The movie posits that better tracking is needed, that accuracy is left wanting, and suggests that satellite owners share their satellite positioning with one another. The documentary also proposes that the Kessler Syndrome can be remedied by removing existing space junk ― a project that would involve chasing the objects at hypervelocity (7km/second), latching onto the object and pulling it out of orbit.
Beyond limiting the creation of space junk, the documentary suggests that there are a few methods (some in development, some currently being attempted) that can help with large space junk clean-up:
- Electrodynamic Tether: this method uses the Earth’s magnetic field by generating drag with a strong current, pulling the object back into the Earth’s atmosphere.
- Netting: Japan’s space agency is working on a method of netting objects out of orbit, using the Earth’s magnetosphere.
- Lasers: lasers would be used to strike small objects, slow them down, making them fall back into the atmosphere.
- Solar sails attached to modern satellites could be used once the satellite is no longer needed, in order to de-orbit.
What’s the Matter?
Currently there are over 11,000 pieces of orbital space debris greater than 10 cm in diameter in orbit around the earth, which are being monitored by the United States Space Surveillance Network. Another 100,000 objects between 1-10 cm are also orbiting, but elude monitoring due to their small size. It’s the impact from these small pieces of debris that cannot be shielded against or manoeuvred around. Many more millions of pieces, smaller than 1 cm, pose risks to operating satellites everyday.
The International Space Bubble
Depending on size, orbiting objects can travel at a velocity of 10 km/sec to 16 km/sec. As shown above, manoeuvring out of space junk’s way is possible, even for the football-field-sized ISS. Beyond slaloming space junk, the ISS employs shielding on high impact areas of it’s exterior. The shielding is made up of layers of material, with spaces in between so as to form concentric bubbles of protection.
The burning question, of course, is what happens if it falls? Could you or I be hit by space junk gone rogue? Well, theoretically, yes. Fortunately for us, most space junk that falls out of orbit is burned up in our atmosphere and only a few pieces ever make their way to the ground. Even then, the risk is only one in a trillion that we would ever be injured. What’s more, according to the NASA website, there is only one known case of someone being struck by falling space junk, and that person was never harmed. We like them odds!