The very recent news about the bus sized asteroid that flew close to our planet, along with the wide coverage of the entry of the Russian probe (Phobos-Ground, sometimes translated as Phobos-Grunt) that was designed to sample the Martian moon Phobos, has brought a temporary interest to the subject of stuff falling on our heads from space. But is this a temporary concern, or is this a subject that we should pay attention to for the long term?
Actually it is a long term concern that people should be aware of, and potentially take action about. Not that we should go out and buy tin hats, but we can have our elected officials support changes that make us safer.
First some background: All man-made space items (that can reasonably be tracked) are watched by the U. S. Air Force and cataloged by them. All of these will eventually re-enter the Earth’s atmosphere. Fortunately, the Air Force predicts re-entry dates and locations as well as they can. We also have natural debris entering the Earth’s atmosphere, the Jet Propulsion Laboratory in California, among others in the world, tries to identify and track asteroids (some of which will hit the Earth) but that is a far more difficult task. Did you know that the common “shooting star” that people see at night is a piece of rock from space that is burning in the Earth’s atmosphere? It could be as small as a grain of sand or could be much larger.
In Houston, Texas, the Johnson Space Center has an Orbital Debris Program Office, they work with the Air Force unit in California that tracks satellites and they also try to educate people who launch rockets to help them minimize the number of space debris items that are created.
How does a re-entering satellite differ from an asteroid? We do have rocks as well as man made space debris of various sizes entering the Earth’s atmosphere all the time. Fortunately, the total affect of almost any entering man-made object would much smaller since satellites are traveling far slower than anything from deeper space. We hear more about satellites re-entering since we have far more warning of their impact. Asteroids seldom cause problems but they have created large craters such as the meteor crater near Odessa, Texas and a larger crater in Arizona. In contrast, re-entering satellites hit the Earth’s surface far more often but cause little damage.
Since these re-entries or man-made objects happen all the time, we need to understand that this is a normal event now. But by making some changes we can reduce the problem. For instance we can design rockets and satellites so we can steer them into the ocean at the end of their lives. We can design rockets so that they vent their fuel at the end of their launch phase, so the fuel does not react in space and potentially cause a breakup. Recently a science spacecraft was turned off and it will re-enter the Earth’s atmosphere in a few years. It could have been designed to be steered into the Pacific Ocean, where it would splash down harmlessly. For instance there have been many capsules that have been carefully steered to a precise entry, such as the recent Dragon test capsule made by the SpaceX Corporation. It did not have a crew and yet was steered to a specific spot so that it would be safe and could be recovered.