Combustion Science Experiment

The Shuttle Tragedy

I thought for quite a while trying to decide how appropriate it was to do an experiment about this week's shuttle tragedy. I have received several science questions about the news coverage, and I thought it was something that people would find interesting. I worried that it was too soon, that all of you would still be too sad to be interested in doing a science experiment about this terrible event. Then I remembered that the people who lost their lives were scientists. They dedicated their lives to the wonders and joys of science. Once I realized that, I knew that it would be OK.

The most common question I have received is about the debris from the shuttle. On reentry, a shuttle experiences tremendous heat. That is the reason for the special tiles. Some of the pieces of debris that have been found were materials that would be quickly destroyed if exposed to that much heat. How did those materials make it to the ground without burning up?

To investigate that, you will need:

• paper
• a ball

First, lets look at what causes the tremendous heat that the shuttle encounters as it enters the atmosphere. Many sources say that it is due to friction with the air. Rub your hand together quickly and you will feel some heat produced by friction. While that sounds good, actually the heating of the shuttle (and objects such as meteors) is due to the air in front being squeezed. When air is compressed, it gets hotter. The next time that you add air to the tires in your car or pump up a basketball, feel the valve stem as soon as you finish. It will feel quite warm. The more you squeeze the air; the hotter it gets.

The shuttle is traveling very fast as it enters the atmosphere. It is pushing its way through the air. If you have ever held your hand out the window as your car drove down the highway, you have felt your hand pushing through the air. The same happens with the shuttle. Some of the air is pushed aside, and some of the air is pushed ahead of the shuttle. This squeezes the air in front. The faster an object is moving; the more the air in front will be compressed. The more it is squeezed; the hotter it gets. With the shuttle, it gets up to over 2300 degrees F (1260 C). This hot air then heats the parts of the shuttle that are pushing against it.

There is a good side to this though. As the shuttle pushes and compresses the air, the air pushes back on the shuttle, slowing it down. By pointing the nose of the shuttle upwards, the entire bottom of the shuttle is pushing against the air, making a very effective braking system. The down side is that the entire underside of the shuttle gets VERY hot in the process. Special tiles are used to protect the shuttle from that tremendous heat.

This Saturday morning, something went terribly wrong. We do not know what yet, but scientists hope to use the debris from the shuttle to help figure it out. How could that debris survive the tremendous heat of reentry? Why didn't it burn up?

Go outside and find an area where you have plenty of room. Pick up a ball and throw it across the yard. Be sure not to hit anything breakable, such as windows or younger brothers. Notice how far the ball went. Now pick up a sheet of paper and throw it just as hard as you threw the ball. Did it go as far?

No. The paper was slowed very quickly by the air ahead of it. As the paper pushed against the air, the air pushed back to slow the paper, just as it does with the shuttle. The paper has a large surface, so it pushes against a lot of air. It is also not very dense, so it does not take much of a push to slow it down. The ball is a lot denser, so it takes a lot more push from the air ahead to slow it down. It is also round, so it has less surface area in front and less air to push out of the way. If you crumple the sheet of paper into a ball, it will go farther, although is still does not go nearly as far as the ball.

Light debris with a large surface, such as the uniform patch that was found, would be slowed quickly, just as the paper was. That would let it reach the ground without burning up. Also, these less dense pieces of debris would not travel as far, just as your bits of paper did not travel as far across the yard as the pebbles. It is important for the investigators to know exactly where each piece was found, as that location could help figure out what happened. If you are in the debris area and you see something that might be a piece of the shuttle, please leave where it is and report it immediately.

Have a marvelous week.

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