Just why do the space craft have to re enter the aptmospere so fast?

If you slowed a spacecraft down you could come into the atmosphere very safely and land. The problem is that to orbit the Earth you have to go so really fast. Why? Well, first you have to understand a bit about orbits…

Here’s a simple way to think of how something gets into orbit around the Earth. Imagine a ball on a table. Now you push the ball and it rolls off the edge of the table. It lands on the ground near the table. Now you put it back on the table and push it faster – it rolls off the edge of the table but lands farther away. Now, say you pushed it so fast it landed a mile away from the table.

Keep in mind that the Earth is round… and now you push the ball so hard that it travels 100 miles. As it’s traveling along, you would see it “disappear” over the horizon. This is because the earth is round – and even though the ball falls toward the ground, the ground curves down away from the ball.

Now you can imagine pushing it so fast that it landed half-way around the world. Finally, if you pushed it so fast that the the earth was curving away from the ball the same amount that ball was falling – it would never land! It would just keep going around and around the Earth – it would be in Orbit. That speed is called “orbital velocity” and orbital velocity for the Earth is about 17,000 miles per hour – which is almost 5 miles per second! Now that’s fast.

It takes a lot of energy to get something going that fast. When you see the Space Shuttle take off it has that big orange tank full of rocket fuel for its engines and two additional white rockets attached to the sides of the tank. It takes all of that to get the shuttle to 17,000 miles per hour. Plus, it has to get high enough to get out of the atmosphere so there’s no drag to slow it down. Then, once it’s going 17,000 miles per hour, it can shut off it’s engines and just keep going around and around.

Then to land, it has to get its speed from 17,000 miles per hour back to zero. If they tried to do that completely with rocket engines, it would take just as much fuel to slow it down as it did to get it going! To haul that much extra fuel would mean the rocket would be to heavy to lift off in the first place.

Instead what happens is the shuttle turns around backward and fires two small engines (you can see them on each side of the tail of the Space Shuttle). These engines slow them down just a very small amount. But it’s enough that they start to get closer and closer to the ground. As they get closer, they start to hit the atmosphere. The atmosphere rubbing against the shuttle causes drag (friction), which causes them to slow down even more. Eventually, they are slow enough to land – this whole process takes about an hour from the time they fire the small engines.

Incidentally, when they first hit the atmosphere, they are moving through the air so fast, that the air rubbing against the side of the Shuttle causes it to get really hot, and this is why they need all of the protective tiles. It was a hole in of one of these tiles that lead to the destruction of the Space Shuttle Columbia in February 2003.

I hope this helps you understand why they have to being going so fast when then come in.