Steps to Countdown
Space Shuttle being moved toward the launch pad on the crawler

Many things must be done before a shuttle can launch.
The external tank being moved on a barge

The shuttle has many parts. They are made in different places in the United States. The finished parts are sent to NASA's Kennedy Space Center in Florida. The external tank is put together in Louisiana. It rides on a barge to Florida.
Train pulling three railcars containing parts for the Space Shuttle

The solid rocket boosters come from Utah. They ride on a train to Florida. The orbiter is the part of the shuttle that looks like an airplane. When the orbiter returns from space, it lands at Kennedy Space Center.
Woman inspecting tiles of the Space Shuttle

Sometimes the orbiter has to land somewhere else due to bad weather in Florida. Then it rides piggyback on an airplane to Florida. Before taking off at Kennedy Space Center, the orbiter gets a checkup. It may need repairs. It may need some new parts.
Vehicle Assembly Building

Then the orbiter moves to the Vehicle Assembly Building. The VAB is one of the largest buildings in the world. The external tank and solid rocket boosters are waiting in the VAB. NASA workers connect the orbiter to these parts. NASA calls it "stacking."
Space Shuttle on the crawler just before it reaches the launch pad

After all of the parts are put together, the whole vehicle is called the Space Transportation System. Now it's time to move to the launch pad.

The Space Transportation System rides on a crawler. The top of the crawler is as big as a baseball diamond. The crawler has tracks of wheels like a tank. It is very, very slow. It moves about one mile per hour on a road called the crawlerway.
People standing near a large countdown clock showing five seconds remaining

When the shuttle gets to the launch pad, NASA has more work to do before countdown. The shuttle may sit on the launch pad for weeks. This is the countdown clock. It tracks the amount of time until launch.
Space shuttle taking off

The astronauts get into the orbiter about 3 hours before launch. Everyone waits for the words, "3… 2… 1… Liftoff!"