 We have a go for landing and start. Five, four, three, two, one, zero, booster ignition, and lift off of Columbia. A new decade of spaceflight begins. The first one, it is one, it's the cake. Yeah, you're off. Thank you, touchdown. We board the Space Shuttle Atlantis 280 miles above the Earth. It's a busy time up here right now. Two of our crew members are preparing for one of space travel's most exciting adventures, spacewalking. At NASA, spacewalking is known as extra-vehicular activity, but most of the time, we just call it an EVA. EVAs allow us to do a lot of useful things in space. We can do many interesting experiments in the payload bay and test new types of equipment. We can also spacewalk out to an orbiting satellite to work on it. But doing an EVA involves a lot more than just opening the door and stepping out into space. EVAs take us into an environment that's entirely different from the one we live in on Earth, an environment that's hostile to human life. That's because space is almost a perfect vacuum, and that presents us with several problems, that take a good knowledge of science to solve. The first problem is no air to breathe. The sun poses another problem for spacewalkers, because in space, there's nothing to protect us from as harmful ultraviolet radiation. The radiation from the sun also affects the temperature in space. In direct sunlight, the temperature can soar to over 120 degrees Celsius, more than hot enough to boil water back on Earth. But when we get away from the sun's rays, the temperature can drop to minus 100 degrees Celsius, far colder than Antarctica in the dead of winter. Space debris is also a problem. So what makes the environment on Earth and the environment in space so different? The answer is Earth's atmosphere. It is a dense mixture of nitrogen, oxygen, carbon dioxide and water vapor that surrounds our planet and makes life possible. The atmosphere filters out harmful radiation and protects us from debris flying through space. As it moves over the Earth's surface, it distributes heat from the sun and balances the temperature around the world. Think of the atmosphere as an ocean of gases. When we're on the surface of the Earth, it's like being on the bottom of this ocean. Like the seawater, all of the ingredients at this atmospheric ocean have weight too. We measure this force as pressure. This pressure pushes against us in all directions, but the pressure can also change. Imagine that Jay and Jerry are on the Earth's surface. We'll put Jay in a dive suit and send him to the bottom of the ocean. On the ocean floor, Jay is under tremendous pressure. But as he starts back toward the surface, the pressure decreases. When Jay reaches the surface, he's still under a small amount of pressure. That pressure is the weight of the atmosphere, and we call it atmospheric pressure. Now watch what happens when we put Jerry in a space suit and send him up to the shuttle. As he rises through the atmosphere, the pressure continues to decrease until he's in the near perfect vacuum of space. There's no longer an atmosphere, and there's no longer any pressure. Luckily, I was wearing a space suit during that demonstration, or I would have been in big trouble. Let me show you what I mean. Imagine that this balloon is my body and the water inside is my body fluids. We'll put the balloon in a jar. Now we're going to pump all of the air or atmosphere out of the jar so it will be similar to the vacuum of space. Look what's happening. As air is removed from the jar, the balloon swells and the water begins to boil like a soda pop. That's the same thing that would happen to me if I didn't have on a pressurized suit. Where did pressure suits come from? Aviation pioneers like Wiley Post were among the first to use them. That's because those pilots who wanted to fly at high altitudes had to come up with a way to take their environment with them. Early pressure suits came in all shapes and sizes. And although most of them were stiff and hard to move around in, they laid the foundation for the suits we'd later wear into space. Roger, zero. We know that space is a vacuum and we're going to have to take our environment with us when we go EVA. So let's build a spacesuit. First it's going to get pretty hot in the suit after we've been working for a while. So we need a garment laced with small tubes. Now we can flow chilled water through the tubes to cool us off. On top of that, we place a garment that creates the pressure we need and holds in oxygen for breathing. Now we need something to protect us from the extreme hot and cold of space and protect the entire suit from tearing and from tiny meteorite impacts. We will use many layers of thermal insulation covered by a tough layer of white fabric. Let's give ourselves a helmet to enclose our head and we'll include a visor to protect our eyes from the sun's ultraviolet radiation. On the front of the suit, we'll put a console with some valves and gauges we'll need. Everything else we'll need, like oxygen tanks, pooling water, batteries and a radio, we'll put in a backpack called the Primary Life Support System. Donning the suit is just a matter of putting on the pants, just like I'd put on a pair of jeans. Then slipping into the top and locking the two halves together at the waist. Next come the gloves and finally the helmet. I've also got some tethers to keep me from floating off and this wrist mirror so that I can read the dials on my life support system. Putting the suit on is not the only thing Jay and Jerry have to practice. They also have to practice working in the suit and that's done here at the Weightless Environment Training Facility or WETF. This big swimming pool holds almost half a million gallons of water. That's big enough to hold a full-size mock-up of the Orbiter Payload Bay. Scuba divers are adding weights to Jerry and Jay's suits to make them neutrally buoyant. This means that they won't float to the surface or sink to the bottom. The WETF isn't the perfect simulation of weightlessness but it's the closest we can come to on Earth. We spend a lot of time in the water practicing until it's time for the real thing. In the next few hours Jerry and Jay are going to experiment with new ways of moving people and equipment around in space. In the future we'll be going EVA to service satellites in orbit and to help build space station freedom. Beyond that people will work on the moon from permanent lunar bases and even explore the surface of Mars. The space suit has a big role to play in our use and exploration of space. And as new challenges come our way we're going to develop better suits but no matter where the EVAs take us one thing will always remain the same. As long as humans venture into space we will always have to take some of our environment with us.