How can floating underwater mimic the zero gravity condition of outer space? - Samantha Zhang, age 10
Going into space is hard. Really, really hard. Astronauts work with some of the most complicated and expensive technology ever made, in an environment that's both highly dangerous and completely unlike anything they're used to. If you make a mistake on a space station hundreds of miles above the Earth, you might not get a second chance to make things right. Before going into space, you have to make sure you can do every part of your mission perfectly, 100% of the time, and that means practice, practice, practice.
Unfortunately, there’s no easy way to train for space travel; outer space is (literally!) like nothing on Earth.
One of the hardest things to train for is weightlessness. Although there is gravity in outer space, astronauts in orbit don’t feel it in the way most people do: on Earth, the force of gravity pulls us down towards the ground, and the ground supports us by pushing back upwards. Astronauts in space are in unsupported freefall: although gravity is what keeps them in orbit, relative to their surroundings, they are “weightless.” (Weightlessness in orbit can be a little confusing: this video gives an okay explanation. The important thing is that there is gravity in space! Astronauts don't feel that gravity directly, but without it, they wouldn't stay in orbit around the Earth!)
|The size of the Neutral Buoyancy Lab (from oceaneering.com, which employs most of the divers who help at the NBL)|
NASA’s Neutral Buoyancy Lab is a way of simulating weightlessness on Earth. An object that floats in water is called “buoyant”; depending on their density, most objects simply float (positive buoyancy) or sink (negative buoyancy). But if you adjust the density of an object very carefully, it neither floats nor sinks; it has “neutral buoyancy,” and stays put in the water at any position. Astronauts training underwater are wearing specially weighted suits that make them neutrally buoyant, so they hover just as they would in space.
Inside the giant pool at the Neutral Buoyancy Lab are life-size models of the parts of the International Space Station or Hubble Space Telescope that astronauts will work with. An astronaut will rehearse their mission underwater many times before going into space, spending six to eight hours in the pool for every hour of actual spacewalking, so that they're sure they know how to get around in a weightless environment.
|Astronauts training with a model of the Hubble Space Telescope for Servicing Mission 4 (from nasa.gov)|
Why is it so important to train for weightlessness? On Earth, we take being supported by the ground for granted. When you push open a door or turn a handle, you’re kept stable by the friction between your shoes and the floor, which is caused by the force of gravity pressing you downwards and the force of the floor pushing up. If an astronaut floating in space pushes on a door, they’d just push themselves backwards; if they tried to turn a handle without properly supporting themselves, they’d start spinning round in space instead of the handle! The same goes for astronauts in a neutral buoyancy pool. By training underwater, astronauts learn what it’s like to work in a weightless environment, and how to keep themselves stable without relying on gravity.
You may think that a giant pool doesn’t really sound very similar to outer space, and frankly, you’re right. Water is thicker than air, while the vacuum of space is thinner; this means it’s harder for objects to move through water, and they have a tendency to stay put, while slightly tapping an object in space could send it flying away at surprisingly high speed. Even though the astronaut may move around as if they're weightless, they're really not: if they float upside down, blood will still rush to their head in a way it wouldn't in space. And moving through water causes currents, which can push objects around in unexpected ways. NASA avoids these problems a little by keeping the water in their pool very still and making astronauts move extra slowly, but this training technique definitely isn't perfect.
If astronauts training underwater looks a little silly to you, it's because training people for life in space is hard, and there are no perfect solutions. The Neutral Buoyancy Lab is just one of many methods to get astronauts ready for an environment totally different from life on Earth. Some of the most interesting equipment at NASA isn't even meant for going to space, just simulating it! Astronauts also train with high-tech computer games, pilot models of their spacecraft mounted on mechanical arms that lurch about just like the real thing, and have to endure intense spinning in a giant centrifuge to deal with the stress of a spacecraft launch. Neutral buoyancy isn't even the only way to train for weightlessness: you can also simulate the freefall of orbit by, well, falling! Astronauts in training can feel the full effects of weightlessness by taking a plane to a high altitude, then letting the plane fall freely out of the sky. Since the astronaut and the plane are both falling, the astronauts are weightless relative to their surroundings, just like in space! This only lasts a few minutes, though, before the plane has to pull up so it doesn't crash into the ground. It's not enough time to train for a mission, but it does expose astronauts to the unique feeling of weightlessness; that strange feeling you get in your stomach at the top of a rollercoaster is what being in space feels like, all the time. (This is why the plane used for weightlessness training is sometimes called “the vomit comet.”) It also gives enough time to shoot a crazy music video.
For more information:
Check out the NASA Neutral Buoyancy Lab's site!
See a visit to the Neutral Buoyancy Lab.
The most extreme training NASA's ever done was for astronauts on Apollo missions to the moon. They needed to prepare for life in space, on the moon, and wherever they landed, and they trained without modern computer simulations! See what they did to prepare.
Ben Tolkin works for Neuron, a journal of neuroscience, by day, and writes and performs poetry and nonfiction by night. He got really excited about science when he was a child, and then forgot to stop.
Some great events to check out in the science festival...
Workshop: Mission to Mars with MIT Society of Women Engineers
Cambridge Explores the Universe