They’re Not in Zero Gravity. They’re Falling!

If you’ve seen any pictures from the ISS or other space craft, the astronauts and the objects around them are floating.

The ISS is always traveling in a straight line, but Earth’s gravity is constantly pulling it, so that its straight path of flight bends around the Earth instead of continuing endlessly into space. If the Space Station wasn’t constantly propelling itself through space, Earth’s gravity would cause it to come crashing down. Those two factors together — Earth’s gravity and the forward motion of the craft — are what keep the ISS orbiting our planet.

That means the ISS and everything in it is in a constant state of falling! Have you ever been on a roller coaster or free fall amusement park ride? For just a few moments, you actually float above your seat. That’s what is going on constantly inside the ISS!

In practical terms, the astronauts and everything inside the space station experience weightlessness the same as if there was no gravity, but instead it’s called microgravity. Now you know.

Liquids and Gases

No air in space means no air pressure. So what is air pressure?

Earth has an atmosphere (all the air around Earth) that allows us to breathe. It doesn’t float off into space because it’s held in place by, you guessed it, gravity.

But believe it or not, all that air is heavy! The air we breathe down here on the surface of the Earth is pushed down by all the air on top. If you go up to a very tall mountain that is high above most of the Earth — there isn’t much air on top to push on the air there. Without so much air pushing them down, the molecules of air on a mountain are farther apart and the air is much thinner.

Liquids change into gas when you heat them because the heat gives the molecules more energy to move faster. When they move faster, they can escape. You can see this happen when you boil water. The water molecules get energy from the heat and move faster and faster until they escape the water and float away as a gas (which we call steam). Up on the mountain, without all that air pushing down on it, it’s easier for the water molecules (or any liquid) to become a gas and float away. You don’t need so much energy (heat), so liquid boils into a gas at a much lower temperature. Water turns to steam and floats away before it gets very hot. If you want a cup of coffee, the water will boil away before it’s hot enough for your drink!

Out in space, with no pressure at all, there is nothing pressing down on liquid to keep the molecules close together — liquids boil straight into gas even if they aren’t hot at all!  So if you go into space, your cup of water will boil away before you can even drink it. There’s no pressure to keep liquids from turning into gases. There’s no pressure to keep gas molecules together. The gas molecules spread farther and farther apart and float away.

That would include all the liquid and gases inside a human body also. Your body has a lot of liquids (like blood) that carry a lot of very important gases (like oxygen) that need air pressure to keep the gases inside the liquids. So, if a human goes out into space, they need a pressurized space suit that keeps all the liquids and gases (such as the oxygen in their blood) inside their bodies where they belong.

The Sound of Music

So an astronaut goes out into space with his special space suit to keep all his body’s liquids and gases exactly where they belong — in his body. It’s a little lonely out in space with not so much as a gas molecule to keep him company, so he grabs his MP3 player and speakers to blast his favorite tunes into space…

…and he hears nothing. Sound waves need air to travel. Without air to carry the sound waves, all that he hears from his speakers is silence.

But at least he can enjoy the view. Without all those air molecules, or anything else for that matter, there is nothing to distort the view. He has a crystal clear view of an endless number of stars. He will see more stars than any Earthbound creature could ever dream of seeing.

Space Crystals

It’s harder to make fire in space than on Earth, which is probably a good thing, since the nearest fire station is pretty far away. But crystals can grow much better in space than they do on Earth.

Do you know what a crystal is? Crystals grow when something is dissolved in a liquid and then the liquid evaporates, or when material dissolved in a liquid starts to clump together. Salt is a crystal and sugar is a crystal. But there are lots of other crystals, and those crystals can be used to make medicines and other things that people need.

On Earth, gravity can pull the heavier ingredients in a liquid to the bottom and the lighter ingredients to the top, so that only very small crystals can be formed on Earth. Voila — in microgravity there’s no difference between the heavier parts and lighter parts and they don’t separate in a liquid. Space becomes the perfect place to grow bigger, more symmetrical crystals!

Great Balls of Fire

Let’s say our future generations are planning to spend Chanukah vacation in space. They light their candles (after making sure their menorah is tied down so it doesn’t float away, and that they are inside a space craft where there is air) and sit to watch the flames dance, just like on Earth. But what’s that? What funny little flames! Instead of the dancing flames we see on Earth with flames rising upward, each wick is surrounded by a little ball of fire. Why is that?

On Earth, as the flame heats up, the gases in the flame get hotter and lighter. Since they are lighter, they rise up, forming the teardrop shaped flame we are used to seeing. As the gases in the flame rise, more air is sucked into the base of the flame that make the flame continue burning. But in the microgravity of space, there is no lighter or heavier gas. No gases rise up as they get hotter, so the flame looks like a little ball on top of the wick. Without the hot gases rising up, no new fuel (like oxygen from the air) is pulled into the bottom of the flame to keep it burning. If oxygen isn’t pushed into the flame, it will go out.

Space Salad

When moms on Earth pack up for a trip, they always bring a lot of FOOD! But food is heavy. It’s a challenge to get enough food into space for the astronauts. (Wait. I just told you that in outer space things are virtually weightless, so why does it matter how heavy the food is? Because the rockets carrying the food blast off from Earth, and gravity definitely matters there!)

Wouldn’t it be cool if we could just grow food in space? Plants need carbon dioxide to grow, and produce oxygen. People need oxygen and produce carbon dioxide. A perfect match! In space, plants would use up all that extra carbon dioxide and give space citizens the crucial oxygen they need to breathe!

Scientists managed to create a system for growing plants on the space station: They used artificial lights instead of sun, nutrient-filled clay “pillows” instead of earth, and fans to blow the carbon dioxide toward the plants. And wonder of wonders, space lettuce tasted like… lettuce!

Many scientists thought that without gravity, the roots and stems would get all mixed up – with some roots growing upward and the stalks growing down or sideways or any which way. There were some early experiments where plants really grew this way, but aside from being harder to grow things in space, once they manage to get plants to grow, they are pretty similar to their Earthly counterparts.

If Only I Could Taste It

On Earth, gravity pulls the fluids in our bodies down, so our bodies work hard to pump them up against gravity (so your blood doesn’t all collect in your feet, for example). But up in space, fluid tends to gather in a person’s head — kind of like when you have a cold. And when you have a cold, your food tastes a little bland. To make matters worse, in microgravity, the smell of the food floats away before it reaches your nose — and a lot of what you think makes food taste good is really the smell and not the taste.

So, after all that work growing your space salad, you can barely taste it.

Yikes, Flying Cracker Crumbs!

One of those microgravity realities is that the dust never settles in the ISS. So, if you’re dreaming of kicking back in your lounge chair (after strapping yourself down, so you don’t float away) and watching Earthrise as you munch on potato chips — forget it.

The crumbs will float around forever, and all those floating crumbs could get in someone’s eyes and hurt them or in their throat and make them choke. Sensitive and expensive equipment could be seriously damaged by a stray crumb. It could be really dangerous; crumbs in space are no joke. So any crumbly food (bread, crackers, potato chips) is strictly forbidden on today’s spacecraft.

And if all that talk of potato chip crumbs is making you thirsty, I’ll just point out that to keep your drink in its place, space citizens drink out of pouches, to keep the liquid from escaping.

Take a Hike

Can you go for a walk in space? Sure! Sort of. Make sure you’re securely tethered (attached with a special rope) to your spacecraft and step out of the airlock into space. You take a step forward, but all that happens is that your leg moves, while you stay in the same place. You can spin around in a circle, but you can’t actually get anywhere.

Without gravity, there’s nothing to push off of when you walk. If you’re inside your spacecraft, you can push off the walls or other objects that are held in place. But if you venture out into space and there’s nothing to push off from, you’re going to need to use tiny rockets to boost you in the direction you want to go.

Space Sprinklers

But if liquids in space have to be contained, so they don’t float all over the place, how do you take a shower?

In a giant juice box, of course. Well, not exactly a juice box — but a sealed, human-sized tube. Bathers can spritz themselves with water (it wouldn’t help to open a faucet without gravity to make the water fall), grab a floating blob of water and soap themselves up. After they’re squeaky clean again, they use a kind of vacuum to suck up all the water floating around.

Isn’t it amazing how many things are different in space?

We only realize how perfectly suited our world is to life when we see all the trouble we have to go to if we leave it. But wouldn’t it be fun if one day you had the chance?

(Originally featured in Mishpacha Jr., Issue 937)