Education and
Public Engagement
at the Lunar and Planetary Institute
Health in Space

Space Stations - Measure Up!


Children work in pairs to measure each other's ankles with lengths of string before and after lying on their backs with their feet in the air for 1 minute. This models the microgravity of space, where everything — including body fluids — floats!

Activity Time

5 minutes

Intended Audience

Families or other mixed-age groups, including children as young as 4 years old with assistance from an older child, teen, or adult
School-aged children ages 5–7 and 8–9
Tweens up to about age 13

Type of Program

Facilitated hands-on experience
Station, presented in combination with related activities
Passive program
☐ Demonstration by facilitator

What's the Point?


For the facilitator:

For Each Group of 2 Children



1.  Share ideas and knowledge.

Earth’s gravity still affects the space station and the astronauts, but since they are continually falling around the Earth (i.e., orbiting), they constantly experience that free-fall feeling we occasionally experience on amusement park rides. Astronauts aren’t riding a roller coaster, though; they are riding the International Space Station at 17,500 miles (28,000 kilometers) per hour, 200-250 miles (about 320-400 kilometers) above the Earth! Since the astronauts, their food and supplies, and their spacecraft are all falling together in orbit around the Earth, everything appears to float.

Use the terms “free-fall” and “microgravity”; the terms “zero gravity” and “weightlessness” are don’t give an accurate impression about how gravity works in space.

With older children, explain that the free-fall environment that astronauts experience in space is called microgravity. As they orbit Earth, the effect of gravity is so small (“micro-“), that it does not matter that a feather, a person, and a spacecraft all have different masses (i.e., are made up of different amounts of matter).

2.  Measure the same changes that astronauts experience in space.
Encourage each pair of participants to take turns with the following steps:

3.  Compare observations and connect them to the “real world.”Prompt the participants to compare their ankle measurements before and after lying on their backs with their legs against the wall. Prompt them to connect that experience to what astronauts experience in space.

4.  Explain that in space (a microgravity environment), objects “float.” This includes fluids, such as drinking water — and fluids (blood and water) inside the human body. This fluid shift causes the upper portion of astronauts'' bodies to swell, and their lower extremities to shrink. By lying upside down, the fluid in each partner’s body shifted. It was pulled down out of his or her ankles by Earth’s gravity.

On Earth, our bodies actively pump fluids back from our arms and legs. In a microgravity environment, astronaut’s bodies’ do not have to fight gravity to return blood and other fluids to the torso and head. Because we are on Earth, we have to lie down to cause our bodies’ fluids to shift in this same way.

Our bodies are made of 60% water, most of which is contained in our cells and circulatory system. Our bodies are well adapted to dealing with Earth's gravity; our hearts pump our blood and keep it from pooling in our feet. In microgravity conditions, however, things float. This includes the fluids in the human body! Without gravity pulling fluids into their legs, astronauts' bodies preferentially keep fluids in the torso and head. Within minutes of experiencing microgravity, fluids in the astronauts' bodies shift, causing puffy faces and shrunken legs and extremities — what they call "chicken leg syndrome!"

5.  Conclude.
Summarize that there are many challenges astronauts face as they live and work in space, and they must be very fit to take on all the changes that happen to their bodies in space. Pictures of astronauts on the International Space Station show that their faces are fuller there than on Earth. They may also suffer from headaches and stuffy noses. The symptoms go away within a few days after they return to Earth.


Weightlessness Demonstration
This Windows to the Universe® activity outlines facilitator steps to illustrate the effects of free fall using cups and water. Appropriate for ages 10–18.