Skydiving from a Space Station? Here is why this wouldn’t work

This captivating video presents a vision of our potential future: humanity at ease with open space. An astronaut opens a hatch and gracefully dives into the cosmic void. But what exactly did he exit: a space station or an airplane? Given how small the Earth looked beneath the craft, it should be the station. Yet, the astronaut walked and jumped as if he were on a plane grounded by gravity. Of course, artistic imagination isn't bound by the laws of physics. But why not root this flight of fantasy in real physics and use it to explain why we remain affected by gravity on the planes, while astronauts on the International Space Station float in weightlessness?

Fig. 1.  Between art and reality: a jump that only imagination can make

Why walking in airplanes feels like walking on Earth

An airplane maintains an altitude due to aerodynamic lift, which balances the downward force of gravity (Fig. 2). The wing design and engine propulsion generate the lift as the plane moves through the air. The wings are slightly curved on top and angled upward, resulting in higher air pressure below them than above. This pressure difference generates the upward force, which increases as the aircraft's speed grows. When the speed reaches a point where the lift equals the aircraft's weight, the airplane enters a cruising stage, maintaining a stable altitude.

Fig. 2. The Four Fundamental Forces Acting on an Aircraft: Lift, Weight, Thrust, and Drag.

The lift impacts the airplane, but not the passengers inside. Passengers do not have wings or airflow around them to create the upward force necessary to counteract the force of gravity. Instead, they are supported by the plane's floor, much like the ground supports us on Earth. If this support is lost, such as during engine failures when the airplane sinks, the passengers enter free fall, experiencing weightlessness. However, during normal flight, their weight is practically the same as on the ground. A scale onboard would measure only a half-percent reduction in weight due to the decrease in gravity at the plane's altitude, which is too small for us to notice. Therefore, during the cruising phase, we can walk inside planes as we do on the ground.

How orbital motion creates microgravity

In contrast, a space station maintains its altitude through orbital mechanics, rather than aerodynamic lift. At the station's altitude, the atmosphere is negligible, so no meaningful lift can be generated, nor is lift required in the first place. Instead, a stable orbit exists because the station is moving forward at a speed that takes it away from a collision course just enough to trace a continuous curved path around Earth. Gravity constantly pulls the station downward, but its orbital velocity keeps it at a consistent distance from the planet (Fig. 3). This precise balance between gravitational pull and forward velocity enables the station to orbit Earth continuously, without the need for engines or counteracting forces, such as aerodynamic lift, to combat the effects of gravity.

Fig.3. The ISS remains in a stable orbit because its forward orbital velocity is precisely balanced by gravity, which curves its trajectory into a loop.

Crucially, everything inside the station, astronauts, tools, and even the air, is moving at the same velocity, while Earth’s gravity is pulling them with equal force. Even without the station, the internal contents would continue orbiting Earth along the same curved path. Because no object has an advantage in terms of speed or gravity, neither exerts pressure on another. This condition creates a microgravity environment in which astronauts feel weightless. A scale onboard would show zero weight, just as it would on an airplane during free fall. However, the free-falling plane, along with its passengers, would crash on the ground. In the case of the space station, its sideways velocity is dragging it away from the crash path, making it fall around the Earth.

Fig. 4. Experience microgravity with ESA astronaut Thomas Pesquet, who takes you on a tour around the International Space Station

In a microgravity environment, astronauts can't perform acrobatic stunts that look so impressive in movies. In airplanes, where gravity is fully present, pushing against the floor results in an upward leap because the ground provides a strong opposing force. However, in orbit, pushing off a surface only causes a slight relative motion between the astronaut and the station. Without gravity to hold them down, astronauts glide gently in the opposite direction of their push, drifting slowly rather than launching forcefully. In true microgravity, movements are subtle, focusing on conserving momentum rather than the bold, dramatic gestures we are used to on Earth.