Could a satellite fall on your head?

This is not crazy stuff,” said researcher Sebastian Willems as he walked past glass cases filled with futuristic models of sleek silver spacecraft in the German Space Agency’s (DLR) wind tunnel facility in Cologne. Nor will you find anything crazy in the grand, retro control gallery with its huge console of gauges, switches, and knobs.

Entering the windowless room through a huge blast door, the walls are scorched, and the air is filled with the unsettling aroma of explosives. This is where they strain the aerodynamics of rocket engines. But this is not crazy, either.

Willems’ “crazy” experiment uses one of the center’s wind tunnels to simulate a satellite’s re-entry.

There are a bunch of satellites in orbit, and sooner or later, they will fall. ‘And our question is, what is the likelihood of a collision?

In other words, what are the chances that some of the dead satellites will re-enter and hit something or, worse, someone?

The wind tunnel set up for Willems’ experiment looks like a giant vacuum cleaner attached to a pressure cooker that has been disassembled and laid out all over the concrete floor. This gleaming machine is covered with tons of pipes and wires. Capable of generating air currents 11 times the speed of sound, the wind tunnel is used for aerodynamic experiments on supersonic and hypersonic aircraft.

At its center is a 2-meter-high spherical metal chamber to which the test object is secured with special clamps. Instead of this fixture, however, Willem ejects the object with an air current of 3,000 km/h (more than twice the speed of sound) to simulate atmospheric re-entry.

The idea is to make an object fall in a stream of air,” Willems says. We want to observe the object as it falls freely through the flow.

The experiment lasts only 0.2 seconds, but we can take many pictures and measurements during this time,” he says. Data from the experiment will be fed into a computer model to improve how the satellite will fall to Earth.