“Up there, two fundamental characteristics of terrestrial life are drastically modified”

Flames. Five hours fifty minutes! This is the length of one of NASA’s last live broadcasts, to find on SpaceX’s YouTube channel… With the intensity of a Swedish post-war film, we see the Crew Dragon capsule approaching to the millimeter near the International Space Station (ISS), docking there with majestic slowness while the ISS crew prepare for the arrival of the encapsulated astronauts, then we have to wait and wait again before the new ones, at last, slip out of the entrance corridor and indulge in the agreed photos and speeches. We salute in passing the performance of the two commentators, responsible for densifying the soundtrack … This moment of spatial history, served by sublime images, reminds us that the life of an astronaut is not only hectic, that it is filled with checklists, promiscuity and waiting.

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Some of these constraints are dictated by physical laws, because up there two fundamental characteristics of terrestrial life are drastically modified: our relationship to inertia, on the one hand, and to gravity, on the other. Inertia is this property according to which a moving body keeps its speed in the absence of interaction. A particularly remarkable discovery of Galileo, because it completely goes against our first intuition: we tend to believe rather Kurt Neumann, the author of the misunderstood Twenty-four hours among the Martians (1950), for which a broken rocket slows down and stops! This is because we are used to being in direct or indirect contact with our Earth with which we interact and exchange impetus: thus, surprising as it may seem, the force responsible for our progress when walking is exerted by the Earth on our body, and not by ourselves.

A caress finish

In space, you can no longer transfer your inertia (or more exactly your “momentum”) to a good big Earth, and the only way to change its speed is to separate with the greatest possible ejection speed. of part of its mass, the basic principle of any rocket engine (and Iron Man’s shoes, although, in his case, one wonders where the ejected mass is taken from). For the inhabitants of the ISS, the structure of the station itself plays the role of an exchange medium and, in fact, the astronauts always rely on it to move or move objects. Moreover, this same principle of inertia makes heavy loads difficult to set in motion and to stop, such as a diving suit or the Crew Dragon capsule itself, which must oblige itself, during mooring, to a finish ” caressing the daisies ”…

The other major change in space is our relationship to Earth’s gravity. Contrary to what one might think when seeing the astronauts float freely, it is not canceled at all! This is because the ISS and its occupants “fall” together in the same gravitational field (a property that inspired Einstein’s theory of general relativity). This “weightlessness” offers an exceptional context for researchers who, through the intermediary of astronauts, engage in unthinkable experiments on Earth. However, it brings new problems for the operation of the ISS, which the basic Earthman does not immediately think of.

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An example is the management of the air in the station: weightlessness in fact removes the natural convection which easily mixes the air masses on Earth, where hot air tends to rise. In the NASA film, we see that ventilation is installed to avoid toxic concentrations of CO₂ by homogenizing the atmospheres of the ISS and the capsule, atmospheres which are said to not smell of roses. … Apparently that does not bother our astronauts, in view of their happy faces. They look comfortable, floating weightlessly like fish in water. Pesquet, fish… Are there any predestined names?

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“Up there, two fundamental characteristics of terrestrial life are drastically modified”

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