It took a genius like Issac Newton to invent the laws of motion because friction, air resistance, and other forces on Earth make things so complicated that it’s hard to see the underlying forces. In space, however, much of this is removed, and we get to witness physics in raw form, like a body in motion that stays in motion unless acted on by a force. The European Space Agency (ESA) has provided a great example of this with images of astronauts inside the International Space Station (ISS) during a reboot.
Instead of stopping suddenly, Earth’s atmosphere gradually thins as you go higher. Even at the ISS altitude of 400 kilometers (240 miles), there is still a slight drag, causing the orbit to slowly decay. Consequently, from time to time the ISS needs a boost, in this case provided by a resupply cargo ship firing its thrusters for a few minutes to bring the station to the proper altitude. Astronauts, and anything else that isn’t tethered, aren’t equipped with rockets of their own, so as the space station moves around them, they continue in its orbit.
However, for a camera fixed in the ISS reference frame, it looks like this (the footage has been sped up x 8, according to ESA):
Clearly, the process of making the station speed up next to you is so much fun that the astronauts are itching to propel themselves into the time pool to go through it all again, like pandas on a slide. We’re not sure why the ESA sped everything up eight times; personally, we’d love to see a four-minute video at real speed.
In the comments, one individual tries to calculate the acceleration of the station and concludes that it is around 0.005 ms.-two. If so, it would feel like a gravitational pull of 0.0005 g, or 0.05 percent of Earth’s gravity, to the astronauts on board. The figure is based on some rough estimates of the time it takes for astronauts to get from one end of the corridor to the other and the distance they cover. A more precise estimate of a different boost, based on figures provided by the ISS agencies, gives a figure of a third of that amount.
For comparison, astronauts on the Moon experience 0.17 g. Even on Ceres, gravity is 0.03 g. To replicate this feeling of almost, but not quite, prolonged weightlessness, you would need to visit a small moon or the asteroid-like Martian moons Phobos and Deimos. Alternatively, we could get the experience down the road, if future Mars missions choose ion thrusters instead of rapid-firing rockets.