"Your safety tether is like a reel. It's a wire tether on a spring-loaded spool that tends it, and that is attached to you and the space station at all times, because if you should ever let go of the station, the tether will pull you back in, or you can grab it and pull yourself back in. If you didn't have that tether and you let go, even if you're two inches away from the station, you can't swim over there. There's no water to create forces against. So it's critical from a safety perspective that you be tethered at all times."