From: nuny@bid.nes   
      
   On Tuesday, June 7, 2016 at 12:22:15 PM UTC-7, Christopher Rice wrote:   
   > I've been writing a short story, and was wondering if one of the maneuvers I   
   > was writing about was possible. In my story, one of the astronauts is ejected   
   > from her ship in a violent fashion, putting her in a state where she is   
   > rotating on more than one axis. What I want to know is twofold: assuming she   
   > were ejected from the center of a 4 meter by 10 meter cylindrical room in the   
   > direction of the short axis, pressurized to standard atmospheric pressure,   
   > what would her final velocity be?   
      
     Your standard SF film depictions of explosive decompression are bullshit;   
   let's get that out of the way first. You seem to be assuming that only the   
   room your astronaut is in suffers decompression, so all of the other   
   compartments' air doesn't    
   contribute to the breeze blowing her out.   
      
     She doesn't fit snugly into the room so the gun-bullet analogy you're   
   probably thinking of doesn't work. Think more of firing a .22 bullet out of a   
   .60 musket- the gunpowder's combustion products will mostly blow past the tiny   
   slug, which will rattle    
   its way down the barrel and drop immediately to the ground if it even gets all   
   the way to the muzzle.   
      
    If the hole is as large as the ex-wall, the pressure in the room drops   
   rapidly and more or less uniformly, so she's going to be drifting rather   
   slowly along with the air, a few m/s at best.   
      
     The smaller the hole, the greater the pressure difference and therefore the   
   available force *at the hole*, so depending on her initial location she could   
   have more final velocity, but also the farther from the hole the less force   
   she feels not just    
   initially but as the room decompresses there's less force pushing her toward   
   the hole.   
      
   > Would it be different if she were ejected in the direction of the long axis?   
      
     Yes, but again it depends on the size of the hole, how far she was from it   
   initially, and so on. I'd stick with a few m/s which is inconvenient enough   
   unless your story really needs her to be far away in short order, in which   
   case you'll need more    
   force, say by an airtight emergency door to the next compartment failing.   
      
   > And second,  would it be possible for her to reduce or eliminate her overall   
   > rotational momentum by strategically spinning her arms about her head? I   
   > checked on Project Rho: Atomic Rockets to see if I could find anything, but   
   > there was nothing there, and that's really the only space SF resource site   
   > that I know of, other than here. Any help would be great. Thanks ahead of   
   > time!   
      
     Angular momentum is conserved, so no, no more than she could begin a   
   constant rotation. She can however exchange the momentum of revolution about   
   one axis with another to at least reduce her disorientation by waving her arms   
   and legs around just right.    
   That's how cats reorient while falling, by using their tails as a sort of   
   rotating counterweight. NASA and ESA train their astronauts to do this not for   
   emergencies, but to orient themselves aboard space stations- just fanning the   
   air isn't enough. Watch    
   some YouTube videos of astronauts on the ISS carefully and observe how they   
   orient themselves when there's nothing to use as a grab handle.   
      
     Try this at home. Sit in a swivel chair with your feet off of the floor,   
   hands in your lap. Stick both hands out in front of you and swing them to one   
   side; you'll rotate a bit the other way (proportional to the difference   
   between your hands' mass and    
   that of the rest of your body). You can keep turning a bit by repeating but   
   once you put your hands back in your lap and keep them there, you stop turning.   
      
     The only way to stop (or start!) rotating is to throw something along a line   
   that doesn't pass through your center of mass, the inverse of say giving spin   
   to a billiard ball with a glancing collision. That's the equivalent of a   
   vernier rocket but it    
   means throwing away something attached to her suit, something she may need   
   later.   
      
      
     Mark L. Fergerson   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)