From: alain245@videotron.ca   
      
   On Nov/5/2020 at 02:22, JF Mezei wrote :   
   > On 2020-11-03 18:47, David Spain wrote:   
   >> Will NASA use it?   
   >>   
   >> No. But a private company might.   
   >   
   > If you're carrying humans (or Martians, apparently they have bee voting   
   > illegally in USA :-), I have to assume that shielding requirements will   
   > be very hefty. Does all that extra mass make this type of propulsion   
   > worthwile?   
      
   You just put the reactor far from the crew and put a little shielding   
   near the reactor. You also have to put shielding around the crew, which   
   you would have to do even if your propulsion method was chemical. There   
   are all kinds of radiations in space, you need shielding.   
      
   > And out of curiosity, how does nuclear propulsion work?   
   >   
   > I am aware of nuclear batteries that generate electricity.   
   > Am aware of nuclear reactors that heat water into steam and drive   
   > turbines.  But how is nuclear fission used as propulsion?   
      
   There are several different methods. But basically, if you heat a gas to   
   high temperature, whether you heat it by chemical reactions, nuclear   
   energy or some other method, the gas wants to expand. You just have to   
   make sure that the expansion happens in the opposite direction to where   
   you want the rocket to go.   
      
   Nuclear has some important advantages over combustion. Low mass   
   molecules move faster at the same temperature than higher mass   
   molecules. So if you are heating hydrogen to 3000 °C, the molecules of   
   hydrogen will move faster than water at the same temperature. Therefore   
   heating hydrogen with a nuclear reaction can give more push than burning   
   it and exhausting water.   
      
      
   Alain Fournier   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)