From: mikkelhaaheim@gmail.com   
      
   Le mercredi 16 novembre 2016 04:41:50 UTC+1, Rick Pikul/Chakat Firepaw a   
   écrit :   
      
   >    
   > NASA's figures are 26 kg/day of water per astronaut for hygiene purposes.   
      
   As I said, "negotiable". This figure for hygiene is NOT considered a mission   
   requirement. Rather, it is the data from records of actual astronaut usage   
   (which, incidentally, INCLUDES the 4kg allowance of water that actually IS   
   required). The actual    
   hygiene water intake could easily be reduced to less than 1kg/personne*day...   
   assuming some basic conservation measures. As it happens, it REALLY doesn't   
   matter, because the one thing you are going to have an incredible   
   overabundance of is H2O (remember,    
   we've been talking about a supply of a kilotonne to soak up 40 000 kW*days)   
      
      
   > Calling it 30kg of consumables per man-day means about 10 tonnes per man-   
   > year for the consumables alone, your lower numbers still hits ~5 tonnes/   
   > man-year.     
      
   Yes. That is about right.   
      
   Since you want stealth, you can't consider high-impulse or    
   > brachistochrone trajectories, meaning you will have travel times    
   > comparable to Hohmann transfers.   
      
   This is incorrect, especially since there is no real reason why a stealth ship   
   should have to be in stealth mode from launch. That depends on the mission.    
      
      
   > 1000 tonnes of water means about 40 tonnes of tanks using Robert Zubrin's    
   > figures.  Add 50 tonnes of structure, a similar amount of consumables and    
   > you are now down to ~100 tonnes for everything else.  You suggest a    
   > VASMIR, so that's at least 10 of those remaining tonnes, (and that's for    
   > a pokey little thing that dreams of putting out a kilonewton), power    
   > systems that can generate megawatts are going to be at least as much.     
   > Let's not forget your heat pumps and thermal shades....   
      
   As I recall, Zubrin's figures are for (highly) pressurised propellants. Keep   
   in mind that we are dealing initially with ice. Solid. It provides its own   
   tankage mass, requiring no additional structural mass. Even when the ice is   
   melted, the remaining    
   water will be under very low pressure, requiring very little tankage mass to   
   contain it. For that matter, the ice will be more than capable of providing   
   the bulk of structural mass when you need it. Towards the end of the mission,   
   when the ice is all    
   melted, there will be very little need for structural mass, as the craft will   
   be subject to very limited stress.   
      
   I will have to doublecheck my sources (AdAstra). As I recall, the VASIMR   
   itself has a mass of not much more than 1 tonne. I believe your 10 tonne   
   figure includes the projected mass for the power systems. Current proposals   
   suggest that waste heat be    
   handled by a regenerative system, meaning that it is fed directly as   
   propellant, once it has soaked up the waste heat. Current research suggests   
   that the waste heat will bring the propellant temp up to 200°c, before being   
   heated further by the initial    
   RF antenna.   
      
   You can do alot with 50 - 100 tonnes of useful load.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)