From: chakatfirepaw@gmail.com   
      
   On Sat, 05 Nov 2016 05:03:55 -0700, Mikkel Haaheim wrote:   
      
   > Le mercredi 5 octobre 2016 19:51:29 UTC+2, Rick Pikul/Chakat Firepaw a   
   > écrit :   
   >   
   >   
   >> Mass, travel times.   
   >   
   > Travel times are a function of mass, for any given thrust level, so   
   > let's just focus on mass. The majority of this mass will be the coolant   
   > H2O, which will also serve as the propellant... and which will also   
   > provide all the necessary drinking (4 kg/person*day max) and utility   
   > (5-10 kg/person*day, negotiable) water.   
      
   NASA's figures are 26 kg/day of water per astronaut for hygiene purposes.   
      
   > The LOX for the oxygen supply (2   
   > kg/person*day  max rate) can also be pressed into service as coolant.   
   > This leaves nurishment and miscellaneous consumables (1-2   
   > kg/person*day), structural mass, and payload mass.   
      
   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.  Since you want stealth, you can't consider high-impulse or   
   brachistochrone trajectories, meaning you will have travel times   
   comparable to Hohmann transfers.   
      
   For most potential trips that means you are going to have to have a life   
   support system that can last you a couple years.  Longer if you want it   
   to not be another Doolittle raid.   
      
   (Oh wait, there's another problem with stealth ships:  Since they can't   
   take the high-deltaV trajectories, I know when they can launch for any   
   given target and what trajectories they have to take.  So, unless you can   
   also hide your bases for decades on end, you might have a little problem.)   
      
   > This will add perhaps   
   > 250 tonnes, max (sorry, that is INCLUDING the consumable water and air,   
   > which I am keeping for reserve, rather than applying it to the main   
   > coolant budget). Total initial mass is 1250 tonnes. With 1000 tonnes   
   > propellant, a minimal VASIMR Isp of 1000s should be sufficient to   
   > provide a 10 km/s delta-v.   
      
   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....   
      
   --   
   Chakat Firepaw - Inventor and Scientist (mad)   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)