[amsat-bb] Re: Water as a rocket fuel

[Bruce Bostwick]

On Aug 27, 2009, at 10:48 AM, John Heath wrote:

> On boeard electrolysis of water to produce  Hydrogen/Oxygen rocket  
> fuel.
>
> An most interesting paper on the subject at https://e-reports-ext.llnl.gov/pdf/236614.pdf
> It does work in space.

Well, using a URFC for the electrolytic separation takes care of most  
of the ullage and gas separation problems I mentioned in an earlier  
post.  (And having arrived at that solution independently, I'm  
convinced it's a viable research path if nothing else. ;)  It also has  
the benefit of being able to turn the separated H2 and O2 back into  
water and electrical power (minus losses, of course) if needed -- not  
sure what additional support systems that would need, but it's a  
tantalizing side benefit.

Storing the water still requires some means of eliminating unnecessary  
headspace in the water tank to avoid the requirement for ullage -- I'm  
still partial to the idea of a sylphon-type bellows inside a slightly  
larger tank pressurized with helium or nitrogen -- to maintain water  
flow into the FC.

And as before, these are *not* hypergolic fuels, so using them in  
engines still requires exactly timed valve opening/closing rates and  
synchronization between fuel/oxidizer valves and ignition on startup,  
which are considerably more complex systems than the ones used to  
control hypergolic engines and RCS thrusters.  (All a hypergolic  
engine has to do is open and close the fuel/oxidizer valves at the  
right rates and relative timings.)

That being said, it's an intriguing idea.  Regenerative fuel cell  
based electrolysis is pretty interesting in and of itself.  :)