Internal Combustion in Space

[Beowolf]

Last night I ran across docs on NASA & ULA's Integrated Vehicle Fluids initiative. NASA wants fuel depots in space, and the ability to easily and robotically transfer LOX and LH2 from ship to ship.

Part of that is getting rid of all the other normally required consumables, like hydrazine for RCS, helium to maintain pressure in fuel tanks, and loads of batteries. That's the IVF part; coming up with ways to make LOX/LH2 do those other jobs.

LOX/LH2 RCS thruster have been built before, so no big problem. You can recycle waste gasses to manage pressure in the tanks. But for electricity would you believe a generator hooked to a six-cylinder gasoline-style engine running gaseous hydrogen & oxygen? I'd have expected a fuel cell, but...

The ICE is cooled regeneratively by the incoming cold hydrogen gas from the main vehicle ullage spaces. This gas

would be vented as waste boiloff in a traditional system. The exhaust gases from the ICE are used to produce

settling thrust. Using waste propellants to produce power and settling results in a major mass reduction. The lower

energy conversion efficiency of an internal combustion engine as compared to traditional fuel cell systems is more

than compensated for by the use of this waste thermal energy to settle the vehicle and store energy for tank

pressurization. In effect IVF is a cogeneration system where lower energy gases are put to beneficial use. Because

of this the utility of the energy released approaches 100% and ancillary cooling systems are not required.

...so I guess not. Anyway, ULA's thinking they can shave 10% off the dry weight of their upper stages so we gain advantages even before fuel depots are available.

Lots of info here:

http://www.ulalaunch.com/uploads/docs/Published_Papers/Extended_Duration/Integrated_Vehicle_Propulsion_and_Power_System_for_Long_Duration_Cyrogenic_Spaceflight_2011.pdf

http://www.ulalaunch.com/uploads/docs/Published_Papers/Supporting_Technologies/Space_Access_Society_2012.pdf