One of the the main challenges, for some hybrids, may be to find the right combination of fuel system and reactor design to achieve maximum average drift velocity of the exiting particle stream in anaerobic mode, while still maintaining exemplary overall performance in aerobic mode.

Emerging manufacturing techniques for rocket nozzles imply the possibility of systematic proportional cooling in key components of a hybrid design.

Assuming hybrid sections are inline, traditional air flow cooling might be used up to near the transitional phase, however it seems likely some form of precooled liquid will be required for anaerobic operation.

While the overall execution of a hybrid design may be highly problematic the main enabling feature might be a novel fuel system, allowing precooling to very low temperature while maintaining appropriate properties for handling by pumps and also flow characteristics, through cooling channels, before entering the reactor.

The widespread use properties of this novel fuel imply that for safety considerations the mixture should preferably be non-toxic and have a very high flash point temperature.

Thermodynamic considerations imply the fuel remain a low viscosity liquid down to the liquid nitrogen range, combined with excellent thermal conductivity and heat capacity characteristics.

Combustion considerations imply the new composition will ideally burn very quickly, completely and cleanly in anaerobic mode, at high temperature, with minimal undesireable byproduct species.

In summary novel hybrid structures may imply high peak reaction chamber (combustor) operating pressure and temperature, possibly combined with new forms of cooling using nanotechnology engineered fuels.