Hybrid possibilities

What kind of uses do you think hybrids will see in the rocket industry in the future? I've been doing some reading, and it seems that between the development of high regression-rate paraffin fuels and the Vortex Injection hybrid of OrbiTech, hybrids might start playing a more prominent role in space propulsion.

For instance, RocketPlane is currently planning on using hybrid motors in it's rocket-jet, and the SpaceDev DreamChaser is visualized as using a hybrid stack to get into orbit. SpaceDev has a SS1-style N2O/HTPB system in mind, but RocketPlane is looking at the Orbitech vortex idea, IIRC.

From what I've read, LOX-paraffin hybrids can get close to the same Isp as LOX-kerosene, since the two fuels are chemically similar.

What I am interested to find out is, will these technology breakthroughs put hybrids in as real launcher options, or is there something I'm missing?

Like solids, hybrids are much more expensive to refuel than liquids. This is a big issue for development & testing, and in service too, if the engine is re-usable.

I imagine hybrids as possible boosters, perhaps replacing SRBs as a more cleaner, and reliable not to mention safer propulsion system. Yet I dont see them replacing liquids, or being the main propulsion system for a rocket only for a booster. But hybrids to have a big potential in suborbital spacecrafts, and the space tourism business. Take a look at SpaceShipOne, it runs on a hybrid engine.

Like I said hybrids have real potential in the business of suborbital space tourism.

Hybrids are going to become popular; they offer a number of advantages, as you have pointed out.

However, even if you can get "close to the same ISP" as LOX-hydrocarbon motors, you will never get equivalent performance. A hybrid shares one principal fault with an all-solid motor, and that is this: The ENTIRE CASE must be built strong enough to withstand the combustion pressure required. In an all-liquid engine only the (relatively small) combustion chamber needs to be as strong.

That means that the hybrid will always be more massive and less efficient per unit of propellant energy.

I will be very surprised (not just suprised, but actually impressed) if SpaceDev really does fly to orbit on an all-hybrid stack. I think we'll see a lot of hybrid motors in first-stage/sub-orbital/strap-on and OMS type applications, but an all-up hybrid stack just doesn't seem practical.

What about the aspect that chemicals are in different physial states or phases at different distances from the sun? Closer to her they are gaseous, a bit farer liquid and very far away solid – so hybridity seems to change from distance to distance.

What might this result in in the far future regarding development?



Dipl.-Volkswirt (bdvb) Augustin (Political Economist)