I think Branson would probably rather go with one of the more established firms. Having to wait now over 10 years for SS2 due to Rutan’s struggling with the engine etc, I think Branson would be eager to move up to the bigger,more solid and capable, suppliers.

>..The tradeoff is the failure mode set size is much larger.

Not sure about that. Anyway, not a lot of failures in professionally made liquid engines. Solids seem to stil fail more often.

Thanks for your thoughtful reply. In the context of ICBM’s, storability and reliability are essentially the same thing. When you need a missile, you need it RIGHT NOW, even if its been sitting in a silo for a few decades. I’m sure the Titan II maintenance requirements caused more than a few grey hairs.

For repeatable, reliable access to space, liquids are the way to go, for sure. The tradeoff is the failure mode set size is much larger.

Sadly Rutan made the basic mistake of assuming hybrid’s were innately completely safe, then assumed his company could build their own just fine. These mistakes cost years and lives – and likly contributed to Branson informing them that scaled wouldn’t be involved in the next space ship 3 project, and Rutan deciding it was time to turn the rest of Scaled over to Northrup and retire.

>..Not sure I agree that solids are hard to scale reliably…

The solid parst are flexible, and the burn rate varies with exactly how they flex. Calculating the extra movement of a extra scale material while its burnering – and the burning throwing around shockwaves disrupting oxidizer flow…. You can do it, but its nor easy – and the result makes for a rough ride.

Solids are used as a quick and dirty solution for launchers

> All US ICBM’s use solid rockets, and reliability is a primary concern…

Actually storability is the big concern. Once cast the solid motors are relatively insensitive to being left that way for years – or decades. Liquids you worry about moving parts lubricants drying out, things leaking out in confined silos/launch tubes, etc. Solids are a bit dangerous to be around – but a good mix can be parked for years to decades without degrading.

>.. I’m wondering where there is sufficient storage space on SpaceShipTwo, and
> how the added mass of fuel will affect payload….

The mass of a similar performance liquid will be less due to higher ISP of most any liquid system that I can think of – though I’m not sure how bulky it would be in comparison?

Hybrids are hard to use. Or at least use the way they want to.

I don’t know why they don’t just make up some large JTOW type solid rockets that they can jettison off after making space.

Then just using a liquid fuel rockets of even hybrid jet engines for landing.

Not sure I agree that solids are hard to scale reliably. Shuttle used solids for primary boost, and the one failure was forseen and avoidable. All US ICBM’s use solid rockets, and reliability is a primary concern. I agree with your assessment of the advantages of liquid-fuel rockets, but I’m wondering where there is sufficient storage space on SpaceShipTwo, and how the added mass of fuel will affect payload. If seating has to be reduced, then any cost savings from re-usability will be compromised.