The BAC MUSTARD was a novel concept for a reusable space launch vehicle in which three near-identical lifting bodies were joined together for launch. There were links for manifolds connecting all the engine sets so that each vehicle's fuel could be emptied. When empty, each vehicle would separate and glide back to Earth for a runway landing. Only the final body makes it to orbit before returning to a runway landing.
The idea came from English Electric in the early 1960s and finally died in 1970 at BAC, having never left the drawing board in Lancashire, never mind Earth.
This represents the end of such a project that is now 50 years late and has little more than historical interest as part of the UK's decline as a major power and its inability to create international teams for the common good.
Historians have constructed items from the past to learn how to build them. Replicas and Clones of WW2 aircraft are numerous, but no one has ever built a vehicle that did not get beyond the drawing board. There are detailed plans for TSR2 that could, in theory, be dusted off. While BAC claimed that the design was complete in 1964, that is unlikely to mean that each component was designed in detail.
But let us suppose that AI exists to take whatever exists and finish it. How would you build it? Part by part and the assemble or perhaps a whole body slice at a time, switching between multiple materials on each pass?
Hot Mustard
MUSTARD, as conceived, had three identical elements. The technology available meant that they had to be manned, so that is, three cockpits, each of which would be occupied. It also means three payload bays, two of which would be empty, just taking up space and adding mass.
Today manning would be optional, so for just a launcher, the cockpits could go. That leaves the triplicated payload bay. That is not very efficient. In reality, the original MUSTARD is a none starter today.
To reuse something from the concept, we need to avoid redundant triplication. That means the internal payload bay has to go with the payload mounted externally to the orbital vehicle. We could use the attachment points used for the interconnects. Energia used a side load arrangement when launching Polyus. The Shuttle and Buran were also side-mounted and crewed, so a small space plane is viable.
It might be better to have a conformal unit that contains a payload bay or crew area to reduce drag. This way, additional heat shielding is not needed to protect the crew. Though, it might mean rating the units for longer endurance in space.
On the face of it, this seems pointless. However, Falcon Heavy & Delta IV Heavy also use replicated sections. Usually with some modification. A Falcon Heavy booster has been reflown, as the core in a standard Falcon 9.
I have never been a fan of propulsive landings. There is just too little time to recover from any problem. The Dream Chaser uses a lifting body for its recovery. A MUSTARD II would be a fully reusable heavy launcher that uses a similar lifting body system. If anything like MUSTARD ever flies, I imagine it will be a fully recoverable launch vehicle with something like a Dream Chaser strapped to its back!
