British Secret Projects 5: Britain's Space Shuttle by Dan Sharp

[Owens Z]

So approximately 0.85 propellant mass fractions. Interesting. I have a G.D Triamese detailed document on my HD, same mass fraction.

Since author Dan Sharp did not include the weights for 1967's final version of MUSTARD (pp228-230,255) in his otherwise excellent book, like he did for earlier iterations, this weight breakdown from him (attached) is helpful. It states that the vehicle's final version had a takeoff weight of 935,715 lbs (424.4t). I was going to do some further research into the combined category here "Unusable Fuel + Consumables" before I tried to compute a propellant fraction to four digits (I suspect residual propellant would be 1% at most, and I don't know how much of the final MUSTARD's propellants were reserved to power the three landing approaches), but your "approximately 0.85" is close, Archibald. That this, as you say, is about the same as what General Dynamics figured for its contemporary triamese space launcher makes sense. A mass of 0.15 for everything else would have been challenging for the late 1960's (or even today) but perhaps doable: the UK still had a strong aviation industry then and a pool of talented, can-do engineers from the WW2 generation.