SSTO Structure Fraction
For this conceptual design, we want to be realistic, but
optimistic, when it comes to estimating the weight of materials. If we
used the Space Shuttle as
our data base, we'd be way off. Just switching from riveted and welded
components to machined components turned out on an NC mill will reduce
the structural weight by 30%. Tuning the structure to just what's
required to carry the loads can knock off 50% of what's left.
With GLOW being about 500 tonnes, the mass breakdown is:
These are reasonable assumptions because the cost of manufacturing using
NC milled components is much lower than parts assembled from little pieces.
As long as you're going to mill the structure, you might as well tune it.
The difference is only software, and the software is already in the systems
we'll use. The example I'm using is a Unigraphics CAD system used for
design, feeding directly into the milling machines. Unigraphics is very
happy to adjust the shape of a structural component using any complex
equation you can feed it for structural performance. It works
(examples: C-17, Delta III,
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