SSTO Concept Design Project Team
Section 6.8.7.
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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:

Fuel92%460 tonnes
Structure6%30 tonnes
Cargo2%10 tonnes

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, F/A-18.)

SSTO Concept Design Project Team

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