Isotopic Separation via gas centrifuge can be a relatively cheap process, (costing $10's-100's/kg in large scale), particularly when there are large mass ratio differences and the metal can be turned into a gas easily at low temperature (eg Nickel or Iron Carbonyl, Uranium Hexafluoride, Titanium Tetrachloride). The newly developed Silex laser enrichment process is apparently as little as 10-30% the cost of gas centrifuges.
Not worth the trouble. Easier to save weight by optimizing systems and structure and simply using lighter materials where possible.I suspect you seriously underestimate the cost of this.
At that point if lightweight isotopes are cheap enough to fit in with your weight saving economic cost target (eg $500/kg for commercial jets) then you are sensible to do that too.
Do you have any links that describe separation processes and/or the companies that offer this?
Just realised that I have been looking at the cost saving numbers wrong. 25% Ti46 at $30/kg saves 1% weight for $3000/kg saved50% Ti46 at $100/kg saves 2% weight for $5000/kg saved.95% Ti46 at $330/kg saves 4% weight for $7500/kg saved.So probably useful for fighters and spacecraft but not for commercial aircraft excepting possibly the engines.