Via spaceflight now:With a recent decision to switch the Space Launch System (SLS) core from aluminum-lithium to non-lithium alloys, NASA has come full circle on a journey that started nearly twenty years ago with the development of Shuttle’s Super Light Weight External Tank (SLWT). The switch is not just about reducing costs, but it will also prove to be more optimal for the stresses that SLS will endure. (Scotts take: Notable that this material change saves the tax payer 30 million per flight)