> Makes me think they are leaving something big out of the article. I'm certainly not leaving anything out on purpose! Speculating, though, I imagine it's a q

> Makes me think they are leaving something big out of the article. I'm certainly not leaving anything out on purpose! Speculating, though, I imagine it's a question of risk versus reward. There have definitely been advances in rocket designs since the 1960s—the RS-25 is a great example of a more modern high-efficiency, high-performance design (the MSFC propulsion engineers I interviewed a couple of years ago for my F-1 piece likened the RS-25 to a Ferrari, while the F-1 is more like a giant Mack truck). But developing rocket engines has until relatively recently been the domain of big aerospace companies on big government contracts, and under those circumstances it's often far more short-term cost efficient to go with the sure thing and either use an existing rocket or design one with a conventional bell nozzle. Rocketdyne in fact proposed an annular aerospike engine for the space shuttle when the program was in early development, but the technology wasn't considered mature and the RS-25 was designed instead.