One of the first things that I got told in my materials class was that for the strength and weight, carbon steel and aluminum are essentially the same. Steel is about 3x as dense, but also 3x as strong, and does not fatigue like aluminum.
I'm assuming that NASA knows this, and chose aluminum for another reason that I'm not aware of.
I'm assuming that NASA knows this, and chose aluminum for another reason that I'm not aware of.