Почему нижняя ступень ЛМ завёрнута в фольгу, а верхняя нет?

The entire ascent stage structure is enveloped with a thermal and micrometeoroid shield, which combines a blanket of multiple layers of aluminized polyimide sheet (Kapton H-film) and aluminized polyester sheet (mylar) with a sandwich of Inconel skin, Inconel mesh and nickel foil or a polyimide blanket with a single sheet of aluminum skin. The blanket panels, formed in various shapes and sizes, consist (outboard to inboard) of 15 layers of 0.0005-inch-thick H-film. In a few ascent stage areas that have different thermal-protection requirements, the number of layers in a blanket panel varies slightly. Outboard to inboard, the the sandwich comprises a 0.0015-inch-thick Inconel skin and one or more layers of Inconel mesh alternated with 0.0005-inch-thick nickel foil. the number of Inconel mesh and nickel foil layers in a sandwich and the thickness of the aluminum skin vary considerably at different areas of the vehicle, depending on the duration and intensity of RCS thruster plume impingement at those areas. The combined thermal and micrometeoroid shield is mounted on low-thermal-conductive supports (standoffs), which keep it at least 2 inches from the main structure... The aluminum or Inconel skin (the outermost material) serves as a micrometoroid bumper; the sandwich and blanket material serve as thermal shielding...

The aluminized Mylar blankets insulate the structure against temperatures up to +350 (deg) F. On the TCA support truss members, which are subjected to temperatures in excess of +350 (deg) F due to engine radiation, an additional 20 layers of H-film are installed. H-film has an insulating capability up to +1,000 (deg) F. Additional H-film blankets are also used in other areas of the ascent stage that will be subjected to temperatures in excess of +350 (deg) F.