A dewar includes an inner dewar and a dewar thermal shield. The dewar thermal shield has a thermal shield body formed of a layer of radiative insulation, an inner layer of fiberglass cloth overlying the layer of radiative insulation, a metallic screen overlying the inner layer, and an outer layer of fiberglass cloth overlying the metallic screen. The dewar thermal shield also has a thermal shield tail cap attached to the thermal shield body. The tail cap is formed of a layer of radiative insulation, a layer of fiberglass cloth overlying the layer of radiative insulation, a layer of thermal foil overlying the layer of fiberglass cloth, the thermal foil being formed of thermal conductors embedded in a film adhesive matrix with the thermal conductors extending to the body, and a top layer of fiberglass cloth overlying the layer of thermal foil.