in a vacuum environment as in space is preferable in the embodiment the flexible thermal control material 10 d is adhered to the pif heat insulating layer 31 on the surface of the liquid hydrogen tank by the bonding layer 18 but the flexible thermal control material 10 d can also be adhered to the surface of the liquid hydrogen tank by a fastening member as the fastening member a fastener for fastening and fixing a component to another component can be used for example a rivet can be used for example as the fastener fig3 is a diagram in which the flexible thermal control material 10 10 a to 10 f is provided by the bonding layer 18 using a polyimide foam heat insulating layer 41 instead of the pif heat insulating layer 31 of fig8 the polyimide foam heat insulating layer 41 is a foam in which air bubbles have an open cell structure and exhibits an effect of vacuum insulation a thickness of the polyimide foam heat insulating layer 41 is for example preferably approximately from 10 mm to 50 mm fig1 is a diagram in which the flexible thermal control material 10 10 a to 10 f is provided on a heat insulating layer 42 having a laminated body structure of two layers which are the pif heat insulating layer 31 of fig8 and the polyimide foam heat insulating layer 41 the polyimide foam heat insulating layer 41 is a foam in which air bubbles have an open cell structure and exhibits an effect of vacuum insulation a thickness of the heat insulating layer 42 of two layers which are the pif heat insulating layer 31 and the polyimide foam heat insulating layer 41 is.