To provide a heat-resistant felt spacer eliminating the step of a heat insulating material connection section adapted to a space shuttle.

The thickness of the heat insulating material is set according to the heating rate distribution of an airframe for an airframe structure section 30, the thickness of the heat insulating material differs by place, and a step is generated at the connection section. Although the connection section of the heat insulating materials 20, 21 has a step, a wedge-like spacer 10 is inserted and stuck between the heat insulating material 21 thinner in thickness and the airframe side structure section 30. The heat insulating materials 20, 21 are made equal in height at the connection section by the spacer 10, the thinner heat insulating material 21 is inclined in a tapered state and gradually made lower, and the abrupt step shown in the past disappears. The breakage caused by overheat and dynamic pressure at the connection section is eliminated, the heat insulating material 21 is not required to be raised to the level of the heat insulating material 20 to eliminate the step, and a weight increase is prevented.