Low thermal conductivity

small additional mass and good mechanical strength are basic requirements for the thermal insulation of liquid hydrogen and liquid oxygen tank on the rocket. Polyurethane (PU) foam is the most widely-used material in the insulation of the cryogenic tank in rocket due to its light mass

good thermal and mechanical performance. However

long-time exposure to large temperature gradient will incur additional mass due to moisture uptake

which also deteriorates the thermal performance. Thus it is important to determine the exact additional mass for the design of the rocket thrust. This paper designs an experimental apparatus for the test of PU foam specimen

one side of which is cooled to about 45 K and another is exposed to temperature controlled at 30°C and relative humidity of > 95%. Two home-made pulse tube coolers are used to provide the cooling power

which are installed on a vacuum room. Totally 4 groups with each 2 specimens are tested

and the data are compared to the test results at temperature of 78 K. The results reveal that the effects of cryogenic pump for 78 K and 45 K on one side have no effects on the moisture uptake and the butt-jointed structure.