Considerable astronomical interest has been directed towards the infrared observations in space using cooled telescopes. The design needs the use of advanced technology in many areas, especially in cryogenic. Observations in the infrared from the space environment are free from the absorption and emission by the earth's atmosphere. Telescopes and detectors cooled to a temperature near to absolute zero improve the sensitivity tremendously, because of reduction of the background noise. The use of liquid helium is essential to achieving such temperature level. Superfluid helium may be the best coolant for this purpose, owing to its excellent heat transport capability. On the other hand, several potential difficulties have been pointed out with respect to the containment of superfluid helium in tanks on board. One of such difficulties was the phase separation between vapor and liquid under zero-gravity condition. Now, it seems that this is solved by the use of the porous plug or the active phase separator. More than five space infrared missions have been planned to be launchned in the 80's. Some are presently in preparation and others are under consideration. These missions are expected to reveal stellar and planetary formation in clouds of gas and dust. The dust radiates primarily in the infrared and obscures shorter wavelengths such as the visible radiation. The Galaxy and several external galaxies are important objects which can be well studied in the infrared. We are also proposing an infrared telescope on board a Spacelab (IRTS). Relating fundamental studies and preliminary design consideration are under way. These all missions are ambitious projects and give a challenge to cryogenic physicists and engineers.
Since heat pipes were introduced into space-related technical society during sixties, their terrestrial applications have been enthusiastically sought and many improvements in their manufacturing processes as well as in the system design have been done. Main application fields in the terrestrial use of the heat pipes are (1) the civil engineering use in cold and snowy region for frozen protection, (2) the cooling of machines and electronics, and (3) the waste heat recovery systems. The terrestrial operation of the heat pipes is inevitably influenced by the earth gravitaional field, and the thermosyphon mode of their operation is most common. The dynamic flow effects necessarily induced during such operation have brought strong impetus to the fundamental research scientists of the non-equilibrium, multi-phase flow field within the heat pipes. Thus the concept of the heat pipes are greatly expanded into “a closed system within which phase-changing process is taking place”, and such new ideas as heat pipe=engine and heat pipe-heat pump have been introduced and studied widely.