Vacuum and cryotechniques in space research

Abstract

There are three types of installation in space research laboratories in which vacuum and low temperature are concerned. These are: 1. 1. Space simulation chambers used to investigate the thermal balance of the satellite (solar simulation testing). 2. 2. Vacuum-temperature chambers in which the satellite or its component parts can be tested in the working condition for reliability under extreme temperatures (thermal-vacuum testing). 3. 3. Special installations for the study of particular phenomena or for the development of components. Only the first two types of installation are dealt with in this article. The two installation types can also be combined. In these installations, the test object is situated under vacuum in a chamber which is closed by a thermal wall. For the solar simulation testing, the thermal wall is cooled to a temperature of between 80 K and 100 K by means of LN 2, in order to simulate the cold ambient conditions applying in space. A temperature range of from 100 to 370 K is covered during thermal-vacuum testing. The construction of a thermal wall is explained, together with the various systems of obtaining and maintaining definite temperatures. using LN 2 and GN 2. In the first generation of installations, simulation of the vacuum applying in space was obtained in the USA by a combination of 20 K cryopumps and diffusion pumps, whereas in Europe only diffusion pumps were used. During the past few years, new projects in space research have shown the provision of an ultra-clean vacuum in space simulation chambers to be an urgent necessity. Thus the original conception of a vacuum pump system has been changed in favour of the following combination of pumps: 1. 1. Titanium sublimation pump with LN 2-cooled getter surface, 2. 2. Sputter-ion pump and/or turbomolecular pump, 3. 3. 20 K cryopump. Installations built in the USA during recent years have used 20 K cryopumps as the main element providing the pumping action, whereas in the new installations in Europe, this function sublimation pump. The developments described are illustrated by means of examples, in particular by the IABG 4 m infrared space simulation and thermal-vacuum chamber in Ottobrunn, near Munich. This plant was completed a short time ago for use in connection with the research work on the Helios sun probe.