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A thermal model of an IR-radiator with 1000 W nominal power and about 300 mm length is developed. Using the thermal software ESARAD and ESATAN the radiation field of one or an arrangement of a set of IR radiators is calculated quantitatively. This thermal model of the IR radiator arrangement can be integrated as part of the thermal model of the test article or the test set-up. Defined test runs can be simulated and the thermal behavior can be predicted. The theoretically defined radiation field of a volume of 2m x 2m x1m was compared with a measured field of an IR radiator. There is a good agreement between the calculated and the measured values. Differences are in the range of 1% to 2.5% for the standard deviation. The 3-dimensional radiation field is stored in equidistant steps in a matrix. This matrix is the basis of a superpositioning program which allows to calculate the radiation field of defined fields of IR radiators.

The thermal shroud of a thermal vacuum chamber is in most cases not perfectly closed. There are holes for windows and feedthroughs and some stands inside the shroud which influence the thermal behavior of the test article. Size and thermo- optical properties of the covers of the holes determine the effect on the temperature change of the test article. This influence is investigated for different cases as they occur in a thermal test chamber. Covers made of aluminized or black KAPTON and painted metal sheets are investigated. Mechanical fixtures are needed for installation of the test articles. By constraints of the test setup these fixtures often can't be designed as adiabatic or actively temperature controlled. For the case of large test articles with relatively low thermal heat capacity as reflectors for telecommunication satellites, the influence of the fixture on the final temperature is discussed for different cases and an optimized solution is presented.

The standard method of the application of videogrammetry during space simulation tests will be summarized. Some improvements, test setups and solved problems will be described. For a videogrammetry measurement a number of pictures are needed. The different views of the test article can be achieved by several methods Test setups with a rotating reflector or a camera on a rotating arm will be presented. If the distortion of the front and the rear side has to be measured simultaneously, two cameras one with view from the top side and an other with view from the bottom side was used. The tilt of the mounting interface with respect to the shell can be measured by means of an additional sophisticated structure attached to the rear interface. Special precaution has to be taken to reach the extreme temperatures in a reasonable time and with modest effort. A number of tests were performed.

Two methods for measuring thermal distortion of antenna dishes under simulated space conditions are described: Photogrammetry Holography With modern photogrammetry an absolute resolution of 20 μm at 1 σ for antenna dishes with a diameter of 1 to 3 m can be achieved. Statistical methods are used to evaluate the 10 to 30 pictures of the test item which are taken from different positions. Double exposure holography has as an interferometric method a much higher resolution in the order of 20 nm to 100μm. But only differences between two shapes will be measured and only in one direction. Both methods are used in our space simulation facility WSA/TVA and several tests are successfully performed.

Various test set-ups are described which illustrate how to obtain very hot and cold temperatures during thermal cycling with the additional requirement that at the extreme temperatures the specimens - in our case white painted antenna dishes- must be visible to perform distortion measurements. In the cold case the number of thermal leaks or holes in the shroud must be small i.e. the effective shroud temperature shall be as low as possible. If a solar simulator is used to irradiate the specimen in the hot case, the absorbed energy can be enlarged by using a removable curtain in front of the antenna, which changes the thermo-optical surface properties to higher αs/εH. In the case of the CASSINI reflector the requirements for the cycle temperature are Tantenna= -160°C and + 150°C. The coating is white paint with αs/εH = 0.2/0.85 and it is not possible to insulate the rear side. More than 3000 Watt/m2 must be absorbed to obtain the high temperature in a space environment.