Dimensional stability investigation of low CTE materials at temperatures from 140 K to 250 K using a heterodyne interferometer
- Paper number
IAC-17,C2,IP,14,x39807
- Author
Mr. Ruven Spannagel, DLR, German Aerospace Center, Germany
- Coauthor
Ms. Ines Hamann, DLR (German Aerospace Center), Germany
- Coauthor
Dr. Jose Sanjuan, DLR, German Aerospace Center, Germany
- Coauthor
Dr. Felipe Guzman, DLR (German Aerospace Center), Germany
- Coauthor
Prof. Claus Braxmaier, ZARM - University of Bremen, Germany
- Year
2017
- Abstract
Light weight materials with excellent dimensional stability are increasingly needed in space based applications such as telescopes, optical benches, and optical resonators. Glass-ceramics and composite materials can be tuned to reach very low coefficient of thermal expansion (CTE) at certain temperatures, including room temperature and cryogenics, where a growing number of instruments in scientific and earth observation space missions are operated. Very accurate setups are needed to determine the CTE of such materials. With our laser-interferometric dilatometer setup we are able to measure CTEs of a large variety of materials in the temperature range of 140 K to 250 K. Special mirror mounts with a thermally compensating design enable measurements of the expansion of cylindrical tube-shaped samples using a heterodyne interferometer with demonstrated noise levels in the order of 10 pm/$\sqrt{\rm Hz}$. The temperature variation of the sample is obtained by a two stage controlled heating/cooling setup where a pulse tube cooler and electric heaters apply small amplitude temperature signals to cool/heat the sample radiatively in order to reach a homogeneous temperature over the whole sample. A carbon fiber reinforced polymer (CFRP) sample was selected to run CTE measurements, achieving results in the 10$^{-8}$ K$^{-1}$ range including all known uncertainties. The limitations of our setup have been identified and the largest uncertainty contribution has been determined to be tilt-to-length coupling of the sample due to temperature variations. Several improvements are currently underway to minimize our uncertainty budget. New results with the enhanced setup will be presented- Abstract document
- Manuscript document
(absent)