Characterizing Lightweight and Dimensionally Ultra Stable Structures for Space Application

Paper number

IAC-13,C2,2,4,x19154

Author

Mr. Ruven Spannagel, DLR, German Aerospace Center, Germany

Coauthor

Dr. Thilo Schuldt, DLR, German Aerospace Center, Germany

Coauthor

Mr. Martin Gohlke, DLR, German Aerospace Center, Germany

Coauthor

Dr. Jose Sanjuan, DLR, German Aerospace Center, Germany

Coauthor

Mr. Boris Messerschmidt, Airbus DS GmbH, Germany

Coauthor

Mr. Stefano Lucarelli, Airbus DS GmbH, Germany

Coauthor

Dr. Ulrich Johann, Airbus DS GmbH, Germany

Coauthor

Dr. Dennis Weise, Airbus DS GmbH, Germany

Coauthor

Prof. Claus Braxmaier, ZARM - University of Bremen, Germany

Year

2013

Abstract

Lightweight and dimensionally ultra stable materials and structures are getting more and more important for spaced based applications. For scientific and earth observation missions, instruments with ultra high precision requiring ultra-stable structural materials are necessary to achieve the mission goals. Ultra stable glass ceramics have a very good behavior in terms of dimensional stability, but its huge mass is a disadvantage for space missions. Composite materials like CFRP (Carbone Fibre Reinforced Plastic) are lightweight and their CTE (coefficient of thermal expansion) is tunable to get low CTE at a specific temperature. On the other hand these composite materials are changing their geometry during time and environmental situations caused by moisture release and outgassing. 

Structures, which combine the stiffness and lightweight properties of CFRP and the dimensional stability of Zerodur are a key technology for future space missions. Building such structures is one part of the challenge, the other part of the challenge is to determine the stability of such ultra stable structures. 

Our focus is to measure the dimensional stability of lightweight and dimensionally stable structures for LISA/NGO and GRACE-FO. For LISA, we characterized an optical breadboard consisting of two 5mm thick Zerodur plates connected via a CFRP honeycomb structure leading to a weight reduction of 70\%. For GRACE-FO the thermal stability of the triple mirror assembly of the laser ranging instrument consisting of a 0.5m CFRP spacer and Zerodur end-fittings on each side was characterized. For these measurements, a new facility was built. 

To measure the CTE of the structures, a heterodyne interferometer is used to detect the expansion of the device under test. Two beams are reflected at two mirrors attached representatively to the samples on each side. The noise level of our interferometer was demonstrated to be below 2pm/\begin{math}\sqrt(\rm Hz)\end{math} ensuring an ultra-high accuracy of our measurements. The temperature is detected using PT100 sensors at the sample. Temperature changes are applied radiatively by a heating system in vacuum. 

We present our new measurement facility, its characterization and first measurements of the thermal stability of the two structures for LISA/NGO and GRACE-FO.

Abstract document

IAC-13,C2,2,4,x19154.brief.pdf

Manuscript document

IAC-13,C2,2,4,x19154.pdf (🔒 authorized access only).

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