Rittweger, Andreas

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Preferred name
Rittweger, Andreas
Official Name
Rittweger, Andreas
Alternative Name
Rittweger, A.
Prof. Dr. Rittweger, Andreas
Main Affiliation
ORCID
GND

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    Item-typ:Veröffentlichung,
    Laser-interferometric dilatometry
    (2017-10-04)
    Spannagel, Ruven
    ;
    Rittweger, Andreas
    ;
    Braxmaier, Claus
    ;
    Braxmaier, Claus
    Highly dimensionally stable materials and structures are particularly needed in optical systems such as ultra precise optical clocks, as well as materials with excellent dimensional stability and light weight properties for space applications such as telescopes, optical benches, and optical resonators. Also, the dimensional stability of mounting technologies of materials with different properties is of high interest for such applications. Glass ceramics and composite materials can be tuned to reach a very low coefficient of thermal expansion (CTE) at different temperatures, enabling best stability in the operating temperature for certain applications. In order to determine the CTE of such highly stable materials, very accurate set-ups are needed. In this thesis, metrology set-ups to measure the CTE of a large variety of material samples are designed, realized and verified, measuring dimensionally stable glass ceramics. The set-ups are able to characterize tube shaped samples at a temperature range of 140 K to 333 K. Due to our unique mirror mount design all kind of materials can be characterized. The optical dilatometer set-ups are based on a heterodyne interferometer with a displacement sensitivity at the sub-nanometer level. This instrument is used to measure the expansion of a sample when applying controlled small amplitude temperature signals. A carbon fiber reinforced polymer (CFRP) sample was characterized where CTE levels of 10 -8 K -1 from 140 K to 250 K were measured and a detailed uncertainty analysis was performed. The verified metrology set-up for tube shaped samples was adapted for CTE measurements of larger structures. Therefore, a large thermal chamber was set up and a 0.5 m CFRP spacer with Zerodur endfittings as a representative joint technology demonstrator for the GRACE Follow-On space mission at 302 K was investigated.
    Dissertation
      433  216
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    Methodology for the Design and Verification of Small Body Landers with a Crushable Impact Absorber
    (2023-05-15)
    Grimm, Christian
    ;
    Groll, Rodion
    ;
    Rittweger, Andreas
    ;
    Witte, Lars
    ;
    Scharringhausen, Marco
    The interest for the exploration of small solar system bodies has increased significantly over the past 2 decades and has since evolved from a side topic to one of the corner stones in the international science community. Major disciplines include studying the formation of the solar system, the evolution of life within, planetary defense against potential hazardous objects, as well as human exploration and resource utilization. Recent missions and studies showed that a common understanding was established to enhance high-class missions with carrying-along capabilities for detachable and specialized systems. Specifically the touchdown and landing on the surface is a very risky maneuver, but enables unprecedented high resolution in-situ investigations. However, non-propelled landing systems were designed so far to land on very small objects only with mean diameters of < 4 km (e.g. Near-Earth objects). The general interest has shifted only recently to larger bodies with mean diameters of > 10 km (e.g. Main-Belt and Trojan objects). But with increasing size and density of the target the gravitational attraction on a separated lander increases significantly, which results in much higher touchdown velocities and potential harmful impact loads. For these types of landers, however, no adequate protection system currently exists! For this reason, this thesis reviews existing methods of impact and crush mechanics, which were recombined and partially extended for the defined scope of application, to formulate a new system context and a coherent design and verification methodology for such a new technology. More specifically, this dissertation investigated the concept to enhance deployable non-propelled small body landers with a crushable and expendable exo-shell, with the main objective to sustain higher landing velocities in the range of 1 – 5 m/s by simultaneously lowering impact loads to < 100G. Furthermore, the work aimed at creating a comprehensive and applicable guide from the first concept idea to a verified innovative system design. It therefore performed the entire processing chain, including concept analysis and evaluation, system design and functional demonstration as well as empirical investigations using laboratory experiments and numerical simulations in the to be expected low gravity environment. Hereby providing fundamental details and the required tools to be applied by system and project engineers in the future to effectively design and verify small body landers with increased system performance and reliability as well as reduced overall development costs.
    Dissertation
      213  152