Development and Testing of a “Backlash-Free” Gas-Tight High-Precision Sample Dosing Mechanism for the ExoMars 2018 Rover

摘要

This paper presents the development and testing by OHB System AG of the Powdered Sample Dosingrnand Distribution System (PSDDS) with specific focus on the bearing and sealing design. The PSDDS is arnsample handling mechanism on the Rover of the European Space Agency 2018 ExoMars Mission, arncooperative mission with Roscosmos including a scientific instrument contribution from NASA. It isrnentirely developed by OHB as a subcontractor to Thales Alenia Space Italia who is the prime contractorrnfor the whole ExoMars program. The PSDDS is the third part of a chain consisting of four individualrnmechanisms that compose the Sample Preparation and Distribution System (SPDS).rnThe main task of the PSDDS is to receive powdered samples from a stone mill (Crushing Station) andrndistribute the samples in defined quantities to two different kinds of receptacles, a refillable container andrnseveral one-time use Ovens, which are mounted on a carousel (4th mechanism). The sample distributionrnis performed by a redundant Dosing Station (DS). As these powdered samples are quite sensitive torncementation, two counter-measures have been implemented. A Piezo to vibrate the Dosing Station and tornloosen the sample material as well as a device to bypass the two Dosing Stations which is able torndistribute the sample in a more robust way but without the capability to control the amount (AlternativernTransport Container (ATC)). Another task of the PSDDS is to clean the refillable container to allow itsrnreuse without cross contaminating the samples (Cleaning Device).rnThese components and procedures need to be compatible with the Martian environment. This includesrnsample handling and challenging demands for cleanliness and contamination control resulting in strongerrnconstraints for the mechanism’s design and ultimately requiring the development of unique designrnsolutions.rnThe PSDDS design as well as the results of the qualification test campaign under Mars-like conditions arerndescribed in this paper.