53 attention is given to the three main design topics: pre- torque device, bearing concept and dynamic feedthrough. In the subsequent section , the test results and lessons learned of the  described design topics  are presented. The paper concludes  with a short summary including an outlook  to future activities . 

Design Drivers  

The main design drivers can be divided in to the following four groups:   • Design drivers derived from the positioning demands for the hand- over of the sample;   • Design drivers originated from Planetary Protection, Cleanliness and Contamination Control  requirements preserve Mars  and analyzed Martian Samples from Earth contamination;   • Design drivers imposed by the planetary environment on Mars ;  • Design drivers created by the behavior of the powdered sample.  

The first group of design drivers requires   a high radial and angular PSDDS positioning performance in  order to be able to dose the powdered sample into the small receptacles accommodated on the ensuing  mechanism (PSHS). These receptacl es are 32 single- use pyrolysis O vens plus one multiple use  Refillable Container . The pyrolysis O vens are the most critical receptacles in terms of sample dosing  requirements. They have an inlet diameter of few mm and shall be accurately filled with about 0.2 ml of  powdered sample. The dosing performanc e is therefore also dependent upon the relative position ing of  the Dosing S tation output funnel and Ovens inlet. To ensure that the sample is correctl y delivered to the  Ovens, the PSDDS shall comply with an abso lute position accuracy of approx. ±0.055°. This requirement  has been derived from an absolute position accuracy of ±0.1 mm of the dosing funnel w ith respect to the  nominal position of the O vens at the hand- over port, this considering that the dosing funnel s are at a  distance  of 105 mm from the PSDDS rotational axis.    The second group of major design drivers is imposed by Planetary Protection, Cleanliness and Contamination Control requirements. Any kind of contamination originated from Earth could lead to false positives and false negatives findings of the ALD Analytica l Instruments while searching for traces of  extraterrestrial life on Mars. For this reason, an Ultra Clean Zone (UCZ) has been designed and implemented within which the PSDDS as well as the other SPDS mechanisms operate. A priority  requirement is therefore to control and minimize the organic contamination (molecular, particulate and  biological) to an extremely small extent , which allow s in the end to  arrive at  a total organic contamination  of the whole UCZ of very few tens of nano- grams (ng). Moreover, for Planetary Protection reasons and to   preserve UCZ sensitive items  from microbial contamination, all UCZ parts are also treated with a rigorous   bioburden reduction process ( Dry Heat Microbial Reduction) which will bring the UCZ Hardware   bioburden to a level of 0.03 spores per square meter maximum. To achieve these very challenging  Planetary Protection, Cleanliness and Contamination Control requirements, all UCZ constituent parts are  integrated in an  ultra-clean environment (ISO3 AMC -9 [or] glove boxes train) and to avoid risk of  recontamination the UCZ will be over -pressurized from the moment of its sealing after integration in the  ultra-clean environment until the first opening on Mars. Since actuators as well as sensors and other  electrical components are a high source of contamination, SPDS electro- mechanics components are not  allowed inside the UCZ. This calls for the need of dynamic feed- through that, on the one hand needs  to  be gas -tight and, on the other hand, need to avoid high parasitic torques to allow smooth motion and a  low system weight. These are two contradictory requirements that require the adoption of carefully  balanced compromises. Furthermore,  all structural parts of the mechanism that enclose the UCZ need  gas-tight seals on their interfaces requiring a stiff structure with a minimum number of internal interfaces.  Other origins of contamination are different types of materials or coatings. Basically, the only material group that is acceptable ins ide the UCZ is metals. When unavoidable a very limited use of specific  polymers and low temperature grease is allowed. Also the choice of coating is limited by several factors such as its  compatibility with the ultra- cleaning processes applied to the parts before entering in the ultraclean integration environment (which includes bake- outs, ultra- sonic baths with different solvents,  bioburden reduction and CO 2 snow -cleaning), chemical compatibility with instruments analy sis, and the