418 mounted to provide t emperature control of the M otor Unit. A single PT-1000 sensor , used to monitor the  temperature,  was mounted in the back plate of the Motor Unit and covered with a Spring Support part . The  DC motor, heater and PT -1000 were components for which DLR was responsible.  

The MA is finished with the already mentioned Spring S upport , which guides all 6 cables , protects their  solder points  (covered completely with 3M Scotch Weld Epoxy Adhesive 2216 B/A Gray) , and provides   space for beginning of a Wire Helix formation. The Wire H elix is a bundle of cables partially thermally formed  and distributed along a Wire G uide (a gentle compressive spring) wrapped together into a continuous splice  using lancing tape. The Brake Spring is a relatively narrow compression spring located inside the Spring  Support  (Wire Helix remains in parallel to it - outside the Spring Support). For this reason it is  prone to  buckle, but the Spring S upport is long enough to provide constant guiding of the Brake Spring together with  the corresponding Inner G uide o n the side of the Payload Cage. The actual desc ription of the rest of the  HP3 mole penetrator system including Pa yload cage and Outer casing can be found in [ 5]. 

Worth mentioning is that in some sense each penetrator, including  the HP3 instrument, may become a self - destructive device  if is not designed correctly . Consequently , each joint and connection between parts have  to be selected  carefully, and, given the very limited volume for the mechanism, most of them have to be  connected permanently. For instance, Araldite AV138/HV998 adhesive was used on threads to protect  them from unscrewing, tight fit dowels used to connect Cam with the H ammer , press -fits and riveting of the  Roller parts  and welding in the Tongue Assembly  elements . In most cases , disassembly of such  connections is not possible without partial destruction of the mechanism.  

Design Improvements and S ignificant Technological Features  

The actual cooperation with DLR in the field  of the Hammering Mechanism redesign and development  began in late 2013. As a result of this cooperation, the final hardware was significantly improved in  compa rison to the previous versions [1, 2, 3] . Having an easy access to the in- house workshop and vast  herita ge in penetrators ’ design, the Space Research Centre PAS and Astronika, in cooperation with  Warsaw University of Technology that provided tribological surfaces, was capable of rapid changes in the design and actually developed a new Hammering Mechanism for the HP3 mole instrument . The actual  concept change  was provided in November 2013, design f reeze in December 2013 and successfully  working pre- PFM model operating in February 2014. Six models were developed in total  in years 20132015 : pre- PFM, HM -1, HM- 2, HM-3 (Life Test Unit), HM- 4 (FM) and HM- 5 (FS).  The final design consists  of 38 individual parts  and components (82 total parts). The main des ign changes are described below and  are related to three main domains : mechanism architecture and principl es (rearrangement of  subassemblies’  layout and order), increase of efficiency and simplification of the design (i mprovement of  tribological properties and bearings implementation),  and functionality (launch lock redesign).  

No preload on the drive springs   In the previous design the drive spring was preloaded, which theoretically could result in better utilization  of the spring’s characteristics . In fact , it is particularly important to sustain a free movement of the Hammer  and the Suppressor -Mass i n this ty pe of mechanism, even at the expense of preload benefits . For this  reason the preload option was removed and replaced with a free movement of all assemblies. This simplifies the behavior of the mechanism and consequently travel phases of each assembly and its impact  moments  can be clearly distinguished. The preloaded spring constrained the previous design to have the  drive spring located between the rear part of the H ammer and front of the Motor A ssembly. This caused  the improper load distribution on the H ammer ; namely it was pushed from behind instead of being pulled  from the front, as it eventually was solved. Application of the pulling force in front of the H ammer ( precisely   on the Hammer Nut) naturally stabilizes the Hammer movement in the Hammer Housing and cancel all  clamping possibilities or friction losses. The actual loading sequence is shown in Figure 3.