416 Casing with  the Payload. The original idea of the system was provided in [1] and in principle, the Hammer  is pulled up on its C am by the rotational movement of  a motor axis with a r oller which periodically loads the  Drive Springs located between the Hammer and the Suppressor Mass. After release from the Cam, the  Hammer accelerates downwards eventually hitting the Outer Casing and causing its penetration, whereas  the Suppressor  Mass travels upwards and its movement is compensated by a Brake Spring and Wire Helix  in its rear part.  

a)   b)   Figure 1.  a) HP3 Hammering Mechanism (FS), b) HP3 overall system (credits: DLR)   The energy distributed between the Suppressor Mass and the Hammer depends on the mass ratio between  those two assemblies.  In some  sense, the penetrator behaves like a mechanical diode, with high  penetrating force provided by the Hammer ’s impact on the Outer Casing and a small pulling up reaction  force. The Suppressor Mass travels up adequately and its kinetic energy is compensated by gravitational  potential and compression of a Brake Spring located between the Suppressor  Mass and the Outer C asing.  The reaction force of the Brake S pring should be less than the holding forces of the Support Structure that  guides the penetrator at  the beginning of movement , and later the friction force between the Outer Casing  and the regolith. The detailed sequence of operation was provided in [5]  for HP3  and also in [ 6] and [7] for  CBK’s KRET developments.   

The HP3 penetrator uses  a cam mechanism to perform the strokes , which has clear advantages like: the  simplicity of control (just powering the motor  in one direction), straightforward locking and unlocking of the  system using the rotating movement of the motor , and space heritage through  the development of PLUTO  for the Beagle 2 mission  [1, 2, 3]. The disadvantage is a relatively short compression of the drive spring   (and hence stroke energy) , which is limited by the height of the cam.  Inspired by PLUTO ’s design,  NASA  engineers also developed a spring- loaded mole -type penetrator [8].     Contrary to DLR ’s solution, CBK developed another mechanical penetrator –  KRET, which also  accumulates stroke energy in a spring, but this solution used a special latch grip which allowed the motor to perform  multiple rotations before the hammer was latched. As a result higher compression values could  be achieved as well as higher stroke energies (2.2 J in KRET 1 and 3.5 J in KRET 2), see [6]. In this solution  the motor’s current was monitored and the direction of movement of the motor interchange d accordingly.    Aside from the mechanical solutions , electromagnetic ones are known and utilized, for instance the space  flown  (TRL 9)  MUPUS device for ESA ’s Rosetta mission [9]. This type of penetrator has the energy stored  in a capacitor and released through an  electromagnet ic coil with a hammer accelerated as a moving core  of the electromagnet. Based on this design further developments were  provide d, such as the CHOMIK  device for  the Phobos -Grunt mission [ 10], and the prototype of a High Energ y and Efficiency Penetrator   [11]. The d isadvantage of such a solution is that it requires a capacitor that  should be close to the drive coil  Support Structure   Science Tether   HP3 penetrator   (with HM inside)