173 When the mechanism is operating,  the oscillating hammer creates a sine- vibration environment for other  parts of the coring drill and other turret mounted instruments,  even when no impacting is occurring. This  environment becomes much more pronounced during impacting , when a maximum of 6.2  g’s of  acceleration between 34  and 42  Hz is experienced by neighboring actuators and parts on the turret .  

Mechanism Advantages  

The Mars 2020 percussion mechanism has several unique features and advantages compared to similar  extraterrestrial sampling technologies.  

Variable Output Force  The ability to drill with a wide range of impact force makes it unique from the most common and highest  heritage space drill percussion mechanisms which are typically of a cam and spring type. These  mechanisms often use a helical cam to push a hammer back against a spring until the end of the cam  profile is reached and then the hammer is shot forward by the spring and into the anvil  or bit . Examples of  mechanism that use this type of percussion are t he lunar dri lls used by  the Apollo astronauts  [3] and the  HP3 instrument on the InSight mission to Mars  [4]. Also, the vast majority of handheld commercial rotary  hammer drills also have a single fixed level of  percussion output . On Mars 2020, variable output force was  a derived requirement that flowed from a science requirement specifying the quality for core samples   (essentially how intact  the collected cores should be) . Variable percussion output enables soft rocks to be  cored with the minimum required force, thereby improving core quality, without foregoing the ability to  penetrate hard rocks  using higher levels of force. Variable output force has the additional benefit s including  improving the power efficiency of the corer by not using only the power required for a given operation ,  lessening the harshness of the operational environment  and therefore accumulated damage/fatigue for  neighboring turret components , and genera lly creating a more flexible tool for the overall sampling system  by providing ancillary functions described in the Mechani sm Function section.  

The MSL SA -SPaH drill also had a percussion mechanism capable of variable output force, but it was a  very different type of mechanism that used a voice- coil actuator to provide hammering functi on. Although  both systems have similar capabilities, there are also some advantages to the Mars 2020 percussion  mechanism design,  as compared to the MSL voice coil percussion.  

High Level Output Compared to MSL   It was understood early in the project that creating a Mars 2020- sized core by cutting an annulus into a rock  was going to require a more powerful drill than MSL used simply due to shear volume of rock to be removed  and face area of the cut . Force dyno testing from MSL show impact forces with a maximum value of 6 kN  under the drill bit . By contra st, the Mars 2020  drill can deliver more than 15 kN under the bit . Partially this  is due to a more powerful actuator that was used for the Mars 2020 Percussion, but there is also reason to  believe that the improvements in the cr oss section of the percussive part chain have also contributed to the  higher force output . Measurements taken directly under the hammer of the Mars 2020  percussion show  peak impact force values of approximately 40 kN as measured by a Kistler 9041A load was her. Due to the  higher output forces achieved by the Mars 2020 percussion, significantly larger  ROP values  (roughly a  factor of 5 or greater)  were achieved when comparing each system in equal strength rocks – this should  enable significantly longer bit lif e. 

Simple, Robust Parts Bear Impact Loads   The MSL voice coil uses a very unique and highly efficient actuator to directly create linear hammer motion.  However, with the MSL heritage architecture of a wound wire coil and permanent magnet pair there is a  challenging durability problem where the coil must be connected to a driver by wires that must move with  the striker and therefore subjected to high-cycle  bending fatigue . The Mars 2020 percussion system has  the advantage that the hammer and its assembly are essentially simple steel  lumps and springs which are  generally easier to design for tolerance  to repeated shock loads and to meet the life requirement by fatigue  analysis . This was a major reason for opting to develop a different style mechanism for Mars 2020 as  opposed to sim ply re -sizing the MSL mechanism.