255 CHIMRA’s capacity to adapt to any singular element failu re and maintain the ability to process and deliver  drilled sample was primarily accomp lished through design configuration. If a component of the 150micron portioning mechanism malfunctions, such as a failed portion actuator or jammed portion tube, the  150-micron sample can be rerouted to the scoop and distributed through the 1-millimeter portioning  mechanism. A failure of the scoop or thwack actuator was more problematic to accommodate in design.  This is because the internal configuration of CHIMRA that maximizes the internal viewing surfaces results  in using both the tunnel and scoop to route sample inte rnally. This meant that an actuator failure in an  open configuration could ultimately cause all sample to be lost during processing. To address this, the primary reservoir diverter (Figure 10) was implemented to ensure that samp le can still be internally routed  to a portioning device without losing the majority of the bulk sample in situations where the tunnel or scoop has failed open. A failed scoop actuator will also  not impede sample drop-off to the rover inlets.  The relative configuration of the 150-micron porti on tube and the scoop swept volume allows CHIMRA to  be lowered down to the rover deck to deliver samp le even if the scoop actuator is failed open.   It would be naive to assume that CHIMRA potential ma lfunctions are limited to actuator failures; internal  clogging is also a concern. The inclusion of two radically different means of motivating sample within CHIMRA, sinusoidal vibration and high energy impact  events, maximizes the likelihood that particles  stuck within its cavities can be removed. A notable exception to the self-sufficient redundancy of CHIMRA is a scenario in which the device failure occurs within the vibration mechanism. While the development plan for this scenario was to motivate sample through a portioning chamber by using a thwacking device to vibrate CHIMRA, initial testing suggests that utilizing t he drill’s percussive voice coil (1) will be more  effective in generating internal CHIMRA dynamics.    Although the previously discussed guidelines were already culled from a far greater list that covered implementations more unique to CHIMRA, there are three universal concepts that, above all else, will make CHIMRA a robust and useful tool to the scie nce community for a lifetime on Mars. The first is the  ability to view all of the internal areas within CHIMRA to allow ground oper ators to understand how  sample is behaving within CHIMRA and to troubles hoot any problems that arise during mission life.  Second, a science sample can be delivered to the rove r instruments even in the event of a malfunction.  Third, the design configuration allows for multiple methods to motivate sample through CHIMRA. Finally, it is worthwhile to explicitly addr ess the conflict of interest in desi gning a sample processing stage within a  constrained volume. A number of changes can occur during subsystem design maturation: actuator volumes can increase, external volumes can become  encroached upon, and st ructural components or  interfaces are increased in size. Each of these changes can be reacted to by shrinking internal  passageways; compromising on  the features that will ultimately ma ke the device a su ccessful sample  processing device. All effort should be made by subsystem configuration engineers to afford the sample processing device a greater volume than is thought to be needed.   Thwack! - Development of the Primary Thwacker Mechanism   The complexity of the PTM and STM does not lie in t he mechanism itself as both are essentially simple  latch and pawl mechanisms. Instead, the difficult y was in the amalgamation of typical mechanism  robustness metrics with the nonstandard and undefined mechanism goals: clearing a screen clogged with an unknown particle type.    Both the PTM (Figure 11) and STM have enough similariti es that only the development of the PTM will be  discussed in detail. The input to the mechanism is the tunnel base (shown in blue in the cross section). This is the same structure that supports and mani pulates the tunnel that facilitates sample movement  from the 150 micron screen to the portion box. Contained inside the tunnel base is the latch cartridge and  tang assembly. The latch cartridge houses a spring-pre loaded Vascomax latch. This latch has redundant  rotating surfaces: the latch itself pivots around a pin and the pin is able to rotate independently via the bronze-impregnated, steel-backed bush ings that provide the straddling support. The tang assembly is a  Vascomax pawl with an internal set of duplexed back-to-back bearings that allow the tang to rotate independently within the tunnel base. The output of the mechanism, shown as yellow in the cross section,  NASA/CP-2010-216272