254 accommodate growing volumes of delivered actuators. Although ultimately reduced, this “order of  magnitude” rule of thumb has proven to be succe ssful during development testing of the device. In  addition to tracking the aspect ratios of sample passa geways, all sample chambers were sized to have at  least twice as much internal volume as the maximum sample volume that would be contained, an  achievable goal because the sample volume acquired from the drill and the scoop can be controlled and therefore designed around. To avoid unexpected particl e behavior in a 3/8 G environment or for a unique  rock type, the CHIMRA design intentiona lly minimizes the frequency of scenari os in which it has to rely on  sample to act in a certain manner, such as remaining within one chamber or returning backwards through a screen it had just been sorted through. This latte r requirement was stipulated for two reasons: most  industry sieves are not symmetric and have a pref erred sorting direction and the CHIMRA method of  screen unclogging would only unclog sample from a single direction. A common form of clogging found in early testing occurred when an elongated particle would pass though a two-dimensional orifice, change  direction and not be able to return through that same entrance. To alleviate this behavior and to ensure  that a non-spherical particle does not get trapped within CHIMRA, the exit of any particular chamber was designed to be significantly larger than the entrance. This  feature is most notably seen in the exit from the  1-millimeter grate (Figure 9), where a clearing channel was introduced to prevent sample less than 4 millimeter in diameter but greater than 1 millimeter in diameter from becoming stuck between the two  screens. Another feature incorporated within CHI MRA was to align the interface between a door and  CHIMRA with the rotation axis of the door. This re moves the tangential motion between a closing door  and CHIMRA which could foreseeably result in a perfec tly sized particle creating a Morse taper effect and  wedging the door shut.                           Figure 9. Features to minimize clogging        Figure 10. Sample Diverter Operation    Of equal importance to anti-clogging features ar e design elements that allow troubleshooting when  performance of the sample processing device begins to  degrade. Specifically, the internal layout of  CHIMRA allows almost all of the internal surfaces to be visually inspected by an external camera. Additionally, a rover camera can inspect sample prior to  delivering portions for instrument ingestion; this  provides a checkpoint to give ground operators the op tion to triage samples that look troublesome for the  instruments. CHIMRA minimized the black-box desi gn architecture (sample in/sample out) whenever  possible to provide ground operators with maximum oppor tunity to assess problems as they arise and to  adapt operations to prevent repeat incidents. The samp le transfer tube that funnels sample from the drill  into CHIMRA is the exception to this as it was not possible to include a method of internal visual  inspection.     4-millimeter grate 1-millimeter screen  Exit channel  NASA/CP-2010-216272