122 Planetary Protection and Contamination Control   Because integrity of the collected samples is essential for future scientific  evaluation on Earth, stringent  Planetary Protection (PP) and Contamination Control (CC) requirements were levied on t he ACA hardware  to ensure samples would not be compromised by e arthborn contaminants . Contamination c oncerns  significantly drove design and material  choices as well as  assembly methods  and resulted in less than  straightforward  test and qualification flows . Special hardware handling techniques were developed for both  assembly  and testing of contamination sensitive hardware.  

ACA hardware is classified in terms of cleanliness needs based on proximity to collected sample material   (i.e., Martian rock and dust) . Hardware that directly contact s sample material is defined as Sample Intimate  Hardware (SIH) . Hardware that contact s SIH items, but not  directly sample material is deemed Sample  Handling Hardware (SHH), while all remaining ACA hardware is  considered Other . SIH items , including the  sample tubes , hermetic seals, bits, and volume station,  have the most stringent handling constraints  and  required  sterile assembly techniques in an ISO 5 cleanroom . SHH items include the hermetic seal  dispensers, gloves and covers, and the vision station, which were assembled in similar conditions to the  SIH hardware.  

Other hardware included  the Sealing Station, SHA, E E, Drop- off Station, and Parking Lots , which did not  require sterile assembly and handling constraints . While t he Sealing Station directly contacts a sample tube   prior to seal activation , it is considered Other since  a hermetic seal will be installed in the sample tube at  this point and the potential for introducing contamination into the sample tube is not credible. The BC  actually falls into both SHH and Other categories, with internally and externally located hardware requiring  different levels of cleanliness . Since the BC houses the bits used to collect material, internal cleanliness  was important to not introduce contaminants to sample tubes during interactions; however, aseptic  techniques were not levied due to the materials required for mechanism functionality over environments,  such as wet lubrication. External cleanliness was equivalent to the Other items since  the BC enclosure  provides protection to the internal hardware . 

All piece parts were precision cleaned prior to assembly using approved solvents for the implemented  materials and coatings . SIH hardware was cleaned to very stringent cleanliness levels, which all owed  approximately one particle of no more than 50 microns in size per 0.1 m2, defined as Particle Cleanliness  Level (PCL) 50. Other hardware was cleaned to typical cleanliness levels, which allows for one particle of  no more than 300 microns in size per 0.1 m2, defined as PCL 300 . As the particle size decreases , the  number of allowed particles per 0.1 m2 increases, as defined in industry standard IEST -STD-CC1246,  Product Cleanliness Levels – Applications, Requirements, and Determination. In addition to a s tringent  PCL  count, SIH hardware required Non- Volatile Residue (NVR) cleanliness verification to ensure contaminants  such as oils and greases were sufficiently removed to a level of A/10, which means no more than 0.1 mg  per 0.1 m2 remained after cleaning . For a number of SIH items, precision cleaning more than once was  required to achieve the required levels . Hardware was not released for assembly until cleanliness  verification was completed.  

To ensure SIH  cleanliness could be maintained as the hardware was manipulated per the operational  sequence , steps were taken to avoid contact  between SIH and Other items . A glove, which is attached to  each sample tube,  was implemented to prevent  the EE tube gripper from directly interfacing with a sample  tube. The glove is “clean” on the sample tube interface side, and “dirty” on the EE interface side . Each  sample tube with glove attached is stored within a sheath. Clearances between the sample tube and sheath  ensure th e sample tube only contacts surfaces considered clean, while also accounting for position  accuracy of the SHA during sample tube manipulations at a sheath. The glove serves as a Fluid Mechanical  Particle Barrier (FMPB), which based on Computational Fluid D ynamics  analysis constrains  contamination  from reaching clean hardware. The FMPB does this  by restricting flow into the sheath via specific  (tight)  hardware clearances between the glove and sheath in critical locations , which results in a maximum  expected penetration height for particles that may enter a sheath, deemed the “bug line” . During insertion  into and removal from a s heath, a sample tube may contact sheath surfaces if they are located above the  “bug line” , which are deemed clean. The hermetic seal dispensers and volume station employ covers with