change in state of the contact switch  might indicate that preload was lost, or the drill slipped off the rock surface.  A compression spring keeps the  switches normally open. As the Butterfly is preloaded against a surface, the spring is compressed, and the switches are closed. The Butterfly sub-assembly also includes a set of three Alignment Cup (5)  features. Currently these features are  designed as simple tapered bushings. These bushings can be used to mate with a Bit Storage Station or Sample Cache, providing a more accurate interface.  ROPEC Z Axis Subassembly Design The Z-Axis sub-assembly utilizes an  off the shelf ballscrew and nut, as well as an off the shelf linear rail and rollers. The ballscrew is driven by a set of spur gears, and a felt seal  prevents debris from migrating into the drivetrain housing. The ballscrew itself has a set of seals which  seal the nut, preventing debris from jamming the reciprocating balls. An inductive proximity sensor is used as a limit switch to home the Z-Axis mechanism, providing a consistent starting position. A thin strip of  sheet metal is cantilevered off of the moving carriage. This strip of sheet metal triggers the Proximity Sensor.  ROPEC Flex Cable Design In order to consolidate cabling on the ROPEC drill, a custom flex cable was designed. A set of two almost  identically shaped flex cables are laid on top of one another with a third cable in between to act as shielding. One flex cable has traces for motor power, and the other for encoder and hall sensor signals.  A detailed investigation was performed early in the design process to determine the amount of layers  required on each flex cable. More layers typically results in a higher cost of the flex cable, as well as a stiffer cable with a larger bend radius. It was important that the flex cable have a low stiffness in this design because the flex cable needs to bend as the drill head is moved along the length of the Z-Axis  Guide Rail. To keep the overall volume of the drill low, it was desirable to have as small a bend radius as  possible. To perform this analysis, the number of wires for each motor, limit switch and other sensors was tabulated, along with the peak electrical current which that wire was expected to experience. Using the peak expected current, a maximum copper trace width was determined, based on standard industry  practice for flex cables and printed circuit boards. Adding all of these widths together and accounting for  gap space between each trace, the required width of the flex cable was determined. ROPEC End Effectors The ROPEC Auger Chuck is able to autonomously lock and unlock a drill bit. With this ability, and the degrees of freedom available, a number of end effectors have been designed to increase the versatility of the ROPEC Drill to different mission architectures. These end effectors are shown in Figure 11 and discussed as follows. These end effectors are demonstrated in the video at the URL below. http://www.youtube.com/watch?v=VhfL3htrtZ8Figure 10. ROPEC Drill Butterfly Subsystem (1) Contact  Switch Housing (2) Contact Ti ne (3) Angular Hardstop (4)  Pivot Shaft / Bushings (5) Alignment Cups 41 52 3 205