Development of the RANCOR Rotary-Percussive Coring System for  Mars Sample Return Gale Paulsen*, Stephen Indyk* and Kris Zacny* Abstract A RANCOR drill was designed to fit a Mars Exploration Rover (MER) class vehicle. The low mass of 3 kg  was achieved by using the same actuator for three functions: rotation, percussions, and core break-off. Initial testing of the drill exposed an unexpected behavior of an off-the-shelf sprag clutch used to couple and decouple rotary-percussive function from the core break off function. Failure of the sprag was due to  the vibration induced during percussive drilling. The sprag clutch would back drive in conditions where it was expected to hold position. Although this did not affect the performance of the drill, it nevertheless reduced the quality of the cores produced. Ultimately, the sprag clutch was replaced with a custom ratchet system that allowed for some angular displacement without advancing in either direction. Replacing the sprag with the ratchet improved the collected core quality. Also, premature failure of a 300-series stainless steel percussion spring was observed. The 300-series percussion spring was ultimately  replaced with a music wire spring based on performances of previously designed rotary-percussive drill  systems. Introduction In 2010, NASA considered three mobility architectures for the  next Mars mission. These included the MER-size rover, MER+  rover which was approximately 30% heavier than MER, and the  MSL-size rover [1]. Since the goal of the future mission was to  capture rock cores and cache them for potential sample return,  Honeybee Robotics was tasked with a development of a core drilling system. The drill had to be mass optimized to fit either the MER or the MER+ platforms. It should be noted that the MER robotic arm, called the Instrument Deployment Device or IDD,  was designed to carry approximately 2 kg of payload at its end. It was assumed that a slightly larger arm on MER or MER+ could potentially carry 3 or even 4 kg of payload. With that in mind, the driving goal of the project was to design a drill that would weigh  approximately 3 kg or less. It should be noted that at the same  time parallel drill development efforts focused on other aspects of  the rotary-percussive coring systems such as reducing the sampling complexity [2].  To help reduce the mass of the RANCOR drill, a number of mechanisms were designed to be driven by a single actuator. The result was a two actuator drill that drives 4 degrees of freedom. One of these actuators drives three degrees of freedom. These are the auger and bit rotation, percussive  mechanism, and the mechanism used to break off the core. The second actuator is used to lock and unlock the drill bit from the chuck so that bits can be removed and inserted into the drill head and also to  enable bits to be removed from the drill head at any time (i.e. if the bit is stuck in a rock). When complete,  *Honeybee Robotics Spacecraft Mechanisms Corporation, Pasadena, CA /g51/g85/g82/g70/g72/g72/g71/g76/g81/g74/g86/g3/g82/g73/g3/g87/g75/g72/g3/g23/g21/g81/g71/g3/g36/g72/g85/g82/g86/g83/g68/g70/g72/g3/g48/g72/g70/g75/g68/g81/g76/g86/g80/g86/g3/g54/g92/g80/g83/g82/g86/g76/g88/g80/g15/g3/g49/g36/g54/g36/g3/g42/g82/g71/g71/g68/g85 /g71/g3/g54/g83/g68/g70/g72/g3/g41/g79/g76/g74/g75/g87/g3/g38/g72/g81/g87/g72/g85/g15/g3/g48/g68/g92/g3/g20/g23/g16/g20/g25/g15/g3/g21/g19/g20/g23Figure 1. Weigh-in picture of the  final mechanical assembly of the  RANCOR drill 217