4 The modular approach was not exclusive to the design phase. A team of supporting engineers, working  closely with the flight hardware engineers, designed, built and executed twelve Drill Development Tests (DDT) across several test platforms starting in S eptember 2007 and completing in June 2008 (see Table  1). DDT-3 through 6 were performed using a prototype dr ill, mounted to a robot arm, that was functionally  equivalent to the flight Drill featuring: a flight-like bit assembly, chuck (passive), spindle, voice coil  actuated percussion mechanism, representative stabiliz er kinematics and a weigh-on-bit force sensor.  Drilling tests (DDT-3) in various rock types with natur al surfaces generated the design requirements for:  spindle torque and speed, impact energy, and weight-on-bit. This test activity also yielded algorithms for autonomous drilling that will be implemented in flight system software. Other test platforms utilized  duplicate prototype Drill subassemb lies so that those tests could be performed in parallel.  

Table 1. A list of completed Drill Development Tests indicating the usage of flight-like   prototype mechanisms: bit assembly (B), spi ndle (S), chuck (C), percussion (P)   Italicized text indicates tests performe d using an arm-mounted prototype Drill 

DDT-1 Cold Spindle / Bit Drag (B,S) DDT-2 Bit Exchange (pickup only) (B,S,C)  DDT-3 Drilling Parameters (B,S,C,P) DDT-4 Drilling from a Compliant Arm (B,S,C,P)  DDT-5 Dynamic Environment due to Drilling (B,S,C,P) DDT-6 Bit Life (B,S,C,P)  DDT-7 Sample Flow in Lo w Pressure (B,C,P) DDT-8 Bit Release Under Load (B,C)  DDT-9 Sampling at Low Pressure (B,S,P) DDT-10 Bit Retraction Force (B – tube and bit only)  DDT-11 Force Sensor PQV DDT-12 Percussion Cable Cycle Life 

Lastly, the modular design extends into flight Drill integration and testing. All the mechanisms in the Drill  are fully assembled and qualification tested prior to being integrated into the Drill top level assembly.  Thus, some of the lessons learned during the as sembly and test of one Drill sub-mechanism was  preemptively applied to others. Some of these disc overies included: manufacturing defects, cabling  process errors, chamber frost mitigation and electronic ground support equipment operation.   Drill Design Description 

Autonomous sample acquisition is a complex process that requires a device with high functional density. The Drill is comprised of 7 sub-elemen ts depicted in Figure 3. Starting at the business end of the Drill,  there is a bit assembly that cuts the rock and collects the sample (Figure 3a). Supporting the bit is a subassembly comprised of a chuck mechanism (Figure 3b) to engage and release the new and worn bits, respectively, and a spindle mechanism (Figure 3c) to rotate the bit. Just aft of that, is a percussion  mechanism (Figure 3d) which generates hammer bl ows to break the rock and create the dynamic  environment used to fluidize the powdered sample. The aforementioned components are mounted to a translation mechanism (Figure 3e) which provides linear motion and senses weight-on-bit with a force sensor. There is a passive contac t sensor / stabilizer mechanism (F igure 3f) that se cures the Drill’s  position on the rock surface, and flex harness man agement hardware (Figure 3g) to provide the power  and signals to the translating components. The remai nder of this paper describes the Drill mechanisms,  highlights how their design features  enable the execution of reliable ex traterrestrial dr illing, and expands  on various design challenges.      NASA/CP-2010-216272