ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
Thermal activation Shape memory polymers (SMPs) are specialized plastics with a low transition temperature (relative to its  melting temperature), at which the plastic becomes malleable and can be molded into a new shape. When cooled, the plastic retains that new shape until heated again past its transition temperature. We experimented with 0.79-mm (1/32-in) thick sheets of shape memory plastic as a means of actuating a  deployable solar array, as can be seen in Figure 8. Figure 6. (left) The shape memory plastic folded into a quad-flasher.  (right) Deployed configuration The shape memory plastic can be folded into the pattern for the array and then thermally activated to  return to the flat (or deployed) configuration. Alternatively, strips of the plastic can be affixed to the rows of panels that wrap around the central bus, rather than having the shape memory plastic cover the entire back surface of the solar array. This reduces the material thickness that must be added to the array, but may complicate the thermal activation if the strips are fully isolated from one another. As the added volume of the SMP to the array is very slight, this method of actuation has potential application to deployable arrays on CubeSats or other small satellites, where volume is especially critical. Lessons Learned Once deployed, certain methods of passive actuation (such as centripetal acceleration and stored strain  energy) may require an additional mechanism to lock the panels into their deployed state to keep the array flat. As uncontrolled methods of deployment are undesirable, such a latching mechanism is  necessary to reduce the chance for failure with these methods of actuation.  For communications applications, the requirements for the final shape are more stringent than for some  other applications. At this stage, the flatness of the final deployed configuration has not been evaluated, but the latching mechanism described above could provide a solution to keep the panels at a consistent flatness. During testing, we observed that some of the actuation methods caused strong vibration loads on the  panels. This was especially the case for the centripetal acceleration method and stored strain energy  method, but was also observed to a lesser degree in the pneumatically actuated model. Further analysis and selection of final materials are needed to determine how detrimental these vibration loads will be to  the structure and wiring.  If thermal activation of a shape memory polymer can be achieved for in-space deployment, this method  will be most promising for the CubeSat array. The actuation is slow enough to not induce vibration loads in the panels, and the material has a thin profile which takes up little of the constrained volume. 193
References Lang, R. (1997). /g50/g85/g76/g74/g68/g80/g76/g3/g76/g81/g3/g36/g70/g87/g76/g82/g81/g17 St. Martin's Griffin. Shafer, J. (2001). /g50/g85/g76/g74/g68/g80/g76/g3/g87/g82/g3/g36/g86/g87/g82/g81/g76/g86/g75/g3/g68/g81/g71/g3/g36/g80/g88/g86/g72/g17 St. Martin's Griffin. Zirbel, S., Lang, R., Thomson, M., & al., e. (2013). Accommodating Thickness in Origami-Based  Deployable Arrays. /g45/g82/g88/g85/g81/g68/g79/g3 /g82/g73/g3 /g48/g72/g70/g75/g68/g81/g76/g70/g68/g79/g3 /g39/g72/g86/g76/g74/g81/g15/g3 Vol. 135, paper no. 111005, DOI:  10.1115/1.4025372.  194
is discussed below, followed by details of the design which are critical for understanding the lessons  learned and any unique mechanism features. The objective of this publication is to provide detailed information on the design of the ROPEC Drill, focusing on educating future mechanism designers of similar devices. This work was funded by the National Aeronautics and Space Administration (NASA) Planetary Instrument Definition and Development Program. Driving Requirements The ROPEC drill is designed to support a “One Bit-One Core” approach to delivering rock samples to a  sample return canister [4]. This method dedicates a single drill bit to the acquisition of each returned rock  core, as shown in Figure 1. After the core has been separated from the base rock and captured within the drill bit, the entire bit is delivered to and stored within the sample cache in an enclosed casing, to  ultimately be returned to Earth. This method simplifies the process of caching rock cores by eliminating  additional mechanisms required to extract rock cores from drill bits and place them within sealed canisters. The “One Bit-One Core” technique lead to one of the driving requirements on the ROPEC drill which was the ability to autonomously change end effectors. Since each core would have a dedicated drill  bit for sample caching, the ROPEC drill and its bits have been designed with dedicated tool change features. This also allows for alternate end effectors, such as the Rock Abrasion Brushing Bit (RABBit), Powder and Regolith Acquisition Bit (PRABit), and Core PreView Bit. The ability to change bits drives many aspects of the ROPEC design.  Figure 1.  “One Bit One Core” Mars Sample Return Architecture The “One Bit-One Core” architecture also requires that each drill bit be as light weight and volume  efficient as possible to ensure that they could be returned to Earth at a later stage. At present, the return of the cached samples has not been explicitly defined as a mission by NASA. However, if approval for the mission is obtained, it will likely consist of two separate missions [5]. The first mission will consist of a Lander, Fetch Rover and a Mars Ascent Vehicle. Landing close to the sample cache, the small Fetch Rover would drive to the cache, retrieve it, and return it to the Lander, where it would be placed inside the Orbiting Sample (OS) within the Mars Ascent Vehicle (MAV). The MAV would then launch from the  Bit CoreBreak-off tubeEach core stored in  individual bits [Spare Bits Available]Each bit placed inside a  sleeve within the cache and sealed Orbiting SampleBit Assembly Bit Sleeve Assembly Sample Cache  transferred to Orbiting  Sample by later  missionSample Cache Assembly 196
surface, escape Martian gravity, and jettison the OS into Mars orbit. The second mission would retrieve  the OS some time later and return it to Earth onboard an Earth Entry Vehicle. While the design of the MAV has not been finalized, Volume and Mass dedicated to the Sample Cache and OS is likely to be highly constrained. This drives the Bit Assembly to be as small in diameter and length and as low mass as possible. The small form factor of the bit is a significant driver on the allowable size of internal components within the ROPEC drill. An animation showing this Mars Sample Return architecture is available at the following URL: http://www.youtube.com/watch?v=NphWPvi9cy4 Another driving requirement on the ROPEC design was the ability to lock the Auger stage rotation  position during the Core Breakoff routine. Previous coring drill designs have had difficulty shearing rock cores, particularly in high strength igneous rocks. It was found that rotation of the bit inner shearing tube within the main drill bit would sometimes cause the latter to rotate with the shearing tube due to friction between the tubes overcoming the Auger actuator holding torque. This would negate the breakoff effect, and simply cause the entire bit to spin around the rock core, which was still attached to the base rock. For this reason, the SASSI drill was the first coring drill to implement an Auger Locking Mechanism to lock the position of the Auger during the breakoff sequence. This requirement has since been implemented on the  ROPEC drill and all other Honeybee Robotics coring drills that use the eccentric tubes method of breaking off rock cores. This requirement is a significant design driver for the ROPEC drill. Lessons learned from previous Honeybee Robotics developed coring drills suggested that the core  breakoff mechanism worked well in shearing the rock core from the base rock, but that core quality needed to be improved in order to maximize science return. Figure 2 illustrates a number of different rock cores collected using Honeybee Robotics’ SASSI Drill, showing the range of core quality obtained. While core quality depends on a number of different factors including rock type, internal bit clearance and cutterdesign, one of the ways to minimize the chance of low grade cores is to couple the Bit Breakoff Tube rotation with respect to the Bit Auger Tube during drilling. These two are then decoupled during the core breakoff routine so that the Bit Breakoff Tube can be rotated with respect to the Bit Auger Tube. The SASSI drill did not initially have this capability and thus was more likely to produce lower quality cores. The prerequisite to couple and decouple these tubes within the drill bit is one of the driving requirements in the ROPEC design. This eccentric tube core breakoff mechanism is explained in further detail in the following sections. Figure 2. Core Quality Grading Scheme Grade A  Grade B Grade C Grade F Grade D 197
Another significant design driver is the ability to separate the Auger rotary drivetrain from the Percussive  hammer system. Rotary only drilling is ideal for weak rocks or while performing a hole-starting routine, while rotary-percussive drilling is best suited for penetrating harder rocks but may ruin a softer rock sample. Hammering action alone can be used for hole starting routines in rocks with steeply sloped or very rough surfaces. Hammering alone can also be used to dispense regolith, powder, and cores, if desirable. These operational modes were successfully demonstrated on previous drilling systems, leading to the requirement to separate Auger rotation from Percussive hammering. In addition to various performance requirements (Auger speed greater than 350 RPM, percussion  frequency of 1500 BPM, percussive energy greater than 0.5 Joules, breakoff torque greater than 10 Newton-meters, weight on bit greater than 40 Newtons) dictated by previous successful rotary percussive  drilling systems, the mass of the ROPEC drill was desired to be less than 4 kg. During the requirements  derivation phase, the Mars Sample Return architecture at the time assumed that the drilling and caching rover would be slightly larger than the Mars Exploration Rovers. This rover would use a Robotic Arm similar in design but larger than the Instrument Deployment Device (IDD) on the Mars Exploration Rovers (MER). The IDD has an approximately 2-kg end of arm payload capacity, and it was estimated that a drill  weighing less than 4 kg could be deployed using a robotic arm suitable for the larger, MER Plus rover. After completing design and assembly of the ROPEC drill in December of 2012, it was announced thatthe initial drilling and caching rover would utilize a Mars Science Laboratory rover, which enables a significantly larger Robotic Arm and end of arm payload. While mass is no longer a significant design driver, during the development phase, it was critical that the ROPEC drill be as light weight as possible. As a result, the ROPEC drill mass is less than 4 kg. Design Discussion Mechanism Overview The ROPEC Drill is a flight-like prototype, five actuator system. Four of these actuators are mounted to a  linear translation stage driven by a ball screw. These actuators are used to drive the Auger axis, Breakoff mechanism, Percussive system, and Pushrod mechanism. The linear translation stage is driven by the Z-Axis actuator. The ROPEC Drill uses these actuators, as well as a number of electronic sensors to perform various tasks, described as follows. Figure 3 illustrates the ROPEC drill and its corresponding actuators with the latest flex cable design and Figure 4 shows the fully assembled drill with standard cable harnesses and a cable guide. 198
Figure 3. ROPEC Drill Design with Revised Flex Cable /g120Auger Actuator – The Auger actuator is the primary driving force behind the drilling action. The drill bit  is connected to the auger and needs to rotate continuously during drilling. The auger axis can be locked in position during the core breakoff routine where the rock core is sheared from the base material. The absolute position of the auger’s output can be determined using a reed switch and a magnet located on the auger output shaft.   /g120Breakoff Actuator – The Breakoff actuator is not used during the drilling process. During the core  breakoff routine, the Breakoff actuator uses a high gear reduction to shear the core. Due to the high  gear reduction, this actuator is normally not engaged with the drill output drivetrain during drilling; however an automated gear meshing routine is used to couple the Breakoff actuator to the drill output drivetrain during the core breakoff routine. This eliminates excessive drag torque associated with back-driving the high-reduction Breakoff Actuator while drilling. /g120Percussive Actuator – The Percussive actuator drives a cam, spring, and follower mechanism that  produces high-frequency, high-impact loads on the auger output shaft. The percussive wave from  these impacts is then transferred through the drill bit down to the cutting elements and into the rock.  The percussive mechanism uses a helical rotating cam to drive a rotating follower that is spring  preloaded against the internal drill housing. As the helical cam rotates, it contacts the follower, which rolls along the surface of the cam until it reaches a drop off point. At the drop off point, the follower is released, and the potential energy stored in the spring is used to create the percussive impact by way of a hammer and anvil arrangement.   /g120Pushrod Actuator – The Pushrod actuator is used to control a long pushrod within the center of the  ROPEC Drill. In a previous Mars Sample Return architecture developed by Honeybee Robotics, it  was determined that a pushrod could be useful for inserting the drill bit and rock core into the Sample Cache. In the current “One Bit-One Core” architecture, it is no longer required. While the pushrod has  the capability to extend far outside the drill, it is also used in a number of internal routines, such as  Flex  CablePercussive  Actuator AugerActuator Drill BitAuger Chuck Preload Tines /  ButterfliesPushrod Actuator Linear Stage Ball ScrewBreakoff Actuator Z Axis Guide Roller Rail 199
locking the auger axis during core breakoff, and coupling the breakoff actuator to the output drivetrain while shearing the core. /g120Z Axis Actuator – The Z-Axis actuator drives a precision ball screw which controls the depth of  penetration of the drill bit during drilling operations. Motor current feedback from the actuator can be  used to estimate weight on bit. A non-contact inductive proximity sensor is used to home the linear extension stage. /g120Preload Tines – The Preload Tines, or “Butterflies” are used to stabilize the ROPEC drill during  drilling. These tines are placed on a rock surface, and a pair of limit switches within the Butterflies  provides feedback as to whether the tines have made contact. Once contact is confirmed, the Robotic Arm continues to preload the tines against the rock, stabilizing ROPEC for drilling operations. Figure 4. Assembled ROPEC Drill without Flex Cable Auger Subsystem Design The ROPEC Auger sub-system is shown in Figure 5. The maximum auger output speed is 375 RPM. The  90 Watt Auger Actuator (1) transmits power to the Auger Gear (4) through a system of Idler and Transfer gears. The Transfer Gear (3) also has a tab feature which allows it to lock, preventing the auger drive  train from moving in one direction. Locking the Auger drivetrain is accomplished by allowing the torsion  spring-loaded Auger Lock (6) to pivot into position, where it eventually contacts a tab on the Transfer Gear; temporarily acting as a hard stop. During drilling, the Auger Lock is pivoted out of the way of the  Transfer Gears locking tab. This allows the Auger drivetrain to spin continuously. Pivoting of the Auger Lock is performed by raising and lowering the position of the Auger Locking Cam (7), which is controlled by the position of the Pushrod, as discussed in follow on sections. Calculations were performed to size the actuator and drivetrain based on previous drilling data obtained  using a similar drilling system. As shown in Figure 5, the Auger Transfer Gear transmits power from the  Auger actuator to the Auger Gear (4). A spline in the Auger Gear (not shown) transmits torque to the  Auger Chuck, while allowing the Chuck to slide axially over a short distance. With the Auger Chuck  connected to the Drill Bit, this axial motion is necessary in order to allow impact energy from the percussive system to be transmitted to the Drill Bit without significant losses. A spring energized seal (5)  around the Auger Chuck prevents debris from migrating into the mechanism. 200
The Auger Gear is constrained with a duplex pair of angular contact bearings which support Weight on Bit  loads. While the Auger Chuck (12) is free to slide within the Auger Gear along the spline connection, it is constrained on one end by a flange on the chuck itself, and by a thrust needle bearing below (11).    Figure 5. ROPEC Drill Auger Subsystem (1) Auger Pinion Gear (2) Auger Actuator (3) Auger  Transfer Gear (4) Auger Output Gear and Splin e (5) Auger Dust Seal (6) Auger Lock (7) Auger  Locking Cam (8) Percussive Actuator (9) Percussive Follower and Hammer (10) Percussive Cam (11) Thrust Needle Bearing (12) Auger Chuck Percussive Subsystem Design The 100-Watt Percussive Sub-System delivers 0.56 Joule per blow at up to 1500 blows per minute and is  also shown in Figure 5. The percussive system uses a helical Percussive Cam (10) which is driven by the Percussive Actuator (8). As the helical cam rotates, it raises a Percussive Follower and impact Hammer (9), preloading a spring. The helical cam raises the follower for approximately 3/4 of its revolution, and then releases it. Once released, the follower and impact hammer contact the top surface of the Auger Chuck, sending a percussive wave through the chuck and drill bit, ultimately impacting the rock surface.  The Percussive Follower is mounted on preloaded angular bearings which allow the follower to rotate relative to the hammer. This rotation is critical in order to reduce friction and wear between the cam and  follower. The hammer utilizes a custom ball spline, allowing it to move axially with minimal frictional  losses. The cam and follower percussive system has been employed in all of Honeybee Robotics’ rotarypercussive drills. The percussive system in the SASSI drill has been successfully operated for 2 million cycles in a vacuum chamber at Mars pressure, which is equivalent to approximately 19 hours of operation.   ROPEC Breakoff Subsystem Design The ROPEC Breakoff subsystem uses two nested tubes to shear the rock core at the bottom, and capture  it for extraction from the base material [7]. The outer tube forms the main drill bit consisting of the bit shank, which connects to the ROPEC Auger Chuck, the helical fluting for cuttings removal and the tungsten carbide cutters at the base. The center bore of this outer tube is offset from the central axis of the exterior of the bit. The bore of the inner tube has the same offset. When the tubes are nested  21 3 1076 8 9 4 511 12 201
together, they can be aligned such that the bore of the inner tube is coaxial with the outer surface of the  outer tube. During the drilling process, these tubes are in this orientation, and need to spin simultaneously to avoid prematurely shearing the core. When core breakoff is  desired, the outer tube is held stationary, while the inner tube is rotated using the Breakoff Shaft. This rotation shifts the bore of the inner tube relative to the central axis of the outer tube. This  small shift is enough to shear  the rock core at the base, and also capture it inside the bit, preventing it from falling out  during extraction from the base material. This process is illustrated in Figure 6. This method is patented by Honeybee Robotics and has been used on a number of successful coring drill designs. A recently concluded study with the SASSI drill and 140 coring tests in several rock types has shown that  the inner breakoff tube successfully sheared and captured cores in 94% of cases, while partial core loss  was observed in 6% of tests [8]. No full length core loss was observed. Some of the cores successfully captured included the “F” grade cores shown in Figure 2.  The Breakoff subsystem is shown in Figure 7. This drivetrain has the ability to selectively mesh and demesh the main Breakoff Output Gear (3). This subsystem is designed to produce enough torque to shear  a rock core. This high torque is based on data from similar mechanisms, including a comfortable amount of torque margin. Due to this high torque requirement, the planetary gearhead on the breakoff motor has a multiple stage reduction, making the back-drive torque very high. Since the breakoff shaft needs to be  coupled to the auger shaft during drilling, if the breakoff drivetrain were permanently coupled to the motor,  the auger actuator would need to back-drive the breakoff motor. This back-driving rotation would require a  prohibitively large amount of torque, which would result in a significantly larger auger actuator. The  solution to this problem is to selectively decouple the breakoff drivetrain from the main breakoff shaft. This is accomplished by moving the Breakoff Cluster Gear (2) axially to de-mesh the drivetrain during drilling,  and mesh the drivetrain during core breakoff. A magnetic Absolute Position Sensor (6) is used to provide  position feedback to the control system, telling it exactly what position the breakoff drivetrain is in so that gear meshing is performed smoothly. The Breakoff Cluster Gear is translated using the Pushrod sub-system.Figure 6. Core Breakoff Method Ready to  Drill Drilled to  DepthShear &  Capture  CoreExtract  Core OPEN CAPTURED 202
Figure 7. ROPEC Drill Breakoff Subsystem (1) Return Spring (2) Breakoff Cluster Gear (3)  Breakoff Output Gear (4) Non-Meshed Gears (5) Br eakoff Actuator (6) Absolute Position Sensor (7)  Breakoff Pinion Gear (8) Meshed Gears ROPEC Pushrod Subsystem Design The Pushrod subsystem is shown Figure 9. In a previous  iteration of the “One Bit-One Core” architecture, a pushrod was necessary in order to load a drill bit containing a rock core into the sample cache for sample return. The current  “One Bit-One Core architecture does not require a Pushrod any longer, however due to the original requirement, a Pushrod with a long stroke has been included in the ROPEC design. The pushrod system uses a 1/4-28 threaded  leadscrew and nut arrangement. The Pushrod Actuatordrives a series of gears, which ultimately rotates the Pushrod Nut (5). As the Pushrod Nut rotates, the threads cause the Pushrod (1) to move axially. The Pushrod Ground Tube (3) is connected to the surrounding housing structure. The Pushrod is keyed rotationally with respect to the Ground Tube but is able to slide axially relative to it. In addition to the option of pushing a drill bit into a sample  cache, the Pushrod also helps actuate a number of different mechanisms within the ROPEC drill itself. The Pushrod is shown in both the drilling position and in its fully extended  position in Figure 9. Once drilling is complete, the Pushrod is  retracted further into the drill. This motion raises the Auger Locking Cam (Component 7 as shown in Figure 5), which actuates the Auger Lock (Component 6 as shown in Figure 5) near the top of the drill, which locks the Auger Transfer Gear in place, preventing the Auger drivetrain from rotating during the core breakoff routine, as described previously. 2 4 51 6 7 8 Drilling Mode Breakoff Gear Not Meshed3 Breakoff Mode Breakoff Gear Meshed Figure 8. ROPEC Drill Pushrod Subsystem (1) Pushrod (2) Locked  Balls (3) Auger Chuck (4) Unlocked  Balls (5) Breakoff Shaft 21 534 203