ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
20 accommodate the anticipated coring handling implementation. This necessitated designing a coring bit  with a relatively large cutting annulus to yield t he space required by the core handling mechanisms. 

Figure 3. Drilling Breadboard Fixture Used for Coring Bit Evaluations.    A bit design expert was consulted to a ssist in the analysis of earlier co ring results obtained with COTS  bits and to develop a custom coring bit design specif ically for this application. After two iterations, a  successful bit design was obtained to core targeted rock materials.  The first custom coring bit, Revision A, used a single  sloping cutting tooth profile  as shown in Figure 4.  The cutting teeth were fabricated from grade C2 carbi de. This coring bit cored basalt successfully, though  chipping of the carbi de was observed. Unfortunately, the bit had stability i ssues in softer materials. The bit  tended to wander, breaking the softer cores into numerous  pieces. On a positive note, the flutes designed  into the tool body were effective in carrying away rock fines. In previous testing with non-fluted COTS coring bits, a shop vacuum was used to clear away the fines, and debris clearance was anticipated to be  much more of a challenge than was actually encountered.  Revision B, the next coring bit desig n iteration, addressed the stability issues found in  the previous  version. This design used a crow n-shaped symmetrical tooth profile. A different grade of carbide,   GC-012F by General Carbide, was used in an atte mpt to improve the cutting teeth life and reduce  chipping. This coring bit design solved the stability issues in soft rock and still cored basalt well, though  the teeth still chipped when coring basalt and even iron  spot brick. Nonetheless, because this coring bit  design cored well and the chipping did not cause a si gnificant difference in coring performance, it was  decided to proceed with this basic design and focus remaining project resources on the development of the integrated corer.   Hammer  Position  Transducer Brushless DC  Hammer Motor  (drives hammer  cam via belt; not  shown)  Brushless  DC Rotary  Motor Hammer  Follower and  Cam  Hammer Timing Belt to  drive coring bit  (coring bit not  shown)  Rock Clamp  NASA/CP-2010-216272
21        

Figure 4. Revision “A” (left) and “B” (r ight) Coring Bits with Basalt Cores 

(2) Core Handling Mechanisms   The core handling mechanisms identif ied in Phase I – core retention,  break-off, and ejection – required  prototyping and testing to verify thei r suitability. This reduce d the risk of a possibly failing subassembly to  negate the total design and effort.  Core breakage from the parent rock material was a major concern from the beginning of Phase 2 since it was not explored during the Phase 1 effort, which focused primarily on coring. A number of concepts for breaking cores were investigated, including scoring the base of the core to weaken the rock. A Milwaukee 48-20-5005 coring bit was modified to provide a means of scoring existing core samples at the base of  the core. This method looked promising as the forces required to snap the rock core were found to be minimal. However, the concept wa s eventually discarded because of  the complexity involved with  integrating such a device into the corer design.  Next, a collet concept was conceived to break the ro ck core samples. Two different design approaches  were considered and explored, shown in Figure 5. The first was a conventional axial collet much like the type of collet found in a machine shop. This was test ed on rock samples in a variety of rock breakage  modes: tension, bending, and compression. The other collet concept used nestled eccentric tubes that generated a shearing force on the rock core when the tubes were rotated with respect to each other. Mechanisms were designed and built to test these concepts, and both methods were found to be effective. Both approaches required approximately the same amount of input torque to snap rock  samples. In the end, the eccentri c collet concept was selected as the core breakage method of choice  because it was observed that the concept would be easier to implement into an integrated corer design, and that it would be simpler and more tolerant of stray rock particles.  During testing with the collet mechanisms, input to rques and displacements were measured and recorded  to characterize the forces and strains required to br eak the rock cores reliably. These results then helped  define the design parameters for the integrated corer.   (3) Prototype Corer Development

Development of a fully integrated corer prototype was performed following the successful demonstration  of the individual core handling mechanisms. As menti oned earlier, it was decided that the integrated corer  should be designed to utilize the eccentric collet concept  based on the results of the testing with the core  NASA/CP-2010-216272
22 handling mechanisms. However, the problem of cont aining and transferring the core sample remained  unaddressed. A containment sleeve was attractive with  the realization that m any cores would not be  intact, and maintaining the order of the pieces of a disrupted core is a requirement. However, designing  provisions for a sleeve into the integrated corer without interfering with the breakage mechanism and  providing a clear exit path out of the corer for the slee ve was a challenge. Analysis of the dimensions of  the rock cores generated during the core breakage testing revealed that only a very small clearance  typically existed between the outside di ameter of the rock cores and the insi de diameter of the coring bits.  The clearance was so minimal that it became clear that  ejection of the containment sleeve out the front of  a coring bit would be impractical because it would nec essitate a containment sleeve of nearly zero wall  thickness.        

Figure 5. Core Breakage Collet Prototypes   Consideration was thus given to an integrated corer de sign that allowed the ejection of the rock core  containment sleeve out the rear of the assembly. This concept was comp atible with the eccentric collet  breakage design, and seemed the most straightforward in achieving all of the corer objectives of coring, breakage, retention, and ejection. Because there was a clear exit path through the entire corer assembly,  an external plunger mechanism to push the sleeve containing the corer could be housed in the sample  system on the base platform to “ramrod” the sample out  the rear of the corer. Th is significantly simplified  the integrated corer assembly and also incrementally  simplified the requirements of the robotic arm to  which the corer would be mounted by reducing mass and required electrical connections.   Other design considerations were addressed prior to finalizing the overall concept of the integrated corer  design. A decision was made to use a single motor to drive a spring-loaded rotary-percussive cam mechanism, much like the original LSAS drill. Although it was desirable to have the flexibility of independent control over the hammer and rotary functi ons in the manner of the drilling breadboard fixture,  the single-motor rotary-percussive mechanism offered simplicity and low mass. An additional motor was incorporated in the design to accomplish core break-off. While it appeared possible to leverage the rotary-percussive motor to achieve this function and save mass, it was much more straightforward to add a second motor. See Figures 6 and 7 for CAD views of the prototype design.    NASA/CP-2010-216272
23 

Figure 6. Integrated Corer Prototype Cross-Section  Hammer Brushless DC  Gear Motor  Assemblies (2)  Exit path  of core  sample  10-mm  Coring Bit Driven Gear, RotaryPercussive  Mechanism   Thin-Walled  Sample  Containment  Sleeve Driven Gear, Core  Break-Off  Mechanism   Hammer Springs  (Qty. 3-6)  Hammer Cam  Followers (3) Removable Hatch  for access to  Hammer Springs Duplexed  Bearings (2)  Eccentric Core  Break-off Collet   Core BreakOff Ball and detent bit release  mechanism (not fully  visible)  NASA/CP-2010-216272
24  

Figure 7. Integrated Corer Prototype (housings omitted)  Hammer Cam  Followers (3) Hammer  10-mm  Coring Bit Torque-transmitting Cam  Follower Assys (3) Hammer Springs  (Qty. 3-6) 90-Watt Core  Break-off Gear  Motor Assembly 120-Watt  Rotary-Percussive Gear  Motor Assembly  NASA/CP-2010-216272
25 A limited amount of analysis was performed prior to fina lizing the integrated corer design. In view of the  successful coring achieved with the breadboard fixture, the rotary-percussive motor and gear drive  mechanisms were sized on the integrated core r to achieve the maximum hammering energies  investigated with the breadboard fixture. Because gaining an understanding of the coring problem was  deemed more important than strict mass reduction of the in tegrated corer prototy pe, the motors were  sized with extra torque margins to ensure that all dat a points of interest could be obtained during testing.  Finally, attention was given to developing efficient ha mmer cam profiles to minimize the amount of power  required by the integrated corer. The hammer cam profile was modeled and simulations run (see Figure  8) in order to optimize the shape of the cam profile  and to ensure that correct timing of the hammer  strikes was obtained. 

Figure 8. Hammer Cam Profile Analysis   It became clear during the cam profile analysis that a rotary-percussive mechanism can only operate within a narrow speed range and still be effective. If the mechanism rotates too slowly, the hammer loses energy by not being cleanly released by the cam mec hanism. If the rotary-percussive mechanism rotates  too fast, the hammer can be picked up before contact with the coring bit takes place.  An additional design concern regarded the mounting of the corer to the robotic arm or test fixturing. Early  concepts assumed that advancing the unit down the coring axis could be accomplished by coordinated  movements of the robotic arm joints. However, wo rk performed on another project showed that low  velocity, coordinated moves were very difficult and required positioning accuracy and control beyond the capabilities of current robotic arms. Power requirements were also quite high because all arm joint motors  were energized along with the corer. In response, the simple solution of mounting the corer to linear slides with preload springs was implemented. The arm would press the corer against the target rock and  preload the springs. The arm motors would be turned off, engaging the joint brakes. Coring would then begin and the corer assembly would be advanced by the preload springs. The preload springs could be re-compressed by shutting off the corer and advanci ng the robotic arm, then the process repeated until  NASA/CP-2010-216272
26 the desired core length was achieved. See Figure 9 for the completed Integrated Corer Prototype  mounted on spring-loaded linear guides. 

Figure 9. Integrated Corer Prototype   (4) Corer Testing

The integrated corer prototype was then functionally tested in a laboratory environment with a variety of  rock samples. See Table 1 for a summary of the result s. The tests were narrow in scope because of the  limited funds remaining on the program. However,  the testing was adequate to demonstrate the  successful performance of the integrated corer against the rock types anticipated to be encountered on Mars. It is hoped that additional more comprehensive testing be performed in the future as funding becomes available.  Coring Performance

Sandstone: This material had been found to be very abrasive and hard on the coring bits in the past, and this experience was repeated during testing with the in tegrated corer. Run 3H with a virgin coring bit  through sandstone started to reach a performance plateau towards the end of the run. The coring bit  teeth, while not fractured as during the runs with basalt, exhibited substantially worn cutting edges at the  conclusion of the run.  Basalt: All coring bit runs in basalt produced chipping of  the teeth, as evident in Figure 10. In two extreme  cases - Runs 2I and 3I - the brazed joints on some of the cutting teeth failed as shown in Figure 11,  causing the coring bits to lose cutting teeth. In the case of Run 3I, two adjacent cutting teeth were lost, resulting in a large side load to be imparted onto t he generated core and causing it to inadvertently snap  from the parent rock material. This occurred with the corer set for maximum hammer energy (1.09 J per  blow) ２. Subsequent Run 4I was performed with reduc ed hammer energy (0.61 J per blow) with much  better results. One possible reason for failure was th at the highest hammering energy was too aggressive  on the coring bit teeth. In addition,  the current coring bit design had cu tting teeth that overhang the coring  bit body by a substantial amount, making the teeth susceptible to failure. A future design change to the  coring bit should be considered to minimize this overhang.  Shale: Coring penetration rate was the highest of the three materials tested, and the coring bit was in good condition at the end of the run.                                                        ２ ”Hammer energy“ used here refers to the approximate change in potential energy the hammer springs experience  between two points: (A) when the hammer is fully “up” (cocked)  and (B) when it first strikes the coring bit. This is not  the same amount of energy that is act ually transferred to the coring bit and imparted to the rock, which would require  extended detail analysis to predict. However, hammer potential energy was an easily calculated, convenient  reference when comparing the different hammering settings.  NASA/CP-2010-216272
29   In all cases of successful rock sample retrieval, lo ose rock was found to remain with the parent rock. In  some cases, a substantial amount of rock core wa s unaccounted for when comparing the length of the  retrieved samples versus the leftover rock. It was evident that some of the cored rock is pulverized during the core generation process. It would have been useful to understand why this was happening to  maximize the yield of retrieved rock cores and to avoid potential problems with debris jamming. The addition of a passive sample retention feature to t he open end of the containment sleeve could have been  a possibility.  Because of schedule and budget constraints, the core breakage mechanism was tested only against a sample of basalt, the most challenging material of  interest for this application. Though this test  demonstrated the success of the breakage function agai nst the strongest sample type, it would have  been more rigorous to perform testing against all types of anticipated rocks and m easure the actual strain  displacements needed to break the cores reliably. Havi ng a statistically signific ant amount of breakage  data could have enabled the development of a smaller,  more compact design. A conservatively large  amount of eccentricity was designed in the collet brea kage mechanism to ensure success. However, this  makes the corer larger and more massive, and the co ring bit annulus subsequently larger, thus requiring  more power during coring.  

Figure 12. Containment Sleeve at Rear of Integrated Corer (left), Sleeve with Basalt Core (right). 

Conclusions and Recommendations   Most, though not all, of the goals for the integrated corer were met and the results are encouraging. The  65-watt power requirement, previously thought to  be insurmountable because of the high power  consumption seen with the breadboard fixture, is clearly achievable. The low WOB target of 50 N was exceeded during test, but this was primarily caused by an oversight in the setting of the preload springs. Based on the relative ineffectiveness of higher WOB va lues briefly explored during testing, it is believed  that sufficient coring performance is achievable with a lower WOB provided other measures are taken to  improve coring performance.  Improved coring performance is likely achievable with design changes to alter the hammer/rotary phasing relationship in the integrated corer, since the coring  bits cored much more efficiently on the breadboard  fixture than in the integrated corer. The coring bits were the same in both cases, but the natural drift  between hammering and rotary action on the breadboar d is a major differentiator. Indeed, witness marks  NASA/CP-2010-216272
32 The mission required that the antenna would be capable of transmitting and receiving multiple carriers  simultaneously. In order to meet this requirement, the antenna is designed to be low PIM. PIM effectively  raises the noise floor of the receiver system , reducing the sensitivity of the system.   

Figure 1: Stowed TacSat-4 UHF Antenna 

Figure 2: Deployed TacSat-4 UHF Reflector on Comm-X Payload  NASA/CP-2010-216272
33  

Figure 3: Tacsat-4 UHF Antenna Design 

Major Design Trades 

Make vs. Buy   The initial design trade of the antenna was a make versus buy decision. Several of the recognized private industry providers of space qualified reflectors were approached and provided ROM estimates for meeting the TacSat-4 antenna design requirements. Several companies provided estimates for building an antenna; however, no vendor could meet the design requirements within the schedule and budget constraints of the program. The industry estimates were approximately two to five times the available schedule and budget. Additionally, because of the extrem ely aggressive schedule of the program, most  necessary derived requirem ents were determined in parallel, not serially, with the antenna development.  It was therefore decided that the UHF antenna would be built in house at the NRL to meet the program’s  budgeted cost and schedule.  Deployment Schemes

Several deployment schemes were initially traded  for the antenna. The two best options were a  tensioning band around the deployable ribs and a top release “pie plate” approach which would release the ribs from the tips. It became apparent that the de ployment approach would affect the relative sizing of  the fixed and deployable portions of the reflector.    The “pie plate” approach required t hat the deployable ribs would need to  reach above the UHF feed of the  reflector to meet RF and PIM requirements (no metal in RF field). This meant that either the fixed portion of the reflector would be smaller than structurally desired or the ribs would need to be unnecessarily long to reach the top of the UHF feed. The release band approach allowed flexibility of fixed and deployable reflector sizing enabling the design to be optimized for mass and stiffness. The band design also did not require any additional metal in the RF field once deployed. For these reasons a release band design was used for the antenna.  NASA/CP-2010-216272
34 Further analysis proved that a band loca ted at a midpoint between two circumferential rings with v-block  interfaces provided the hi ghest stiffness and least complex design. These rings and v-blocks were  fabricated from Ultem 2300® to provide necessary strength and tribology for reliable release while  meeting RF requirements.   The release device selection and band design was a complex and essential part of the antenna development. Thermal knifes and other flight-qualif ied separation mechanisms were traded for the  release device. Program requirements did not allow the use of any pyrotechnic devices and therefore  were not included in the trade space. A low-mass re lease device was needed to minimize deployment  dynamics differences between all ribs. Furthermore, because of the length of the band (~2.5 m or 100  inches) and the kinematics of the deployment, it was decided to deploy the band in two halves rather than  one long piece (shown in Figure 4 and Figure 5). This was done to minimize possible snagging and friction forces. A TiNi Aerospace Frangibolt ® device was selected for the re lease of the band. A single  device was selected to release both band halves over  two devices because of complexity and risk  implications on the antenna design. Early full-scale breadboard testing of the release concept ensured  confidence in the release design approach for proper function as well as working out band tightening techniques. 

Figure 4: Release Device Assembly 

NASA/CP-2010-216272
36 width of the antenna gores. An industry survey showed there were a limited number of vendors that were  capable of processing parts of this size. There wa s a learning curve for handling and tooling the antenna  gores mostly due to the cover-lay pr ocess in the part manufacturing. 

Figure 6: EDU Gore Layout 

 Gore Fasteners

As previously stated, the low PIM requirements on the antenna forced a capacitive coupling approach  throughout the antenna design. This capacitive coupli ng relies on an even preload to be maintained on all  RF joints, which includes the joints between individu al gores. Many fasteners were used to maintain the  equal preload required across the entire joint. These fasteners hold the reflector gores to each other and to the ribs.    There are over 2000 fasteners used to hold the reflector gores both together and to the individual antenna ribs. Standard metallic fasteners were not an option bec ause of the mass and RF implications. Several  non-metallic space-qualified materials were traded to find a suitable substitute for metal in the fasteners.  Additionally both socket and pan head screws were ev aluated. Pull testing and radiation testing were  done on the top two choices of the trade. After testing, socket head Ultem 2300 ® was selected for the  material of the fasteners, washers, and nuts for atta ching gores. The screws needed to be fabricated in a  special run, and the end cost was roughly $4 per fast ener. The fasteners were not as strong as metal  fasteners so free running nuts were used to keep the running torque as low as possible. A torquing technique was developed and each fastener was staked for backout prevention.    Gravity Offloading

The 60-Hz stiffness and 27-kg (60-lb) mass requir ements for the antenna meant that materials and parts  would need to be light weighted and optimized for on orbit deployment loads. However, because of the  ground testing requirements and program budget, a highly complex gravity offloading scheme was equally unfeasible. It was critical to show sufficient deployment force and energy margin to qualify the new design using as relatively simple ground testing fi xtures to meet cost and schedule goals. As a result  the antenna was designed to withstand ±0.3 g deployment  forces. This required that a gravity offloading  fixture be designed in order to test both positive and negative deployment forc e and energy margins.  Testing was performed in both air and thermal vacuum (TVAC).  The final gravity offloader design was a single plate with individual mechanisms interfacing with each of the deployable ribs of the antenna. Each rib offloader had a cam profile fit to match the theoretical gravity  1.67 m 0.60 m  NASA/CP-2010-216272