ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
jam, it does not need to move back; it can continue adding tension to the lead screw and hold the doors in  the closed position using the interface on its new attachment point.  Right Come-Along  Left Come-Alon Tool Section  Figure 19. Redundant Tool Sections  Design for Reliability  Reliable functioning of the Come-Along Tool is necessary to ensure that door operation is completed; if  the doors are not properly closed, the HST cannot continue its science mission. Since no human will be  available to perform unanticipated workarounds it is especially important the robotic tool be dependable.  The robustness of the Come-Along Tool’s design is due to its simple mechanisms, hard stops to prevent  position overrun, and ability to continue its task if a mechanisms failure occurs.  Mechanical Hard Stops  The Come-Along Tool has mechanical hard stops to ensure that the tool sections do not rotate too far or  run off the end of the Lead Screw. To prevent the Lead Screw from pitching out of position, the tool  housing provides a stop. Collars on the edges of the Lead Screw prevent either tool section from running  off.  Lead Screw Hard Stop 3- Collar  Stop on Tool Housing to  prevent Lead Screw Pitching -  Night Tool  Section  Figure 20. Hard Stops  Simde Mechanisms  In order to reduce complexity and thereby increase reliability, the Come-Along Tool incorporates simple  mechanisms to hold the doors in place, provide visual indication of tension between the doors, and allow  each tool section to rotate about the Lead Screw. During earlier generations of the Come-Along, a ratchet  mechanism, used to lock the doors in the closed position, required a ratchet gear, pawl, pawl spring, and  motor actuated pawl release. To simplify the tool, the ratchet mechanism is replaced with a nut to lead  screw connection that does not allow the gear train to back drive. Avoiding use of electronics eases  temperature requirements on the tool and eliminates the need for batteries.  One of the challenges of operating the Aft Shroud Doors is that the angles of the door handrails vary with  the doors rotation. To remain attached to the handrails as the doors open and close, each of the tool  355
sections must rotate with respect to the Lead Screw. To accomplish this in a simple manner, a property of  miter gear connections is used: as long as the apex of the two mating miter gears pitch cones remain  aligned, one miter gear can rotate about the other. The miter gear connection allows power transfer  through a rotating joint.  Pivot  Housing. Main  Housing a  Right Tool Section  (Nominal Position) Stationary Miter Gear  Right Tool Section Pivot Point  (Rotated Position)  Figure 21. Rotation Relative to the Lead Screw  Sinale Fault Tolerance  One of the mission level requirements of the Come-Along Tool is that it be single fault tolerant, meaning  that it shall continue to operate even if any single mechanical failure occurs. The tool accomplishes this by  including a redundant tool section. Should a part on one tool section fail, the other tool section can be  used to continue operating the Aft Shroud Doors.  Conclusion  Reliable operation of the Aft Shroud Doors with the Come-Along Tool is critical to performing the COS  Task and achieving the scientific objectives of the HRSDM. The tool’s current design overcomes a difficult  set of obstacles to make door operation possible. Through testing and development of the tool, we gained  insight regarding Aft Shroud Door operation, reliability issues involved with Robotic Tool design, and the  use of telerobotics.  Robotic missions require a high level of reliability since there are no humans to perform unanticipated  ‘work arounds’. After first struggling to operate more complicated prototypes, the Come-Along Tool design  was optimized through use of simple and redundant mechanisms. Functions for closing the doors,  clamping the handrails, and holding the doors in place were combined into one. If any part of one tool  section fails, redundant features on the other tool section can be used to complete operation.  Important lessons were also learned about telerobotic operation. Using the force-feedback capability of  the robot, it was discovered that certain human operations could be performed robotically. The simple task  of acquiring the handrail of an unrestrained door was at first difficult to perform with the robot, and later  made easier by adding additional features, such as Handrail Fingers to the tool and adjusting the door  capture operation to first press the door shut. The execution of operations to overcome door jams  successfully combines the capabilities of a robotic tool and robot to perform a difficult task that requires  two astronauts working in tandem.  The results of developing the Come-Along Tool are applicable not only to the HRSDM, but also to future  robotic missions as we begin to realize NASA’s vision for space exploration. Development of the Come-  Along Tool furthers NASA’s goal to “. . .implement a safe, sustained, and affordable robotic and human  program to explore and extend human presence across the solar system....”* The Come-Along Tool’s  356
ability to operate interfaces made for humans and coordinate with other robotic systems is pertinent to the  next generation of space exploration in which robotics will play a key role.  References  1. Tomlin, Faile, Hayashida, Frost, Wagner, Mitchell, Vaughn, and Galuska. “Space Tethers: Design  Criteria.” NASA Technical Memorandum 708537 (July 1997).  2. Martin, Gary L. “Level 0 Exploration Requirements for the National Aeronautics and Space  Administration.” NASA Document No.: SA-0001 (4 May 2004), p. 5.  Acknowledgements  Development of the Come-Along Tool would not have been possible without the thoughtful work of Dick  McBirney, Jenny Xu, Carl Anders, Randal Frey, Kevin McMennamin, Justin Cassidy, Paul Nikulla, John  Bishop, and Giles Robinson. Thank you for your help and insight.  357
e, I I I *  rr\ 't ''J I  Figure 1. ARES Entry, Descent, and Deployment sequence  Concept Description  The primary functions of the AES are to support the airplane through launch, interplanetary cruise, and  entry; and then to guide the airplane safely out of the backshell during extraction. During launch, cruise,  and entry, the airplane is held by three kinematic mechanisms to prevent stresses from building up in the  airplane structure by allowing the aeroshell and airplane to deform independently. During the extraction  phase, six pyrotechnic separation nuts will fire releasing the AES and airplane assembly. The backshell  will be free to roll up the AES guided by rollers on the AES's central ring and tracks on the backshell's  parachute can. The forces of differential aerodynamic drag between the backshell's high drag supersonic  parachute and the low drag free falling AESIairplane assembly will cause the separation. As the  parachute can reaches the end of the AES, a second set of pyrotechnic separation nuts will release the  airplane from the AES. The folded airplane is then in free fall in the atmosphere until the drogue chute is  deployed (Figure 2). The following tests verify the extraction function of the airplane extraction system.  A w  Figure 2. Extraction concept. Left illustration shows stowed airplane stowed inside  the backshell just after heatshield release. Right illustration shows the extracted  airplane prior to release from the AES.  AES Requirements  Key AES Requirements:  Low mass Hold 175-kg airplane securely through Earth launch, interplanetary cruise, and Mars entry  Guide the airplane out of the backshell and release it in the Martian atmosphere  Reduce stresses on the airplane due to thermal expansion and contraction  Fit within the volume of a bi-conic, 2.65-meter-diameter aeroshell  Airplane/AES minimum natural frequencies, 15-Hz lateral, 35-Hz axial  Withstand 15-9 launch loads  360
AES DescriDtion  The AES shown in Figure 3 is approximately 2.4-meters wide, 0.9-meter tall, with a mass of 56 kg. It is  composed primarily of titanium tubes. Hard stops on the top of the central ring prevent the AES from  coming off the parachute can.  Figure 3. Airplane Extraction System  AES Roller Confiauration  Central to the success of the AES is the roller configuration. The configuration is based on the successful  MER extraction hardware modified to work with anairplane. Like MER, three tracks are equally spaced  on the central parachute can. However, the vertical spacing of the rollers along the track is much greater.  The nominal clearance between each pair of rollers and the track is +/-0.25 mm. The clearance in the  system ensures there is no binding as the backshell is pulled away. Yet, the tolerances are close enough  to guide the backshell without damaging the plane. The clearances are needed to compensate for  machining tolerance stack-ups and thermal growth. Theoretically, this system will still work even if the  rollers do not turn, although sliding friction would result. Figure 4 through Figure 8 show the various  movements allowed. In each figure, the illustration on the left shows a schematic top view. The red ring  and rollers represent the AES. The blue cylinder with three protuberances represent the parachute can  and tracks. The right illustration shows a schematic side view for each figure. The four red circles  represent one vertical set of AES rollers. The blue rectangle represents one parachute can track. Table 1  summarizes the movements.  -  Figure 4. AES roller configuration, nominal clearance  36 1
1 E  Figure 8. AES roller configuration, Y tilt  Table 1. AES Clearances and Maximum Movements  Nominal  Radial Thrust Rotate  X Tilt  Y Tilt f 0.25 mm clearance between rollers and track * 0.28 mm side to side thrust * 0.1 deg axial rotation * 0.1 deg tilt from vertical axis * 0.09 deg tilt from vertical axis  Test Description  In order to demonstrate the extraction design approach and operation of the AES, a functional 1/3 scale  model of the backshell, AES, and airplane was created. To simulate the potential orientations in which  separation would occur, the model was statically held at various angles and rotations on an A-frame in  the high bay of building 1250 at NASA Langley Research Center. Figure 9 shows the test apparatus.  Earth gravity was used to simulate the differential drag between the backshell and AES/airplane  assembly. Although in actuality the backshell, AES, and airplane are in freefall together, practical  considerations for testing dictated that the backshell be held statically for this set of tests. The relative  motion is still the same and most of the dynamics are captured. A scale of 1/3 was chosen for ease of  manufacturing and handling while testing. High-speed video was used to determine proper extraction.  Figure 10 shows a multi-exposure sequence of a typical test.  Turntables  AES  Backshell  Figure 9. AES test apparatus  363
Figure 10. Multiple exposure picture of a typical extraction test  Kev Test Obiectives  Key test objectives were:  Determine electrical cable clearances. Demonstrate proof-of-concept for an airplane extraction system from a backshell under various  axial and lateral loading conditions.  Demonstrate no binding as the airplane extraction system/airplane assembly rolls down the  parachute can.  Demonstrate dynamic clearance between the backshell, the airplane extraction system and the  airplane.  Determine the timing sequence for airplane release.  Determine effects of the kinematic mounts on release of the airplane.  Determine airplane attitude after release.  Test Hardware  The 113 scale model of the backshell, AES, and airplane were not miniature replicas of the full scale  concept. Because of cost, schedule, and practical considerations, some compromises were made. Figure  11 shows a CAD model of the test backshell, AES, and airplane. The following sections give a brief  description of the major components.  Figure 11. 113 scale model of the backshell, AES, and airplane  364
Backs hell  The scale-model backshell is an aluminum skeleton structure that represents the interior volume of the  full-scale backshell. Its mass properties are not represented because it is a form only, static structure. The  backshell skin has been eliminated in order to have a clear view of the extraction sequence. - AES  The scale-model AES is made of welded aluminum for ease of construction. It has approximately  equivalent mass, cg, inertia and leg stiffness as the full scale titanium structure. The central cylinder is  missing some stiffening rings for ease of manufacture, but they were needed only for high launch loads  (1 59) and not lightly loaded (29) extraction loads.  Airplane  The scale-model plane is a foam, fiberglass, and wood structure. The airplane represents the correct  mass properties and roughly the correct volume. However, the stiffness of the airplane has not been  matched. The mass, cg, and inertias are scaled from the full-scale airplane. The plan form of the airplane  is correct as well as the positioning of the tail booms.  Kinematic Mounts  The kinematic mounts duplicate the correct function but are greater mass because miniature spherical  bearings were not readily available. The fixed point, hinge point, and swivel points of attachment between  the AES and airplane functionally match the full-scale model.  Release Mechanism  The full-scale AES and airplane are released with pyrotechnic separation nuts (Figure 12). To reduce cost  and safety concerns, electromagnets were used on the scale model. While electromagnets do not release  as cleanly (residual magnetism, longer response time) as pyrotechnics, these devices allow for multiple  tests without replacing hardware. The electromagnets also increase the mass of the AES.  I.  Figure 12. 1/3 scale model release mechanism  Parachute Can  The parachute can is made of thick aluminum for ease of manufacturing as opposed to the thin titanium  on the full-scale hardware. Also, a steel track instead of an aluminum track was used because of its  durability.  Rollers  The rollers for the scale model are mounted on three independent rings for ease of construction and the  ability to move their locations easily (Figure 13). The full-scale AES has three axial trucks instead of three  rings. The important parameter is the location of the rollers in relation to the tracks and not the structure  that holds them.  365
Figure 13. 1/3 scale model rollers  Fraction  1 /3 Scaling  The apparatus is dynamically scaled to 113 with the proper mass, center of gravity, and inertia properties.  The scaling factors are summarized in Table 2.  Decimal  .333 Table2. Sc  Length  (1 /3)"3 = 1 /27  (1 /3)/\0.5  (1 /3)"3/( 1 /3)"3  (1 /3)/( 1 /3/\0.5) .037  577  1  .192 m/sec Mass  Time  I I Force kg*m/sec' kg  sec  Pressure  Rotation deg/sec  Inertia (1 /3)"3*( 1 /3)"2 =  1/27*1/9 = 1/243 ng Factors  1/3 Scaling Factor I 1/3 Scaling Factor  .0041 (1 /3)/( 1 /3/\0.5)"2 = 1  (1 /3)"3*1 = 1 /27  (1 /27)/( 1 /3)"2 = 1 /3 .333  I  1/(1/9.5) 1.732 I  Mass Properties  The mass properties of the apparatus are summarized in Table 3. The full scale information was  extracted from a ProEngineer CAD model of the ARES concept. The actual scale model information was  extracted from an as built ProEngineer CAD model with selected information verified by measurement.  The actual hardware corresponds well to the calculated properties. The mass of the airplane increased  from configuration 1 to 2 to better reflect the calculated mass. The mass of the AES was greater because  the electromagnets holding the airplane are heavier than an equivalent pyrotechnic device would be. The  full-scale airplane has a slight x cg offset, however, the x cg of airplane2 is essentially zero for ease of  366
Table 4 shows the test matrix. The azimuth refers to the position of the airplane about the release axis.  Zenith refers to the position of the apparatus in reference to the vertical. Zero degree is vertical. The roller  configuration column refers to the placement of the rings of rollers vertically along the central canister.  The first group of tests positioned rollers in all three possible location, top, middle, and bottom. The  second group of tests positioned roller sets only on the top and bottom ring. The release trigger point  refers to the point at which the airplane is released relative to the top of the parachute c2n. The airplane  was tested in two configurations. The first one had a smaller mass than the second. The video number  refers to the video file name. The frame rate was reduced from 500 to 250 frames/sec for some of the  high zenith angle tests in order for the video data for each test to fit on one compact disc.  Tests 1 - 39 were conducted with the video camera isometric to the test apparatus to capture movement  in all three axes. For tests 40 - 47 several improvements were made. The video camera was moved  perpendicular to the motion of the airplane and targets were added. These improvements allowed specific  points on the airplane to be tracked without compensating for the angle of the video camera. LED  indicator lights showing power to the AES and airplane electromagnets were placed in the camera’s field  of view. This gave precise information as to when the AES and airplane were released.  Table 4. Airplane Extraction System Test Matrix  369
Obiectives Met  Table 5. Objectives Met  assembly rolls down the parachute can I with damaged rollers -  of the airplane  Determine electrical cable clearances  Determine airplane attitude after release  Problems Discovered  One point of interest was that the bottom rollers were damaged after many tests because the airplane negatively  Yes No cable hang-ups  Yes Determined from video  extraction system would rebound after airplane release. Thisis not a problem for the actual flight since  the AES must only work once and is then discarded, but it may be a problem if ground testing is required  on flight hardware. A wedge or positive stop at the end of travel is being considered to eliminate this  motion.  High-speed video revealed a pitching motion in the airplane after it was released for some extreme  orientations. This is a problem in two ways. First, the pitch may cause the airplane to hit the backshell or  AES under certain circumstances, although it was not observed in this set of tests. Second, the airplane  now is starting to tumble. This motion must be counteracted by the drogue chute to avoid problems while  unfolding the tail and wings. The ideal case would be to have the airplane to separate without a pitching  moment.  There are several possible causes for this pitching. Since the AES and airplane are not symmetric about  the vertical parachute can axis, there is a cg offset. This offset can cause the airplane to pitch after  separation. Second, after the next to the last set of rollers leaves the track, the AES is free to pitch slightly  under the influence of gravity and aeroloads. Third, the electromagnets used to release the airplane and  the airplane extraction system contains residual magnetism after they are turned off. Sometimes this  causes the aft end of the airplane to release after the wing points have separated. This influence appears  small, and will be eliminated with pyrotechnics for the flight hardware. Design modifications are being  considered to address the other issues.  370
Future Work  The next series of subscale tests should have the entire bzckshell, AES, and airplane assembly free fall  in order to capture the effects of dynamics as the backshell rotates and swings during entry. This complex  interaction should reveal new insights.  A full-scale high-altitude balloon drop test is scheduled for 2006. This test will include a form, fit and  function backshell, AES, and airplane called the High Altitude Drop Demonstrator 2. The goal of the test  is to verify all aspects of the EDD at simulated Mars conditions from 30,000 meters in Earth’s  atmosphere. I+  Conclusions  Extraction is a critical event in the entry, descent, and deployment sequence for the Mars airplane. This  development and subscale testing proves the viability of the concept. Subscale testing demonstrated a  clean release of the airplane in every instance. Yet testing also showed that pitching of the airplane needs  to be addressed.  References  Wright, Henry S. et al., ARES Mission Overview - Capabilities and Requirements of the Robotic Aerial  Platform, AlAA 2003-6577  Levine, Joel S. et al., Science from a Mars Airplane: The Aerial Regional-Scale Environmental Survey  (ARES) of Mars, AlAA 2003-6576  MER Aeroshell Critical Design Review presentations, May 30-31, 2001  Acknowledgements  I would like to acknowledge the contributions of the many people who made this development a success:  * Gary Qualls for photogrammetry Henry Wright for funding and guidance  Charles Bailey and Joseph Hickman for assembling and modifying hardware  Tom Lash and Norman McRae for development of the electromagnetic release system  Paul Bagby for capturing high-speed video  371
the complexity of both the associated control system (proportional/servo control becomes simply “on/off”)  and the tab position sensing (“up/down”) (Figures 2 through 4). Aerodynamic “resolution” of adjustment is  provided through the incorporation of several tabs in a spanwise fashion, thus providing true “digital”  adjustment for blade tracking.  plastically  eformable tab  I i- c F  SMA actuator wire  (one on each side)  Figure 1. Phase I concept demonstration for agonist/antagonist SMA-based tracking tab  concept.  1 \ L  ,/- --  I. 4  I  Figure 2. “Digital” rracning rap aernonsrrarion concepr on rraiiiny edge of a CH-47 blade.  This design approach change incorporates all the features of the agonistlantagonist plastically-deforming  tab, namely:  Use of SMA wires as prime movers driving pre-stressed structural components in a hybrid fashion  provides large strain and force capability for the actuator system, without the attendant bulk  required with other “smart” or active materials for enhancing actuator mechanical advantage  Electric power is only used during transitions for changing tab position  The devices are retrofit-capable onto existing rotor blades  The tabs are adjustable in-flight  The physical size and weight is minimal due to the use of SMA wires as the prime mover 0  0  0  0  0  In addition, the digital concept includes the following unique advantages:  0 0 Position sensing is trivial, in that only one of two possible states may exist  The precise shape of the device is dictated from geometric features of the base material  Control of the device is simplified to a “change position’’ command  Use of multiple spanwise units provides robustness as an individual unit failure implies only a  partial degradation in total system performance  374