ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
Moment M applied to the sliding bearing significantly increased the friction. It is required to balance the  moment to 0 in order to make the selected 8.2-kg loading capacity motors work for this mechanism.  Following the modifications, the balanced-weight loading point was moved as close as possible to the  panel CG to remove the moment from the bearing. Then, the panel can be easily driven up and down  within the motor’s loading capacity.  Lessons Learned 3  The constant-force spring off loading system is not ideal for small-driving capability actuator systems  because the internal friction inside the constant-force spring is significant. For the 250-kg offloading  system used for Radarsat-1, the best results obtained during the calibration was a force between 28 kg  and 30 kg required to move the panel up and down. It significantly exceeded the specified motor  maximum capacity.  Conclusions  The 6-degrees-of-freedom Range Adjustment Mechanism principle was successfully used for Radarsat-1  and -2. The basic principle was debugged and improved from Radarsat-1 and successfully re-used for  Radarsat-2. The mechanism is very cost effective and provides good adjustment and alignment results.  The Radarsat-1 launched in 1995 for a 5 years design mission life has just celebrated its 10th anniversary  and is still working very well in orbit. Radarsat-2 SAR panels were delivered to David Florida Laboratory in  Ottawa for final integration and will be launched in 2006. This basic principle of the 6-degrees-of-freedom  adjustment mechanism can be widely used for any on-ground large flight structure alignment and test.  Offloading methods for this mechanism were presented along with the calibration of the system using a  mass dummy to represent the flight hardware. Picture 1 shows the -X outer panel during the range test  and Picture 2 shows the SAR system final range test.  Acknowledgements  The authors would like to thank their retired colleague Alex Csaki for his technical advice through out the  project. Thanks also go to Nathalie Hadida and Catherine Yi Zhang for their sincere effort in editing this  paper.  References  1. Derek Louie “Panel Alignment software - SAR antenna” MDA SPACE/ SPAR 823870 (Feb.1992) 6-8.  2. Erick Charbonneau “Project 601 8N Radarsat-2 4-SAPA alignment report, Technical Report RML 009-  2005-1 55.  343
Come-Along Tool Development for Telerobotic In-Space  Servicing of the Hubble Space Telescope  Jonathan Penn*  Abstract  The Come-Along Tool was created for the Hubble Space Telescope (HST) Robotic Servicing and De-  Orbit Mission (HRSDM). During the mission, an unmanned spacecraft rendezvous with the HST and  deploys a robotic arm, which manipulates the Come-Along and other robotic tools to perform servicing  operations originally intended for astronauts. Developed at Goddard Space Flight Center (GSFC), the  Come-Along Tool overcomes a difficult set of obstacles to open and close the HST Aft Shroud Doors by  accomplishing tasks in separate robotically feasible steps. The final design incorporates lessons in  functionality, operator visibility, mechanism reliability, and design for ease of robotic operation pertinent to  telerobotic tool development for future missions.  Introduction  Beginning in 1993, NASA has conducted a series of four highly successful astronaut missions to service  and repair the HST, however, after the loss of the Columbia Shuttle in 2003, the next shuttle mission to  deliver critical repairs to the HST was deemed unsafe for astronauts and canceled. It was at this point that  the HST Program Office at GSFC, commenced developing the HRSDM, creating a unique opportunity to  develop telerobotic technology. In order to replace the HST’s ailing gyroscopes and batteries and add  more powerful science instruments, robots would be used to eliminate the risk to human life. The HRSDM  makes use of a Dexterous Robot to manipulate various robotic tools to make repairs and improvements to  the HST. Operation is termed ‘telel-robotic because ground operators command the robot using telemetry.  I I -  Hubble Telescope Space J  Dexterous Robot - ‘b  Spacecraft  Figure 1. Hobot Servicing Hubble Space Telescope  * Swales Aerospace, Beltsville, MD  Proceedings of the 3dh Aerospace Mechanisms Symposium, Langley Research Center, May 17- 19,2006  345
One of many robotic tools created for the HRSDM, the Come-Along Tool is used during the Cosmic  Origins Spectrograph (COS) Task. The Come-Along Tool opens the HST Aft Shroud Doors so that the  Corrective Optics Space Telescope Axial Replacement (COSTAR) can be removed and replaced by COS,  improving Hubble’s sensitivity to ultraviolet wavelengths by a factor of ten. Operation of the Aft Shroud  Doors is a challenging undertaking that pushes the limits of what can be accomplished by a telerobotic  system. Intended for use during crewmember extra-vehicular activity (EVA), these doors have proven  troublesome on previous missions. During the first mission to service the HST, astronauts spent over two  hours attempting to close the doors and it was concluded that the door operation is a two-person task.  Even with two robotic arms, it would not be easy to mimic the dexterity of two astronauts performing EVA,  and for this task, only one robotic arm is available.  The Aft Shroud Doors are difficult to operate because they have shear plates at their top and bottom that  tend to jam during closing even when properly aligned. Other tasks involved with operating the doors,  while easy for an astronaut, are difficult for a robotic system. Acquiring an unrestrained door was at first  difficult to perform during ground testing of the robotic system because efforts to hook the handle of the  door pushed the door further away. Pushing both Aft Shroud Doors closed at the same time is a two-  handed astronaut operation and challenges arose designing a mechanism that could perform this using a  single robotic arm.  Hubble Space  Telescope 1  Left Aft  Shroud Door Right Aft  Shroud Door  - Door Handrails  Figure 2. Aft Shroud Doors  Through creative problem solving and ground testing, the Come-Along Tool design evolved to overcome  the difficulties associated with operating the Aft Shroud Doors in a manner that optimizes reliability, visual  indication, and ease of robotic operation. The Come Along Tool is able to perform its role because it has  features and an operation sequence that require the robot to move in only one degree-of-freedom at a  time. Reliability is attained through use of simple, robust mechanisms and redundancy that allows the tool  to perform its task even if a single failure occurs. The addition of features within the field of view of the  cameras mounted on the robot allow the ground operator to watch gears rotating, discern whether the  door handles are under control, and measure the tension force applied to close the doors. The ability of  the tool to perform its function is further improved by combining the functionality of mechanisms to reduce  the number of robotic actions and ooeration time. The details are further described in this DaDer.  I  Figure 3. Come-Along Tool  346
Background  Robotic Svstem  The robotic system for the HRSDM is composed of a spacecraft, a robot, and various robotic tools. The  spacecraft is unmanned and intercepts the HST using a grapple arm. Once the HST is captured, the  Dexterous Robot, attached to the spacecraft via a boom, is deployed to begin servicing and upgrading the  telescope. The Dexterous Robot, built by MacDonald Dettwiler Robotics for use on the International Space  Station, has two identical arms, one of which serves as backup in case the first fails. At the end of each  arm is an Orbital Tool Change-out Mechanism (OTCM) with jaws to clamp a “Micro Fixture” interface and  a socket that advances onto and rotates a 7/1&inch hex head. The Dexterous Robot was designed to  move large payloads on the International Space Station, not to perform the precision operations necessary  to service the HST. Bridging the gap between the Dexterous Robot and the HST, Swales Aerospace  developed over twenty robotic tools for the HRSDM, each customized to specific tasks necessary to  service and upgrade the HST such as manipulating connectors, attaching to science instruments, and  opening bay doors.  Micro Fixture  Figure 4. Dexterous Robot Orbital Tool Change-out Mechanism and Micro Fixture  Worksite  The Aft Shroud Doors on the ‘-V2’ face of the HST must be opened to access COSTAR. Restrained by  four latches, the Aft Shroud Door set has gaskets along its perimeter and shear plates where the doors  interface each other and the HST structure. The gaskets protect the optical equipment inside the  telescope from light and contamination and become stiffer at cold temperatures. Providing attachment  Doints for the Come-Alona Tool are EVA handrails on each door.  Hut  I loor i’ A Shear Plate  Locations Marked  ‘X‘  Right Door  Right Door  Handrail  * Tool Attachment  Points  Figure 5. Worksite  347
Door operation is complicated by sets of mating shear plates at the top and bottom of each door and at  the interface between the doors. These shear plates transfer structural loads from the Aft Shroud Frame  and require the right door to close before the left to mesh properly. Operation of the '-V2' door set during  the first mission to service the HST revealed that the shear plate on the bottom left door tends to jam even  when the door is properly aligned. Temperature gradients distort the shape of the telescope's outer frame  potentially exacerbating this problem.  Svstem of Tools to Operate the Aft Shroud Doors  In order to perform the COS Task, the Aft Shroud Doors are operated by three robotic tools: the 90  Degree Door Latch Tool, the Door Restraint Tool, and the Come-Along Tool. The Door Latch Tool is used  to release the four door latches during opening, and is used to reengage the latches once the doors are  closed. Helping to control the doors once released, the Door Restraint Tool is used to hold the doors open  during operations inside of the Aft Shroud, and is reconfigured to hold the doors nearly closed. The Come-  Along Tool, described in this paper, controls the opening of the Aft Shroud Doors and closes and restrains  the doors in the shut position.  Door Latch Tool Door Restraint Tool  Figure 6. The Door Latch Tool and the Door Restraint Tool  Come-Alona Tool Requirements  The Come-Along Tool must satisfy mission level and task specific requirements. During door openina, the  Come-Along must attach to the leh and right door handrails,' hold the doors shut while &e DooiLatcLTool  is used to release the latches, and slowly release the doors such that the pressure from the gaskets does  not throw the doors open. The Come-Along Tool must then release from the right door handrail so that the  doors can be fully opened. When it is time to close the doors, the Come-Along Tool must reacquire the  handrail of the right door which is now free to move. The Come-Along Tool, hooked on to the left and right  door handrails, closes the doors by applying a tension force between the two door handrails causing the  doors to rotate along their respective pivot points. The tool must then hold the doors in position until the  door latches can be reengaged.  Tension to Close Doors  -- -* \& .-.4 Come-Along Tool  Left Aft Shroud Door  A/ Door Pivot Point Right Aft Shroud Door  Door Pivot Point  -e \-  Figure 7. Bottom View of Operation to Close Doors  The Come-Along Tool must also satisfy requirements for design for minimum risk and single-fault  tolerance, meet weight restrictions, and provide the ability to overcome jams at the door shear plates. The  tool must be able to perform all of its functions using only one half of the robot's force and moment  348
capability in an environment that cools to below negative 80°C. Satisfying these requirements with a  robotic tool that is easy to use and that provides good visual cues provided a great engineering challenge.  Concept Development  The Come-Along Tool was developed from May of 2004 through July of 2005, culminating in an  Engineering Test Unit. Tests were performed at GSFC using a door trainer constructed to flight drawings  and a ground trainer Dexterous Robot. With each successive generation, features were added to  incorporate lessons learned from previous testing.  Door Trainer Right Door  Left Door Ground Trainer  Dexterous Robot  Left Tool Section  Left Door,  Handrail Right Tool ’ Section  Right Door  Handrail  Generation 1  In order to begin to understand door operation using the ground trainer Dexterous Robot, a mockup of the  Come-Along Tool uses hooks and a modified tape measure reel. This mockup demonstrates the ability to  attach to the Left and Right Door Handrails.  Generation 2  This generation is more robust, containing c-clamp type jaws that actively clamp the Left and Right  Handrails. The ground trainer Robot closes the doors by winding a cable reel that is coupled to a one-way  ratchet, holding the doors shut.  Figure 9. Generations 1 I  & 2 Come-Along Tool Prototypes  349
Generation 3  With the addition of a DC motor, the third generation prototype can disengage the ratchet system and  control door opening. The tool can capture the handrails when the doors are latched closed, but not in the  more difficult situation in which the doors are unrestrained.  Generation 4  In this generation, the DC motor is removed to simplify the tool. The handrail clamps are lengthened to  spread the load of pitch moments induced by the ground trainer Robot to overcome door jams. Finger  features are added to the clamps allowing the tool to capture the handrails of unrestrained doors.  Generation 3 Generation 4  Figure 10. Generations 3 & 4 Come-Along Tool Prototypes  Generation 5  The Engineering Test Unit incorporates many new design features and successfully performs all reiuired  door operations. The cable system is removed, alleviating complications associated with tethers , and  replaced with a threaded Lead Screw. This makes the tool more reliable by reducing the number of parts  and providing a rigid link between tool sections. Operations of clamping the handrails, opening and closing  the doors, and holding the doors in the closed position are combined into one to improve ease of robot  operation. The robot grips the tool via Micro Fixture robotic interfaces. The most significant addition is the  spring-loaded Lead Screw Strut, which provides visual indication of the tension force between the two  doors.  The added benefit of the spring-loaded Lead Screw Strut is that it continues applying a closing tension to  the slightly ajar doors. This allows the robot to release the tool and perform contingency operations in case  either the left or right Aft Shroud Door is jammed.  Micro Fixtures  Come Along  Tool \  Lead Screw- Dexterous Robot  Ground Trainer  Figure 11. Generation 5 Come-Along Tool Engineering Test Unit  350
Design for Functionality  The ability to perform certain tasks associated with operating the Aft Shroud Doors was achieved by  separating operations into discrete steps that the ground trainer robot could accomplish by moving in only  one degree of freedom at a time. During early phases of development of the Come-Along Tool it was  difficult or impossible to acquire the handrail of an unrestrained door or overcome a door jam because  complex robot movements were required that involved various combinations of translations and rotations.  This approach to telerobotic operation is not effective because it assumes that a robot is able to  coordinate movements with a level of dexterity approaching that of an astronaut. By breaking down  movements into small simple steps, functions were made feasible.  Acquire Unrestrained Door Handle  The task of acquiring the handrail of an unrestrained door was at first difficult and later made easy by  separating operational steps. During door closure, when the doors start open and are free to move,  attempting to hook a tool section onto the handrail of a door is difficult because any inadvertent bumping  of the handrail sends the door off into another position. The robot then has to reposition the tool for  another attempt at handrail capture. This operation is made possible by adding a ‘finger’ feature to the tool  and first pushing the door against the door seal to lock out its movement before sliding the clamp over the  handrail. This new operation requires two steps that are pure translations and can be performed easily by  the robot operator. Implementing this same strategy also was successful for more difficult tasks.  Handrail  Fingers ‘f w \  ’1 Right Door  Right Door  Handrail - Ground Trainer  Dexterous Robot  \ Right Tool  Section  I  Figure 12. Come-. ..-ng Acquiring Door Handrail  Overcome Door Jams  The ability to overcome door jams was achieved by separating actions into simple steps. As mentioned  before, it took two astronauts working in tandem more than two hours to close the same door set during  the first mission to service the Hubble Space Telescope. Door jams were induced in the ground trainer  door set testing and early attempts to lift, pull, and twist the door into place were unsuccessful. Ultimately,  it was discovered that applying a pitch moment to a door overcomes jams. To allow greater moment input  without damaging the door handrails, the tool’s handrail clamps are extended to spread the loading.  Operation to overcome a door jam is made possible by completing the following steps: (1) pushing the  door closed until it jams, (2) applying a pitch moment in the up or down direction to relieve the jam, and (3)  completing door closure.  35 1
Pitch Moment applied by Dexterous  Robot. 13.6 N-m f 10 ft-lb)  Come-Along Left  Tool Section 4  Left Handrail \  Figure 13. Pitch Moment Application  Design for Visual Indication  Ability to view the worksite is essential to completing sequential operational steps. Mounted to the robot,  cameras are intended to alert the operator if a dangerous situation arises and provide views so that the  robot operator has confidence that the tool is performing as intended. However, these cameras are only  effective if the tool design makes good use of them. The addition of features within the field of view (FOV)  of the cameras mounted on the robot allows the operator to watch gears rotating, discern whether the  door handles are under control, and measure the tension force applied to close the doors.  Primary OTCM  meras Come-Along  Tool + Cai -. __ \\ OTCM / Handrail Finger  Features  h +  Right Tool 1  Section . ConicalShapes /  Represent FOV from  OTCM cameras  Figure 14. Field of View r  Handrail Capture  To hook the Come-Along Tool onto a door handrail, the robot operator needs to know the tool’s distance  from the handrail while making an approach. The gap between the tool and the handrail is difficult to judge  when the finger feature, shown below, is in-line with the camera. To gain an offset view, the finger features  are placed on the edges of each tool section at the periphery of the OTCM camera’s field of view. This lets  the operator discern the changing gap between the fingers and the handrail during handrail capture.  352
Finger Feature /  Finger 4  Fentiire  Come-  Alnnri Tnnl -  Handrail - /  Handra I  I . Come-  Alnnn Tnnl  In-Line View: Gap Not Visible Offset View: Gap Visible  Figure 15. Indication of Distance from Handrail  Tiahtenina and Loosenina Doors  Visual indication of whether mechanisms in the tool are operating is necessary during door opening ana  closing. During operation, the robot operator sends a command to input torque to the tool's gear train,  causing the tool to move along the lead screw which tightens or loosens the doors. Since the movement of  the doors is slow, it is difficult to ascertain whether the command had the intended effect or when the  operation is complete. Cutaways were added to the tool's housing so that views of rotating gears can be  seen. By watching gear rotation, the operator can tell when the doors are moving and when they have  stopped.  I Miter Gears  Cut Away Section  Cut Away Section  Figure 16. View of Rotating Gears  Measurement of Tension Force Between Doors  Applying tension between the doors is a sensitive operation; if the operator applies too small a force the  doors will not close and if he applies too much he could damage the tool or the handrails. In order to  provide the operator with force information, a spring-loaded gauge is added in line with the lead screw.  The gap between the gauge housing and indication mark varies with the tension between the two Come-  Along Tool Sections.  353
Gauge Housing  Threaded Lead Compression Spring  Screw \ \ Distance varies with tension  L  Indication Mark  Figure 17. Tension Indicator  Design for Ease of Operation  The Come-Along Tool is made easy to operate by minimizing the number of times the Robot must  disengage and reattach since each reattachment has an associated risk of error that could cause damage  to the tool, robot, or telescope. This is accomplished by allowing the robot to control all aspects of door  operation using a single mechanism and by including a backup of this same mechanism.  Combine Operations  The Come-Along Tool is optimized for ease of operation by allowing the robot operator to control the  following three functions from a single attachment point:  1. Apply tension to close the doors  2. Release tension to open the doors  3. Hold the doors in place  This is made possible by the design of the gear train. When attached to a tool section the robot powers  the tool’s gear train using its ‘advance’ mechanism. A 7/1&inch hex socket extends from the robot  engaging a mating male hex in the tool. Rotational motion from the robot travels through the tool’s gear  train through two right angle bevel gear connections. Clockwise input rotates a nut about the lead screw  causing the tool section to translate along the lead screw and apply a closing tension on the doors; a  counter clockwise input causes the tool section to travel in the opposite direction along the lead screw  allowing the doors to open. The non-back driving nature of the nut on lead screw connection is sufficient to  lock the doors in place. This arrangement is easy to operate since the robot operator does not need to let  go of or reattach to the tool during nominal operation.  HexHead  (Robotic Interface)  Bevel Gear \ Stationary  Miter Gear  Bevel  Pinion  L a Pivoting Miter  Drive Nut  -kd Screw  Figure 18. Gear Train  Perform Operations from Either Tool Section  Adding the same gear train mechanism on both tool sections further optimizes the Come-Along Tool for  ease of operation. It was found during ground testing that the Robot must attach to a door to overcome  that door’s jam. In the case in which the tool lets go of one tool section and moves to the other to relieve a  354