ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
303   Figure 12: Focus Group Preload Mechanism 

The Focus Group, like the MAHLI focus lens group6, utilizes a single compression spring, shown in Figure  12, for preload in all directions. The spring, mounted to the fixed structure of the lens assembly, applies a force to the Focus Group that counteracts backlash in the lead screw. This spring force also creates a moment and removes the play in the linear bearing. The long arm feature on the focus group places the spring at the location necessary to create this moment while keeping the spring force relatively low.   Lessons Learned   The nature of the zoom lens mechanisms designs posed high risks for meeting life cycle requirements of 1 Martian year operation plus margin. A large number of unique frictional interfaces created numerous failure points. The ability of each interface to withstand design loads was not completely understood, especially in the case of the coated aluminum surfaces. For these reasons a regimen of component life tests was planned and executed to 3x life requirements in order to prove the design. When appropriate, the tests were performed at temperature extremes as well. These tests revealed several issues with the baseline design. Two lessons learned from component tests are discussed below.  Integral Bearing Design for Smooth Operation  The unorthodox design of the integral bearings poses a risk to meeting lifetime wear requirements for the zoom mechanism. However, employing a traditional steel bearing set is prohibited by the unacceptable strain that would result over the temperature range. Relatively large diameter bearings are needed to accommodate the light path, the optical elements, and the moving lens carriers housed within. Typical steel bearings would undergo CTE-driven contraction differentials with the aluminum lens structure. The diametral mismatch would, with tightly fit parts, deflect and stress the delicate cam tube as well as the lens structure on which the cam tube mounts. This strain would move optic elements out of alignment, degrading camera performance. The integral bearing architecture poses no such CTE issues. In addition, the integral approach has a smaller form factor and less mass compared to a standard bearing set.   The integral bearing scheme is less precise than a traditional bearing, but precision is not critical in this application. These bearings do not influence zoom lens cell decenter or tilt alignment which are maintained by their linear bearings as described previously. Although the integral bearings do determine axial position through the cam slots in the cam tube, axial (despace) position requirements are less restrictive than other alignment parameters.   A relatively benign loading profile is also conducive to the integral raceway methodology for this bearing set. The linear bearings support most of the mass in the mechanism by restraining the lens cells and optic elements in all but one degree of freedom. Except in the axial direction, the integral bearings support only
309 Acknowledgements 

The Mastcam mechanical lens assemblies were designed at MDA Information Systems, Inc., Space Division, in Pasadena (MDA) (www.MDAInformationSystems.com) under contract to Malin Space Science Systems (MSSS) (www.msss.com). Michael C. Malin (MSSS) is the Mastcam Principal Investigator, and the engineering work for the cameras was overseen by Mastcam Instrument Manager, Michael A. Ravine (MSSS). The authors give special thanks to Robert Bell and Rick Gelbard at Panavision for initial direction and support in the design effort; Jeffrey Lince of Aerospace Corp. for his expertise with MoS 2  lubricants and assistance with tribological testing; Larry Lipp for his tribological knowledge and support; Yuichi Ikeuchi of IKO Nippon Thompson Co., LTD. for his knowledge of linear bearings; Keith Campbell at Castrol Industrial for his expertise on the Braycote® lubricants; Greg Levanas for help trouble-shooting motors; and Mark Balzer of JPL for his willingness to share mechanism knowledge and advice. Also, the authors thank the Mastcam review board members, and all other reviewers, for their time and help guiding the project. Finally, the authors thank Helen Aslanian, Jennifer Baker, Todd Cameron, Cole Corbin, Sean Dougherty, Rene Espinosa, Richard Fleischner, Richie Gov, Jay Harland, Ross Hironaka, Jacques Laramee, Brett Lindenfeld, Anthony Matthews, Todd McIntosh, Richard McKenzie, Jim Ostroff, William Reed, Chris Thayer, Dorian Valenzuela, and Tom Vanderslice of MDA for their tremendous sacrifice and work developing the Mastcam lens assemblies. The Mastcam project could not have been completed without the dedication and energy placed forth by them as well as many others at MDA and MSSS.
310 References 

1. NASA/JPL "Mars Science Laboratory." Website, cited 2 January 2012 <http://mars.jpl.nasa.gov/msl>.  2. Malin Space Science Systems "Mars Science Laboratory (MSL) Mast Camera (Mastcam)." Website,  cited 2 January 2012 <http://www.msss.com/all_projects/msl-mastcam.php>.  3. NASA/JPL "MSL Science Corner: Mast Camera (Mastcam)." Website, cited 2 January 2012  <http://msl-scicorner.jpl.nasa.gov/Instruments/Mastcam/>.  4. Malin, M. C., M. A. Caplinger, K. S. Edgett, F. T. Ghaemi, M. A. Ravine, J. A. Schaffner, J. M. Baker,  J. D. Bardis, D. R. DiBiase, J. N. Maki, R. G. Willson, J. F. Bell III, W. E. Dietrich, L. J. Edwards, B. Hallet, K. E. Herkenhoff, E. Heydari, L. C. Kah, M. T. Lemmon, M. E. Minitti, T. S. Olson, T. J. Parker, S. K. Rowland, J. Schieber, R. J. Sullivan, D. Y. Sumner, P. C. Thomas, and R. A. Yingst.  "The Mars Science Laboratory (MSL) Mast-Mounted Cameras (Mastcams) Flight Instruments." 41st  Lunar and Planetary Science Conference , Abstract 1123 (2010).  5. Malin, M. C., J. F. Bell, J. Cameron, W. E. Dietrich, K. S. Edgett, B. Hallet, K.E.Herkenhoff, M. T.  Lemmon, T. J. Parker, R. J. Sullivan, D. Y. Sumner, P. C. Thomas, E. E. Wohl, M.A.Ravine, M. A.  Caplinger, and J. N. Maki. "The Mast Cameras and Mars Descent Imager (MARDI) for the 2009  Mars Science Laboratory." 36th Annual Lunar and Planetary Science Conference , Abstract 1214  (2005).  6. DiBiase, D. R. and J. Laramee. "Mars Hand Lens Imager: Lens Mechanical Design." Proceedings of  the 2009 IEEE Aerospace Conference  7–14 March 2009, Big Sky, Montana (2009).  7. Jones, W. J. Jr. and M. J. Jansen. "Lubrication for Space Applications." NASA CR-2005-213424, p. 6.  8. Hilton, M. R. and P. D. Fleischauer. "Lubricants for High-Vacuum Applications." Aerospace Report  TR-0091(6945-03)-6 (SMC-TR-93-14) (15 March 1993), p. 37.  9. Stone, D. and P. Bessette. “Chapter 8: Liquid Lubricants.” In Space Vehicle Mechanisms: Elements  of Successful Design , edited by P. L. Conley, 185-213. New York: John Wiley & Sons, Inc., ©1998,  p. 208.  10. Conley, P. L. and J. J. Bohner. "Experience with Synthetic Fluorinated Fluid Lubricants." Proceedings  of the 24th Aerospace Mechanisms Symposium  (1990), NASA CP-3062, pp. 213-230.  11. Stevenson, Milt Jr. Vice President and Chief Technology Officer, Anoplate Corporation, Syracuse,  NY. Telephone interview, 7 February 2012.  12. MIL-A-8625F "Anodic Coatings for Aluminum and Aluminum Alloys." US Military Specification (10  September 1993), pp. 16-17.  13. Norton, Robert L. Machine Design: An Integrated Approach. New Jersey: Prentice-Hall Inc., ©1996,  pp. 518-519, Chap. 7.
312   Figure 1.  Wet-chemistry Sample Processing System  This project was funded by NASA’s Mars Instrument Development Program (MIDP), and directed by Dr.  Luther Beegle as the principal investigator (PI) from JPL. Ball Aerospace performed the design, construction, and demonstration under subcontract to JPL.   2.0 REQUIREMENTS AND OVERVIEW OF FUNCTIONALITY 

2.1 Requirements  To develop a sample processing platform that could be used on multiple missions, the PI set a baseline  list of requirements for planetary science investigations. The device could include more capability as long as these requirements were met and the project stayed within budget. An underlying design goal during development was to craft the mechanism such that it is as close to a flight-like system as possible, while operating within cost and schedule. Requirements included:  (a) mechanism capable of processing 20 samples, each capable of holding a 100 mL of solid material and be mixed/processed with a reagent solvent; (b) the ability to process methanol at high temperatures and pressures in the range of 150°C and 10.3MPa (1500 psi) for a period of 1 to 2 hours; (c) as little risk of sample cross contamination as well as instrument delivery cross contamination as possible; and (d) the delivery of the soil sample into the sample cell.  As the mechanism developed, initial requirements were met and exceeded by maintaining a  flexible and modular design, and productive and regular communication with the PI.    The design consisted of a screw on cap which provided the practicality of reuse. The reusable sample cell drove the WASP design to increase in complexity, but it provided greater serviceability for field use and lowered the refurbishing costs of the assembly. The minimum number of sample cells was increased by 50% and the processing temperature and pressure requirements were 200°C and 13.8 MPa (2000 psi).
313 By increasing the minimum test cell quantities to 30 test cells, the mechanism scalability was  demonstrated while maintaining the mass goal of less than 15 kg. 

Figure 2.  WASP Internal Compone nts – shown in see thru housing  Because of budget limitations, the fluid handling pump and valve components that have been selected do not have direct links to space-rated components. However, their method of operation does mimic that of the space-qualified, solenoid-driven fluid control devices that are manufactured by Valcor Engineering Corporation. By focusing funds and capacity on the challenging aspects of the sample cell design instead of developing existing technologies such as space qualified valves and pumps and using commercial-off-the-shelf (COTS) components when appropriate, the design goals were achieved and enhanced. WASP evolved to include 30 reusable sample cells and three fluid reservoirs.   2.2 Operation and Functionality  This section explains the components of the WASP mechanism and how the components interact with each other. Figures 3 and 4 provide a visual reference for what these components are and where they are located on the mechanism (reference Figures 3 and 4 to associate the descriptions below):  a) The mechanism is initialized and a sample cell is positioned underneath the inlet funnel b) The funnel is lowered into the cell c) A solid sample is delivered into the funnel, flowing into the sample cell d) The sample cell is driven to the capping station e) The capping arm is raised, allowing a cap to slide under the arm and load the capping station f) The capping arm drives the cap down into the sample cell, blocks other caps from feeding  into the capping station, and pushes the cell into a bore hole feature containing an injector needle  g) The test cell bottoms out at a hard stop and the capping arm pushes the cap until it snaps  into place and seals the sample cell
314 h) As the test cell bottoms out into the injector needle, the needle pushes the bottom plunger  valve open  i) While the test cell is bottomed out in the injector station, a solvent is selected on the multiport  valve and then pumped into the sample cell  j) The capping arm is retracted and a spring housed under the sample cell pushes it back to its  neutral position; an O-ring keeps a seal with the needle, preventing any leaks as the plunger  valve closes  k) The sample cell is now driven to the heater station where it makes contact with electrical  terminals to provide power to the cell’s heater; temperature is monitored by an infrared thermistor  l) Once temperature and dwell time is achieved, the sample is positioned back under the  capping station and allowed to partially cool down  m) After cooling the sample (to lower internal pressures), the capping arm is actuated and the  sample cell driven into the needle of the injector assembly  n) A delivery port is selected and a fluid pump actuated to extract the solute form the sample  cell  o) After the solute is delivered, another port is selected to rinse the tubing and inject the  cleaning residue into the emptied cell.  p) After cleaning the solvent pluming, the capping arm retracts and the sample cell goes back to  its neutral position and the mechanism is ready to process another sample 

Figure 3.  WASP Components – Mechanical Components
315   Figure 4.  WASP Components - Fluid System  3.0 MECHANICAL SUBSYSTEMS  WASP’s integrated system consists of control software and electronics, and four multifunction mechanical  systems as listed above and further described below (sample cell subsystem – including the inlet funnel, carousel/cell-positioning subsystem, capping subsystem, and fluidics management subsystem).   To minimize the number of mechanisms required to perform all the required operations for a field wet chemistry processing system, many of the mechanical drivers/motors perform several functions. Additionally, the design included improvements to the sample inlet and interface with the sample cells to reduce the risk of sample cross contamination and increase the general cleanliness of the mechanism. This capability was not part of the original scope for this project but was imperative to address. See Section 4.0 for more information.  3.1 The Sample Cell Subsystem  The sample cells are the key component of the WASP mechanical design. The sample cells determined the approach we needed to take in designing the sample delivery, capping mechanism, fluid injection, sample extraction, and overall sizing of the mechanism. The sample cell was the first component we developed, and the one that took the most research and development.  The sample cell subsystem consists of a cylinder with two open ends. One end is fitted with a valve port and the opposite end is the sample inlet, which is capped after the sample is delivered, creating a sealed vessel. An external heater is bonded to the cylinder and external rings attached, acting as electrical heater contacts. An optical reflector is slipped onto the sample cell and used to accurately read the cell temperature with an optical infrared thermometer. Part of the cell’s internal components includes a filter to prevent the sample from clogging the valve port.
316    Figure 5.  Sample Cell - Components  The ability to heat the sample with methanol at high pressure (200°C and 13.8 MPa) for a minimum of   1 hr is a critical requirement for WASP. A high pressure vessel is required that can be capped, sealed, heated, and accessed to extract the processed solute. Methanol is a very challenging solvent to seal, given that it is a small molecule with high vapor pressure, and it is also highly corrosive to rubber and  most synthetic polymers . To seal the pressure vessel the most promising chemical and temperature  resistant materials were determined to be Teflon.    An engineering development unit (EDU) of the capping module was developed to perform a proof of concept. This EDU assembly was of essence, ensuring the development of a successful approach showing the means to seal the sample cell and the cap feeding mechanism. If the sample cell capping was not properly developed, no further progress could be attained expanding the other subsystems for WASP. The use of a prototype capping device that reliably demonstrated the capping process and helped understand its nuances was an invaluable investment in resources providing the highest returns. This assembly helped develop the required features on the caps and the mating components, ensuring a smooth process when capping the cells. The EDU capping module consisted of a COTS linear motor that plunged the caps into the sample cell, and a cap feeding assembly that was synchronized with the capping actuator to control the cap flow. Because motors add significant cost, an approach was determined to control the cap feed rate and cap the cells with a single actuator.
317 

Figure 6.  EDU - Capping Station  A cap rail guide or runnel with a Teflon slide to house and store the caps was designed to feed the caps  into position. The Teflon slide was passively actuated with a constant force spring box that pulled the cap slide and forced the caps into the capping station underneath the plunger. To prevent the caps from jamming, the plunger, or capping head, attached to the motor shaft was elongated to block and control the dispensation rate. To ensure the caps were properly captured when positioning them in the capping station, a spring loaded cap guide was developed that slid to receive the next cap before the plunger was fully retracted to allow the cap to slide into position for the next actuation.   

Figure 7.  EDU Capping Station - Capping Sequence
318 The caps are self-aligning to allow for misalignments and position themselves when applied under load.  Fillets and chamfers are used on the interfaces wherever required to assist the cap flow and help the transition into the sample cell. Chamfers on the sample cell cylinder avoided damaging the seals during the capping process and helped the cap position itself as it was pressed on. This chamfer angle took some debugging. Testing showed that the hard Teflon seals resulted in high peak loads to get the O-ring over the sample cell; therefore, it was necessary to reduce the abruptness of the angle on the chamfer to reduce peak loads. Later cell designs incorporated a longer chamfer which reduced the capping loads to a more linear response and also served as a self-aligning feature for the caps.   After developing the capping approach the next step was solvent injection and sample extraction. A Zirk fitting type of valve was the initial baseline, but the operational temperatures and pressures directed the search for other options as these components could not meet our requirements. A valve based on O-ring technology was developed for its low cost, relatively mature technology solution, and parts availability. Because O-ring based valves are susceptible to particulate contamination, a means to keep the solvent and sample from contaminating the valve was required. Filtering of the liquid sample after solvent extraction was accomplished by a two stage approach:  a paper filter to capture the course particulates, and a COTS metal sintered cylinder to act as the refining filter that also works as a spring retention interface to keep the valve closed. 

Figure 8.  Sample Cell Cross Section  After developing the sample cell sealing and valving, the heating approach was addressed. To increase heating efficiency, reduce complexity, and provide redundancy, each sample cell has its own heater assembly. Kapton heaters were selected for their affordability and reliability. To reduce weight, cost, and wiring complexity, the heater leads to the sample cells were eliminated by incorporating heater contact rings instead of flying leads. To monitor the cell’s temperature, a remote infrared sensor captures the cell’s temperature; this option removed the requirement of having localized thermocouples installed on each sample cell. To power the heater, the sample cell is positioned by the carousel to a heating station with matching connectors that slide and contact the contact-rings. Once contact is achieved, power can be applied to the heater; simultaneously, the infrared sensor monitors temperature. This heating station can be easily duplicated to provide redundancy.
319   Figure 9.  Heater Station  The capping of the test cell proved to be a challenge and the design-kernel for the overall mechanism  development. Initially, the sample cell was developed with a single-use flight mission in mind. This approach led us to develop a simple test cell that proved successful after some development. However, we quickly realized of the cost-impact this approach would have for ground testing and further development. For this reason, a re-usable cap and sample cell was developed. Although the new reusable cap added more complexity and initial cost, it served the end user in the long run, reducing overall development costs. We also choose the harder and more difficult Teflon seals to ensure we had a viable design.    A final feature to the sample cell was the addition of a dust tray that is sealed when the cell is capped. The dust tray serves as an alignment and vibration damping feature and dust contamination mitigation device.  3.2 The Carousel System  The carousel system serves as the housing and positioning mechanism for the sample cells. It houses 30 test cells and drives them by means of a stepper motor and a worm drive reduction gearing. The worm drive gearing is used to get a mechanical advantage and to lock out the carousel when stopped. Position control is managed by an optical encoder and reduction gearing, resulting in position accuracy of  0.3 millidegrees. Because the carousel houses the test cells, it acts as a structural support platform through which most loads to the sample cells react. To manage these loads, the carousel is mounted on a large bearing, double sealed, and housed in a labyrinth seal to minimize bearing contamination.
320   Figure 10.  Carousel Assembly  The carousel positioning and repeatability is crucial to prevent damage during any operation, such as  sample delivery, capping, heating, and solvent delivery. To obtain these goals, several approaches were considered: motor step counting, mechanical telemetry, and even a bar code approach. We chose an optical encoder because of its accuracy, turnkey solution, relatively low cost, and ability to mount the encoder ring on the outside of the carousel, which allowed the use of the inside area of the carousel for installing other components. The encoder output was integrated with readily available software drivers and subroutines that integrated with the WASP control software based on LabVIEW.  To move the carousel, a ring gear is bolted to the inside wall, close to the bearing to minimize tooth gear loads. A pinion gear attached to a worm drive gear box is used to drive the ring gear with enough gearing reduction to achieve position accuracy, torque margin, and a means to lock the carousel. The worm gear assembly is driven by a COTS stepper motor with flight history and vacuum compatible.   To facilitate assembly and refurbishing of the sample cells, a quick access port was designed into the bottom of the WASP cover through which each cell is accessible and easily removed by taking out a circlip that holds the cell in the carousel. For flight, an internal and external skirt can be added to further mitigate particulate contamination.   3.3 The Capping Subsystem  The primary function of the capping subsystem is to seal the sample cells and to drive the cells into the injector station of the fluidics subsystem. To accomplish this process, the capping subsystem requires a cap feeding assembly, and a capping arm to drive the caps into the sample cell and push the sealed cell into the injector station. The capping arm is driven by a similar setup as the carousel drive: a geared worm drive with an attached stepper motor, and a linear encoder to determine the arm position. As a backup system, mechanical switches are used to determine failed modes and reset the mechanism.