ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
10   Figure 12: Type 6 collector after the final  vacuum test - wear levels are very low, however  the collector bars are partly shorted together by  material stuck between them.    Figure 13: Example from type 5 brush where  material can be seen shorting the collector  bars.   Key Problems for Brushless Motors 

For the BrushLess DC (BLDC) motors, the brush wear problem of course is not present. However,  commutation for a BLDC motor needs a feedback device to tell the control electronics when to commutate (sensorless operation using back-EMF rather than a physical feedback device is not suitable for start stop operation or where high loads can be expected on startup). The most common way of performing this feedback is using hall sensors; however these are vulnerable to radiation damage. The ExoMars mission specifies a total dose threshold of 10 krad, defined as the end of life dose deposited under 2 mm of Al-eq solid sphere shielding with a safety factor of 2. In order to provide additional safety margins, the motor is specified with redundant hall sensors, each set being capable of operating the motor alone. Although a number of radiation hard hall sensors are available, these suffer from the major problem that they are US sourced and hence covered by ITAR. Additionally the sensors that we were aware of are all larger than ideal for a Ø22-mm motor. We therefore decided to test several non-US sourced sensors that maxon uses in various motor lines to see if a standard type could be used.  Figure 14 shows the test setup where 3 examples of each type of hall sensor to be tested, mounted on a PCB, were placed in front of a rotating permanent magnet. During the test, the sensors were in continuous operation. The permanent magnets were rotated using standard RE13 and RE25 motors, thereby simultaneously confirming that the radiation caused no problems for the two main types of brushed motors to be used (no effects were expected and none were seen). The radiation dose was delivered over a period of 90 hours at a rate of 0.079 Gy/min, yielding a total dose of 38 krad (Si). The sensors were additionally retested after an annealing period of 100 hours (at 25°C) to confirm no further changes.  Table 7 shows that only the Infineon TLE4945 sensor passed the test with no measurable degradation of the switching level. This result is not unexpected since the Infineon sensor is of bipolar design whereas the others are CMOS which is known to be more sensitive to radiation. Subsequent low temperature testing of the Infineon sensors was undertaken to ensure their operation at -55°C (the manufacturer only rates them to -40°C). With the successful passing of this test, these sensors were selected for design into the EC22 motors.
11   Figure 14: Test setup for hall sensor irradiation with  test configuration of 4 PCBs, each with 3 hall sensors  of one type, mounted in front of four motors with  permanent magnets attached to their output shafts.    Table 7: Results of Hall sensor irradiation 

Sensor type Behavior during  irradiation Switching  level after  annealing  Melexis US3881LSE Output voltage started dropping after ~20 krad 2.2 V  Melexis US4881LUCOutput voltage started dropping after ~20 krad 0 V  Infineon TLE4945 No change observed 5 V  Allegro A3230 No change observed 0 V 

Qualification Testing 

In order to qualify the motors for operation on Mars, a test sequence was established to fully test all phases of a motor’s life, including ground testing, launch, travel to Mars and of course operation on the Martian surface. The major steps of the test sequence are shown in Figure 15.   Table 8: Shock requirements for ExoMars  mission   The “motor recurrent measurements” shown in Figure 15 was a defined sequence of  measurements, including winding resistance, dielectric strength and inductance, housing capacitance and motor torque constant that was repeated after every major test step. 

Sterilization tests  The ExoMars program has established a document describing the planetary protection requirements that applies to “all ExoMars spacecraft elements” (Kminek 2007). For the purposes of this qualification, a simple test consisting of 60 hours at 125°C in a dry N 2 atmosphere was considered adequate. 

   Figure 15: Motor qualification test sequence  Shock Response (Q=10)  Frequency  Launch  from Earth  Landing on  Mars  100 Hz 25 g 10 g  300 Hz 400 g 30 g  2,000 Hz 1500 g 30 g  10,000 Hz 1500 g 30 g
12 Shock Tests  The requirements for launch and landing shocks are given in Table 8. Only the launch levels were tested  as shown in Figure 16.  

Vibration Tests  An initial resonance search was performed consisting of a sine sweep with frequency 5-2000 Hz, sweep  rate of 2 oct/min ±5% with an amplitude of 0.5 g. Next, a sine sweep at the specified rate (2 oct/min ±5%) and  at the amplitude shown in Table 9 was performed for 2 minutes for each of the three axes. The motors were not operated during this test (reflecting the launch conditions). Finally, a random vibration test was run, also for 2 minutes per axis for all three axes.   Table 9: Vibration parameters for both RE13 and EC22 motor tests  Sine vibration Random Vibration  Input  Freq.(Hz) Amplitude Input  Freq. (Hz) Amplitude   0-20 15.5 mm  peak 20-100 +6 [dB/oct.]  20-100 27.2 g 100-400 0.45 [g2/Hz]    400-2000 -6 [dB/oct.] 

Figure 16: Picture of RE13 & EC22 test motors attached to a stiff mounting cube (note the  feedback accelerometers a ttached to both motors in the left picture) on the shaker (left) and on a  plate for the shock test (right). The powder actuated nail gun used to impart the shock is visible at  the right.   Operating Cycles  The central part of the qualification tests for both motor types were low temperature, 8 mbar CO 2 and  vacuum lifetime tests with representative loads were performed as shown in Table 11. In each case, the test setup consisted of a brake motor (whose braking load could be adjusted via a variable resistor across the windings) and the motor being tested as shown in Figure 17. A bearingless torque sensor was used to couple the two motors together and provide a reading of the actual braking force being applied. The speeds and loads used during the lifetime tests were the reference “worst case” loads given in the ExoMars specifications.
13 Table 10: CVCM per item 

Temperature RE13 EC22 -25°C 0.22 mg 0.57 mg  -50°C 0.37 mg 0.86 mg  -75°C 0.42 mg 0.92 mg 

Table 11: Low temperature, CO 2 & vacuum tests  Motor Test step Temperature  range Load torque & rpm No. of cycles Approx. no. of  motor revs.  EC22  RE13 Low temp. cycles -120°C to +25°C none 10 non-operating 0  EC22 Operating cycles  -55°C to 40°C 25Nm@12,000rpm 10x as in Figure 19 7.2 million  EC22 Lifetime test  (8 mbar CO 2) 25Nm@12,000rpm 500x as in Figure 19 360 million  EC22 Vacuum test 25Nm@12,000rpm 10x as in Figure 19 7.2 million  RE13 Operating cycles 2.3mNm@8,000rpm 10x as in Figure 19 4.8 million  RE13 Lifetime test  (8 mbar CO 2) 2.3mNm@8,000rpm 150+200 as in    Figure 18 22.4 million  RE13 Vacuum test 2.3mNm@8,000rpm 3x as in Figure 19 1.4 million 

Figure 17: Test configuration for the EC22 (a similar configuration was used for the RE13) 

Outgassing performance  To get a good performance from the motors in terms of particulates contamination and outgassing, which is essential for a mission like ExoMars that is searching for traces of life, the motors were baked out at 125°C for five days (the maximum allowable temperature of the windings). Following the qualification tests described above, the motors underwent outgassing tests at the ESA/ESTEC materials laboratory. The tests consisted of raising the temperature from 25°C to 125°C in steps of 25°C every 24 hours in a pressure of 10 -7 mbar. The Collected Volatile Condensable Material (CVCM) and the Total Mass Loss  (TML) were measured by using four Quartz Crystal Microbalance (QCM) plates at various temperatures as shown in Table 10.    Particulates emission from the brushes was a major concern for the RE13 motor since these are carbon  based so several design features were added to make the exit path for wear particles from the motor as long as possible but to simultaneously ensure the minimum amount of material vents through the bearings during launch. However, the outgassing test results showed that there was negligible emission of particles from the brushes. The overall TML and CVCM levels were found to be very low.
14                         Figure 18: Reference cycle for RE13    Figure 19: Reference cycle for EC22          (and certain RE13 tests) 

           Figure 20: TML for RE13     Figure 21: TML for EC22   For the RE13 and the EC22, the TML, measured at 125°C, is 17 mg/item and 122 mg/item, respectively.  Figures 20 and 21 show the TML extrapolated to different temperatures to predict more realistic operating  scenarios. For the EC22, there was some concern related to an aromatic amine and a plasticizer. The TML and CVCM results showed that the aromatic amine and the plasticizer have been clearly removed by the bake-out. The low TML and CVCM levels measured for the RE13 and EC22 during the outgassing tests have resulted in a discussion within the ExoMars project as to whether the current requirement to encapsulate the motors can be dropped. This would save a significant amount of mass on the ExoMars mission, due to the considerable number of motors involved in the mission.  

Qualification Results 

Both motors passed the sterilization, vibration and shock tests with no noticeable problems (as  determined by the recurrent measurements taken after each test step).  The RE13 performed without problems through the life test in CO 2. However, during the vacuum test,  after just 2 cycles (representing just 2 hours operation), increasing current draw was observed and after the 3 rd cycle the test was aborted to prevent damaging the motor and destroying any evidence of the  cause of the problem. Upon strip down of the motor, it was clear that the cause of the problem was as
17 Rotary Percussive Sample Acquisition Tool (SAT):   Hardware Development and Testing 

Kerry Klein*, Mircea Badescu*, Nicolas Haddad*, Lori Shiraishi* and Phillip Walkemeyer* 

Abstract 

In support of a potential Mars Sample Return mission, an Integrated Mars Sample Acquisition and Handling (IMSAH) architecture has been proposed to provide a means for Rover-based end-to-end sample capture and caching. A key enabling feature of the architecture is the use of a low mass Sample Acquisition Tool (SAT) that is capable of drilling and capturing rock cores directly within a sample tube in order to maintain sample integrity and prevent contamination across the sample chain. As such, this paper will describe the development and testing of a low mass rotary percussive SAT that has been shown to provide a means for core generation, fracture, and capture. 

Introduction 

As part of a potential Mars Sample Return campaign NASA and the European Space Agency are mutually working on a Mars 2018 Joint Rover Mission to potentially send a rover to Mars in order to perform in-situ investigations as well as collection of Martian samples for a return to Earth upon a subsequent mission. As such, it is foreseen that a key NASA payload contribution is the development of a Sample Acquisition and Caching subsystem capable of acquiring Martian rock cores and soil samples that could be cached within a return canister. Once the samples have been successfully cached within the return canister, the canister would be placed on the Martian surface. A follow-on mission element would then utilize a fetch rover to pick up the return canister and place it within a Mars Ascent Vehicle which would be capable of inserting the canister into a passive orbit around Mars. A third and final element of the campaign would then rendezvous with the return canister and return it to Earth [1], [2], [3]. 

Figure 1.  Integrated sample acquisition and caching prototype subsystem.  In support of the development of the Sample Acquisition and Caching subsystem, the Integrated Mars Sample Acquisition and Handling (IMSAH) architecture was developed in order to advance the key                                                         * Jet Propulsion Laboratory, Pasadena, CA 

Proceedings of the 41st Aerospace Mechanisms Symposium, Jet Propulsion Laboratory, May 16-18, 2012  SHEC TDD SAT
18 elements necessary for end-to-end sample generation and containerization. The IMSAH architecture has  been presented in depth in previous publications [4], [5], [6], [7], and is characterized by three major subelements as shown in Figure 1:  1. Tool Deployment Device (TDD)  2. Sample Acquisition Tool (SAT)  3. Sample Handling Encapsulation and Containerization (SHEC).  The corresponding operational process of the specified hardware as it pertains to the IMSAH architecture  is depicted in Figures 2 and 3 and defined by the following operational needs [4] [7]:   Sample transfer between the coring tool (SAT) and the caching mechanism (SHEC) is to occur by  means of bit change-out   Acquire samples into individual sample tubes in order to preserve sample integrity and minimize  the risk associated with handling cores of unknown geometry.   Utilize a rotary percussion mechanism for the Sample Acquisition Tool in order to reduce  subsystem mass and maximize efficiency. The use of a rotary percussive coring tool allows for  successful coring at a reduced weight on bit (i.e., lower arm preload), minimizes bit walk due to  spindle rotation, and allows for robust hole start when compared with rotary only alternatives.   The coring tool deployment, alignment, preload, and feed would be performed using a five  degree-of-freedom (DOF) robotic arm. By using the specified deployment arm the system has enough DOFs to provide tool alignment and accommodate modest rover slip.  Figure 2.  IMSAH coring tool deployment Figure 3.  Bit change-out and sample transfer  configuration  Of the three IMSAH sub-elements, this paper will focus on the development of the rotary percussive  Sample Acquisition Tool (SAT) with an emphasis on the tool’s mechanism designs, testing challenges,  and lessons learned.
19 Sample Acquisition Tool Description & Requirements   The proposed IMSAH architecutre allows for a less complex tool to be developed than what has  previously been investigated or developed as it allows for the use of the TDD for both tool deployment, alignment, preload, and feed. These previous tools required stability tines due to the use of an integral 1-DOF linear feed mechanism which in turn results in the need for greater drilling preload and therefore greater demands on the tool deployment system. Furthermore, the use of the TDD as the linear feed allows for the employment of a sprung linear compliance stage between the turret and the coring tool to provide for both dynamic isolation of linear motion as well as extended linear range of motion during  operation under light arm preloads.  In order to satisfy the IMSAH operational needs, as described in the previous section, the SAT was  designed to provide for autonomous core generation, core fracture/retention, and bit change-out. The resulting functions necessary to perform these operations have been identified and listed as requirements  as follows:  1. Acquire rock cores with approximately 1 cm in diameter by 5 cm in length.  2. Acquire at least 20 rock cores for return. 3. Acquire samples from Kaolinite, Santa Barbara Limestone, Siltstone, Saddleback Basalt, and  Volcanic Breccia.  4. Be able to eject a bit that is inadvertently stuck in a rock  5. Be robust to anomalous cores that may be broken in the bit and/or at the bit opening. 6. Account for catastrophic slip conditions where it is presumed the rover experiences a significant  shift in position while the SAT tool is in the ground.  7. Cores need to be of appropriate quality and suitable for caching  It is important to note that during the development effort the determination of the tool’s performance as it  pertains to core quality was a qualitatve assessment that binned the generated cores into three  categories as described below and represented in Figure 4:   Good – full length cores or in a few segments   Acceptable – mostly segments, discs, and/or pucks   Bad – Powder and/or small chunks, stratigraphy not maintained 

Figure 4.  Assessment of core quality based on qualitative parameters.
20 The subsequent sections will provide detailed information associated with the development and testing of  the tool as well as resultant lessons learned. The sections are arranged to give a general overview of the SAT followed by greater detail of the four SAT subassemblies/mechanisms.   Sample Acquisition Tool (SAT) Design & Testing   SAT Assembly Overview  Figure 5 provides a general overview of the completed sampling tool. The developed SAT is a rotary percussive coring tool comprised of four mechanical subassemblies – the Spindle Percussion Assembly (SPA), the Core Breakoff Assembly (CBO), the Magnetic Chuck Assembly (MCA), and the Core Bit Assembly (CBA). The mechanisms are driven by a total of three dc brushless motors mated to gear heads which provide the necessary actuation to complete the critical functions for core generation, fracture, and capture. 

Figure 5.  Rotary Percussive Sample Acquisition  Tool (SAT)  Figure 6.  Core Quality Results  In order to validate the tool’s unit level functionality a series of verification and validation tests have been performed using a rock test suite that encompasses a variety of rock types that are analogous to Martian rocks (as specified in the requirements) and have been used in the past to qualify Martian surface sampling hardware. The results of the testing have shown the tool can successfully generate, fracture, and capture rock cores within a sample tube for all of the rocks within the test suite while maintaining an  appropriate level of core quality, see Figure 6.  SAT General Hardware Development Lessons Learned  Early on in the tool’s development it became apparent, as with most R&D efforts, that schedule and  resources were going to be severely limited. As such, it was assessed that the tool design should be somewhat modular, and implement mechanisms and corresponding subassembly interfaces such that each mechanism could be tested and operated independently of the others. Doing so provided for several  advantages:
21  Mechanisms could be developed relatively independently of the others as long as interfaces were  maintained and negotiated.   Mechanisms could be tested at a subassembly level allowing for early performance/capability  investigations prior to tool integration.   Resultant modularity allows for relatively easy assembly/disassembly of tool during anomalous  behavior investigations and allows for the isolation of possible suspect mechanism behavior. 

Spindle Percussion Assembly (SPA) Design & Development 

SPA Overview  Figures 7 and 8 provide an overview of the Spindle Percussion Assembly (SPA) within the SAT. The SPA is a linked spindle/percussion mechanism that provides the rotational DOF necessary to drive the Core Bit Assembly through the spindle drivetrain. In turn, the rotational DOF is translated to axial motion through the use of a cam and lever which drives a striker mass and provides the necessary impact energy to facilitate rock fracture. Since the tool development was intended to be a single point design, a linked spindle percussion mechanism was chosen early in the development life cycle because it allowed  for a reduction in the number of required actuators and a lower tool mass. 

Figure 7.  General overview of SPA within the SAT  In order to verify the SPA’s ability to generate the necessary impact energy, a standalone test was  devised using high-speed video to monitor the striker velocity upon contact with the anvil for a given spindle speed (see Figure 9). Due to the linked spindle/percussion mechanism, the impact energy is  presented as a function of spindle speed.  The initial SPA design implemented a striker mass of approximately 51 g based on preliminary  percussion development tests. However, due to a design error in the lever stroke length the resultant impact energy was approximately 20% less than the intended design point resulting in the need to increase the striker mass to approximately 61 g. However, during additional testing it also became apparent that the losses downstream of where impact energy was being measured were greater than
22 initially expected. As resources were not available to fully investigate the system losses, a final striker  mass of 121 g (approximately 2x the 61 g striker mass and the largest striker than could be implemented within the assembly constraints) was selected in order to ensure that an appropriate level of margin could  be maintained during drill operations in the harder rocks of the proposed test suite.     Figure 8.  General schematic of  SPA  Figure 9.  Impact energy at a range of spindle speeds for a  variety of striker masses.  SPA Lessons Learned  Several design choices were selected early in the development life cycle because they allowed for either  a reduction in the number of actuators or resulted in a lower tool mass. In addition, a fair amount of effort was spent on trying to provide an optimized system in terms of generated impact energy vs. performance.  However, in retrospect several noticeable drawbacks cropped up by pursuing these routes:   Linked mechanisms provide for reduced flexibility in terms of which “knobs” can be turned when  investigating tool performance and capability. If the required mechanism capability is clearly  defined (i.e., flight like requirements are already known) this may be less of an issue. However, during early development efforts this is not necessarily the case and can actually limit one’s ability  to investigate anomalous behavior due to either ill-defined requirements or test parameters.   Due to the overall complexity of the mechanism, trying to provide an optimized system is very  challenging especially due to the number of variables that can affect performance. During early  development efforts greater emphasis should be placed on ensuring a high degree of capability rather than optimization as the tool will be utilized extensively to derive “flight” capability requirements. The optimization could then more successfully be implemented during the flight development effort. This is especially true for sampling mechanisms. 

   Striker